Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
I TA L I A N H A B I TAT S Rocky slopes and screes 13 Italian habitats Italian Ministry of the Environment and Territory Protection / Ministero dell’Ambiente e della Tutela del Territorio Friuli Museum of Natural History / Museo Friulano di Storia Naturale · Comune di Udine I TA L I A N H A B I TAT S Scientific coordinators Alessandro Minelli · Sandro Ruffo · Fabio Stoch Editorial commitee Aldo Cosentino · Alessandro La Posta · Carlo Morandini · Giuseppe Muscio "Rocky slopes and screes · The hazard of a precarious life" edited by Alessandro Minelli e Fabio Stoch Texts Paolo Audisio · Lucio Bonato · Margherita Solari · Nicola Surian · Marcello Tomaselli In collaboration with Alessandro Petraglia English translation Elena Calandruccio · Gabriel Walton Illustrations Roberto Zanella Graphic design Furio Colman Rocky slopes and screes The hazard of a precarious life Photographs Nevio Agostini 7, 40, 43/2, 49, 63/2, 121 · Archive Museo Friulano di Storia Naturale 33, 35, 70, 87, 99 · Archive Naturmedia 32, 36, 71/2 · Archive Naturmedia (Ferrari-Montanari) 34 · Archive Naturmedia (Tomaselli) 29, 39, 41, 42, 43/3, 50, 51, 61, 64, 65, 67, 69/2, 71/1 · Paolo Audisio 26, 48, 56, 75, 77, 80, 81/2, 89/1, 98, 106, 107, 110, 129, 132, 144 · Alberto Bianzan 59, 60, 73, 74, 128, 131 · Alessandro Biscaccianti 82, 83 · Stefano Bossi 96, 111, 136 · Marco Cantonati 28 · Carlo Càssola 52 · Carlo Corradini 8 · Ulderica Da Pozzo 58, 122 · Vitantonio Dell'Orto 16, 22, 44, 72, 112, 116, 117/2, 118, 120, 124, 125, 126, 138 · Angelo Leandro Dreon 114/2 · Paolo Fontana 89/2, 91, 90, 100/2, 102 · Gianluca Governatori 66, 81/1, 103/2, 104, 113, 134 · Luca Lapini 114/1, 127/1 · Andrea Liberto 94 · Giuliano Mainardis 84, 101 103/1 · Riccardo Marchini 10, 18, 21, 43/1, 55, 62 · Michele Mendi 78 · Giuseppe Muscio 13 · Pierluigi Nimis 30, 31 · Paolo Paolucci 127/2 · Parodi Roberto 115, 123, 139 · Ivo Pecile 57, 79, 130, 135, 141 · Ermanno Quaggiotto 85, 86 · Nicola Surian 11, 15, 19, 20, 24 · Elido Turco 6, 27, 76 · Augusto Vigna Taglianti 46, 54, 63/1, 63/3, 68, 69/1, 88, 92, 109, 117/1, 137, 145, · Roberto Zucchini 133 © 2006 Museo Friulano di Storia Naturale, Udine, Italy All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior permission in writing of the publishers. ISBN 88 88192 27 1 Cover photo: High Cimoliana valley (Carnic Pre-Alps, Friuli Venezia Giulia, photo Ulderica Da Pozzo) M I N I S T E R O D E L L’ A M B I E N T E E D E L L A T U T E L A D E L T E R R I T O R I O M U S E O F R I U L A N O D I S T O R I A N AT U R A L E · C O M U N E D I U D I N E Contents Italian habitats Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Paolo Audisio Climatic and geomorphological aspects . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Nicola Surian 1 Caves and karstic phenomena 2 Springs and spring watercourses 3 Woodlands of the Po Plain 4 Sand dunes and beaches 5 Mountain streams 6 The Mediterranean maquis Flora and vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Marcello Tomaselli Animal life on cliffs and screes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Paolo Audisio · Lucio Bonato 7 Sea cliffs and rocky coastlines 8 Brackish coastal lakes 9 Mountain peat-bogs 10 Realms of snow and ice 11 Pools, ponds and marshland 12 Arid meadows Invertebrates: taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Paolo Audisio Vertebrates: taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Lucio Bonato Conservation and management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Paolo Audisio · Lucio Bonato · Marcello Tomaselli 13 Rocky slopes and screes 14 High-altitude lakes 15 16 Beech forests The pelagic of the domain Apennines 17 Volcanic lakes 18 Mountain conifer forests Suggestions for teaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Margherita Solari Select bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 19 Seagrass meadows 20 21 Subterranean Rivers and waters riverine woodlands 22 23 Marine bioLagoons, constructions estuaries and deltas 24 Italian habitats List of species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Introduction PAOLO AUDISIO Screes and cliffs in montane and submontane areas are often such inhospitable environments, that they hinder or prevent colonisation by plants and animals. Lack of nutrients in the soil, the compactness and extreme steepness of rocky slopes and cliffs, or, alternatively, their opposite - loose screes and rubble - all prevent most plants from rooting. The only exceptions are plants adapted to life on vertical cliffs (chasmophytes) and glareous plants (living on debris slopes with roots in gravelly, mobile soil). Epigean terrestrial invertebrates (those generally living on the surface Scree with purple saxifrage (Saxifraga oppositifolia) of the ground) cannot find sufficiently compact soil with enough water, and therefore only a few specialised species are able to survive. However, many vertebrates, especially birds, colonise these habitats permanently, settling in cliff crevices and cracks, precisely to exploit the inaccessibility of these areas, which protect them from potential predators and disturbing factors, particularly during their mating season. Several arthropods (especially butterflies, bugs and crickets), and a few coldblooded vertebrates (reptiles) visit these areas to bask in the sun and exploit the high daytime temperature of the terrain. Many phytophagous insects have adapted to developing on chasmophytes and glareous plants, giving rise to very peculiar entomological communities. The interaction of these complex and often extreme environmental conditions enables only a few specialised, exclusive or preferential species to survive in these habitats. The Campanile (“Belltower”) in Val Montanaia (Carnic Pre-Alps, Friuli Venezia Giulia) 7 8 Moreover, in their recent evolutionary history, many of these species have survived in isolated areas and gave rise to endemics; this fact have increased their value for conservation. To describe the importance of these habitats better, it is essential to understand their role as fundamental ecological areas from the historicalbiogeographic viewpoint, and as true flora and fauna sanctuaries. During the complex palaeoclimatic cycles of the late Tertiary and Quaternary, particularly during the Ice Ages, the most important rocky outcrops emerging in the montane and submontane areas of centralsouthern Europe were also essential and relatively xerothermic “islands”. Here, large numbers of thermophilous animals and plants managed to survive, often differentiating at species or subspecies level, taking refuge from otherwise cold and inhospitable habitats extensively covered by ice and tundra. This is the well-known nunatak effect, from the Inuit word nun[ae]ttak used by Eskimo communities to indicate large, isolated rocks that rise above perennial ice-caps. Today, isolated rocky walls, crevices and screes are, in many areas, true refuges for phytophagous insects and several species of birds. In addition, due to the so-called “hedge effect”, many xerophilous insects and birds seek Gruppo del Capolago in the Carnic Pre-Alps (Friuli Venezia Giulia) shelter here when fleeing from open areas like meadows, arid grasslands, magredi and xeric glades threatened or destroyed by man. The bases of high cliffs and rocky peaks often contain rills and hygropetric environments - tiny, often temporary springs trickling over surrounding rocks - which, although minute, can support small but important hygrophilous and mesophilous phyto- and entomocoenoses. In ecotonal environments, these conditions may therefore diversify the local animal and plant communities greatly. Entomologists, ornithologists, herpetologists and botanists all know that high, isolated cliffs and their screes, or rocky gorges near narrow river valleys, historically spared from man’s intervention because of their inaccessibility and lack of exploitable potential, can locally host surprisingly large numbers of species, even though the environment surrounding them is deeply affected by humans. Despite the fact that mountain cliffs and screes are “difficult” environments, they are very interesting to scientists, and are frequently subject to direct and indirect man’s impact (such as quarries for the building industry, illegal waste dumping, road building and excavations along rocky slopes, near mountain passes and ridges, and including nets to protect roads and buildings from falling rocky debris, and even sports like free-climbing). They therefore deserve to be thoroughly analysed. This book aims at providing a general view of the most interesting flora and fauna living on montane and submontane cliffs and screes, focusing on the role played by these habitats in Italian ecological networks, specific issues regarding their conservation and management, and the severity of threats jeopardising their biological quality, geomorphology and landscape. The authors have chosen to treat animal and plant populations and their slope and scree habitats, indicated as those rising from the upper mountain horizon to higher altitudes (in Italy, between approximately 1000-1300 m and 2500-2800 m) i.e., above the tree line or at the upper mountain horizon itself. Low-altitude isolated slopes, coastal cliffs (already treated in the Habitat volume “Sea cliffs and rocky coastlines”) and all the magredi, taluses and screes which are not in mountain areas are excluded, although they are undoubtedly particular, interesting habitats from the naturalistic viewpoint. However, the montane/submontane interface environment and high-altitude submontane slopes in river gorges are at least partially treated, and a special note is devoted to the highest river gorges, independently of their altitude, to emphasise their great natural value and the essential role they play in the conservation of an environmental mosaic of natural habitats. 9 Climatic and geomorphological aspects NICOLA SURIAN Cliffs and screes soon catch the eye when we visit mountain environments. They are easily identified because they are well exposed, i.e., either poorly covered by vegetation or totally bare. At the same time, their size and steepness are awesome, and we are immediately attracted by them. They are among the most inaccessible areas to man, and while taluses require all the trekkers’ attention, cliffs are only accessible to expert climbers or along specially equipped paths. In mountain areas, although screes and cliffs are found everywhere, in some places they are certainly more likely to form. Generally, they can be Cliffs and screes are often closely associated landforms (Lastoni di Formin, Ampezzo found at both low and high altitudes, Dolomites, Veneto) but are more frequent near summits. Screes and cliffs are often associated landforms, and deposits of debris are frequently found just below steep rocky cliffs. These are not merely spatial associations, but also genetic ones, as screes are the result of the crumbling of the cliff above. Cliffs are forms of erosion, of rock weathering following several processes, whereas screes are typical debris deposits. The concurrent presence of cliffs and screes cannot be considered a rule, because debris may be washed away by streams flowing at the foot of cliffs, or because cliffs can be composed of rock that does not crumble into coarse rubble, thereby hindering the formation of screes. The formation and evolution of cliffs and screes depends on various geological and geomorphological aspects. The differing types of rocks which make up Italian mountains, and the variety of processes that can affect rocks (gravitational, fluvial, glacial, etc.) give rise to a wide range of Val Masino (Lombardy) 11 rocky faces of various sizes and shapes, and debris deposits with differing morphological and particle size characteristics. It is essential to emphasise here that many Italian rocky faces and debris deposits are the product of human intervention, such as extensive quarrying and excavations of materials for road building. Lastly, a clarification on the words slope and scree, which are widely used but which do not have equal geomorphological meaning. We shall see, for example, that according to geomorphology, classic screes are called taluses or debris slopes, whereas other screes, associated with different landforms, are referred to as landslides and glacial deposits. 1 20 10 13 2 25 20 15 TEMPERATURE (°C) 30 TEMPERATURE (°C) 12 10 0 5 Debris slopes of glacial origin on Monte Canin (Julian Alps, Friuli Venezia Giulia) -10 0 -2 TIME OF DAY 06.00 South East 12.00 18.00 West North Air temperature TIME OF DAY 06.00 Air temperature 12.00 18.00 00.00 Rock surface temperature 3 1 Variations in air and rocky slope temperatures according to orientation of slopes m 3000 2 Variations of rocky slope and air temperature at 3050 m in the Alps (1 = air temperature, 2 = slope temperature) 2000 3 Number of freeze-thaw cycles in Pic du Midi de Bigorre (blue line) and along the Italian versant of the Western Alps (red line) 1000 0 100 200 300 CYCLES ■ Climatology The climate in mountain areas with screes and cliffs is obviously similar to that typical in mountains, with the addition of elements deriving from local geographic factors and direct exposure to sunlight. The typical characteristics of mountain climates are gradually lower temperatures (from lower to higher altitudes), relatively abundant rainfall, which turns into snow at high altitudes and, proceeding upwards, more intense sunlight. In other words, the distinguishing factor is altitude, as atmosphere rarefies with distance from sea level. For a better analysis of the climate of rock faces and debris slopes, this general climatic feature must also consider local geographical conditions, especially those regarding the direction of flanks. For instance, valleys facing east-west are exposed to very different sunlight from those facing south or north. When versants are particularly steep, this difference may become considerable. North-facing versants are exposed to sunlight for far fewer hours than south-facing ones, and there may even be areas which are never 14 directly illuminated by sunlight, especially in winter, when the sun’s rays are more oblique. In addition, screes and cliffs are covered by scarce vegetation because plants find little soil in which to root, and may even be bare, with very low humidity. This reduces their thermal capacity and exposes them to the action of winds. Low thermal capacity causes rapid heating during the day and equally rapid cooling at night, partly because mountain air is rarefied and therefore contains less water vapour. Just like desert environments, the mountains have a marked temperature range between day and night. Their exposure to winds may not be important as far as geomorphological processes are concerned, but it may be an important climatic factor from the ecological viewpoint. One particularly interesting climatic factor that explains the evolution of rocky cliffs are freeze-thaw cycles, which deeply influence the disintegration of rock. These cycles, which are marked by the periodic passage of ground or rock temperature to the critical value of 0°C, depend on altitude and local conditions (exposure of the slope and direct exposure of rock). These cycles become more frequent as altitude increases, but only up to a certain altitude - at about 2000-2200 m in the Western Alps - above which they start decreasing because temperatures are already lower and thaw is unlikely. Local conditions can give rise to greater or lower numbers of cycles. For instance, on a north-facing versant that is frozen for longer periods than one facing another direction, freeze-thaw cycles are less frequent, and the situation is reversed along rocky cliffs exposed to sunlight, which heat up and cool down very quickly during the day. ■ Geomorphology Cliffs. Cliffs are