Download Sandy Coastal Vegetation

INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
SANDY COASTAL VEGETATION
D.S.D. Araujo
Department of Ecology, Rio de Janeiro Federal University, Brazil
M.C.A. Pereira
Herbarium, Rio de Janeiro Botanical Garden, Brazil
Keywords: Vegetation types, flora, community structure, diversity, distribution,
conservation
Contents
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
1. Introduction
2. Landforms and climate in coastal areas
3. Vegetation types and community structure
4. Life forms
5. Species diversity and geography
6. Conservation
Glossary
Bibliography
Biographical Sketches
Summary
U
Sandy coastal ecosystems are severely threatened all over the Tropics due to their
location near the ocean, ideal spots for tourism, recreation and summer homes. They
also provide environmental services to man in the form of buffer zones against storm
surges, reduced beach erosion, and recreation areas, among others. Therefore
understanding the ecology of the organisms that inhabit these regions is extremely
important if humankind is to conciliate the use of the environment with preservation of
ecological processes so as to take advantage of the services provided by these
ecosystems.. Our aim in this chapter is to describe what we know about various aspects
of the vegetation of these sandy coastal plains. To form a backdrop for this scenario, we
first define the landforms that underlie this coastal vegetation and the environmental
factors that have the greatest influence on the plants. Then we stress the extremely
heterogeneous nature of the underlying substrate and how this is reflected in vegetation
physiognomy and structure. We also discuss variations in species diversity at various
scales and how these plants are distributed geographically. Finally, we consider various
conservation aspects of these ecosystems.
1. Introduction
Sandy coastal deposits are found on shores all over the world, from polar latitudes to the
tropics. The forces that create, mold and destroy these deposits are basically wind, sea
level oscillations and the presence or absence of vegetation. Time is also an important
factor in this process, especially on prograding shorelines. A profile of these sandy
deposits represents a time series, from young beach sands to older, often stabilized,
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
inland deposits. Ecological zonation is clearly demonstrated on sandy coasts especially
as one walks from the beach inland. The forces mentioned above create an extremely
varied landscape, from tall dunes and beach ridges where the water table lies deep
below the soil surface to wet slacks that lie between these dunes and beach ridges, some
of which are permanently flooded. This variety is reflected in the diversity of vegetation
types and relatively large numbers of plant and animal species that are generally found
along the coast.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
The plants of these sandy plains are grouped together in communities, or plant
formations, that owe their special physiognomy to habitat conditions found at the site, to
the kinds of species that have managed to arrive and become established locally, and to
the length of time these species have been growing together, free from major
disturbance. The long-term evolutionary history of the coastal plain during the
Quaternary period and the kinds of ecosystems that occupy the surrounding landforms
are two other factors that exert a strong influence on the vegetation physiognomy and
floristic composition of each area of coastal plain. Coastal plains can be regarded as
islands scattered along the coastline because they are often isolated within
amphitheaters formed by coastal mountain ranges or rocky headlands, bordering on
bays or coves. Or they may be isolated from other areas of sandy coastal plains by the
estuaries of large rivers. Extensive dune fields often develop on low-rainfall coasts in
the Tropics (e.g., Lençois Maranhenses, Brazil; Skeleton Coast of Namibia, Africa) and
may extend for many kilometers inland. These often lie near a cold water upwelling that
brings nutrients to the surface from the depths of the ocean, thus providing rich fishing
grounds (e.g., coastal Peru; Cabo Frio region, Brazil).
U
Coastal plain ecosystems are seriously threatened because of their location beside the
sea. Summer houses and seaside resorts spring up overnight in many parts of the
Tropics, resulting in biodiversity loss, environmental disturbance and conflict-ofinterest issues. Many countries have special coastal management programs, but these
focus mainly on fisheries conservation, leaving much to be desired as regards
preservation of plant cover. Coastal conservation units exist in many parts of the world,
but they are often effective on paper only.
Here we present a description of the various types of plant communities that are found
on sandy coastal plains and discuss the main environmental factors that influence the
plants in these communities, what kinds of species are most common and how diverse
are these communities, what is the geographic distribution of the majority of the
species, and what are the most common threats to these habitats. But first we must
define the landforms that underlie these coastal plain communities.
2. Landforms in Coastal Areas
The vegetation which we will be dealing with in this chapter overlies a variety of
landforms or substrate types. These landforms, plus the prevailing regional climate,
greatly influence the plant communities and so it is important to understand more about
them.
