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RAIN FORESTS: FLORISTICS
F. Z. Saiter
Instituto Estadual de Meio Ambiente e Recursos Hídricos, Espírito Santo,
Brazil
T. Wendt
Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
D. M. Villela
Universidade Estadual do Norte Fluminense, Rio de Janeiro, Brazil
M. T. Nascimento
Universidade Estadual do Norte Fluminense, Rio de Janeiro, Brazil
Keywords: Tropical forests,
monodominance, nutrient cycling
floristic
composition,
biodiversity,
Contents
1. Introduction
2. Global Distribution and Main Features of Tropical Rain Forests
3. Floristic Patterns
4. Biodiversity
5. Tropical Rain Forests are Dynamic
6. Nutrient Cycling
7. Conclusion and Outlook
Related Chapters
Glossary
Bibliography
Biographical Sketches
Summary
The tropical rain forest is well-known for its megadiversity and some
important ecological services, especially on climate regulation. This forest
type occurs in all four major tropical zones (America, Africa, Indo-Malaya
and Australia) and covers about seven percent of the Earth’s forest area.
Floristic composition varies largely within and among the main
phytogeographic regions. However, some distinctive characteristics can be
emphasized on family distribution such as the dominance of Dipterocarpaceae
in western Malaysia and species richness of Lecythidaceae in America. In
general, tropical forests show higher species richness when disturbance is at
an intermediate intensity or frequency. On the other hand, monodominant
forests can occur when small but frequent disturbances take place or after
long periods without any relevant disturbance. Early studies associated low
species diversity with low soil nutrient availability, but there is still
controversy in this respect. However, chemical fertility and soil moisture are
among the factors which have been considered important determinants of
species richness in tropical forests. Although tropical forest provides
important services to natural systems and humankind, it still suffers severe
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deforestation in most tropical countries.
1. Introduction
Forests cover ~ 42 million km2 of the Earth’s land surface, which only about
7 percent are within tropical regions. However, tropical forests, and especially
the tropical rain forests, are extremely important for regulation of global
weather and, therefore, of human existence as highlighted by the United
Nations Framework Convention on Climate Change and the Convention on
Biological Diversity. Estimates are that more than 50% of all the Earth
species live in tropical rain forests. Thus, they are a natural reservoir of
genetic diversity that offers a myriad of useful forest products. Despite their
obvious importance, every year thousands of hectares are destroyed
worldwide. Most of the world’s remaining tropical rain forests are located in
developing nations and financial return on timber and farming is crucial for
human survival in many such nations.
Tropical rain forests across the world are very diverse, but share several basic
characteristics. They are limited between the Tropic of Capricorn and Tropic
of Cancer and, because of the high solar energy in this region, tropical rain
forests are usually warm year round with temperatures about 22-34o C.
However, forests at higher elevations can be significantly cooler. Temperature
may fluctuate slightly during the year, which in equatorial forests is almost
imperceptible. As tropical rain forests lie in the intertropical convergence
zone, they are subjected to heavy rainfalls: at least 2,000 mm of rain, and in
some areas more than 10,290 mm per year. In equatorial regions, some forests
do not show precise "wet" or "dry" seasons, although many forests do have
seasonal rains. Even dry periods are usually not long enough to completely
dry out leaf litter. The usually constant cloud cover is enough to keep the air
moist and prevent plant desiccation.
A primary or mature tropical forest often has several layers and three tree
strata. The top layer or upper storey (overstory) is formed by emergent trees
that consist of scattered tall trees that have most of their foliage fully above a
closed canopy layer formed by the crowns of other trees. The middle storey,
or canopy, is the stratum where most of the flowering and fruiting of the trees
take place. A third layer (lower storey or understory) is formed by smaller
trees whose crowns do not meet. Immediately underneath this stratum one
finds the shrubby layer, formed by woody and herbaceous shrubs, and the
ground layer (or forest floor), which is the darkest layer where scattered
herbaceous plants and seedlings of tree species are found.