subvertical or very steep rocky faces. They may look homogeneous or very irregular, according to the rocks composing them. Very resistant, compact rocks, such as granite in Mont Blanc or quartz-diorite and tonalite in the Adamello Massif give rise to very uniform cliffs. Stratified rock, i.e., alternations of rocks with different resistance to weathering, produce irregular versants, like the tiers often found in the Dolomites. The formation of cliffs depends on particular geological conditions and on various phenomena and processes acting at different times and in different ways. Particular geological conditions and, more precisely, the presence of certain types of rocks, are essential requirements for the formation of rocky cliffs. Rocks that can potentially give rise to cliffs are geomorphologically known as hard rocks, because they withstand erosion better than so-called soft rocks. Although the words hard and soft are relative, in Italian mountains hard rocks are limestone, dolomite, sandstone, granite and gneiss. In the Apennines, cliffs cannot be found on outcropping clay or sand, but they form on sandstone, flysch (stratified rock formations composed of alternating resistant and easily erodible materials), ophiolite (basalt, gabbro, etc.) and limestone. ■ Hydrology Although rainfall is quite heavy in the Alps and Apennines, for different reasons cliffs and screes almost totally lack surface water. Water cannot accumulate on cliffs, due to their verticality. There may be small local areas containing water, particularly in fractured surfaces like ridges, or runoff where rocks have varying degrees of permeability. Screes are composed of coarse debris, ranging in size from a few centimetres to a metre, which favours rain seepage underground, thus hindering surface wash and accumulation of water at levels just beneath the surface. The situation changes in landslide and glacial deposits, i.e., screes composed of coarse debris mixed with finer material (sand, silt and clay). Here, water may be found both on the surface and in the underlying rock. Rocky face recently affected by landslide 15 16 Cliff at Monte Vallassa (Ligurian-Piedmontese Apennines) Slopes forming on ophiolite are found in the Ligurian-Emilian Apennines, and an example of a limestone slopes may be seen at Pietra di Bismantova, in the Reggio Emilia Apennines. Another important geological factor is the position of rocks, i.e., how they are spatially arranged. Rock faces may have different gradients, from Evolution of a slope affected by overturn subhorizontal to subvertical, and this inclination can follow the gradient of the versant or not. Favourable conditions for the formation of steep slopes are subhorizontal positions, with alternating hard and soft rocks, and infacing slope positions. Examples of the former type are very frequent in the Dolomites, where limestone and dolomite alternate with Transverse cracks along a versant with head an easily erodible rock like marl. Where scarps hard and soft rocks alternate, weathering is very selective, giving rise to tiered versants with successions of very steep cliffs produced by hard rock and gently sloping ones. Of the processes that cause the evolution of a slope and the formation of a cliff, a very important one in mountain environments is the freeze-thaw cycle, as mentioned above. This gives rise to seasonal soil creep, whereby water penetrates the rock as it thaw, then increases in volume as it freezes, so that the pressure of ice increases, widening pores and fissures in the rock (frost wedging). Rock fractures therefore depend not only on temperature variations, but also on the amount of water in the rock and its fracture condition. Gravity causes fragments produced by frost wedging to roll down the slope and accumulate at its foot. Although this phenomenon occurs continually, it is not visible to the naked eye, as the falling fragments are very small. The situation is quite different when large pieces of material occasionally detach and roll down. This is a true landslide. Landslides on subvertical or very steep slopes are called rockfalls and overturns. When rockfalls occur, the material detached from the slope travels in air before falling on to the slope again, or at its foot. In overturning landslides, the rocky mass rolls from the base. The effects produced by landslides depend on the volume of falling 17 18 rock, but they are certainly more visible than those produced by single fragments or blocks of stone. A rocky slope which has recently been affected by landslide is visually “new”, i.e., it has a different colour from the other versants, the colours of which have been modified by alteration processes. The evolution of a steep rocky face over a longer time-span, i.e., thousands, hundreds of thousands, or even millions of years, depends not only on the above-mentioned phenomena (soil creep, fall of debris, and true landslides), but also on other processes. Tectonic activity, for example, causes rock deformation and uplift, and is therefore the primary, necessary phenomenon causing gradients and mountains containing rocky slopes. Mountains formed by tectonic activity are moulded by gravitational, glacial and fluvial processes. In the Pleistocene, for instance, great masses of ice constantly moved across the Alpine valleys, moulding the versants of the valleys themselves. In warmer, interglacial epochs, like the present one which started about 10,000 years ago, streams flowed across valleys. The versants of Alpine valleys are therefore the result of several gravitational, glacial and fluvial processes which occurred at different times, either separately or together. This is why some transversal Alpine valleys, which have steep versants, are called canyons, although they are not only river valleys, but also the product of erosion by ice. Because Italian mountains vary considerably from the viewpoints of geology (type of rock, tectonics) and geomorphology (shaping processes), they feature different types of cliffs. Unlike many Alpine cliffs, those in the Apennines, Sicily and Sardinia are less well-known. In the Apennines, imposing cliffs can be found in the Gran Sasso, examples being the northern versant of Monte Camicia, with its 1200 m of rocky face, and Monte Porrara in the Majella. Although Sardinia does not have very high mountains (they are generally less than 2000 m high), it does have interesting rocky cliffs. The Supramonte limestone contains several canyons (cordula in Sardinian dialect), and imposing peaks like Punta Carabidda and Punta Cusidore. Valley of obvious glacial origin with subvertical walls (Val Gardena, South Tyrol) Steep rocky face with a debris slide at its foot Screes. We have already mentioned the close association between slopes and screes, the latter being deposits of material detached from slopes. The characteristics of screes (their gradient, particle size of rocks, etc.) depend on various factors, the most important of which are: ● type of process causing weathering, transport and accumulation of material; ● characteristics of the rock composing the versant; ● pre-existing topography. 19 20 Debris slopes and cones. In mountain environments, these are typical landforms at the base of rocky slopes. Debris slopes are masses of debris accumulating at the foot of uniform, continual rock faces; debris cones derive from fractured, crested slopes, and sediments scatter in fan-like shapes at the bottom of these fractures. The rocky sediments produced by the weathering of a rocky slope fall by gravity and accumulate at its foot. The fragments then undergo particle size selection, as larger stones gather more energy and roll further down the versant. The surfaces of debris slopes and cones have gradients between 30 and 35°, also called the angle of repose. Gradients depend on the shape and size of sediments which, in turn, depend on the type of rock from which they come. For example, limestone produces rough, angular debris, and schist flattened fragments. The deposited material is, however, very loose. Its instability is perceptible when trekking along a path. Debris starts rolling downwards at each step we take. In addition to gravity, other processes explain the shape of debris slopes and cones. In summer, surface soil wash, which derives from high-altitude snowmelt or heavy storms, may carry finer sediments contained in debris slopes (creep). Sand and gravel from the upper part of the debris slope are deposited further down. Surface soil wash therefore flattens the profile of the slope. In winter, when debris slopes are covered with snow, rocky debris may glide smoothly downwards on the snow, giving rise to elongated ridges parallel to the slope, which are called roches moutonnées. Debris slopes contain various types of material, with different colours. The hues are given by the types of rocks involved. The colours of debris slopes are less uniform when they are covered by vegetation, indicating that a certain portion of the debris slope has stabilised. This by no means indicates that the slope will never become active again; it simply shows it has been inactive for some time. Debris slopes can actually stabilise for quite long periods. To determine the length of slope inactivity, methods like lichen monitoring, dendrochronology (the study of tree-ring growth) and carbon dating are used. Lichen monitoring is the study of the size of lichens, based on the assumption that these symbioses of algae and fungi colonise surfaces as soon as they stabilise, and that their growth is constant in time. Dendrochronology counts Sediment of a debris cone: large clasts accumulate at base of slope The smooth, steep surface of a debris slope Listed below are the most typical screes, formed as a result of the collapse of rock fragments, as well as other types caused by gravitational, glacial and periglacial processes. 21 and analyses tree-rings, which annually grow in pairs, one darker than the other. Carbon dating, which has frequently been adopted for Quaternary deposits, is used when accumulated debris contains organic matter (wood, peat, bones, etc.). 22 Instability of deeply fractured rocky slopes causes non-classified debris slides Landslide deposits. Downslope movements involving large amounts of material rather than single fragments or blocks, are called landslides. They affect both rocky slopes and loose, coarse or fine material. Here, we deal only with landslides giving rise to screes. When large amounts of rock detach from slopes, there are several types of downslope movement: rockfalls occur when at least part of the movement is in free fall; overturns when blocks of rock capsize, and rockslides when the rock moves down along the slope. The occurrence of any one of these movements depends on the type of rock and particularly on their jointing and fracturing. For instance, deep scarps crossing the slope are likely to produce overturning landslides, and inclined stratified bedrock generally causes rockslides. Downslope movement crumbles the rock in various ways, producing sometimes heterogeneous debris, which is usually coarse and angular, occasionally compact. In the former case, landslide deposits are very similar to debris slopes, although they are generally more irregular and composed of larger fragments. In the latter case, debris deposits do not resemble screes at all, and may easily be confused with local outcropping rock. In the Alps, rockfalls and slides occurred in the late Pleistocene (between 15,000 and 10,000 years ago), following the retreat of the large glaciers that had filled the Alpine valleys. These phenomena had a severe impact on the environment, sometimes clogging valleys temporarily or even permanently. These landslide deposits are still visible today, examples being the Lavini di Marco in Val d’Adige, and the Masiere di Vedana near Belluno. Although these large landslides are in fact huge screes, they look slightly different from debris slopes. Lengthy debris alteration on some of these deposits has produced soil, which in turn has favoured the development of vegetation. Other types of landslides that produce screes are debris flows. In this case, debris movement is not only caused by gravity, but also by water. Debris flows generally occur after intense rainfall, even if it is short-lived (a few minutes of heavy rain are sufficient to trigger movement). Debris flows forming screes generally start in debris slopes and landslide deposits, that is, they simply cause previously fallen material to slide even further down the slope. In the lowest parts of the versants or, more generally, where topographic conditions favour lateral expansion, debris cones form. An example of a large debris cone is the Rivoli Bianchi of Tolmezzo (Carnic Alps). 23 Glacial deposits. Another type of scree can be found at higher altitudes in the Alpine chain (seldom in the Apennines). It consists of debris carried and deposited by glaciers. The Italian Alpine areas with the greatest number of glaciers are the Mont Blanc, Ortles-Cevedale and Adamello-Presanella chains. Glaciers are “conveyor-belts” carrying till, a mixture of rocky fragments of sizes ranging from huge boulders to fine sediments like clay and silt. The transported material is therefore deposited in different areas, along the sides of the glacier, at its foot, or along the slope. Sometimes till accumulated by glaciers does not look like a scree, especially when fine sediment is involved; at other times, deposits and glacial forms show typical scree features. The latter may now be lateral moraines created by ancient glaciers as they gradually moved along. Heavy materials were pushed to either side, leaving what are now elongated, sometimes steep ridges, parallel to the original ice mass. They are found both near glaciers and further down the valley (sometimes several kilometres from the glaciers themselves). End-moraines at lower altitudes formed during the so-called “Little Ice Age”, a period of renewed glaciation which took place between the 16th and the early 19th centuries. The moraines of the Little Ice Age are recent landforms barely colonised by plants, unlike older, Pleistocene moraines, which are gently sloping and covered with vegetation. 24 An example of a rock glacier, a typical high-altitude Alpine landform Rock glaciers. At high altitudes, where periglacial processes are intense, rock glaciers are very common. They are tongues or lobes of angular rocky debris ranging in length from several metres to a few kilometres, with terminal hummocks and ridges. Material contained in rock glaciers originated from debris slopes and glacial deposits. One landform association often observed is rocky wall - debris slope - rock glacier. The surface of rock glaciers is uneven, undulating, with notches and indentations. Coarse material is deposited on the surface, and fine sediments are found underneath. Rock glaciers are particular not only because of their typical morphology, but also because they contain interstitial ice, deriving either from a melting glacier later covered by debris, or by frozen seepage. The presence of ice causes rock glaciers to move, changing shape as their ice contents deform and the water at their base is more or less abundant. However, movement is slow, and the highest velocity of a rock glacier never exceeds one metre a year. Rock glaciers become inactive (stationary) when the ice within them melts. Evidence of inactivity is given by overall sunken forms and plant cover. 