Coasts are dynamic in nature, ever-changing because of a myriad of forces that act upon
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
them. They are constantly evolving, and globally plate tectonics, or movements of the
Earth’s crust, contribute greatly to these processes as do relative sea-level changes.
Remember that in the not-so-distant past (some 18 000 years ago), sea level was 100 m
or more below present levels, and that during more recent times (some 5 100 years ago),
sea level was 4-8 m above its present level. So the coastline we know today has
migrated over considerable distances, especially in areas of low declivity. Sea-level rise
in these areas inundates beaches and swales, and on some coastlines, may totally erode
beach ridges. Older landforms of Pleistocene age lying farther inland at higher
topographic levels are sometimes spared from erosion by rising sea levels, being found
in coastal areas even today. So, coastal plant communities overlie sediments that vary
greatly in age.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
On low coasts, tides play an important role in coastal dynamics, as for example in the
state of Amapá on the Brazilian coast. Here tidal amplitude is up to 12 m, one of the
largest in the world. Another factor that influences coastline evolution is the sediment
source, which may lie quite far inland (sediments brought to the shore by large rivers)
or which may be close by (a broad continental shelf). Winds play an important role in
the dynamics of coastal habitats, such as, for example, in forming waves that upon
reaching the coast erode or rework the sandy sediments of the intertidal zone.
Changes in coastlines are largely the result of changes in sediment supply. The sediment
source may have disappeared, such as when replenishment from rivers is interrupted or
when sediments from the continental shelf have been transported to dune fields. Man’s
interference in coastal areas (attempts to “stabilize” the coastline, occupation of the
narrow strip most affected by storms, etc.) also affects coastal processes and may cause
the retention of sediments or the disappearance of the natural buffer strip that protects
zones farther inland from storm surges.
U
The most common sandy coastal deposits are beaches, beach ridges, dunes, and strand
plains. Beach ridges are long sandy deposits that run parallel to the coastline, often
isolating lagoons in areas of shallow coastal waters, whereas dunes consist of wind
deposited sediments that lie atop the beach ridges or strand plains. Mobile dunes are
often found near the beach, where wind action is more intense, while dunes stabilized
by vegetation usually lie farther inland, behind the mobile dunes.
3. Vegetation Types and Community Structure
As can be seen from the above, sandy coastal environments are characterized by
environmental heterogeneity that is caused in part by geomorphological diversity. They
are found on a variety of landforms and the plants that grow there are greatly influenced
by oceanicity, that is, the influence that the ocean exerts on continental land masses.
The resulting scenario is a mosaic of vegetation types.
The best approach to presenting these vegetation types is perhaps along the natural
gradient from the beach inland. Here we have not only a gradient of factors resulting
from the presence of the ocean (e.g., salt spray, wind velocity), but also a temporal
gradient in the age of the substrate, which increases in this direction. On broad coastal
plains this gradient may not be continuous in a sea-inland direction due to the presence,
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
today or in the past, of rivers, estuaries, lagoons, or other landforms. In this case, the
sequence of natural accretion processes has been interrupted, as for example by the
presence of a former river bed (paleocanal) that reveals where a river once cut through
the sandy ridges to reach the sea, or by the nonalignment of these very ridges that
reveals the presence of strong erosive action during sea-level oscillations.
Near the ocean, plant communities on sandy deposits usually reveal a sharp zonation
pattern subdivided into an outer pioneer zone and an inner dense coastal thicket. Plant
communities farther inland do not necessarily follow a linear sequence across the dune
field or strand plain. However, they are located along a gradient of increasing
community complexity, that is, greater species richness and cover, taller stature, and
greater biomass.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
3.1. Beach Communities
U
Beach vegetation is probably the best known of all the plant communities found on
sandy shores. This vegetation grows on beaches all over the Tropics. Anyone who has
ever walked along a sandy shore is familiar with the strand plants that grow on the
shifting sands of the upper part of the beach. These plants form a dense cover on
sheltered beaches where storm surges are uncommon and there is some degree of
protection from strong winds. On unprotected beaches, subject to the full force of the
waves and prevailing winds, the low shifting foredunes are only partially fixed by
plants. In either case, this vegetation is inevitably washed by the sea at one time or
another.
Figure 1. Strand vegetation reclaiming the beach after a storm surge; the dominant
species is Ipomoea pes-caprae. Note the denser plant cover on a slight rise which was
not affected by the last storm surge. Northern coast of Rio de Janeiro, Brazil.