2. Global Distribution and Main Features of Tropical Rain Forests
The global distribution of tropical rain forests can be broken up into four
biogeographic realms: the Neotropics (northern South America and Central
America), the Afrotropics (equatorial Africa), the Indo-Malayan (parts of the
Indian subcontinent and Southeast Asia, and tropical islands of the Pacific
Ocean), and the Australasian (eastern Indonesia, New Guinea, northern and
eastern Australia). Formerly the Australasian rain forest has been considered
an extension of the Indo-Malayan, and for the purpose of comparison done in
this present chapter we will treat both together.
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2.1. The Neotropical Rain Forest
There are three major blocks of rain forest in Neotropical realms: the largest
one is located in the Amazon River Basin in South America, a second one
along the Brazilian coastline, the so-called Atlantic Forest, and a third block
covers the Andes on the Pacific coast extending through to Central America.
The Neotropical rain forest is consistently more species rich than the African,
Indo-Malayan and Australian rain forest.
The rain forest in the Amazon Basin is known as the Amazon Forest. It
occupies seven million square kilometers which represent over half of the
Earth’s remaining rain forests. As the largest area of tropical rain forest, the
Amazon Forest has unparalleled biodiversity. It is located within nine nations:
Brazil (with major total area, 60%), Colombia, Peru, Venezuela, Ecuador,
Bolivia, Guyana, Suriname, and French Guiana. Due to its vast extent area,
several different vegetation types might be distinguished, which are often
related to the flooding pulses of the main rivers at the Amazon basin. The
Amazon River is the largest river in terms of discharge and the second longest
river in the world after the Nile. Unfortunately, currently the Amazon Forest
suffers the highest rate of deforestation associated with land use change
especially for agriculture expansion (pasture and soybean), commercial
logging and settlements. Deforestation is likely to be the main factor implying
in biodiversity loss. There are also concerns about the releases of the carbon
contained within the vegetation, which contributes to global warming.
The Amazon Forest has an extensive border with the cerrado (savanna
woodland) and caatinga (dry deciduous forest) vegetation types in Brazil,
which separates it from the Atlantic Forest. The Atlantic Forest originally
extends along much of the Brazilian coast, forming a narrow strip between the
ocean and the Brazilian drylands (cerrado, caatinga). While the Amazon
Forest lies at more or less the same latitude and altitude, the Atlantic Forest
spreads dramatically from the coast up into the mountains, and throughout
several latitudinal zones, which confers great variation in temperature and
precipitation rates. Thus, under the "Atlantic Forest" label many forest types
can be found (e.g. evergreen forest, semi-deciduous forest, montane forest),
The mangrove forests found in estuaries, bays and lagoons, and the
xeromorphic coastal sandy plain vegetation, locally called restingas, are
ecosystems associated to the Atlantic Forest. However, less than 10 percent of
the Atlantic Forest remains intact.
The third block of tropical rain forest is found in western Andes, in very
humid regions of Ecuador and Colombia, until the latitudinal limit of 19º
North, in Vera Cruz, south of Mexico. Large areas of deforestation are found
in the lower foothills of the Andes, especially in Peruvian and Ecuadorian
lands. However, from Panama northwards these humid forests present
discontinuities due to the existence of seasonal forests at the Pacific coast.
Central America and Caribbean islands suffered the highest percentage of loss
of forest of any tropical region over the last century, with the forest remnants
being highly fragmented and persisting only in areas which are inaccessible or
are legally protected as conservation units (parks and reserves).
2.2. The African Rain Forest
In the African continent there are two important tropical rain forests: the
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Congo Rain forest and the Madagascar Rain forest. At Central Africa, more
specifically at the Congo river basin, is located the Congo Rain forest. It is the
second-largest dense tropical rain forest, surpassed only by the Amazon
Forest, comprising ca. 2 million km2 that represents 70% of the African forest
cover. The Congo River is the second largest in volume, and its river basin
expands over six nations: Cameroon, Central African Republic, Republic of
Congo, Democratic Republic of Congo, Equatorial Guinea and Gabon.
