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Ecological Flora of the Central Chilterns Section 4: Betulaceae Tongue gall on unripe alder cone Tony F Marshall, M.A. (Cantab.) August 2014 Family: Betulaceae (Birches) 4.1 Silver birch Betula pendula This tree grows commonly and seeds readily across our area, even on the clays, although its more natural substrate is drier sandy soil and it is infrequent on chalk. It colonises heathland particularly quickly. It was an early immigrant following the retreat of the glaciers at the end of the Ice Age. Like the plane-tree, the peeling outer layers of bark help it withstand pollution, so it does well in built-up areas. Identification The peeling silver paper-thin layers composing the outer bark make it a very familiar tree, although care has to be taken to distinguish introduced American poplars. Saplings have a reddish bark. As an older tree it loses its whiteness at the base of the trunk as the bark becomes deeply furrowed and rugged, although it does not reach any great age or bulk. The ultimate twigs are very slender and hang down (hence pendula). The leaves are small, oval, longpointed, with uneven serration that tends to alternate smaller and larger teeth (bi-serrate). The flowers are catkins that produce copious tiny winged seeds spreading all too effectively in the wind. Notable sites It has a presence in almost all our woods, but is rarely a defining or dominant tree. An exception is Sandwich Wood, Little Kingshill, where, after clearance of planted timber, it became the dominant colonising species, even more than ash, and now in parts forms a dense uniform birch-wood. The soil is a very sandy clay (as reflected in the name of the wood). The ground flora contains many plants and fungi rare in this region, typical of acid soils, such as hard fern and oval sedge, which must be survivors from earlier open woodland. This wood may well have been managed as wood-pasture by the monks of Missenden Abbey in medieval times. Nearby is Birchmore Wood (now predominantly beech), which was at the edge of Wycombe Heath before it was enclosed and largely built over. It is likely that birch was a major component of such heaths and commons in our area before the enclosures, at least on the sandier clays typical of parts of the Prestwood and Kingshill region. NVC In the NVC silver birch is shown as occurring at low frequencies in most woodland types. The exception is W16 oak/birch/wavy hairgrass woodland, confined to very acid soils in the southern lowlands. Sandwich Wood, as it was, and as it is now again developing, would probably fit this profile. Galls The most obvious gall on birches is a large ball of proliferating twiglets hanging in the tree and particularly conspicuous in winter, a “witches’ broom” caused by the fungus Taphrina betulina, common across the area. 17 other gall-causers are known, as befits the tree’s long-standing as a native. Six of these have so far been recorded locally: two mites Aceria lissonota and Cecidophyopsis betulae, the aphid Hamamelistes betulinus, & 3 gall-midges: Plemeliella betulicola, Semudobia betulae & S. tarda. The last two gall the seeds and are difficult to find, but are both common. In addition, the crown gall, caused by the bacterium Agrobacterium tumefaciens, which affects many different plants, creates lumpy swellings on birch trunks. Mines Even more leaf-miners are known from Britain on birch (55). Eleven recorded locally are: the agromyzid fly Agromyza alnibetulae; the micro-moths Eriocrania salopiella, Ectoedemia minimella (particularly common), E. occultella, Stigmella confusella, S. lapponica, Caloptilia betulicola (the birch leaf roller), Parornix betulae, Phyllocavella ulmifoliella, and Lyonetia clerkella; and the sawflies Trunk of 30-year-old tree Autumn leaves Male catkins in pollen. Erect female flowers above will later lengthen & droop as seed catkins Scolioneura betuleti (autumn) and S. vicina (spring), the second a recent immigrant, first seen in Ireland in 1942, having mines exactly like the first, but in a different season. Other ecological associates More species have been recorded in association with birch in our area than with any other tree, confirming its firm establishment at the heart of the local ecosystem, at least on the sandy clays. Most of these records are from Sandwich Wood*, and/or the 30-year-old birch-tree in my garden in Prestwood^. A few others are from other sites (eg Angling Spring Wood, Lodge Wood) bordering the Prestwood-Kingshill plateau. These associated species include: Large white-moss Leucobryum glaucum. 