25 Flora and vegetation MARCELLO TOMASELLI ■ Plant life on cliffs Although cliff environments are certainly unfavourable to plant life, the number of organisms living in these habitats is surprising, thanks both for their diversity and to the presence of unexpected systematic groups. Cliffs may host algae, lichens, bryophytes, ferns and various angiosperms. Unexpectedly, plant diversity is particularly high in rocky mountain environments, especially along rock walls above the tree line, and in overhangs at lower altitudes, near the typical cirques of the Pre-Alps and Apennines. It is surprising to see how Yellow saxifrage (Saxifraga aizoides) and fairy’s thimble (Campanula cochleariifolia) plants manage not only to grow but also to produce often brightly coloured, vigorously blooming flowers. From the phytogeographic viewpoint, these environments are sometimes more important than other high-altitude habitats. This is due to the role they played as refuge habitats during periods of glaciation, ensuring the preservation of ancient plant species. The various plants that stably inhabit cliffs occupy true micro-environments, establishing very close relationships with the rocky slope, according to the ways in which they manage to grow on it. It is therefore impossible to identify limiting environmental parameters common to all cliff plant communities. It is easier to focus on the characteristics of the rocky slope environment and the ways in which it affects plant life by analysing the groups of organisms that live, grow and reproduce in this seemingly homogeneous habitat, which is actually very particular and diversified. Alyssoides (Alyssoides utriculata) and Mt. Nebrodi joint pine (Ephedra major) 27 28 ■ Algae and lichens Epilithic algae. Epilithic algae, those growing and reproducing on stone, are not very numerous and are divided into three main groups. The first and most numerous includes prokaryotic algae of the Cyanophyta division, also called cyanobacteria, cyanophyceae or blue-green algae. The second and third groups are composed of eukaryotic algae of the Chlorophyta The chlorophyte Trentepohlia (200x) division, also known as green algae, and Bacillariophyta or diatoms. Among blue-green algae, the most frequent epilithic species are those of the genera Gloeocapsa, Scytonema, Stigonema, Calothrix and Nostoc. Among green algae, one genus including epilithic species is Trentepohlia, and epilithic diatoms are found among the genera Tabellaria and Melosira. Unlike other lithophilous plants, algae can grow on bare, compact stone devoid of even minimal cracks - by adhering to the rocky surface (esolithic algae) or penetrating it (endolithic algae). Epilithic algae can be found on any rocky substrate. Some species are associated with silica (Gloeocapsa ralfsiana), others are exclusive to limestone (Gloeocapsa sanguinea). Colonisation by epilithic algae is caused by seepage on to the rock surface. Seepage must last for at least a few weeks, enabling the algae to complete their life-cycle. These conditions generally occur along north-facing versants. Growing epilithic cyanobacteria turn reddish or blue-green. When seepage ceases and the algae become dehydrated, surviving in dormant conditions, their thalli become darker, and they can be identified as vertical bluish-black stripes that groove the rocky face along the seepage line. A few cyanobacteria are able to colonise southfacing versants because they can withstand drought as well as the great daily temperature variations of such locations. Blue-green and green algae (Gloeocapsa, Aphanothece and Trentepohlia) living on limestone substrates are endolithic, and creep within the rocks, although only to a few millimetres’ depth. This is due to their capacity for “melting” rock by releasing carbon dioxide through respiration, thus transforming the insoluble calcium carbonate of rocks into soluble bicarbonate. Algae can therefore burrow microscopic niches inside the rock walls, initiating the process of epigean karstification on limestone. A few endolithic algae can tolerate excessive calcium by accumulating it in the form of calcium carbonate crystals in the mucilaginous membrane that envelops their cells. Epilithic lichens. A few epilithic algae of the cyanobacterial and chlorophytic divisions cannot colonise rocky surfaces autonomously, and need a close structural and functional association with species of fungi. The result of this association, which is quite frequent in nature also in other types of environments, is called lichen symbiosis, and the organisms produced by this close interaction are called lichens. In lichen associations, algae are the partners that can use light as a source of energy (phycobionts), and fungi are the components (mycobionts) which use the organic matter produced by the algae as a source of energy. Most epilithic lichens are crustose, and only a few are foliose. Their names depend on their exterior form. Crustose lichens, which grow very slowly, resemble thin crusts of varying shapes and sizes that adhere to substrates with the underside of all their thalli. Foliose lichens have laminar, lobate thalli which cling to surfaces by means of interlaced hyphae (stalks) called rhizinas. Cliff lichen 29 30 Unlike epilithic algae, lichens that colonise slopes do not simply attach themselves to the surface, forming patinas, but are able to enter through microscopic rock fissures by means of their densely intricate rhizinas. They are so firmly rooted that it is almost impossible to remove them barehanded. Lichenologists must resort to geologists’ hammers to extract them for analysis. Although epilithic lichen species are quite numerous, no census has yet been carried out. Among epilithic crustose lichens are manna lichens of the genera Rhizocarpon, Lecidea, Lecanora, Protoblastenia, Caloplaca, Umbilicaria and Acarospora and, in the Verrucariales order, the genera Verrucaria, Polyblastia, Staurothele and Thelidium. Most crustose lichens, despite their intimate contact with surfaces, are esolithic (and therefore do not penetrate rocks). Limestone is the only type of rock hosting lichens that dissolve calcium carbonate by means of acid secretions and burrow niches underneath the rock surface, from which only the fruiting body of the mycobiont emerges. These crustose lichens are therefore called internal or endolithic. They include the species Petractis clausa, Protoblastenia immersa and Staurothele immersa, names which refer to their endolithic position. Lichens are among the few living forms that can be found at very high altitudes, where Protoblastenia incrustans temperatures are extremely low and periods of drought are long, due to frozen water. Some lichen species can survive at temperatures as low as -196°C without particular damage and can still assimilate carbon dioxide at -24°C. For a few species, the best temperature for photosynthesis ranges between 0 and -10°C. Due to their great capacity for adaptation to low temperatures, lichens are among the very few organisms that can be found on rocks in the snow belt. Cliff lichens carpet rocky surfaces with variable but continuous covers, often forming closed communities or phytocoenoses which exclusively contain these types of organisms. They are thus called cliff lichen vegetation, and have been analysed and classified according to the principles and methods of classical phytosociology. Lichens are usually divided into two main classes. The first is Protoblastenietea immersae, which includes crustose lichen communities colonising limestone, and the second is Rhizocarpetea geographicae, which comprises lichens growing on silica. Further down the classification hierarchy (orders, associations), they are distinguished by their floral composition, type of growth on rock (esolithic or endolithic) and formation (crustose or foliose). Another distinguishing factor for lichen classification is rock humidity. Rhizocarpon geographicum 31 32 Grimmia, a genus of epilithic moss The genus Grimmia (fringe moss) is a perfect example of epilithic moss. It comprises 150 species (41 in Europe, 33 in Italy), generally found in areas with temperate climate, but also in Alaska, Tierra del Fuego, Siberia, and mountain areas in Indonesia and Central Africa. Although the growth of fringe moss is generally quite typical, it is not determined genetically, and may change according to the substrate, shade, humidity and exposure where it develops. Species that usually grow in the shape of hemispherical cushions (G. alpestris, G. montana) may develop tufts of hair near crevices in the rock, just as other species (for example, G. ovata), which usually look like scattered, dense blackish hair in south-facing rock fissures, may sometimes produce loose, green cushions on humid, north-facing versants. Except for G. pitardii, which grows in more evolved soil, all the European species of Grimmia colonise rocks of various types, acid (G. montana, G. alpestris) or base-rich (G. tergestina, G. anodon, G. crinita). Species that grow on base-rich rocks live in warm, dry habitats, and acidophilic species prefer cold, humid areas. Fringe mosses grow in various colours, and European species are usually bluish-green, like G. alpestris and G. caespiticia, reddish-brown Alessandro Petraglia (G. torquata, G. teretinervis) and nearly black, like G. pitardii, G. sessitana and G. atrata. Their colour is due to exposure to sunlight, as moss cushions growing in sunny areas are normally yellowish-brown or even bluish, whereas those in shady habitats are dark green. One of the most typical features of Grimmia is the white hairs forming on their leaftips. The hairs reduce evaporation during drought, capture dew, humidity and airborne particles, thus carrying out an essential function for species living in exposed, dry habitats. Slightly different habitats may host the same species with hairy or non-hairy forms, just as different forms of the same species living in the same habitat may grow short or very long hairs. Species such as G. arenaria, G. curviseta and G. crinita, which colonise dry, sunny habitats, have apex hairs that are even longer than their leaves. According to geographic distribution and habitat frequency, there are seven known Italian species that need to be protected. G. apiculata, G. limprichtii and G. teretinervis are found only in alpine areas and are extremely vulnerable to pollution and restriction of their habitats. G. anomala, G. arenaria and G. atrata are found in a few exposed habitats, and G. pilosissima is a rare species of the Mediterranean mountains which, in Italy, grows only in Sardinia. Epilithic bryophytes. Both mosses and liverworts, i.e., bryophytes, are well-adapted to life on slopes. There are therefore several species of slope bryophytes, divided into various families. The two orders of mosses with the greatest number of species living on slopes are Grimmiales (genera Grimmia, Racomitrium, Schistidium, etc.), and Pottiales (genera Tortella and Tortula). In the Andreaeales, the only genus growing on rock is Andreaea. Among liverworts, there are several genera with species developing on humid rocks in shaded areas, like Preissia, Pellia, Metzgeria, Marsupella, and others. Tortella tortuosa Bryophytes attach themselves to rocks in three different ways. Some species closely adhere to compact rock through their dense felts of rhizoids, just like epilithic crustose lichens. Other bryophytes require very thin rock fissures. The base of the moss felt containing rhizoids creeps into the fissures and roots the moss firmly. This is a typical feature of chasmophytic mosses which, as we shall see later on, is developed by superior plants. Lastly, there is a large group of bryophytes that can attach themselves to rock only if it is covered by an even minimal amount of debris. When colonisation begins, debris is either carried by rocky fragments falling from above, or by winds. Later, when the moss cover has become firmly attached, the mossy carpet itself can cause disintegration of the substrate, which gives rise to additional debris. As colonisation continues, the moss mat grows, causing the formation of decomposing organic matter deriving from the decayed parts of the mat itself. Bryophytes adopting this type of colonisation are called comose. The development of bryophytes on rocks is due to ecological parameters, the most important of which is the chemical composition of rocks. Bryophytes include many acidophilic cliff species, such as those of the genera Andreaea and Grimmia, and the cushion moss Oreas martiana. There are also species growing on base-rich substrates, like Hypnum dolomiticum and Barbula bicolor. 33 34 Bryophytes and pteridophytes on wet cliffs Plant species including bryophytes and pteridophytes growing on humid cliffs with trickling water belong to the phytosociological class Adiantetea. In these areas, rills contain carbonates that favour the development of typical tuff deposits. They are colonised by dense, compact bryophytic layers containing pteridophytes, especially maidenhair (Adiantum capillus-veneris). This type of vegetation is typical of cirque environments at low altitudes in the Mediterranean area. At higher altitudes, the class Adiantetea is replaced by the class Montio-Cardaminetea, whose communities are better suited to harsh conditions. As already noted, humid cliffs are colonised by communities of the class Adiantetea, which replace the chasmophytic class Asplenietea trichomanis typical of dry environments. In addition to maidenhair, typical Adiantetea species are the thalloid liverworts Preissia quadrata, Conocephalum conicum and Pellia endiviifolia, and the mosses Eucladium verticillatum and Hymenostylium recurvirostre. Communities of mosses such as Eucladium verticillatum, Hymenostylium recurvirostre and Didytmodon tophaceus colonise warm, sunny vertical cliffs with trickling phreatic waters poor in nutrients or streaming carbonate-rich water. These plants can be found on both limestone and silica substrates and occasionally tolerate even lengthy periods of summer drought. Alessandro Petraglia Other communities of the same class grow on shady schist cliffs in narrow cirques with rills, or near waterfalls. Such cliffs, which are wet even in the driest summers, are colonised by lush hygrophilous bryophytes and pteridophytes. Acid substrates host royal fern (Osmunda regalis), and neutral, slightly alkaline cliffs rooting chainfern (Woodwardia radicans). The latter is a tree fern found in subtropical mountain areas and, in Italy, grows in a few locations in Sicily, Calabria and Campania. It is extremely rare in the Mediterranean area, where it colonises exclusively humid cirques. Woodwardia radicans, which is protected by international conventions and is contained in the list of Italian plants at risk of extinction, is a relict of tropical flora of the Tertiary in Mediterranean areas. Maidenhair (Adiantum capillus-veneris) Sunlight is another important factor affecting temperature and, indirectly, water supply, which in turn depends on the type of substrate and its gradient. Some bryophytes are typically sciaphilous (i.e., they thrive on shady, cold, humid slopes), and live in areas with less light than phanerogams, penetrating into deep cracks, caves and karst sinkholes. Those living along south-facing slopes can withstand very high temperatures (up to 70°C) and lengthy periods of drought (thermo-xerophilous species), and during such periods they gradually suspend their biological activity and Barbula crocea become dormant. Bryophytes often have thick cushion shapes, which enable them to retain water and protect their interior. In some cases (e.g., several Grimmia species), the cushions are silvery due to the dead leaftips that reflect light and restrict transpiration. Just like epilithic lichens, cliff bryophytes tend to aggregate in exclusively or mainly moss communities, which are classified according to the same criteria used for vascular plants. The vegetation classes that mainly include mountain slope communities of bryophytes are Racomitrietea heterostichi, Grimmietea anodontis and Ctenidietea mollusci. Racomitrietea heterostichi includes communities with several cushion bryophytes that colonise siliceous rock along various versants and substrates with changing humidity. The class Grimmietea anodontis has thermoxerophilous communities, living even at low altitudes in walls and rocks, generally limestone. A few communities of this same class can be found in the montane level, and are therefore examined in this Habitat volume. The class Ctenidietea mollusci includes communities linked to limestone in cool, shady areas. The class Adiantetea must be analysed separately. It is a community of bryophytes and ferns that colonises slopes and walls with rilling or streaming water on limestone. It is typical of the Mediterranean area, and therefore grows in central and southern Italy, especially in cirques. 