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
The dominant species in this community are pioneer plants, that is, they are the first
flowering plants to colonize the sand as it is deposited along the shore by wave action.
They are called psammophytes because they prefer sandy substrates. Storm surges
sometimes destroy these plants or bury them in sand, but as the storm abates, the beach
profile becomes stable once more (even though it may be only for a short time), and
long runners of Ipomoea pes-caprae or Sporobolus virginicus, two pantropical species,
soon appear, advancing over the reworked sands towards the water’s edge (Figure 1).
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
The physiognomy of beach vegetation is basically the same all over the Tropics. In the
pioneer zone, plants must be able to take advantage of the new habitat that is made
available for colonization on prograding coastlines. Low creeping plants usually form
sparse cover on foredunes, increasing in density inland along a disturbance-inundation
gradient. Many of these species are grasses, sedges, or creepers that have long, fastgrowing stolons or rhizomes to keep pace with sand burial. In contrast, it is rare to find
large woody species here because they usually do not tolerate wave disturbance and
sand movement. Some plants also have succulent leaves and stems as a mechanism for
water storage. This is the case of the beach scaevola (Scaevola plumieri), a low, pioneer
plant from the Goodeniaceae family that inhabits beaches and dunes on the tropical
shores of North America, South America and Africa. The seeds of this species roll
down the slope of the beach from the dense clumps of Scaevola growing on the
foredune crest and germinate in drift material. They are carried to other sites on the
same beach or to other beaches, where the plant becomes established. Scaevola plumieri
plays an important role in sand stabilization and foredune development because of the
continuous growth of its stem and root system (Figure 2).
Figure 2. A foredune stabilized by Scaevola plumieri; Cabo Frio region, Brazil.
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
Beach vegetation usually forms a very narrow strip on the upper beach of many coasts.
However, in areas of low rainfall or where mobile dunes lie in a wide band next to the
beach, the species found on the upper beach may penetrate as far as two kilometers
inland.
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
Landward of this stretch of creeping psammophytes on primary dunes we find a totally
different vegetation type, and the boundary between these two types is usually quite
sharp. Here, active sand interchange with the beach is nonexistent, over-wash frequency
falls off sharply and disturbance from the sea is rare. This gives rise to a dense, stunted,
sometimes thorny, thicket that defies human penetration. The vegetation is low towards
the beach, gradually increasing in height inland and sometimes merging into a low
forest (Figure 3). At first glance, the woody plants seem to have been neatly pruned.
Wind is the factor here, together with salt spray, which kills off the shoots on the
seaward-facing side of the thicket. In the Neotropics, cacti and bromeliads with thorny
edged leaves are often common in this vegetation type, while some shrubs have sharppointed branch tips that contribute to the impenetrability of the woody barrier. The herb
layer is usually quite sparse because the dense, shrubby canopy limits light penetration.
Figure 3. A preserved stretch of coastal plain vegetation in southern Rio de Janeiro
state, Brazil, where rainfall is ca. 2000 mm annually. Note the wind-pruned aspect of
the woody vegetation.
This vegetation type is common on the coast of Brazil and in many other parts of the
world such as most of Africa, New Zealand, Australia, the gulf coast of the United
States, Mexico and Central America.
Some species are restricted to this narrow strip of vegetation even though they may
have a wide distribution along the tropical coast. For example, Jacquinia armillaris
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
from the Theophrastaceae occurs only in this narrow strip of coastal scrub and in saline
areas near lagoons in Brazil, but it grows all along the tropical Brazilian coast, to
northern South America, Central America, and the Caribbean.
3.2. Open Scrub Vegetation
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
In many parts of the world, extensive areas of sandy coastal plains are covered by open
scrub vegetation that may lie behind the coastal thicket described above or farther
inland. The presence of this vegetation is closely related to the topography of the strand
plain (Figure 4). Where series of abandoned parallel beach ridges alternate with
depressions (swales) in a regular pattern, dry open scrub vegetation occurs at the higher
elevations, that is, on the crest of the beach ridges, while wet open scrub lies in
depressions. The beach ridges follow a chronological sequence of increasing age
landward, the innermost ridges being older than those closer to the ocean. These can be
dated when a sequence of aerial photographs is available. Open scrub vegetation also
grows on partially stabilized dunes.
Figure 4. Aerial photo of a strand plain with (A) alternating series of long, parallel
beach ridges with dry open scrub vegetation interspersed with (B) seasonally flooded
forests associated with lagoon arms and (C) wet open scrub occupying the swales.
Northern coast of Rio de Janeiro state, Brazil (Photo scale - 1:8000).