34 fungi: Amanita citrina (including var.alba)*, A. fulva, A. muscaria* (Fly Agaric, abundant in Sandwich Wood), A. rubescens*; Clitocybe odora*; the webcaps Cortinarius anomalus*, C. delibutus*, C. triumphans^ and C. violaceus*; Hebeloma crustuliniforme*^ (very common); Laccaria laccata*, L. proxima*; Lactarius glyciosmus*, L. pubescens^, L. rufus*, L. tabidus* (birch milkcap, abundant in Sandwich Wood), L.torminosus^, L. turpis*, L. vietus”; Leccinum roseofractum^, L. scabrum*^ (brown birch bolete), L. variicolor*, L. versipelle (orange birch bolete, a particular feature of Sandwich Wood); Lenzites betulinus (birch maze-gill); Paxillus involutus (brown roll-rim, abundant under my birch tree, where it often forms fairy rings); Piptoporus betulinus^ (birch polypore, whose brackets are common on the older trees); Russula aeruginea^, R. betularum*^ (birch brittlecap), R. exalbicans^, R. fragilis, R. gracillima*; Tricholoma fulvum (birch knight); Melampsoridium betulinum^ (birch rust); Nectria cinnabarina (coral spot on dead birchwood); and Hypoxylon multiforme on fallen twigs. 6 plant-bugs, especially birch shield-bug Elasmostethus interstinctus*^, Elasmucha grisea^, and Kleidocerys resedae^. 2 plant-hoppers, Oncopsis flavicollis and O. subangulata. 4 aphids. Lacewing Wesmaelius betulinus^. 5 beetles: leaf-beetle Cryptocephalus bipunctatus, two weevils, Deporaus betulae^ (a leaf roller) and Apion simile, and two found in birch polypore brackets, Cis micans and C. setiger. Four other beetles associated with birch were recorded before WWII, two of them now Notable B, and may still exist. 12 micro-moths, most commonly Ypsolopha parenthesella and Apotomis betuletana. 19 larger moths, most commonly Large emerald, Buff-tip^, Lime hawkmoth, Lesser swallow prominent, Broken-barred carpet^, Scalloped hazel^, Pebble hook-tip^, Scarce Umber^ and Pale oak beauty^. I saw the usually high-flying Orange underwing once at long grass beneath a birch tree. 2 sawflies, Arge clavicornis and A. ustulata. Redpolls are most likely to be seen in winter feeding on birch seeds. Human associations According to Hooke (2010), individual trees were rarely referenced in Anglo-Saxon place-names, although birchwoods do so more commonly, no doubt due to the paucity of aged specimens. It features, however, in folklore and its wood was used for timber, young flexible branches for whips (hence "to birch"), and bundles of long twigs for brooms. One of the first trees to come into leaf, it acts as an early sign of spring. Derivation From Anglo-Saxon berc, itself of ancient origin, as in the Sanskrit bhūrja. The Latin betula has the same root. 4.2 Sandwich Wood, Little Kingshill - young birchwood Birch polypore bracket Mines of Ectoedemia occultella Mine of Scolioneura vicans 4.3 Silver birch tree showing fine drooping twigs Crown gall on birch Downy birch Betula pubescens There are no records for this species for our area in Druce (1927), but recent records show it occurs quite frequently in the wetter parts of woods on acidic clays in small numbers, usually with silver birch. It does not seem to be a heathland tree with us, as it is elsewhere. All the specimens I have seen were young trees, so it may be a recent immigrant or descended from planted hybrids (x aurata), which are inseparable in the field. Identification The leaves are more rounded and not attenuate at the tip as in silver birch and are more uniformly serrate, not bi-serrate. Young twigs and leaf-stalks are densely downy, but this is soon lost with age. The bark of older trees is greyish, not the bright white of silver birch. Notable sites Lodge Wood is the best place to look. Ecological associates Basically the same as for silver birch. Leaf-miners seen specifically on pubescens locally are the moth Eriocrania cicatricella, the sawflies Fenusa pumila and Scolioneura vicina, and the fly Agromyza alnibetulae. Downy birch leaves 4.4 Downy birch leaves with mines of Eriocrania cicatricella (left) & Fenusa pumila (centre) Downy birch: mine of Agromyza alnibetulae Hazel Corylus avellana The familiar "nut-tree" seldom exceeds a large bush. It is ubiquitous in hedgerows and wood-edges on all soils, and may also occur within woods and as part of scrub on chalk. It was usually coppiced in the past, either to form a dense boundary or as a source of hazel poles, regularly re-cut on a cycle of up to 10 years, so that the boles may be of great