35 ■ Vascular plants 36 Numerous species of ferns and angiosperms colonise rocky slopes in very different micro-environmental conditions. This is why they are the most extensively treated in this book. Vascular plant biodiversity on slopes depends not only on environmental characteristics like exposure to the sun, temperature, water and nutrients, i.e., on variations in microclimatic and substrate conditions, but also on the capacity of these environments to preserve traces of plants of past epochs, acting like refuge habitats, especially at lower altitudes. We first analyse the variations in slope environment conditions, focusing on those aspects that influence the life of vascular plants directly, and then pass to the importance of slopes as refuge habitats. Gruppo Del Vescovo (Pontremoli, Tuscan-Emilian Apennines) Plants and cliff environments. Only vascular plants (those with specialised tissues) have true rooting systems, i.e., those which enable them both to anchor themselves to the substrate and to absorb mineral nutrients dissolved in the soil. Although the rhizinas of epilithic and endolithic lichens and the rhizoids of cliff bryophytes certainly carry out the former function efficiently, nutrition through root absorption directly from the substrate is a characteristic of vascular plants. It replaces the capacity of lower plants to absorb minerals from streaming water along versants or from airborne particles. The physical characteristics of rocky faces (that is, their morphology) therefore become extremely important in determining the diversity and living conditions of cliff vascular plants, as rooting depends on them. The lithology of cliffs is also important because it influences the mineral nutrition of vascular plants. Typical cliff plants grow on vertical or subvertical walls, the gradients of which may exceed 90° in overhangs. Vertical cliffs have complex microclimatic conditions that require specific adaptations on the part of vascular plants. If gradients are less steep, the environment is also milder, enabling colonisation by unspecialised vascular species. However, vascular plants cannot survive on compact vertical walls that provide no hold for their roots and are therefore impenetrable. Cliff flora can develop on rocky faces that offer at least a few cracks, ledges and holds, no matter how narrow and small they are. This condition is easily found on limestone, in which dissolution caused by surface water flow combined with meteorological events like temperature variations and freeze-thaw cycles, give rise to rock weathering. This is why limestone cliffs are generally richer in vascular plant species, and in the summer may look like natural rockeries. 37 38 The chemical nature of the rock influences plant diversity indirectly, through variations in its morphology, and, more deeply, it also affects the quality and quantity of mineral nutrients available for root absorption. The difference between limestone and silica cliff flora is based not only on the richness of species, but also on their quality. This means that limestone cliffs are colonised by species different from those found on silica cliffs. One of the reasons is the quantity of calcium, an essential plant nutrient found in the scanty soil inside limestone cracks and ledges. This mineral is totally or almost totally absent in silica cliffs. Plants growing on limestone are therefore called calcicoles, or calcium-loving. In ecological terms, this means that they can absorb - and tolerate when in excess - the great quantity of calcium in the soil. Soils rich in calcium have neutral or alkaline pH, and this explains why calcicolous species are also called basophilic. Instead, silica cliff plants are calcifuge, i.e., they have adapted to minimal quantities of calcium in the soil and cannot withstand its excess. Soils that are poor in calcium have acid reactions, and calcifuge plants are therefore called acidophilic. Alkaline reactions of the soil have specific consequences on the supply of indispensable mineral nutrients for plants. In base-rich soil, phosphorus, iron and manganese are generally fixed in insoluble compounds and are not readily available to plants, whereas molybdenum is easily found. In acid soil, some elements may hinder plant growth because their quantity is insufficient. Among these is nitrogen, which is mineralised very slowly in this type of soil, phosphorus, most of which is linked to iron and aluminium oxides, and molybdenum, which is generally less available. Concentrations of other elements (aluminium, iron, manganese) may sometimes be so high that they are toxic to plants. In addition to the micromorphology and lithology of rocky walls, cliff plant populations are deeply affected by topographic parameters, the variations of which cause the formation of microclimatic gradients that directly influence the growth of vascular plants. The first of these is altitude, with which temperature is associated. As altitude increases, air temperature decreases, more regularly so at higher altitudes. At Italian latitudes, the annual average temperature decrease is calculated at 0.55°C every altitude increase of 100 m. This may reach 0.70°C in summer, which coincides with mountain plant dormancy. In eco-physiological terms, temperature is important in regulating the metabolic activity of plant cells, especially carbon dioxide assimilation and therefore the productivity of vascular plants. Among cliff plants there are both eurythermal species, i.e., those able to live in a wide range of temperatures and altitudes, and stenothermal species, which can only withstand slight thermal and altitude variations. One eurythermal species is Apuan globularia (Globularia incanescens), which grows at altitudes between 200 and 1900 m, from the Ligurian coast to the summits of the Apuan Alps. One of the most impressive stenothermal cliff species is the crimped bellflower (Campanula zoysii), typically found on limestone in the Carnic and Julian Alps between 1700 and 2300 m. In addition to micromorphology, lithology and altitude, cliff plant diversity is due to exposure, another fundamental topographic parameter. The exposure of rocky walls is important because its variation influences the quantity and quality of light available to plants, air temperature and water supply. To understand how exposure can produce strikingly different microenvironmental conditions, let us analyse the situations of two versants facing opposite ways, one south and the other north. During plant dormancy, cliffs facing south are exposed to intense, prolonged daytime light. Plants can thus suffer light stress, jeopardising their photosynthesis. A side-effect of intense sunlight is also the rising temperature of the rock which, at altitudes above the tree line, may reach 50°C on the hottest summer days. At night, temperatures fall and at higher altitudes may drop to 0°C, even in the warmest periods. Apuan globularia (Globularia incanescens) 39 40 Cliff plants growing on south-facing versants may therefore undergo daily temperature variations of up to 60°C. Intense sunlight and high temperature favour evaporation from the meagre soil and plant transpiration, which is enhanced by windiness, a typical feature of mountain environments, especially at the summits. Therefore, in addition to the dangers posed by intense sunlight and heat, plants may also undergo water stress. Conversely, rocky versants facing north are illuminated by direct light for only short periods during the day, and sometimes only during their dormancy. If cliffs are overhanging, the plants Crimped bellflower (Campanula zoysii) growing on them, or protected by them, are only illuminated by indirect light, even in summer. Obviously, these conditions pose no threat of stress due to excessive light; on the contrary, these species show the typical adaptations of plants living in the shade. Temperature variations are also restricted in north-facing versants. During their life-cycles, the species living in this habitat must withstand temperatures that may drop below 0°C, incurring stress from cold as the temperature of their sap falls below freezing point. In winter, this condition is the norm because lack or scarcity of snow cover - due to cliff steepness - deprives plants of the insulation provided by a layer of snow. To avoid winter stress, cliff species resort to dormancy, a condition that enables them to withstand temperatures far lower than 0°C. Water supply for plants living along north-facing cliffs is sufficient, to the extent it can be along vertical cliffs whose capacity for retaining water is practically nil. Along snow-covered versants, flowing of melted snow can guarantee sufficient water supply for most, even the whole vegetative season. It should also be remembered that in the Alps summer is the period with most rainfall. Restricted sunlight also contributes to limiting water loss through transpiration, so that plants never suffer from water stress. The only exceptions are species living in or under jutting walls where neither snowmelt nor rain can reach them. These species, which live in conditions of total shelter from rain, may feature adaptations typical of xerophytes. A particular vascular plant species living in “shelter from rain” conditions is cobweb saxifrage (Saxifraga arachnoidea), endemic to the Trentino Alps and mountains near Brescia since before the glaciations. It is covered with thick hairs resembling cobwebs that trap water, providing the plant with sufficient water supply. Types of growth and adaptations. Like bryophytes, vascular species rooting in rock crevices are also called chasmophytes. They are perennials that grow very slowly due to the scanty nutrients contained in the meagre soil, which is full of coarse material accumulating on the bottom of crevices. Some nutrients derive from rock disintegration, some from the recycled organic matter of the dead and decaying parts of the chasmophytes themselves, which are mineralised by decomposing organisms (bacteria and fungi). The recycling process is more evident in pulvinate chasmophytes. The roots of chasmophytes may creep into even tiny rock crevices, enabling these plants to cling to the walls very firmly. Sometimes the length of roots penetrating into fissures in search of water and nutrients is greater than the subaerial part of the plant (up to 1m). The roots penetrating fissures look like elongated cones with apexes facing the interior of the rock wall. The apex is covered by secondary, fan-like roots creeping laterally into even narrower rock fissures. In larger, tubular Cobweb saxifrage (Saxifraga arachnoidea) 41 42 crevices, secondary roots are thicker and parallel to the main root. When fissures are deep and large enough, chasmophytes generally have a single, long, straight root. The subaerial part of chasmophytes looks like a rosette or a cushion (pulvinus). In rosette-shaped or rosulate chasmophytes, the bud axis has limited growth, and the spaces between the two successive leaves (internodes) are therefore short. All the leaves emerge from the same point of the stem, forming what is called a rosette. When flowering, the apex of the bud develops a scapus, on top of which the flower or inflorescence forms (as in livelong saxifrage, Saxifraga paniculata). Once flowering and fructifying are over, the plant sometimes dies. These are monocarpic species, and the most typical cliff example is the ancient king (Saxifraga florulenta). Cushion-shaped or pulvinate chamaeophytes have early aerial shoots growing from the stem and developing radially (in all directions). Growth is uniform, and flowers develop at the same time at the apexes of several stems. According to the shapes of their pulvini, chasmophytes are divided into the moss-cushion type (like moss campion, Silene acaulis), with short, central stems perpendicular to the rock, and longer, prostrate peripheral stems. When growth is uniform in all directions, cushions may be Livelong saxifrage (Saxifraga paniculata) hemispherical, when the base grows directly on the rocky surface, as in Swiss rock-jasmine (Androsace helvetica) and Vandelli’s rock-jasmine (Androsace vandellii), or perfectly round when the base is free because, between the point where stems grow and the pulvinate base there is an elongated shoot, as in Alpine rockjasmine (Androsace alpina). One very frequent morphological characteristic of stems and leaves in chasmophytes is their hairiness, which is an adaptation to a series of factors. Plants living on south-facing versants need hairs for protection against excessive sunlight and heat. These species avoid dehydration stress with special tissues that retain water, called water-bearing parenchymas. These tissues makes leaves and stems typically pulpy and succulent. Stem and leaf succulence are characteristic of the stonecrop family (Crassulaceae), especially the genera Jovibarba, Sedum and Sempervivum. Many species living on north-facing versants also feature hairiness. In this case, hairs prevent the subaerial part of the plant from freezing when temperatures fall below the freezing point of tissues. However, not all cliff plants can develop roots inside rock fissures, and their nutrient requirements may be more stringent than those of chasmophytes. These plants can colonise rock walls only when their seeds germinate near jutting stones, 43 Moss campion (Silene acaulis) Alpine rock-jasmine (Androsace alpina) Vandelli’s rock-jasmine (Androsace vandellii) 44 ledges or narrow terraces, which provide sufficient fine debris for them to root. Their fan-like roots penetrate the thin debris cover from which they absorb nutrients. Higher nutrient concentrations produce faster, lush growth. These vascular plants are also called comose, like bryophytes with similar ecological behaviour. Comoses are typically tufted, because many lateral shoots depart from the central one, as in Alpine fescue (Festuca alpina), one of the few cliff species of the grass family. Phytogeographic aspects. In addition to “experimental models” of how plants can adapt to very harsh environments, cliff plants also give us retrospective information on the history of plant populations in Italian mountains, because they preserve the “genetic memory” of their geographic territory. This is especially true of vascular plants colonising valley slopes, gorges in the Alps, southern Pre-Alps and Apennines (from the Apuan Alps to Calabria), and all mountains on the major Italian islands. These areas preserve ancient species, some of which bear no strict resemblance to any of the living species, and are therefore totally isolated from the systematic viewpoint. The reasons for the older age and systematic isolation of cliff flora proceeding from the Alps Cobweb houseleek (Sempervivum arachnoideum) to mountains on the islands is explained by the effects of glaciations on Italian mountain flora in general. The main, although not exclusive effect was floral impoverishment and the extinction of many species. This process was more severe on the Alps than on southern chains precisely because these imposing mountains were deeply affected by glaciations. However, the ice cover was not uniform along the Alps. Peripheral areas of the south-western Alps and all the south-eastern Alps, from Lake