The water table underlying dry open scrub vegetation is always several meters below
the surface, and therefore the area is never flooded. Woody thickets of various sizes and
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
shapes with sparse herbaceous undercover are scattered over the sandy substrate. The
area between the islands of woody vegetation is occupied by a very sparse, mostly
herbaceous cover, exposing a great deal of bare sand. In the Neotropics, it is common to
see dense carpets of bromeliads in the herb layer underneath or on the edge of these
thickets (Figure 5). Species of cacti and a geophyte palm (Allagoptera arenaria) are
also present. Woody species dominate and vines are also common components of the
vegetation islands because of high exposure to incident light. The shrubs support few
vascular epiphytes, but in the denser, more humid patches, lichens and bryophytes are
quite common.
Figure 5. A typical thicket of the open scrub vegetation with a dense layer of bromeliads
(Vriesea neoglutinosa) underlying the 5-meter-tall Clusia hilariana shrubs; the stemless
palm in the foreground is Allagoptera arenaria. Northern coast of Rio de Janeiro state,
Brazil.
These vegetation islands often have one or more key species that facilitate (at least at a
certain life-cycle stage) the arrival of other species, thus constituting a positive
interaction between plant species. On Brazilian coastal plains, this may be a pioneer
plant such as Allagoptera arenaria whose seeds germinate on the bare sand even when
soil-surface temperatures reach 70oC. The leaves of this palm provide shade and reduce
temperatures for other arriving species. Another key species in this region is Clusia
hilariana (Clusiaceae) which germinates in the tank of a bromeliad (Aechmea
nudicaulis). The young plant escapes from the tank when the outer bromeliad leaves
die, and upon reaching a certain size favors the establishment of other species in this
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
community. Positive interactions between species are especially important in structuring
communities that occur in resource-poor environments, such as sandy coastal plains.
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
The patchy organization of dry open scrub communities has intrigued researchers for
years, raising questions as to the origin of vegetation islands. Some think this
community is maintained by human interference (e.g., trampling by animals or vehicle
use on the coastal plain, frequent fires), but a consensus has not yet been reached.
Patchiness may be due to unequal distribution of soil nutrients or other habitat factors,
or it may be an inherent characteristic of the vegetation itself. Studies of dry open scrub
vegetation on strand plains in Brazil have shown that the processes of patch formation
and evolution vary from one strand plain to the next. Open scrub vegetation grows on
dunes, but vegetation structure is apparently quite different. A variety of species play
the role of pioneers, resulting in functional model diversity.
Figure 6. A) Wet open scrub in the dry season; B) Water table floods low-lying open
scrub after a heavy rain; C) Rusty colored water due to the presence of humic acids; D)
Thicket carpet of lichens growing under dense vegetation islands.
Wet open scrub vegetation is found in low-lying areas that are subject to flooding
during periods of heavy rainfall due to a rise in the water table. These areas may once
have been lagoons; they often lie in the middle of the strand plain (see Figure 4),
interrupting the continuity of ridges and swales. Here, the water table normally lies only
about 50 cm below the soil surface. The water that drains from these areas is a rusty
brown color, which reveals a build-up of peat deposits and high concentrations of humic
acids (Figure 6). At higher topographic levels within these areas, open scrub vegetation
is physiognomically similar to that described above; however, the area between the
vegetation islands is covered by a dense herb layer. Even these areas are flooded briefly
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
after a heavy rainfall. In lower lying areas where water-table levels are above-ground
for most of the year, the shrubby vegetation is taller and denser, with a closed canopy..
Species composition varies along this gradient and termite mounds are common; it is
common to find lichen species in the herb layer of more humid areas. Where flooding
frequency is greater, the plant community is poorer in woody species, but richer in
herbs. Bonnetia stricta (Theaceae), a low tree widely distributed in the Neotropics, is
often monodominant in these areas.
3.3. Coastal Plain Forests
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
The forests of these coastal plains are usually governed in structure, species diversity
and composition by topography and, to a certain extent, by sediment age and soil
salinity. Dune forests grow in areas where the water table is deep below the surface,
while in wet areas such as the slacks between dunes or beach-ridge swales, there are
seasonally flooded forests or sometimes permanently flooded forests (swamp forests).
Well-developed dune forests are found on older beach ridges or on dunes that have been
stable for a long time. Although these forests do not measure up in stature to most
tropical rain forests, they often have high species diversity. The canopy is usually ca.