antiquity. It was one of the earliest colonising species after the last Ice Age, but numbers have probably been increased by deliberate planting in hedgerows in early times for its fruit and coppice. Identification The round leaves, typically 8-9cm across, although larger on new shoots, have attenuate tips and short white hairs, more or less decumbent, above, and longer soft white hairs beneath on the veins. Twigs and leaf-stalks have dense brown glandular hairs. The long male catkins develop towards the end of the year and become bright yellow with pollen in our area about the beginning of February. The female flowers are much smaller and inconspicuous apart from their bright red styles that emerge after pollen is shed, ensuring crossfertilisation. The nuts are encased in two densely white-hairy pale green bracts, hardly overlapping at the base and exposing most of the nut, which ripens hazel-brown. Fully developed nuts typically 1.9cm long, 1.5cm wide. Notable sites An old coppice stool of 3.6m girth was recorded by Edward Milner by the River Misbourne between the Mobwell and Great Missenden. Former coppiced hazel hedges can be seen in many places, such as the track past Andlows Farm and at the back of Binders Industrial Estate, Cryers Hill. It grows abundantly in scrub at Prestwood Picnic Site; in the derelict old orchard beside Widmere Field, just south of the west end of Lodge Lane, Prestwood; and in Rignall Wood. Galls Of the six galls on hazel in Britain, half have been recorded locally: the mites Phyllocoptruta coryli, which distorts the catkins, and Phytoptus avellanae, which enlarges axillary buds, and the fly Mikomya coryli. Mines Twenty different leaf-miners are recorded in Britain, of which nine are known locally, all micro-moths. Commonest of these in descending order of frequency are Phyllonorycter coryli (nut leaf blister moth), Stigmella microtheriella, Ectoedemia minimella, Phyllonorycter nicellii, and Parornix devoniella. Other ecological associates Two aphids are recorded, the whitish Myzocallis coryli (hazel aphid) underneath the leaves, and Corylobium avellanae, a red-mottled green or brown species with longer siphunculi under young leaves or on the tips of shoots. Brown Soft Scale Coccus hesperidium is common on twigs. Birch Shieldbug (see above under silver birch) is also found on hazel, along with two other plant-bugs, the common Pinalitus cervinus and Pantilius tunicatus. Green shieldbug Palomena prasina, which can be found on many trees, seems to have a particular affinity with hazel, on which it is often found in large numbers in late summer. Two lacewings tend to be associated with hazel, particularly Hemerobius lutescens. Seven beetles have also been recorded, most notably the leaf-beetle Altica brevicollis, and the weevils Apoderus coryli (hazel leaf roller) and Curculio nucum (the nut weevil that develops in the fruit and can be a crop pest). The colourful green, yellow and black caterpillars of the sawfly Croesus septentrionalis can strip twigs bare of the leaves in hardly any time at all. Five non-mining micro-moths have been recorded, and three larger moths, of which the July Highflyer and the Nut-tree Tussock are particularly frequent. I have also found the pupa of a Small White butterfly on hazel. The hazel dormouse has been recorded in our area a few times, but no established colonies have yet been confirmed. 4.5 Toothwort often grows under hazel, as it does in our one local site, the bottom of Kingstreet Lane, Little Missenden. The moss Ulota bruchii grows locally on hazel. Ten fungi have been recorded in particular association with hazel, five toadstools (of which Greenflush Fibrecap Inocybe corydalina and Leccinum pseudoscabrum are the most frequent), and five that grow on living or dead wood, most notably Cinnamon Porecrust Phellinus ferreus, Hazel Bracket Skeleteocutis nivea, Bleeding Broadleaf Crust Stereum rugosum, and Hazel Woodwart Hypoxylon fuscum. Human associations The hazel is most celebrated for its edible nuts ("cobs"), although the commercially grown "Kentish Cobs" come from the introduced Filbert Corylus maximus (below) which has larger nuts. Shrubs were regularly coppiced to provide the flexible poles used in fencing and thatching. Hazel features frequently in old place-names and as medieval boundary-markers, often with reference to woods and thickets, so it has always been abundant. Locally, Hazlemere derives its name from the shrub, although the former village is now a built-up extension of High