Como to the Julian Pre-Alps, were only marginally covered. Limited effects are shown by palaeo-geographic and palaeo-climatic data, as well as by biogeographic evidence, such as the large number of palaeo-endemic plants found in these areas. Palaeo-endemics are species with diploid or more frequently polyploid chromosome numbers; they date back to pre-glacial times and grow in restricted geographic areas. Many Alpine palaeo-endemics are cliff species. Incapable of genetic adaptations, they have survived on rocky cliffs until today because there they could avoid competition by other species which were more demanding from the nutritional viewpoint and which had escaped man’s colonisation of their territory. These Tertiary species may also be found on nunataks, islands and rocky summits emerging from ice-caps. The conservation value of rocky slopes of hill and montane areas should not only be viewed retrospectively, but also for their present importance. This is true of cliffs surrounding cirques, gorges, and narrow, confined valleys with markedly colder, more humid microclimatic conditions than those found at similar altitudes outside such environments. These conditions at low altitudes favour the colonisation and development of cliff species that generally thrive at higher altitudes. The phenomenon by means of which Alpine species move to lower altitudes, where they are preserved in refuge habitats, is called dealpinisation. Cliff ferns. Cliff ferns on the Italian mountains are not very numerous. The largest number of species is found in the Aspleniaceae family, with the genera Asplenium and Ceterach. Other genera with strictly cliff species are Cystopteris (Athyriaceae) and Woodsia (Woodsiaceae), which may be found up to the snow line. The genera Adiantum (Adiantaceae) and Notholaena (Synopteridaceae) include cliff species which do not live above the snow line. A few cliff ferns are thermophilic. Among these are cloak fern (Notholaena marantae), which grows on winding cliffs to 1400 m, and maidenhair (Adiantum capillus-veneris), which colonises humid or trickling limestone walls to 1500 m. Among the Aspleniaceae, rustyback (Ceterach officinarum) prefers 45 46 calcareous rock, but can live on any substrate to 2000 m, generally on southern versants. The genus Asplenium (spleenwort) includes several cliff species, some of which live exclusively on limestone or dolomite, like Asplenium lepidum, which grows in shady areas with trickling water, wall-rue (Asplenium ruta-muraria), the most frequent species found to 2900 m, Dolomite spleenwort (Asplenium seelosi), restricted to shady, calcareous areas in the central and eastern Alps, and Black Forest spleenwort (Asplenium fontanum), which is also associated with shady, damp, calcareous cliffs in the central and western Alps and northern Apennines to 1800 m. Serpentine spleenwort (Asplenium cuneifolium), as its name suggests, is associated with serpentine and other ophiolitic substrates. In Italy, it grows between Val d’Aosta in the Alps and Val Tiberina in the northern Apennines. Although forked spleenwort (Asplenium septentrionale) is found on ophiolitic rock, it may also grow on acid substrates. Other spleenwort species seem to be indifferent to substrate type, like maidenhair spleenwort (Asplenium trichomanes), which is found everywhere on the Italian mountains and is divided into several subspecies according to distribution and ecology, and green spleenwort (Asplenium viride), found from the Alps to Calabria, at both high and low altitudes. Maidenhair spleenwort (Asplenium trichomanes) The genus Cystopteris includes three typically cliff species that generally grow on shady walls or at their base. Two of them are indifferent to substrate type: brittle bladder fern (Cystopteris fragilis), which is found on all Italian mountains, and Dickie’s fern (Cystopteris dickiaeana), which grows discontinuously along the Alps and Apennines. The third species, Alpine bladder fern (Cystopteris alpina), prefers limestone slopes. Lastly, the genus Woodsia features three cliff species, two of which grow in silica soil, alpine and oblong woodsia (Woodsia alpina, W. ilvensis); the third is calcium-loving, smooth woodsia (W. glabella subsp. pulchella). All three are extremely rare. The most common is alpine woodsia, which grows along the Alps and northern Apennines. Smooth woodsia may be found in Valsesia as far as the Julian Alps, and oblong woodsia is restricted to the South Tyrol and Lombardy. Cliff angiosperms. Although here we only describe plants growing at high altitudes, from the montane to the snow levels, there are several chasmophytic angiosperms on the Italian mountains. The angiosperm genera with the greatest numbers of chasmophytes are Campanula, Primula and especially Saxifraga, whose name clearly refers to cliff habitats. As this volume cannot treat all the chasmophytic angiosperms in Italy, at the end of this chapter readers will find a chart with the most interesting species from the phytogeographic viewpoint (endemics and species with restricted or discontinuous distribution). It lists species living on the Alps (from west to east), as far as those in the mountains on the islands, across the Apennines (see pp. 68-71). Only a few endemic chasmophytes that are very important from the viewpoints of taxonomy, conservation and aesthetics are specifically mentioned below. For the above mentioned reasons, the Ligurian and Maritime Alps are very important locations for endemics. Most of the endemics living there are cliff species of pre-glacial origin. In the Ligurian Alps, they live on limestone and dolomite, common substrates in these areas; in the Maritime Alps, chasmophytes grow in the outcropping gneiss and granite forming the structure of this Alpine chain. Among calcicolous chasmophytes, Allioni’s primrose (Primula allionii) is perhaps the best-known species, for both its rarity and beauty. It grows along the Roia basin on the southern versant of the Maritime Alps in a few shady areas between 500 and 1900 m. Among acidophilic chasmophytes in the Maritime Alps, the most impressive species is the ancient king (Saxifraga florulenta), a mysterious, legendary plant living exclusively on silica cliffs along northern versants between 1900 and 47 3240 m, usually in inaccessible areas. The ancient king is a monocarpic species that flowers and fructifies only once before dying, as it cannot withstand further reproduction. It has been calculated that single plants take between 35 and 75 years to flower. Proceeding northwards to the western Alps, there are other endemic chasmophytes, like Vaud saxifrage (Saxifraga valdensis), endemic to the Cottian and Graian Alps, which grows on limestone and schist between 2000 and 2900 m, and Adriatic bellflower (Campanula elatines), found on shady siliceous cliffs between 300 and 1900 m. Proceeding eastwards, there is another silica-loving species typical of the north-western Alps, dwarf rampion (Phyteuma humile), which is replaced by the Rhaetian rampion (Phyteuma hedraianthifolium) in the Rhaetian Alps. The Italian south-eastern Alps and Pre-Alps, which are mainly composed of limestone, are the most important Alpine locations for cliff endemics. In phytogeographic terms, this portion of the Alps is divided into three districts, each with its own cliff chasmophytes: ● Insubrian, including the mountains between the Lake of Como and Garda and Monte Baldo; ● Dolomitic, with the Veneto Pre-Alps, Feltre Alps and Dolomites; ● Carnic-Julian, including the Pre-Alps and Carnic and Julian Alps. 48 Ancient king (Saxifraga florulenta) Moretti’s bellflower (Campanula morettiana) 49 50 The Insubrian district, besides the already-mentioned cobweb saxifrage, hosts Rainer’s bellflower (Campanula raineri), found in the Lombard Pre-Alps and in isolated locations in Val Sugana and near Vicenza. This gaudy chasmophyte with large, pale blue corollas is found between 700 and 2000 m. In the Dolomites, there is another impressive plant, Moretti’s bellflower (Campanula morettiana), whose bluish-violet flowers dot dolomitic crevices at 1700-2400 m. The list of endemic bellflowers ends with crimped bellflower (Campanula zoysii) found on limestone in the Julian Alps. In the south-eastern Alps, there are a few species of cliff endemics of the genus Primula, all of which have only recently been discovered. In the Insubrian district, there is Grigne primrose (Primula grignensis), described by Moser in 1998, and Monte Alben primrose (Primula albenensis), described by Banfi and Ferlinghetti in 1993. In the Dolomitic district, Recoaro primrose (Primula recubariensis) was discovered in the Little Dolomites by Prosser and Scortegagna in 1998. Our itinerary of endemic species on the Italian mountains proceeds southwards to the northern Apennines. Here, the most important endemic location is in the Apuan Alps. One Apuan endemic is Apuan globularia, which grows between the limestone cliffs near the Gulf of La Spezia and the peaks of Apennine primrose (Primula apennina) the Apuan Alps, on both acid and base-rich substrates. It may also be found on sunny versants of the Tuscan-Emilian Apennines, where it colonises acid fissures in sandstone. The Tuscan-Emilian Apennines do not host many endemics. The only true chasmophyte is the Apennine primrose (Primula apennina), which grows on sandstone cliffs in the north-west, at 1300-1900 m. The Ice Ages did not affect the central Apennines particularly, so that these areas preserve pre-glacial orophilous flora with several endemics. True chasmophytes are Neapolitan bellflower (Campanula fragilis subsp. Mathilda’s rock-jasmine (Androsace mathildae) cavolinii), found on limestone in Abruzzo and Latium at 500-1300 m. Most of the orophilous flora of the central Apennines grows on the other Adriatic shore, in Bosnia and Montenegro. Among these so-called amphi-adriatic species, the rare Mathilda’s rockjasmine (Androsace mathildae) is particularly important. It lives in limestone crevices on the Gran Sasso d’Italia and Majella at 2100-2900 m, and has recently been found on mountains in Montenegro. The southern Apennines have less imposing peaks and therefore fewer endemic chasmophytes. One of the rarest species is the yarrow Achillea lucana, which creeps into fissures in limestone and conglomerate on the Basilicata mountains. On the Sicilian mountains, the situation is very similar, and orophilous cliff flora is scarce due to low altitudes. Imposing cliffs higher than 1500 m can only be found in the Madonie. Among chasmophytic Sicilian endemics there is Gussone’s woodruff (Asperula gussonei), which colonises the dolomitic cliffs of Quacella in the Madonie (1400-1800 m), and Busambra cornflower (Centaurea busambarensis) growing on the limestone cliffs of several Sicilian mountains, to 1400 m. Our floral itinerary across the Italian mountains ends in Sardinia, where lithologic variety with limestone and silica enabled differentiation between calcicole and calcifuge species. Among the former there is Moris’ thrift (Armeria morisii), which colonises limestone cliffs in the Sopramonte di Orgosolo and Oliena between 1000 and 1300 m. Two silicicolous species of the genus 51 52 Helichrysum are worthy of mention, Mount Linas everlasting (Helichrysum montelinasanum), which grows on granite in Mount Linas in south-western Sardinia, and Limbara everlasting (Helichrysum frigidum), a species frequently found on the highest mountains in Corsica, but limited to Mount Limbara in northern Sardinia. Cliff vegetation. According to phyto-sociological taxonomy, cliff plants of the Italian mountains containing large numbers of chasmophytes all belong to the same class (Asplenietea trichomanis), which in turn is divided into two orders (Potentilletalia caulescentis and Androsacetalia multiflorae), which include phytocoenoses of limestone and silica cliffs. Each of the two orders is divided into alliances. The order Potentilletalia caulescensis, distributed along the Alps as far as Sicily, is divided into a large number of well-defined geographical alliances, and includes several communities. The first group contains heliophilous and thermophilic plants generally growing in montane and sub-alpine belts, but which are occasionally found at lower altitudes. The most frequent community within this group is Potentilletum caulescentis, found along the southern Alps. Its predominant species is lax potentilla (Potentilla Pink cinquefoil (Potentilla nitida) caulescens), often associated with dwarf buckthorn (Rhamnus pumilus). Another group is composed of communities that are generally found in the Alpine belt, in sunny areas. The most typical is Potentilletum nitidae, which grows on the highest limestone cliffs of the south-eastern Alps. It is clearly visible for the brightly coloured flowers of pink cinquefoil (Potentilla nitida), which range from pale to dark pink. This community often features the rare Hausmann’s rock-jasmine (Androsace hausmannii). Higher up in limestone of the Alpine and snow levels, the Androsacetum helveticae snow-bed is clearly distinguishable by the pulvini of Swiss rock-jasmine. All the communities mentioned so far do not live on shady, north-facing cliffs, or on poorly lit jutting cliffs, which is where communities with ferns live, especially those linked to the genera Asplenium and Cystopteris, in both the Alps and northern Apennines. The most common community is Cystopteridetum fragilis, with brittle bladder fern (Cystopteris fragilis). In the south-western Alps and Apuan Alps, cliff communities contain several endemic chasmophytes. In the Ligurian Alps, the most frequent community is Saxifragetum lingulatae with thick-leaved saxifrage (Saxifraga callosa = Saxifraga lingulata), which carpets limestone cliffs with its drooping flowers. Another important community from the 53 Saxifraga vandelli Telekia speciosissima Physoplexis comosa Moehringia bavarica Potentilla caulescens Saxifraga arachnoidea Primula spectabilis Daphne petraea Endemic vegetation in limestone crevices in Lombardy 54 phytogeographical point of view, is Primuletum allionii, with Allioni’s primrose, which grows on shady limestone cliffs in the montane belt. The most important community of the Apuan Alps is Sileno lanuginosae-Rhamnetum glaucophyllae, whose typical species are blue-leaved buckthorn (Rhamnus glaucophyllus) and moltkia (Moltkia suffruticosa), which grow on compact cliffs in the montane belt. Limestone in the central Apennines and Sicily hosts several communities of chasmophytes. Two of them may be quoted as examples, as they are typical of the central-southern Apennines. The first is Campanulo cavolini-Potentilletum caulescentis, which colonises limestone cliffs and contains Neapolitan bellflower. The second is restricted to the highest mountains of the central Apennines, where it lives on subalpine and alpine cliffs. This is Potentilletum apenninae, whose typical species are Dolomite cinquefoil (Potentilla apennina) and rock alyssum (Ptilotrichum cyclocarpum). The two communities are the Apennine vicariates (substitutes) of the Alpine Potentilletum caulescentis and Potentilletum nitidae, respectively. Limestone on the Sicilian mountains has only one community of chasmophytes, the Asperuletum gussonei, which grows on the Madonie Thick-leaved saxifrage (Saxifraga callosa) mountains and contains Gussone’s woodruff and Madonie everlasting (Helichrysum nebrodense). Sardinian mountain chasmophytes have not yet been thoroughly analysed. The only data available concerns limestone cliff plants, which are very different from those of the Alps, Apennines and Sicily, to the extent that they constitute an independent order (Arenario-Phagnaletalia sordidae). The most common community at altitudes over 1000 m is the Laserpitio garganicae-Asperuletum pumilae, with southern sermountain (Laserpitium garganicum), Sardinian woodruff (Asperula pumila) and heart-leaved Hairy primrose (Primula hirsuta) micromeria (Micromeria cordata). The classification of siliceous cliff plants is less complex, as there are only three main alliances and fewer communities. The Alps host two communities, the Androsacetum vandellii, along siliceous cliffs of the Alpine and snow levels with Vandelli’s rock-jasmine (Androsace vandellii), and Asplenio-Primuletum hirsutae on the upper montane and lower snow levels. Typical species of this community are hairy primrose (Primula hirsuta) and the gaudy pyramidal saxifrage (Saxifraga cotyledon). The northern Apennines host one silicicolous community, Drabo aizoidisPrimuletum apenninae, which can only be found on the north-facing summits of sandstone cliffs. Typical species are yellow whitlow grass (Draba aizoides) and Apennine primrose. On the Italian Alps, another community colonises sunny siliceous mountain cliffs, Sileno rupestris-Asplenietum septentrionalis, the characterising species of which is rock catchfly (Silene rupestris). The south-western Alps deserve special mention, because their siliceous cliff plants are very different from those of the mountains. The Maritime Alps host Saxifragetum florulentae, which colonises vertical walls of the alpine and snow levels, with the ancient king and Piedmont saxifrage (Saxifraga pedemontana). Siliceous cliffs in the Italian peninsula and Sicily are very rare and little is known about them. Although they are more frequent in Sardinia, their plants are unknown. 