15-20 m above the forest floor, with some emergent trees growing to 25 m tall. This
forest appears to have only one layer in the understory. Dense patches of bromeliads are
common in the herbaceous layer.
Seasonally flooded forests are found in swales between beach ridges, while permanently
flooded forests are usually found near lagoon margins, on peat soils. Overall diversity in
these forests, especially the swamp forest, is usually lower than that of dune forests due
to the dominance of few species. Where the substrate is flooded for most of the year, the
dominant tree species is often deciduous, allowing light to penetrate to the forest floor at
certain times of the year. Here, dense layers of bromeliads provide viable germination
sites for some tree species.
U
3.4. Dune Field Vegetation
Dune fields deserve special mention here. As was seen above, dunes may overlie sandbased landforms such as beach ridges, but they are also built on top of other coastal
landforms such as limestone cliffs (e.g., Africa) or clayey Tertiary deposits (Barreiras
Formation - Brazil). The areal extent of these dune fields depends on ocean currents,
climate, wind direction and frequency, and the topography immediately behind the
beach. The plant species growing on dunes or in wet slacks between dunes are usually
the same as those that occupy ridges and swales, but with varying abundance and spatial
distribution. The herbaceous communities that occupy wet slacks, swales and lagoon
margins are typical of marshes the world over, and are exceptionally rich in grasses and
sedges.
4. Life forms
Plants can be classified ecologically as well as taxonomically. This classification results
in a series of different life forms. The life form spectrum of a given stand reflects the
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
physiognomy of the vegetation, and life form spectra vary across a gradient of different
vegetation types. It is important that we understand life forms because they are the
structural components of vegetation and they also provide us with a way of
understanding the plant’s relationship with the environment without identifying species
using taxonomic nomenclature (a very difficult task, especially in tropical forests!).
In the early 1900s, the Danish botanist Raunkiaer proposed a system of life forms that
classified plants ecologically. This classification is based on a single trait that is related
to the phenology and morphology of the species and that is important for the diagnosis
of the plant’s strategy when faced with adverse climate or environmental conditions
(e.g., fire).
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
A graph of species frequency in relation to life form class is called a biological
spectrum (Figure 7). Raunkiaer constructed life-form spectra for the world’s flora
(known as Raunkiaer’s normal spectrum) as well as for different vegetation types
worldwide. These spectra show a correlation between vegetation type and climate. For
example, in deserts ca. 60% of the species are therophytes - plants that produce seeds
annually and then die. This life form represents maximum escape strategy during
adverse climate conditions (cold or dry season) since the species disappears from the
habitat. Its regeneration module (embryo) is protected by a hard seed coat and awaits
more favorable conditions to initiate the germination process and produce new plants.
On the other hand, in tropical forests where the environment is much milder year round,
phanerophytes (huge trees over 40 m tall to small woody plants ca. 1 m tall)
predominate (65%). This life form represents a tolerance strategy, that is, the buds are
exposed and the aerial part of the plant is present during more adverse conditions.
Figure 7. Life-form spectra of different biome types in Brazil: Restinga (sandy coastal
plain) - Rio de Janeiro, Rain forest – Santa Catarina, High altitude grassland, Rio de
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
Janeiro; and Raunkiaer’s normal spectrum; FAN – phanerophytes; CAM – Camephytes;
HEM – Hemicryptophytes; GEO – Geophytes; TER – Therophytes
Sandy coastal plain (restinga) forests and shrubby vegetation behave like tropical
rainforests, but the herbaceous communities have high percentages of geophytes and
hemicryptophytes. The buds responsible for plant renewal in geophytes are hidden in
the soil while in the case of hemicryptophytes, they are found at soil level, protected by
the litter layer or by the leaf sheaths that have died and remained attached to the plant.
This represents an escape strategy.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
Raunkiaer’s classification system is still used today because of its simplicity in
comparing vegetation types that are made up of different species (from different
environments, on different continents). However, this system does not consider the
behavior of plants during the growing season and this has limited its use in tropical and
subtropical climates where there often is no sharp distinction between seasons. Other
systems have been proposed that use a number of attributes based on our knowledge of
what role these traits play in the adaptation of plants to the environment and how they
contribute to vegetation structure and physiognomy when viewed independently.
In the past 15 years, the use of multiple attributes has been employed to recognize
recurring patterns of traits in dominant species in studies in various parts of the world.
This allows us to identify functional groups, that is, groups of plants that show similar
response to environmental conditions and have similar effects on the main ecological
processes, but are not necessarily related to one another.