Because of its large size, Congo Rain forest serves as a vast carbon sink of
global importance. The forest also regulates regional and local weather
patterns, and ensures the cycling of water critical for a large area of Africa. It
provides a critically important resource which supports livelihood and wellbeing of tens of millions of people both in Africa and beyond. This forest type
is still well-preserved, accounting for less than 6% of the total loss of humid
forest cover in the world. However, deforestation is a severe problem in parts
of the continent.
Another important rain forest is located in the Madagascar that lies off the
coast of southeastern Africa. It has long been famous for its unique and
diverse species of wildlife, especially lemurs, which are small primates found
nowhere else on the planet. Madagascar is home to some of the richest moist
forests on Earth. Well over half of Madagascar'
s species are found in these
forests which lie on the east coast of the island. However, eastern forests of
Madagascar have been threatened by deforestation owing to slash-and-burn
agriculture, logging and mining.
2.3. The Indo-Malayan and Australian Rain Forest
The Asian region holds 60% of the world’s population, and centuries of
tremendous population pressure has significantly reduced forest surface.
Actually, major threats to Asian Rain forests are the paper industry, intensive
exploitation for timber and expansion of palm oil plantations.
The scattered fragments of tropical rain forest in Asia are located in the IndoMalayan Peninsula. The Indo-Malayan Peninsula is the world’s largest
archipelago located between mainland Southeastern Asia (Indochina) and
Australia, lying between the Indian and Pacific Oceans. It comprises around
20,000 islands, with about 6,000 of those inhabited. The biggest islands are
New Guinea, Borneo and Sumatra. Some of the Malay islands are
administratively shared by more than one nation. The Republic of Indonesia
comprises the majority of those islands (17,508).
Southeast Asia’s tropical rain forests are some of the oldest on Earth, and
some present-day forests may have existed over 100 million years ago.
Geologically, the archipelago (chain or cluster of islands) is one of the most
active volcanic regions in the world. Tectonic uplifts in the region have also
produced some impressive mountains, as the Mount Kinabalu (4,101 m) in
northern Borneo. During the ice ages, when sea level lowered, some islands
were connected to the Asian mainland. Therefore, today these islands have in
common with the continent a great quantity of species of flora and fauna.
Geographers believe that New Guinea Island may once have been part of the
Australian continent, although New Guinea'
s flora has more affinities with
Asia, and its fauna with Australia. Today, Australia has small areas of tropical
rain forest in the extreme northeastern part of the continent near the coast.
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3. Floristic Patterns
Regarding the species composition of the tropical flora, three patterns are
recognized for the families of angiosperms:
Large families generally have pantropical distribution.
Few families are entirely restricted to any of the three major blocks of
tropical rain forest.
Families that are entirely restricted to any of the three blocks have few
genera and species.
These patterns appear to be related to major biogeographic events during
Earth’s geological history. Families of Angiosperms that could have been
differentiated in the tropics - after the separation of continental masses
corresponding to South America, Africa, India and Australia, about 100
million years ago - generally have few genera and species, probably because
there was not enough time for greater diversification. Such families are also
restricted to certain realms due to geographical barriers that prevent
dispersion. Examples of small families that have exclusivity for certain flora
are Cyrillaceae (endemic to the Americas), Sarcolaenaceae (endemic to
Madagascar) and Peridiscaceae (endemic to Amazon Basin). Vochysiaceae is
also a small family represented by only 6 genera and predominantly
distributed in the Americas, with only one African species. However, there
are large families, such as Bromeliaceae (Figure 1), composed by 56 genera
and about 3,000 species, which is exclusively American, except for one
species Pitcairnia feliciana (A. Chev.) Harms & Mildbr. that occurs in the
Gulf of Guinea, West Africa.