55 ■ Plant life in screes 56 Debris slopes and cones, whether the result of glaciation in past epochs or of more recent origin, cover extensive areas above the tree line in the Alps and Apennines. At a distance, most of them look perfectly bare, but as we approach them, we soon realise that, concealed between the rocks, are several plant species, some with colourful flowers. Most of them have Debris with mixed lithology (Valle Aurina, adaptations enabling them to survive South Tyrol) in these generally unfavourable environments. These highly specialised species have a particular name: in geobotany, they are called glareous plants. Although cliffs may be colonised by plants belonging to various taxonomic groups, debris can host only plants that anchor themselves to the mobile substrate with specially adapted roots. This excludes algae, lichens and mosses, which do not have true roots. Epilithic lichens and mosses may be found on old, stable clasts, and terrestrial bryophytes may insinuate themselves into the fine material that forms inside crevices between the larger boulders at the base of debris slopes. In both cases, however, these species are normally found on rocks or in communities in grassland and mountain valleys, and therefore cannot be included in the glareous group. Debris cone partially stabilised by vegetation (Massiccio del Gran Sasso, Abruzzo) The debris environment. Debris slopes are extreme habitats for vascular plants, due both to their unfavourable microclimatic conditions and the constant movements of surface sediments. As regards the microclimate, it is the same as that described for cliffs, and topographic factors are important in producing different habitats according to sun exposure, temperature and water supply. In addition, however, another important factor is the quantity and duration of snow cover, which is negligible on cliffs because of their steepness, but essential on debris slopes. Snow cover modifies the morphology of debris slopes or cones as it changes the position of the debris itself, which may slide freely on the snow or start moving when it melts. The quantity and duration of snow cover also provides water in the layer of fine soil that forms underneath the coarse surface debris and from which glareous plants obtain their nutrition. 57 58 The type of rock the disintegration of which produces clasts, the difference between limestone and silica, and how they affect supplies of nutrients to the roots of glareous plants have already been analysed. The only feature to examine now is the type of bedrock, which affects the sensitivity of the rock itself to agents responsible for disintegration, and which also affects the size and shape of clasts and therefore the overall look of the debris slope or cone. The characteristics of the debris environment that most influence plant life are substrate instability, scarce fine soil (silt and clay), and restricted water supply in the surface debris layers. These factors give rise to the peculiar solutions adopted by glareous plants to survive in these conditions. According to the quantity and mobility of debris still falling from the overhanging slope, debris slopes may be active, i.e., continually modified by the addition of new material. They are inhospitable to vascular plants and are therefore almost totally bare. Other slopes may not be actively fed by debris, but are still unstable because clasts are set in motion by freeze-thaw cycles, by streaming meltwater, or by passage of animals and humans. These slopes are more suitable for glareous plants. Lastly, debris slopes may be inactive, i.e., they are not fed by new debris and are completely stable. In certain conditions, these slopes may host vascular species, even those not especially adapted to these habitats. According to the average diameter of the clasts, debris slopes are divided into block slopes when the diameter exceeds 25 cm, Last surviving fragment of a conifer wood, surrounded by a debris slope (Carnic Pre-Alps, Friuli Venezia Giulia) coarse debris slopes when debris diameter ranges between 2 and 25 cm, and fine-grained slopes when the diameter is 2-0.2 cm. The most important factors for colonisation by vascular plants are the amount, distribution and content of water in the fine soil between and under debris. The most inhospitable are block slopes because, even if they are stable, they generally lack fine soil and sunlight, which obviously cannot penetrate the overlapping boulders. Debris slopes at the base of rock walls are not homogeneous environments which may all be colonised by vascular plants in the same way. The apexes of Debris slope with large blocks debris cones and the upper part of debris slopes have fine, unstable sediments, and are constantly supplied with new rock fragments falling from the overhanging rock wall. The debris moves continually and vascular plants are thus incapable of colonising these areas. Proceeding downwards along the slope, the clasts are bigger and their mobility decreases. This environment favours colonisation by glareous plants which, as we shall see in the next section, resort to several adaptive strategies in order to inhabit such slopes. Towards the base of the slope, the clasts are even bigger, and are completely stationary. Debris slope stabilisation gives rise to favourable conditions for colonisation by non-specialised lithophilous plants (those which cannot be considered glareous), which settle in interstices between boulders where sunlight and fine soil are sufficient for their growth. The cross-section of debris slopes or cones reveals a convex profile. Proceeding from the margins towards the centre, there is a first sequence in which the bedrock meets the debris cover, and where friction slows down clast movement, enabling plants to develop. This is followed by the so-called pediment, which is the less elevated slope boundary where coarser boulders are deposited by gravity. Then comes the debris slope and, lastly, the most elevated part, called crest, which contains the finest material, generally covered by coarser, rolling rubble. The most favourable conditions for colonisation by vascular plants are found along the debris slope, where conditions are similar to those in the central areas of the cross-section. 59 60 Adaptive strategies of glareous plants. Most glareous plants produce large quantities of seeds, which are then dispersed by wind. This enables them to colonise areas of the same debris slope or other slopes far away. Many seeds are needed to colonise debris slopes in the very few areas which have clayey substrates - the only ones enabling germination. Experimental analyses have shown that, although the germination rate of seeds of glareous plants is high, the chances that plantules (embryo plants) may actually develop fully are very small. This is due to the fact that glareous plantules have not yet developed the indispensable adaptations to survive in these habitats. The vegetative systems of fully grown glareous plants devise adaptations to anchor themselves to mobile substrates, avoid being buried by falling rubble, and reach the humid layer of soil underneath the surface debris cover. These aims are achieved by the great capacity for reproduction and regeneration of both buds and roots of glareous plants. They secure themselves firmly to the substrate by means of a main root (or a rhizome), which penetrates deeply through the debris cover and fine soil underneath. The root is supported by a surface system of rootlets that reach the layer of fine soil and absorb water and nutrients. The plants then spread and avoid burial by putting out creeping shoots that develop parallel to the slope. A distinction must be made between migrating and propagating shoots. The former are extensions of the mother plant (for example, creeping avens Geum reptans) and grow independently only when severed by falling stones. The latter detach themselves autonomously and produce independent plants. In the first half of the 20th century, European botanists defined the main types of growth of glareous plants. They are divided into five groups: ● Migrating glareous plants, which move passively along slopes ● Creeping glareous plants, which creep or “float” on debris surfaces ● Rooting glareous plants, which extend in depth ● Stabilising glareous plants, which block debris flow ● Mat-forming glareous plants, which cover and consequently block large quantities of debris. Migrating glareous plants can colonise areas of the debris slope where the risk of burial is high. They avoid this by growing creeping shoots that root themselves into the substrate and regenerate the mother plant should it be buried, giving the impression that the plant is “migrating” along or across the slope. This group can be divided into varieties that migrate by extension, by vegetative multiplication, or both. Examples of migrating glareous plants are French sorrel (Rumex scutatus), creeping avens, fairy’s thimble (Campanula cochlearifolia) and round-leaved pennycress (Thlaspi rotundifolium). Creeping glareous plants have a dense network of thin shoots that “float” on the debris surface, and fascicular main roots with thin secondary roots which Scree with grassy tufts in Vette Feltrine (Veneto) Debris slope with parsley fern (Cryptogramma crispa) 61 62 also reach the underlying fine soil. Alpine toadflax (Linaria alpina) and bladder campion (Silene vulgaris subsp. glareosa) are two examples. Rooting glareous plants extend their roots far down, through the debris cover, by means of a strong, branched rhizome that secures them firmly to the substrate. Examples are parsley fern (Cryptogramma crispa), mountain sorrel (Oxyria digyna) and two species of leopardsbane (Doronicum clusii and D. grandiflorum). Stabilising glareous plants capture fine debris by means of shoots formed of dense tufts or thick, intricate patches of roots that grow perpendicular to the slope. Tufted meadow-grass (Poa laxa), silver oat-grass (Trisetum argenteum) and T. distichophyllum are tufted. Glacier buttercup (Ranunculus glacialis) and mountain hawkbit (Leontodon montanus) are easily identified by their thick root mat. Mat-forming glareous plants develop low, creeping undershrub along the debris surface. They may be woody, like mountain avens (Dryas octopetala), or grassy, like alpine gypsophila (Gypsophila repens), which stabilises fine debris by trapping it in the dense tangle of its shoots. Migrating, creeping and rooting glareous plants all grow in the mobile sections of the slope, whereas stabilising and mat-forming ones colonise the stable areas, and their tufts, mats and tangled shoots produce a dynamic type of vegetation that evolves into pioneering grassland. Fairy’s thimble (Campanula cochleariifolia) Endemic glareous plants. The numbers of endemic glareous plants are smaller than those of chasmophytes. Endemics are found in the genera Alyssum, Campanula, Saxifraga and Viola. Below is only a short list of the most important species (for details, see pp. 68-71). In the Maritime Alps, there are two species of the genus Viola: Maritime Alps pansy (Viola valderia), which colonises siliceous debris slopes between 1200 and 2300 m, and Argentera pansy (Viola argenteriae) actually not a true endemic, as it is also found in Corsica - which grows in fine siliceous debris at higher altitudes (1800-1900 m). Berardie (Berardia subacaulis) and simple-leaved milfoil (Achillea erbarotta) are found across the Western Alps. The former is the only plant of its genus and colonises fine limestone debris at 1800-2700 m; the latter is typical of siliceous debris between 2000 and 2800 m. Another glareous plant associated with limestone debris produced by the disintegration of limestone, calcite and mica is large-flowered bellflower (Campanula alpestris), found in the Western Alps. In the Eastern Alps, there is another species of the genus Viola, Comolli’s pansy (Viola comollia), which grows only in the Bergamasque Alps, colonising high-altitude siliceous rubble (2000-2450 m). In the Insubrian district, limestone slopes host Tonzig’s 63 Round-leaved pennycress (Thlaspi rotundifolium) Alpine toadflax (Linaria alpina) Alpine gypsophila (Gypsophila repens) 64 toadflax (Linaria tonzingii) in the PreAlps near Bergamo (1600-2400 m). In the Dolomites, the tiny species (the only one of its genus) alpine scurvygrass (Rhizobotrya alpina) grows on fine, humid limestone debris at 19002800 m. In the Carnic-Julian Alps, Traunfellner’s buttercup (Ranunculus traunfellneri) colonises even stable debris covered with snow at 15002300 m. In the northern Apennines, debris Alpine scurvy-grass (Rhizobotrya alpina) slopes are less extensive and host only two endemics. One is yellow thistle (Cirsium bertolonii), which grows in fine limestone debris in the Apuan Alps and on marl in the Tuscan-Emilian Apennines between 1000 and 2000 m. The other is Zanoni’s murbeckiella (Murbeckiella zanonii), found on fine sandstone debris. The situation is quite different in the central Apennines, where debris slopes are very extensive. The most important endemics are the elegant Apennine pheasant’s-eye (Adonis distorta), whose yellow flowers carpet debris covers to 2000 m. It often grows with Apennean pennycress (Thlaspi stylosum), a small, pink-flowered crucifer that is very similar to round-leaved pennycress in the Alps. The southern Apennines host another phyto-geographically important glareous plant that grows in patches in the Sicilian Madonie, snowy thistle (Ptilostemon niveus). It colonises limestone debris at 1200-1900 m. In Sicily, endemic glareous plants generally develop on the lava slopes of Mount Etna, like Sicilian soapwort (Saponaria sicula), whose pulvini with pink flowers dot lava beds to 2000 m. In Sardinia, there are few debris slopes and endemics. Hairy pearlwort (Sagina pilifera) typically grows on siliceous debris at high altitudes, and on the summits of the mountains in Corsica. Debris vegetation. On Italian mountains, debris vegetation includes several communities. In the Alps, Apennines and Sicily, these communities belong to the class Thlaspietea rotundifolii. Sardinian debris vegetation is still little known. The class Thlaspietea rotundifolii is divided into four orders (Thlaspetalia rotundifolii, Galio-Parietarietalia officinalis, Androsacetalia alpinae, Galeopsietalia). The first two include limestone debris vegetation, the others plants growing on siliceous debris. The