U
The search for these functional groups aims to reduce the complexity of plant species
and their populations in order to create models that will predict how vegetation will
respond to habitat disturbance and future climate changes. These models are expected to
predict more precisely how species will respond when faced with environmental
change. This will provide a basis for decision making concerning which species should
be used in recovery and restoration of disturbed areas. For example, sandy coastal plain
species have the ability to stabilize shifting dune sands so these species can be used to
contain the sands of reject piles resulting from mining activities. Furthermore, since
many of these species originally came from the Atlantic forest and colonized the more
recent coastal plains, some can be used for the recovery of areas of this forest that have
lost plant cover due to climate change. Which species should be used to this end will
depend on how well we know their biology, the functional groups to which they belong
and their role in ecological processes.
5. Species Diversity and Geography
5.1. Species Richness
Sandy coastal plains are usually thought of as being rather poor in plant species. This
notion is probably derived from our concept of the harsh beach environment or the
sometimes rather sterile habitats of active sand dunes. But we must take into account
that these sandy plains may also be occupied by full-fledged tropical forests that hold
their own in species diversity when compared to contiguous montane forests. For
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
example, a well-preserved beach ridge forest near Rio de Janeiro, Brazil, standing some
300 m from the ocean, was shown to have over 110 large tree species (Shannon´s index
> 4.0), which compares favorably to species richness in neighboring low-montane
Atlantic forests. These forests also have a rich understory of shrubs and herbs, and
many epiphytes.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
Species richness, cover, stature and biomass of sandy coastal plain plant communities
increase along a gradient from the sea inland. There is also increasing community
complexity along this gradient, which may possibly be related to an increase in age of
the substrate. Species richness of the vegetation types along a transect from the ocean
to the innermost beach ridges in the Restinga de Jurubatiba National Park, located on a
broad strand plain in Rio de Janeiro state, Brazil, is given in Table 1. The dune forest
and the seasonally flooded forest are probably much richer in species than is evident
from the data, for these forests have not yet been properly surveyed. The open scrub
vegetation types have been quite thoroughly studied and this is reflected in the total
number of species present. Habitat complexity in these two-phase plant communities
probably contributes to species richness since the islands of woody vegetation create a
number of different microhabitats (shaded interior, sunlit canopy, edge) in addition to
the open, sparsely covered areas between the islands. The islands are especially rich in
lianas.
A comparison of species richness on a regional scale, from one sandy coastal plain to
the next along the coast shows that overall richness varies greatly. This is due in part, of
course, to the fact that the number of species is related to the size of the area and the
areal extent of coastal plains varies widely. But habitat diversity also contributes to
increased species richness. Coastal plains that are cut by rivers or have many lagoons
and series of depressions between the beach ridges, or regions that are partially covered
by dune fields tend to have higher species diversity. Historical factors may also enter
into the picture, and former isolation events may have led to greater numbers of
endemic species, which also contributes to overall species richness.
U
5.2. Geographic Distribution
Plant communities by the sea tend to have a high percentage of cosmopolitan species.
The foredune plant community, for example, near the beach (pioneer zone) is
characterized by widely distributed species and genera. These plants occur on beaches
all over the tropics and are said to have a pantropical distribution. Common species that
show this wide distribution are the creepers Ipomoea pes-caprae, Sporobolus virginicus,
Remirea maritima and the succulent shrub Scaevola plumieri. The grasses and sedges
found in the wet slacks between dunes and beach ridges also tend to have a widespread
distribution.
Another group of species that shows a relatively ample geographic range in coastal
areas includes those tolerant of relatively high levels of soil salinity, species that occupy
beaches but also find a suitable habitat in the transition zone between dunes and saline
areas (mangroves, salt flats). Species in this group that tend to extend over several
degrees of latitude along the South American coast are Chrysobalanus icaco (beach
plum), Dalbergia ecastophyllum (coin vine) and Jacquinia armillaris.
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
In the plant communities further from the beach, where factors such as inundation by
seawater, salt spray, and wind speed and frequency are attenuated, the vegetation
consists of species that often have more restricted distributions. Many forest species are
restricted to coastal plain forests and to the vegetation type that lies closest to the coastal
plain. For example, in eastern Brazil, tree species endemic to the coastal plain forests
are quite rare, most species being found also in the contiguous Atlantic forest. In fact,
overall species composition of the coastal plain vegetation is highly influenced by the
neighboring vegetation type, with about 80% of the species occurring also in the
contiguous Atlantic rain forest. Species endemism is rather low in these coastal plain
communities, suggesting that there has not been enough time for speciation after the
geologically younger coastal plains were occupied by Atlantic forest species.