Wycombe, hazel is no longer prevalent, and the "mere" has gone altogether. Derivation Both Anglo-Saxon haesel and Latin corylus derive from the ancient Indo-European root represented in Sanskrit by kosa "case or shell", by reference to the nut that is hazel's chief claim to fame. Similarly the specific name avellana derives from Latin avellare "to pluck". "Cob" occurs in Old English as copp, used for any rounded object, like the top of a hill, and ultimately from a Flemish or Frisian word with similarly wide connotations, including a round loaf of bread, a stumpy horse, or a head. Varieties The variety "contorta" of native hazel (Corkscrew Hazel), with grotesquely contorted twigs and leaves, is sold in local garden centres and grown in gardens. These are probably of hybrid origin. Hedge of neglected old hazel coppice, Russells Water Male hazel catkin, red female flower just above Hazel in leaf, Rignall Wood Hazel nuts, west edge of Hazlemere 4.6 Caterpillar of sawfly Croesus septentrionalis in threat position Mines of Phyllonorycter coryli in hazel leaf Filbert Corylus maximus This SE European species is closely related to our native species and is capable of being fertilised by pollen from C. avellana. It was introduced for its larger nuts and has long been grown in orchards in the region for its fruit, known as Kentish cobs (from its particular frequency in Kent). It can grow into more of a tree than hazel. Identification The leaves tend to be larger than hazel, typically 12cm across, but the best distinction is provided by the nuts. These are larger (typically 2.6cm long, 1.9cm wide) and often completely hidden by the calyx, which is even longer than the nuts (by around 1cm) and pinches inwards at the tip to further hide them. The calyx is not divided to the base, the deepest split being to about half-way to the base (at most two-thirds), and then often overlapping so as to leave very little of the nut exposed. Notable sites The measurements above were taken from a garden tree and a row of specimens in the hedge bordering Prestwood Picnic Site. One old specimen survives in a remnant of an orchard now part of the garden attached to a private residence in Upper North Dean. It was regularly grown in the former orchards of our area. Ecological associates As for hazel. The mines of Phyllonorycter coryli, Stigmella microtheriella and Incurvaria pectinea have all been recorded locally on filbert. Human associations Grown commercially for its nuts (Kentish cobs). Derivation The Normans knew the filbert as noix de Philibert and probably introduced it, as it was known in Britain as early as the 14th century. They named it after St Philibert because the nuts were said to ripen about his day, 22 August. In our area, while well-grown by this date they are probably not fully ripe until a few weeks later. Varieties A purple-leaved variety 'Purpurea' is probably the most often sold commercially these days, but I have not seen it in the wild. Filbert. Leaf has mine of Stigmella microtheriella 4.7 Hybrid cob Corylus avellana x maxima Hazel and filbert are readily inter-fertile and commonly form hybrid trees wherever they exist in proximity. There is some difference between sources as to whether Kentish cobs were pure maxima or this hybrid. The existence of former orchard specimens in our area which correspond to maxima indicates that some, at least, of the planted cobs were that species, but garden trees in the area include true filbert and the hybrid. Identification Intermediate between the parents, the hybrid hazel can show various characters of the two. Examination of local specimens has shown that the leaves are typically 9-10.5cm across. The calyx exceeds the nut by 5-10mm, somewhat pinched or not, split to the base at one side, although usually overlapping to various degrees, so exposing 40-90% of the nut, which on average is 2cm long by 1.7cm wide. (This description corresponds in essential details to that of Wilcox, 2013.) Wilcox (pers. comm.) has also found that the catkins of the hybrid are wider than those of the native. Notable sites Probably widespread but difficult to identify if not in fruit. There are specimens in a hedge bordering the field behind Green Lane, Prestwood (which may once have backed a domestic orchard) and at Prestwood Picnic Site, where both parents occur. It is also probable that many of our apparently native hazels, especially near houses and in newly planted hedges, are hybrids. Although advertised as "native British", many