order Thlaspetalia rotundifolii has the greatest number of communities, which are arranged at various altitudes and latitudes. The differing flora found within each community is due to the lithologic differences in clasts. From this viewpoint, one particular group of communities stands out: it colonises debris slopes produced by the disintegration of limestone, calcite and mica in the Alpine belt. This first group contains the communities Campanulo cenisiae-Saxifragetum oppositifoliae and Saxifragetum biflorae, both distributed along the Alps. The typical species of the second community is two-flowered saxifrage (Saxifraga biflora), which has recently been found in the Swiss Alps at 4450 m, and is therefore the highest-growing vascular plant in European mountains. The other communities of Thlaspietalia rotundifolii colonise limestone debris produced by crumbling limestone and dolomite, and may be grouped according to their geographic distribution, in the Alps and northern Apennines, or in the central-southern Apennines. In both groups, there are communities growing in alpine and sub-alpine belts (sometimes reaching the montane level). Berardie (Berardia subacaulis) 65 66 Many calcicolous glareous plants live in the Alps and northern Apennines. Among those of the alpine and snow levels is Papaveretum rhaetici, typical of limestone-dolomitic debris of the Southern Alps. Its characteristic species is Rhaetian poppy (Papaver rhaeticum), with its yellow flowers. Another community of this group is Leontodontetum montani, associated with finegrain debris of south-facing versants, with the typical mountain hawkbit. The montane and sub-alpine levels in the Alps and Apuan Alps host communities preferring south-facing debris slopes rich in fine sediments. In the sub-alpine belt of the Alps, the most frequent community is the Athamanto-Trisetetum distichophyllii, easily identified by the white umbrella-shaped flowers of athamanta (Athamanta cretensis). The Apuan Alps often host the community Heracleo-Valerianetum montanae, whose dominant species is Apennine cat’s ear (Robertia taraxacoides), a glareous plant found along the Apennines and on Sicilian and Sardinian mountains. Other communities colonise calcareous debris with coarse boulders in shady cirques of the montane belt and in the lower sub-alpine belt of the Alps and Apuan Alps. The particular microclimate of these areas favours the growth of ferns, like Dryopteridetum villarii, dominated by rigid buckler fern (Dryopteris villarii). Rhaetian poppy (Papaver rhaeticum) and white alpine poppy (P. julicum) The montane and alpine levels of the central-southern Apennines are inhabited by numerous communities of glareous plants. One of the most particular is Drypido-Festucetum dimorphae, which colonises mobile limestone debris with fine sediments with the thorny mats of spiny carnation (Drypis spinosa) and the large tufts of Apennine fescue (Festuca dimorpha). Higher altitudes in the central Apennines are the Val di Fassa saxifrage (Saxifraga depressa) preferntial locations of the CrepidoLeontodontetum montani community, with several glareous endemics, like Apennine pheasant’s-eye and Barrelieri’s sneezewort (Achillea barrelieri). A few communities of glareous plants grow in isolation on thermophilic limestone debris slopes of the montane level. Among them is Rumicetum scutati, in which French sorrel is the dominating species, found in the Alps and northern and central Apennines. In the southern Apennines and Sicily, the same habitat hosts snowy thistle, which forms the thermophilic glareous community Senecioni-Ptilostemetum nivei in the Madonie. The list of debris vegetation ends with the orders Androsacetalia alpinae and Galeopsietalia, which include the phytocoenoses of debris slopes formed of crumbling silica. The order Androsacetalia alpinae is found on silica and sandstone slopes in the Alps and Tuscan–Emilian Apennines, especially between the sub-alpine belt and the snow line. Among the most important communities of this order are Androsacetum alpinae, Sieversio-Oxyrietum digynae and Saxifragetum depressae. The last community was recently discovered on vulcanite in the Dolomites and contains Val di Fassa saxifrage (Saxifraga depressa). Lower altitudes of the sub-alpine and montane levels are colonised by Allosuretum crispae, a community with various ferns, especially parsley fern. Allosuretum crispae grows at the base of debris slopes, stable debris slopes with large clasts, and rockeries in the siliceous Alps and Tuscan-Emilian Apennines. The order Galeopsietalia includes phytocoenoses of thermophilic, siliceous montane and submontane debris. Shady debris slopes in Italy host only one community, Galeopsio-Rumicetum. 67 68 Endemics on cliffs and screes Cliffs and screes are conservative habitats par excellence. As such, they obviously contain larger numbers of endemics, which preserve the genetic memory of a territory better than species of other chorological categories. Mountain chains are considered the best areas for the development and formation of endemics and, since Italy is a mountainous country, its flora is duly rich in endemics, generally found in the mountains. Endemics are definitely more plentiful in mountain systems which have aboundant rocky slopes and scress. However, this is not the only and perhaps not the most important reason why such plants grow in these areas. Most important of all is the history of the mountain chain itself, its origin, and the fact that it was more or less isolated from nearby mountain ranges. Palaeoclimatic events, and glaciations in particular, also plaied an essential role in the origin of endemic plants. As already mentioned, the areas with the largest number of endemics are peripheral mountains, and their important role in cliff and scree flora has prompted the compilation of an updated, complete list divided by mountain sector. The list includes plants that are not true endemics, but whose distribution is nonetheless restricted to two distinct phytogeographic sectors. Marcello Tomaselli Ligurian and Maritime Alps LIMESTONE SUBSTRATES ● Cliffs > Ballota frutescens, Campanula albicans, Helianthemum lunulatum, Micromeria marginata, Moehringia lebrunii, Phyteuma cordatum, Potentilla saxifraga, Primula allionii, Saxifraga cochlearis ● Screes > Galeopsis reuteri, Galium saxosum, Iberis nana, Ligusticum ferulaceum SILICEOUS SUBSTRATES ● Cliffs > Saxifraga florulenta, Silene cordifolia ● Screes > Viola argenteria (also in Corsica), V. valderia South-western Alps LIMESTONE SUBSTRATES ● Cliffs > Alyssum ligusticum, Asperula hexaphylla, Campanula macrorrhiza, Moehringia sedifolia, Silene campanula ● Screes > Isatis alpina, Leucanthemum atratum ssp. ceratophylloides SILICEOUS SUBSTRATES ● Cliffs > Galium tendae, Jovibarba allionii, Saxifraga pedemontana, Sedum alsinefolium South-western Alps and northern Apennines LIMESTONE SUBSTRATES ● Cliffs > Primula marginata, Saxifraga callosa North-western Alps SILICEOUS SUBSTRATES ● Cliffs > Phyteuma humile, Potentilla grammopetala Western Alps LIMESTONE SUBSTRATES ● Limestone cliffs including calcschist > Androsace pubescens, Minuartia rupestris ssp. clementei, Saxifraga diapensioides, S. retusa ssp. augustana, S. valdensis, Sedum fragrans ● Screes > Allium narcissiflorum (also on serpentinite), Brassica repanda, Campanula alpestris, C. cenisia, Galium pseudohelveticum, Oxytropis fetida, Saussurea alpina ssp. depressa, Viola cenisia Mt. Cenis pansy (Viola cenisia) SILICEOUS SUBSTRATES Cliffs > Artemisia glacialis, Campanula elatines ● Screes (including calcschist) > Achillea erba-rotta incl. ssp. ambigua, A. nana, Adenostyles leucophylla, Campanula excisa, Coincya richeri, Leucanthemum atratum ssp. coronopifolium, Thlaspi rotundifolium ssp. corymbosum ● Piedmont saxifrage (Saxifraga pedemontana) Eastern Alps - Insubric district LIMESTONE SUBSTRATES ● Cliffs > Athamanta vestina, Campanula elatinoides, C. petraea, C. raineri, Daphne petraea, Minuartia grignensis, Rock mezereon (Daphne petraea) Moehringia bavarica ssp. insubrica, M. dielsiana, M. glaucovirens, M. markgrafi, Primula albenensis, P. grignensis, Saxifraga arachnoidea, S. presolanensis, S. tombeanensis, S. vandellii, Silene elisabethae, Telekia speciosissima ● Screes > Galium montis-arerae, Linaria tonzigii, Moehringia concarenae, Thlaspi rotundifolium ssp. grignense SILICEOUS SUBSTRATES ● Cliffs > Androsace brevis, Phyteuma hedraianthifolium ● Screes > Viola comollia Eastern Alps - Dolomitic district LIMESTONE SUBSTRATES ● Cliffs > Campanula morettiana, Minuartia graminifolia, Primula recubariensis, P. tyrolensis, Spiraea decumbens ssp. hacquetii ● Screes > Draba dolomitica, Festuca austrodolomitica, Rhizobotrya alpina, Saxifraga facchinii SILICEOUS SUBSTRATES ● Screes > Saxifraga depressa Eastern Alps - Carnic-Julian district LIMESTONE SUBSTRATES ● Cliffs > Arenaria huteri, Athamanta 69 70 turbith, Campanula zoysii, Cerastium subtriflorum, Pinguicula poldinii, Potentilla clusiana, Saxifraga tenella, Spiraea decumbens ssp. decumbens ● Screes > Alyssum wulfenianum, Festuca laxa, Ranunculus traunfellneri Traunfellner’s buttercup (Ranunculus traunfellneri) Eastern Alps LIMESTONE SUBSTRATES ● Cliffs > Androsace hausmannii, Campanula carnica, Minuartia cherlerioides, Paederota bonarota, Physoplexis comosa, Phyteuma sieberi, Saxifraga burseriana, S. hostii, S. squarrosa, Valeriana elongata ● Screes (including calcschist) > Achillea atrata, Androsace vitaliana ssp. sesleri, Aquilegia einseleana, Cerastium carinthiacum, Crepis Carinthian mouse-ear (Cerastium carinthiacum) terglouensis, Doronicum glaciale, Galium margaritaceum, G. noricum, Leucanthemum atratum ssp. halleri, Minuartia austriaca, Pedicularis aspleniifolia, Pritzelago alpina ssp. austroalpina, Saxifraga aphylla, Sesleria ovata, Soldanella minima, Thlaspi alpestre, Th. rotundifolium ssp. cepaeifolium SILICEOUS SUBSTRATES ● Cliffs > Androsace wulfeniana, Jovibarba arenaria ● Screes > Androsace wulfeniana Eastern and Dinaric Alps LIMESTONE SUBSTRATES ● Cliffs > Festuca stenantha, Moehringia bavarica ssp. bavarica, Paederota lutea, Saxifraga crustata, S. petraea, Silene veselskyi ● Screes > Alyssum ovirense, Campanula thyrsoides ssp. carniolica, Laserpitium gaudinii, Papaver kerneri, Silene quadrifida, Trisetum argenteum Eastern Alps and Apennines LIMESTONE SUBSTRATES ● Cliffs > Artemisia nitida, Moltkia suffruticosa, Potentilla nitida, Valeriana saxatilis ● Screes > Papaver ernesti-mayeri, Saxifraga sedoides, Valeriana supina Northern Apennines LIMESTONE SUBSTRATES ● Cliffs > Globularia incanescens, Leontodon anomalus, Polygala carueliana, Rhamnus glaucophyllus, Salix crataegifolia, Silene lanuginosa ● Screes > Cirsium bertolonii SILICEOUS SUBSTRATES ● Cliffs > Primula apennina ● Screes > Murbeckiella zanonii Central Apennines LIMESTONE SUBSTRATES ● Cliffs > Aquilegia magellensis, A. ottonis, Artemisia petrosa ssp. eriantha, Campanula fragilis ssp. cavolinii, C. tanfanii, Centaurea scannensis, Cerastium thomasii, Moehringia papulosa, Pinguicula fiorii, Potentilla apennina, Saxifraga ampullacea, S. italica ● Screes > Achillea barrelieri, Adonis distorta, Alyssum cuneifolium, Androsace vitaliana ssp. praetutiana, Cerastium thomasii, Cymbalaria pallida, Galium magellense, Ranunculus magellensis, Aquilegia champagnatii, Campanula pollinensis, Globularia neapolitana, Hieracium portanum, Lonicera stabiana, Pinguicula hirtiflora ● Screes > Leucanthemum laciniatum Sicily LIMESTONE SUBSTRATES ● Cliffs > Armeria gussonei, Asperula gussonei, Aubrieta deltoidea, Centaurea busambarensis, Draba olympicoides, Helichrysum nebrodense, Minuartia verna ssp. grandiflora, Silene saxifraga var. lojaconoi ● Screes > Senecio candidus ● Lava Screes > Anthemis aetnensis, Saponaria sicula, Scleranthus annuus Saxifraga speciosa Saxifraga speciosa, Thlaspi stylosum, Viola magellensis Central and southern Apennines LIMESTONE SUBSTRATES ● Cliffs > Achillea mucronulata, Saxifraga paniculata ssp. stabiana, S. porophylla ● Screes > Carduus chrysacanthus, Ptilostemon niveus (anche sulle Madonie) Central Apennines and Dinarids LIMESTONE SUBSTRATES ● Cliffs > Androsace mathildae, Malcolmia orsiniana ● Screes > Drypis spinosa, Heracleum pyrenaicum ssp. orsinii, Papaver degenii, Saxifraga glabella Central Apennines and south-western Alps LIMESTONE SUBSTRATES ● Screes > Festuca dimorpha Southern Apennines LIMESTONE SUBSTRATES ● Cliffs > Achillea lucana, A. rupestris, Sicilian soapwort (Saponaria sicula) ssp. aetnensis, S. vulcanicus, Sedum aetnense, Senecio aetnensis, S. ambiguus Sardinia LIMESTONE SUBSTRATES ● Cliffs > Armeria morisii, Asperula pumila, Campanula forsythii, Centranthus trinervis, Cephalaria mediterranea, Limonium morisianum SILICEOUS SUBSTRATES ● Cliffs > Armeria sulcitana, Helichrysum frigidum, H. montelinasanum, Herniaria litardierei, Potentilla crassinervia, Saxifraga cervicornis, Sedum brevifolium, Silene requienii ● Screes > Sagina pilifera 71 Animal life on cliffs and screes PAOLO AUDISIO · LUCIO BONATO As we have already mentioned in the introduction, conditions are very harsh for animals living in cliff environments, whether vertical, bare cliffs or consolidated debris slopes like screes and moraines. There are several natural factors that limit and determine the survival of animals living in such areas, the most important of which are described below. The steep, sometimes vertical substrates hinder the development of Rocky walls and screes are often associated mobile fauna living above ground. with each other (Vette Feltrine, Veneto) The mobility and instability of these areas, where landslides and debris flows are frequent, makes the life of non-flying animals extremely arduous. For instance, many terrestrial mammals find it difficult to move over these surfaces, which their feet cannot grasp firmly, preventing them from climbing up, down and over debris slopes and jutting rocks. These surfaces also thwart apodal (legless) species like snakes and a few saurians, and many vertebrates that live underground or in litter, like insectivores and rodents. But they are easily accessible to birds and indeed, several species use them as food sources, breeding grounds, or simply as refuges, favoured by little interspecific competition and low predation of nests. Among these are birds of prey such as falcons, hawks, eagles, ravens and crows. Among the vertebrates, only birds are truly adapted to life in these environments. Invertebrates are favoured by their small size and weight, which enable them to climb steep surfaces easily. However, the animals with the most successful adaptations are those that best adhere to the substrate - terrestrial molluscs whose tiny dimensions enable them to creep inside micro-crevices or under small pebbles. Examples are many microphagous beetles, those associated Chamois (Rupicapra rupicapra) 73 74 with aerial or underground plant parts (which therefore avoid steepness and direct contact with the ground, like many phytophagous insects), and insects that fly only as adults, are phytophagous, phytosaprophagous and parasitic, and adhere to the substrate, like many lepidopterans, dipterans and hymenopterans. The typical lack of nutrient supply in rocky montane substrates usually supports ephemeral, variable plant communities, with low levels of seasonal primary productivity. In these conditions, animal communities too are ephemeral and variable. Unlike fertile pastures, grass- and woodland that develop at high altitudes, food resources on cliffs and screes are generally insufficient. This affects phytophagans, which can only rely on scarce, seasonal plant biomass, and predators, because prey is restricted and varies unpredictably. Nonetheless, a few birds, rodents and carnivores are actually specialised in searching for food on screes and debris deposits, and several insect species are even exclusive to these areas. Another limiting factor is the aridity of