6. Conservation
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
Coastal areas have a long history of human habitation. In eastern South Africa, human
settlements on the coast date to 4 A.D. Early inhabitants were attracted to the coast by
freshwater sources and abundant food. In the New World, we have some notion of how
tribal groups lived in coastal areas due to the presence of shell mounds, that is, sites
where there are accumulations of shells and the bones of animals that were eaten by
these people, as well as evidence of hearth fires. The vegetation surrounding these areas
often contains an abundance of plant species that have a history of use by man.
Therefore, coastal vegetation most certainly has a long history of exploitation.
In arid and semi-arid regions of the Old World, coastal areas are still used by man for
sustenance. Range livestock (sheep, goats, camels, donkeys) is a traditional method of
land use, causing a tremendous impact on the vegetation through over-grazing and
trampling. In areas where a fragile herb layer protects sandy sediments, such intensive
use causes erosion and the activation of once stable dunes.
U
Valuable mineral resources are often found in sandy coastal areas. Dunes are mined for
heavy metals (e.g., ilmenite, rutile, zircon) and diamonds. Dune quarries supply sand for
construction and cement manufacture. Intense disturbance by these activities often
destroys the vegetation completely. Strip mining for diamonds in Namibia removes the
soil, exposing the old rocky sea bed. Oil spills at sea may reach the coast, causing
severe damage to wildlife and polluting pristine areas.
In other places, the vegetation itself is the target of exploitation. It is the source of fuelwood and charcoal. Some coastal species were once harvested for their valuable dyes
(Brazilwood – Caesalpinia echinata; Logwood - Haematoxylum campechianum).
Wildlife habitats are destroyed as beach ridges and dunes are cleared for planting
coconut palms, cassava, groundnuts, okra and pineapple. Grass is often planted under
the palms to serve as pasture for cattle, and wetlands are drained, killing off forests.
Since the 1970s, man has come to regard the seashore as a prime vacation spot. In
Brazil, for example, where the country’s largest cities are located along the coast due to
its colonization history, there is pressure from a growing population that wants to
vacation in areas outside the city. Summer homes and seaside resorts have had a
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
tremendous impact on the vegetation of beaches and sandy coastal plains.
Unfortunately, governments often provide incentives for developing these areas.
Natural processes also take their toll on coastal plant communities. The first obstacle
encountered by hurricanes when they make landfall is beach and coastal vegetation. The
predicted rise in sea level resulting from climate change will have a huge effect on
coastal communities, as it has in the past.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
So what is a tract of coastal vegetation worth? It provides protection against storm
surges, forming a buffer that helps to protect adjacent farmland or urban areas. It
reduces beach erosion and aids in groundwater replacement. It provides a backdrop for
recreational activities and ecotourism. And it contains a myriad of plant species that are
used by traditional fishing communities, among other uses, that can only survive in a
natural setting. In the late 20th century, conservation efforts were focused on plant
inventories, preserving rare species from extinction and maintaining the habitats of as
many species as possible. Today, attention is more sharply focused on understanding
the physical and ecological processes that take place in these habitats. Sustainable use of
coastal areas will depend largely on involving local communities and governments in
the decision-making process so as to effectively manage these areas to the satisfaction
of all users.
Glossary
Beach ridge:
Biodiversity:
Chamaephyte:
U
Creeper:
Dunes:
Endemic:
Flora:
Geomorphology:
Geophyte:
Habitat:
Halophyte:
Hemicryptophyte:
Holocene:
Intertidal zone:
Neotropics:
Oceanicity:
Elongate sandy deposit formed by storm waves and currents,
parallel to the shoreline, separated from each other by shallow
depressions.
The variety of life at three different levels: genetic diversity;
species diversity; and ecosystem diversity.
Low-growing perennial plants having renewal buds at or just
above ground level (50 cm).
A plant that spreads along the surface of the ground.
Sandy elevations formed by sediments transported by the wind.
Native to, and restricted to a particular geographical region.
The plant life of a given region.
The study of the characteristics, origin and development of the
surface features of the earth
A perennial plant having renewal buds buried well below the
soil surface.
The locality, site and particular type of local environment
occupied by an organism.
A plant living in saline conditions.
A perennial plant with renewal buds at ground level or within
the surface layer of the soil.
A geologic epoch within the Quaternary period (ca. 10 000 years
B.P. to the present time).