commercially available hazels, even if propagated in Britain, are originally from continental stock that is in fact hybrid. Hybrid hazel. The leaf at the front has a mine of Stigmella microtheriella Turkish hazel Corylus colurna Occurs only as a planted tree in Priestfield Arboretum. It is easily distinguished by the very laciniate calyx surrounding the nut. (Note tent-mines of Phyllonorycter coryli on leaves in the photo below.) Turkish hazel Hornbeam Carpinus betulus 4.8 As a relatively late invader after the Ice Age this tree has a limited distribution nationally, being native only in south-east England and there not common everywhere, but in our area it is undoubtedly common on all clay soils. It was a favoured tree of hedgerow planters in past centuries because it responds well to laying, and this has probably increased its frequency even further, as with hazel. As well as hedgerows it occurs commonly also as a woodland tree, capable of competing with beech in terms of height. It self-sows readily. Identification The characteristic dark and light brown-grey vertical streaks down the trunk make it easily recognisable even in winter, although old specimens become deeply ridged. The leaves are similar to beech but sharply bi-serrate around the margins and impressed veins. Like birch and hazel, the male flowers, in March-April, are catkins of yellow-green flowers with brownish bracts. The smaller female flowers have tri-lobed green bracts that expand later to hide the small nutlet. These are very conspicuous hanging from the twigs in summer/autumn and distinct from any of our other native fruits. Notable sites Many of our hedgerows and wood-edges contain former laid hornbeams - eg Hampden Road opposite Stonygreen Cottages, Mapridge Green and Hobbshill Lanes, the east edge of Lawrence Grove. Occasional pollards are also encountered. As a woodland component it is particularly frequent in Angling Spring Wood, including some old laid specimens along the southern boundary; it is also frequent in College Plantation, Speen. Hornbeam is not very long-lasting: the largest so far measured was just 2.6m in girth (copse in centre of Big Park, Great Hampden). Another of almost that size (2.55m) stands at the north-west corner of Lawrence Grove Wood - it already looks spectacularly troll-like although it cannot be more than 200 years. The same wood contains other good specimens. Galls The small number of known galls may reflect the native tree's sparse distribution. A fungus Taphrina carpini causes witches' brooms, while two mites and one gall-midge cause leaf-galls. Taphrina, the mite Aceria tenella, and the midge Zygiobia carpini have been recorded locally causing galls on hornbeam. Mines Of the 16 leaf-miners recorded on hornbeam in this country, six (all micro-moths) have been found locally. The mines of Phyllonorycter quinnata and Stigmella microtheriella are very common; P. esperella and tenerella, Parornix carpinella and Bucculatrix thoracella have also been recorded. Other ecological associates Relatively few associates have been recorded locally. Pale aphids on the underside of leaves Myzocallis carpini are specific to hornbeam. The smooth bark is a favourite of the tree slug Lehmannia marginata that ascends in wet weather to graze the lichens. Jays enjoy the nuts along with beechmast and acorns, but hawfinches, who are said to be particularly attracted to the fruits, have not been recorded for a long time, although feeding damage characteristic of these birds was reported beneath a hornbeam in Boss Lane a few years ago. Just three local moths, apart from the leaf-miners, are associated with the tree - small white wave, Ypsolopha parenthesella, and Aleimma loeflingiana. There are, however, some uncommon fungi that tend to be associated with hornbeam, all but one of which have been found under hornbeam in Angling Spring Wood. The commonest is the milkcap Lactarius circellatus, which is likely to appear at any site where hornbeam grows. Three other milkcaps also occur - L. fluens, decipiens and pterosporus. Also frequent is Leccinum pseudoscabrum. Human associations In Anglo-Saxon times this tree seems to have had little significance and rarely, if at all, appears in place-names. Its hard wood was useful for some items of carpentry, however, and, coupled with its suitability for laying in hedges, it appears to have become more favoured in the 17th to 19th centuries. Derivation Anglo-Saxon horn and béam is literally "hard" (like horn) "tree". Local Bucks