substrates, especially in summer. That is, apart from the phenomena of temporary condensation and trickling water, the steepness of cliffs and the great superficial permeability of debris slopes prevent water stagnation and flow. True soil and significant plant cover that can even temporarily trap water or hinder its seepage are almost totally absent. Moreover, direct sunlight and winds accelerate evaporation and desiccation. This is why mountain cliff environments and their associated debris deposits do not include those aquatic or even humid habitats necessary to animal life. Among vertebrates, not only strictly aquatic species like fish, but also those partially associated with freshwater, like most amphibians, are totally missing. Among aquatic insects, flying imagoes of greatly vagile species may occasionally rest on stones, together with a few hygropetric animals, i.e., those associated with films of water colonised by algae which trickle down humid cliffs. Intense sunlight, especially in summer, usually influences substrates with low thermal capacity, i.e., those which warm and cool rapidly. This gives rise to thermal stress, daily and seasonal temperature variations that affect both heterothermic and homeothermic vertebrates. In addition, the climate is normally microthermic, with cold winds and heavy snow, which slides off steep cliffs. Great windiness and exposure to meteoric events responsible for avalanches, landslides and rockfalls may sweep away the animals living on Scree in the Carnic Alps (Friuli Venezia Giulia) Parnassius apollo, with wings damaged by flying in bad weather conditions 75 76 the surface of cliffs and screes, especially tiny invertebrates - including flying species - thus increasing their mortality and hindering potential colonisation. Low temperatures and windiness thwart olfactory and pheromonal orientation and communication, favouring visual capacity. By contrast, the scarce vegetation and evenness of structure and colour make most animals, especially vertebrates, very conspicuous to predators. Regular visitors such as rodents and song birds are therefore elusive. Another important factor is the typical fragmentation of these often isolated mountain habitats. The combination of this and all the above conditions hinders the breeding and reproduction of many species, particularly the most specialised ones with small communities and lower distribution capacity, which are therefore liable to local extinction. Conversely, there are other abiotic factors which actually favour animal life and contribute towards mitigating the otherwise harsh conditions of cliff and scree environments, thus fostering the development and specialisation of animal communities. For example, exposure to sunlight, together with restricted snow cover in winter due to great steepness, favours a local spring-summer-autumn microclimate. This enables many xerothermophilous Mediterranean animals like insects, pulmonate molluscs and a few reptiles to live at unusual altitudes and at very high northern latitudes. However, when snow melts in summer, alpine and high-altitude screes with sufficient debris cover provide the optimal conditions for the life of a few lithoclase arthropods living on incoherent rock debris. The only way of finding these animals in summer is by patiently digging into the scree surface to the depth at which cold and condensation last into the summer. Although wind, lightning and storms negatively affect plants in exposed cliff environments, there is some beneficial influence on animals, especially xylophagous insect species. They find ideal conditions for feeding on the woody parts of suffering, decaying shrubs. Many xylophages are also xerothermophilous, and find their ideal habitat on sunny cliffs. Consequently, also the entire community of insects associated with xylophages (especially hymenopterans and predatory beetles) is favoured. In addition, the “hedge effect” of cliffs and river valley inlets interrupting the landscape profile, provides at its base areas of accumulation for many animals, especially flying insects (and plant seeds), which are carried by wind. Similarly, Steepness and exposure to sunlight restrict accumulation of snow on screes The harvestman Mitopus morio 77 78 Peregrine (Falco peregrinus) high-altitude and crest screes often host low-altitude invertebrates (flying insects like dipterans, coleopterans, hymenopterans and lepidopterans), which are carried from valleys to mountain summits, where they form ephemeral, “drifting” communities. Mountain microhabitats, with higher average summer and autumn temperature, favour temporary colonisation by these insect species, increasing biodiversity in such harsh surroundings. Lastly, the typical fragmentation of these montane habitats, which are isolated from each other and host small animal communities, may favour Extensive debris deposits in upper Val Cimoliana (Friuli Venezia Giulia) genetic differentiation over time, giving rise to possible micro-evolutionary phenomena of speciation, like those that affected invertebrates during the Plio-Pleistocene macroclimatic cycles. Although mountain cliffs and screes are extremely selective environments, it is precisely for this characteristic that colonising animal species, especially arthropods, have very particular features. There are three main categories of animals living in these areas: phytophagans in general, which are variously associated with the aerial parts of typical local plants, including insects which are anthophagous (feeding on flowers), phyllophagous (feeding on leaves), xylophagous (feeding on wood) and spermatophagous (feeding on seeds) associated with chasmophytes and glareous plants. There are also some molluscs, rodents and artiodactyls, microphagous and phytosaprophagous animals associated with selected plant debris deposited in rock crevices and scarce soil (roughly eroded substrates) underneath pebbles and gravel (such as insects, a few isopod crustaceans, millipedes and several molluscs), and predators (arachnids, insects, occasional centipedes, a few reptiles, song birds and raptors). The first group includes animals with specific adaptations to these habitats; the second and particularly the third group include euryphagous animals that require little food. 79 80 River gorges From the natural and landscape viewpoints, few Italian habitats are as fascinating as river gorges, independently of their bedrock geology, altitude, and the rivers or streams that created them. Part of their charm is their brusque interruption of the geomorphological and vegetational continuity of the landscape. In addition, they have always been very difficult to colonise by man, although some populations did find refuge there, either inside karst cavities or by widening natural openings which had recently been used by grazing sheeps and goats. For centuries, therefore, gorges avoided the typical destruction and uncontrolled modification of natural environments, thus becoming, especially at low altitudes, true “natural islands” capable of surviving severe anthropic impact. Gorges are important natural “corridors” between areas, and are also natural traps in which animals living nearby fall. They are refuge areas for many vertebrates escaping predators and disturbing factors, and some bird species also find optimal safe nesting and breeding grounds. The deepest and narrowest gorges reveal considerable vegetation inversion caused by the different positions of the rocky walls. Plants typical of the upper horizon grow in the valley, which is more humid and shaded, and those that normally grow at lower horizons develop high up on sunny versants. This makes unusual stratifications possible, especially along south- and north-facing versants, where xerothermic, sub-Mediterranean and the opposite sciaphilous, cryophilic flora and fauna mix. This gives rise to surprisingly high levels of local biodiversity, with phenomena similar to those of the deep Paolo Audisio · Lucio Bonato · Marcello Tomaselli River cirque in the Abruzzi Apennines dolinas (sinkholes) typical of karst landscapes (see the chapter “Dolinas” in the Habitat volume “Caves and karstic phenomena”). Many of the animals and plants that colonise the vertical or subvertical walls of gorges are the same as those living on mountain cliffs, but the peculiar conditions mentioned above enable larger numbers of species from different areas and with differing ecological requirements to inhabit these gorges, especially the deepest ones. The mixture of xerothermophilous and sciophilous elements is particularly evident in the vegetation growing at medium-low altitudes. Phytoclimatically distinct species with similar behaviour grow within a few metres of each other, like evergreen oak (Quercus ilex) and beech (Fagus sylvatica). There are also rare plants that are exclusive to these areas (palaeo-endemics, species with fragmented distribution or which survived as relics). In the South-western Alps, rocky gorges at medium-low altitudes host phytogeographically important species such as shrubby horehound (Ballota frutescens) and Allioni’s primrose (Primula allionii). Typical inhabitants of these environments in the South-eastern Alps are Carnic sandwort (Arenaria huteri) on limestone mountains east of the river Piave, hairy spiraea (Spiraea decumbens) and, on cliffs with trickling water, the recently discovered Poldini’s butterwort (Pinguicula poldinii). Cirques in the Apuan Alps frequently contain Reichenbach’s butterwort (Pinguicula reichenbachiana), those in the central Apennines short-haired sandwort (Moehringia papulosa), the Gola del Furlo in the Marches and the Gole in Val Nerina house Mt. Nebrodi joint pine (Ephedra major), and cliffs with rilling water columbine (Aquilegia ottonis) and Fiori’s butterwort (Pinguicula fiorii). Among phytophagous insects in particular, there are highly specialised species of great conservative value that are exclusive to these relict areas. Carnic sandwort (Arenaria huteri) Mt. Nebrodi joint pine (Ephedra major) This is the case of snout beetles like the rare weevil Ceutorhynchus pinguis, an Apennine endemic associated with the crucifer diffuse alyssum (Alyssum diffusum), C. verticalis, a southern Apennine endemic associated with vertical cliffs, as its name implies, and living on Aurinia saxatilis, and particularly Mesoxyonyx osellanus, another Apennine endemic which was only recently discovered and is associated with the rare, relict Ephedra major, which are also found at medium altitudes on vertical limestone cliffs of river gorges. Among nitidulid beetles, Meligethes lindbergi is typical of Apennine, Sicilian and Sardinian river gorges. It is monophagous (feeding on a single type of food) and associated with the germander Teucrium flavum (a plant of 81 82 River gorges the mint family). The similar M. nuragicus lives on Teucrium massiliense in analogous inland environments in Sardinia. Meligethes subfumatus is often found on sunny cliffs in the Maritime and Ligurian Alps on another member of the mint family, Lavandula angustifolia, and the Italian sub-endemic species M. scholzi is typical of medium-low altitudes on rocky cliffs and gorges of southern Italy, feeding exclusively on Ballota rupestris (again of the mint family). A few xylophagous, xerophilous Mediterranean and sub-Mediterranean beetles live outside their usual areas on exposed, sunny cliffs of river gorges, like several long-horned beetles and a few buprestids, the larvae of which develop exclusively or preferentially within the dry twigs of evergreen and sclerophyllous oaks (Cerambyx scopolii, Anaglyptus gibbosus, Stromatium unicolor, Trichoferus holosericeus, Deroplia genei, Latipalpis plana, etc.), on Genista (Trichoferus spartii) and figs (Stenhomalus bicolor). Other species typical of mesophilous habitats colonise shady versants and are associated with broadleafs like linden (Exocentrus lusitanus), hornbeam (Axinopalpis gracilis), and even beech (Rosalia alpina, a species of European Community interest), and a few mountain pines (e.g., Arhopalus ferus). Typical bugs of these environments are several lace bugs (Tingidae) of the genus Copium, associated with small cliff germanders (Teucrium). Among hymenopterans, sphecid wasps of the genus Sceliphron attach their mud nests to the cliffs. They hunt spiders on which their larvae feed. A few species of potter wasp (Eumenes) can use the same areas as nesting grounds. Their jug- Paolo Audisio · Lucio Bonato · Marcello Tomaselli Cerambyx scopolii Anaglyptus gibbosus Stromatium unicolor shaped nests have a central bulge, which is moulded after the cells have been stocked with caterpillars and their eggs laid. There are also several lepidopterans, especially the rare papilionid butterfly Papilio alexanor, which lives in isolated locations and is associated with xerophilous umbellifers growing along river gorges in the Maritime Alps, Calabria and eastern Sicily. The nymphalid butterfly Polygonia egea, which is now very rare and localised, generally grows on pellitories (Parietaria of the nettle family). Among preying spiders, the three Italian Segestria species (Segestria bavarica, S. florentina, S. senoculata) can be found all over Italy in cliff crevices and under stones up to intermediate altitudes. River gorges traversing limestone are typically inhabited by hygrophilous and xeric mollusc species, according to the varying degree of humidity of the local, cool microclimate. Among them are several prosobranchs of the genus Cochlostoma, the species of which live in restricted areas, the pyramidulid Pyramidula pusilla and P. rupestris, and numerous species of chondrinids of the genera Rupestrella, Condrina and Solatopupa (all of which live in restricted areas). There are also numerous pulmonate snails of the genera Clausilia and Charpentieria, most of which live in northern Italy, Delima (central Italy), Papillifera, Leucostigma, Medora in the Apennines, and Sicillaria and Muticaria in southern Italy. There are many cliff species of snails living on the cliffs near river valleys, like Chilostoma in the Alps, Marmorana in the Apennines and on the major Italian islands, and Tyrrheniberus in Sardinia. Although for many vertebrates the vertical, rocky cliffs of river gorges are inhospitable environments, some species actually find these areas optimal habitats to shelter and reproduce. Cliffs are inaccessible to predators and unlikely to be disturbed by man, and they also offer environmental (microclimatic) conditions which differ from those of surrounding areas. In southern Italy, these cliffs (below 1000 m) are nesting grounds for birds of prey like Egyptian vulture (Neophron percnopterus), Bonelli’s eagle (Hieraaetus fasciatus) and lanner (Falco biarmicus). Although not exclusive to river valleys, other cliff species regularly breed in these areas, examples being blue rock-thrush (Monticola solitarius), black-eared wheatear (Oenanthe hispanica) and raven (Corvus corax). Unfortunately, river gorges have recently suffered severely at the hands of man. The greatest threat comes from roadbuilding projects, as valleys are obviously natural shortcuts. Roads, motorways, railways, pipelines and power lines have often been built to pass through river valleys, destroying or greatly jeopardising the landscape and biological quality of the valleys themselves and of the rivers flowing through them. In particular, roads and railways are often protected against rockfalls and landslides by controlled explosions, and nets, metal barriers and reinforcements are then set up. River valleys are also affected by the uncivilised practice of many Mediterranean countries, which use them as dumps for civil, agricultural and even industrial waste (especially rubble from construction sites, obsolete household appliances, sewage, animal carcasses, etc.), which have obvious consequences on the local animal and plant communities. 83