The shore zone between the highest and lowest tides.
The tropical region of the New World.
The influence of the ocean on continental land masses.
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
Widespread throughout tropical regions of the world.
The characteristic features or appearance of a plant community
or vegetation.
The first species to colonize a barren or disturbed area.
Pioneer species:
A geologic epoch within the Quaternary period (ca. 1 600 000
Pleistocene:
years B.P. to 10,000 years B.P.).
A coastal region where the shoreline is advancing toward the
Prograding coast:
ocean.
A plant with stems that lie flat on the ground.
Prostrate:
A plant growing in unconsolidated sand.
Psammophyte:
Retrograding coast: A coastal region where the shoreline is retreating.
A horizontal underground stem.
Rhizome:
A vegetation type consisting of low trees and shrubs.
Scrub:
a diversity index that takes into account the number of
Shannon’s index:
individuals as well as the number of species.
Relative species abundance in a given locality.
Species diversity:
The absolute number of species in an assemblage or community.
Species richness:
An elongate, horizontal stem that grows along the ground and
Stolon:
roots at the nodes or at the tips, giving rise to a new plant.
A plant growing on the shore immediately above high tide level.
Strand plant:
A series of ridges typically associated with and parallel to a
Strand plain:
beach forming a coastal plain.
A long, narrow, usually shallow trough between beach ridges.
Swale:
A dense vegetation type with continuous canopy consisting of
Thicket:
shrubs and small trees.
A phenomenon of coastal regions where cold, heavy, deep water
Upwelling:
laden with nutrients flows upward as warm surface water is
drawn away by offshore currents.
The total plant life or cover in an area.
Vegetation:
The distribution of organisms in distinctive areas, layers or
Zonation:
zones.
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
Pantropical:
Physiognomy:
U
Bibliography
Martinez M.L. & N.P.Psuty (eds.) (2004). Coastal dunes: ecology and conservation. 386 pp. Berlin:
Springer-Verlag. (Ecological Studies 171.) [This text is a basic compendium of current knowledge on
coastal dunes in various parts of the world.]
Rocha C.F.D., F.A.Esteves & F.R.Scarano (orgs.). (2004). 374 pp. Pesquisas de longa duração na
Restinga de Jurubatiba: ecologia, história natural e conservação. São Carlos: RiMa. [This text
summarizes a number of seminal studies on sandy coastal plain vegetation in the southeast region of
Brazil.]
Scarano, F.R. (2002). Structure, function and floristic relationships of plant communities in stressful
habitats marginal to the Brazilian Atlantic Rainforest. Annals of Botany 90: 517-524. [This paper
discusses Atlantic coastal vegetation as a complex series, focusing on the positive interactions among
plants in communities that are marginal to this Atlantic forest]
Seeliger, U. (ed.) (1992). Coastal plant communities of Latin America. 392 pp. New York: Academic
Press. [This text provides descriptions of the most common coastal plant communities found in Latin
America.]
Van der Maarel E. (1993). Dry Coastal Ecosystems: Africa, America, Asia and Oceania. 616 pp.
©Encyclopedia of Life Support Systems (EOLSS)
INTERNATIONAL COMMISSION ON TROPICAL BIOLOGY AND NATURAL RESORCES - Sandy Coastal Vegetation D.S.D. Araujo, M.C.A. Pereira
Amsterdam: Elsevier. (Ecosystems of the World 2B.) [This text discusses the ecology of all types of
coastal ecosystems.]
Biographical Sketches
Dorothy Sue Dunn de Araujo teaches Plant Ecology in the Ecology Department and gives a course in
Methods for Sampling Vegetation for graduate students at Rio de Janeiro Federal University. Her
interests are plant ecology and biogeography, especially structure and composition of coastal vegetation,
patterns of species distribution, and conservation.
U
N
E
SA
SC
M
O
PL
-E
O
E
LS
C
H
S
AP
TE
R
S
Miriam Cristina Alvarez Pereira has taught Economic Botany in the Botany Department at Rio de
Janeiro Federal University. Most of her field research has been done in protected areas of Brazil such as
Serra do Cipó National Park in Minas Gerais and Restinga de Jurubatiba National Park in Rio de Janeiro.
She is presently an Associate Researcher at the Rio de Janeiro Botanical Garden Research Institute,
involved in field work in the Cabo Frio Center of Plant Diversity. Her main areas of research are plant
ecology, vegetation structure and functional groups.
©Encyclopedia of Life Support Systems (EOLSS)