names hay-beech and horned beech refer to its beech-like leaves and use in hedges (hay) and winged seeds ("horns"). Hornbeam leaves Laid hornbeams marking ancient boundary bank 4.9 Hornbeam in fruit Old hornbeam, Meadsgarden Wood Autumn colours of yellow and gold Hornbeam trunk showing white streaks, Peterley Wood Tree with witches' brooms Taphrina carpini Alder Alnus glutinosa 4.10 This native wetland tree, typical of riversides ("Alder by the Aqua"), has no native sites in our area, which includes only the upper sections of streams that usually dry up in summer (and these days are often dry all year). It has, however, been planted in two places beside the River Misbourne and in a plantation beside Angling Spring Wood. It grows rapidly but does not reach any great age. Identification The obovate leaves (wider at the tip) and male catkins followed by female cones are sufficient to distinguish this tree from any other natives. Notable sites Two young trees stand in Boug's Meadow beside Link Road car-park in Great Missenden, but the only mature specimens are older plantings in Abbey Park. The largest of these has a girth of 3.07m. Galls Out of ten gall-causers known in this country, four have been recorded locally - remarkable given the paucity of alder trees. These are the fungus Taphrina alni which creates remarkable red tongues on young cones, and three mites affecting the leaves: Acalitus brevitarsus, Aceria nalepai and Eriophyes laevis. Mines Of 22 leaf-miners on alder recorded from this country, a remarkable number (10) are known to occur on alder (including planted species, below) in our area. These comprise 9 micro-moths (Stigmella alnetella, Caloptilia elongella, Incurvaria pectinea, Phyllonorycter falconipennella, P. froelichiella, P. kleemannella, P. rajella, P. stettinensis, P. strigulatella) and one sawfly Heterarthrus vagans. Other ecological associates Four common aphids are associated with alder and may occur locally. Two insects are named after alder - the Alder Fly and the Alder Moth; both occur locally but neither is associated particularly with alder. The fly is associated with water because that where its larvae live, so the fact that alder flies and alder trees tend to occur in the same areas is purely coincidence. The moth may use alder but is equally likely to use any other tree - and, in our area, more likely to do so. A vapourer moth caterpillar was found in 2012 on the alders at Boug's Meadow. Derivation Anglo-Saxon alor and Latin alnus share a common ancient root. The specific name glutinosa "glue-like" refers to the fact that the young twigs and leaves are sticky, unlike its introduced relatives (below). Tongue gall on unripe cone Alder 100-200 years old already decaying Galls of Aceria nalepai 4.11 Galls of Acalitus brevitarsus Male catkins, February Galls of Eriophyes laevis Italian alder Alnus cordata Alien tree from southern Italy planted in several woodlands and as an amenity tree. In our area it is commoner than the native alder. Identification Distinguished by larger flowers and fruit, and glossy leaves that are more or less cordate (cordata) at the base (not cuneate) and pointed, somewhat acuminate at the tip. Notable sites Mixed with other new planted trees in several of the Hampden Estate woodlands - Warren, Widnell and Hengrove. As an amenity planting at the cemetery at Cryers Hills, and by the pond in the grounds of the Chiltern Hospital. Grey alder Alnus incana Alien tree planted in a very few places. Identification The leaves are oval, rounded at the base and pointed, not glossy, more deeply serrate and paler underneath. The cones have shorter stalks than common alder. The bark is somewhat greyer than its congeners, hence the name. Notable sites There is a recent record from Hughenden, and it is also current at Brickfields, Prestwood. 4.12 Hybrid alder Alnus x hybrida (= A. glutinosa x A. incana) This planted amenity tree has been recorded at two sites in our area. Identification A mix of characters of both parents: the leaves are variable, cuneate or rounded, some flattened at the tip, others pointed, with few veins like glutinosa, but distinctly pale beneath and deeply serrate. The cones are unstalked or short-stalked. (See picture below.) Notable sites Planted by Cockpit Hole, Great Kingshill, and by road in front of Prestwood Picnic Site. Ecological associates Probably as for common alder. The mines of Heterarthrus vagans have been found on the trees by Prestwood Picnic Site. Hybrid alder, Cockpit Hole