Figure 1. Bromeliaceae are generally herbaceous plants, with leaves often
lanceolate, and spirally arranged, forming a water reservoir tank among leaf
sheaths. The Atlantic rainforest in Brazilian southeast is one of the main
centers of diversity and shows a high degree of endemism. The family has a
remarkable importance in the vegetation physiognomy, contributing to
structural complexity of the environment which is directly reflected on
richness and diversity of associate fauna and flora.
Other families went through some evolutionary stability in the continent,
suffering only diversification into the lower taxonomic categories. Currently,
some of them may be considered as large families because they have many
genera and species, which may be a unique feature of the taxon, or the result
of the diversification that followed the continental drift. Some of the largest
families of angiosperms more common in tropical forests are listed in Table 1.
Among these, Araceae, Annonaceae, Euphorbiaceae, Moraceae, Myrtaceae
and Rubiaceae are examples of families well represented throughout the
tropical region. Other families, even with pantropical distribution, have
variation in their abundances. Fabaceae (mainly Caesalpinoideae) and
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Passifloraceae are more important in America and in Africa than in Asia.
Lecythidaceae is much larger in the New than in the Old World, especially in
Amazon and Orinoco Basin, both in South America, where there are 105
species of 11 genera. This same pattern is shared by Chrysobalanaceae.
Table 1. Largest Angiosperms families in tropical rain forests.
Dipterocarpaceae, which is a large and dominant family of the flora of
Southeast Asia is absent in Australia, while in Africa it is represented only by
two genera (Monotes and Marquesia) and by the monotypic genera
Pakaraimaea (from Guayana) and Pseudomonotes (from Colombia) in the
Neotropics.
The Gymnosperms, unimportant group in tropical forests, are represented
mainly by the families Araucariacae and Podocarpaceae. Nowadays, the
Araucariaceae is constituted by the genera Araucaria Juss. (Figure 2) that is
confined to the southern hemisphere, with species in New Caledonia, New
Guinea, Malaysia, Philippines, South America, and Northeast Queensland,
Australia. On the other hand, the Podocarpaceae family is represented by 17
genera and about 125 species that are mainly distributed in the subtropical
mountains of the Southern Hemisphere. However, most members of this
family are represented by the genus Podocarpus (widely distributed), but the
genus Sundacarpus, with only one species, Sundacarpus amarus (Blume)
C.N. Page, is native of Indonesian islands (Sulawesi, Timor, Sumbawa, Java,
Sumatra, and Sabah province on the island of Borneo), Philippines (Mindanao
and Luzon), New Guinea and parts of Australia (including northeastern
coastal Queensland) and Malaysia.
Figure 2. In the tropics, Gymnosperms are less representative, but in the
mountainous areas of southern Atlantic Brazil and extends into northeastern
Argentina, we can find the endangered Brazilian Araucaria (Araucaria
angustifolia). Forest with Araucaria angustifolia are easily set apart from
other portions of the Brazilian Atlantic forest. However apparent
homogeneity, Araucaria forests represent an extraordinary mosaic combining
species from a relict coniferous forest (including several Andean genera) with
Atlantic forest species. In this mosaic, several endemic species are found.
Tropical rain forest largely varies as regards to phytophysiognomies due to
differences of altitude (lowland, lower montane, upper montane and cloud
montane), annual precipitation, soil types and the degree of continentality.
Following these changes, the flora also varies to a greater or lesser degree
between forest formations, and the differences in species and genera are the
most striking.
For example, in the lowland Atlantic coastal forest of northeastern Brazil
between south Bahia state and neighboring northern Espírito Santo state,
corresponding to an area of ca 72,000 km², the family Lauraceae is not very
conspicuous (there are just over 50 species throughout the region). On the
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other hand, in only 1 ha of upper montane forest (ca 800 m high) in Santa
Lucia Biological Station, in southern Espírito Santo state, 46 tree species of
Lauraceae can be found, indicating its preference to montane environments.
In addition, although the forest in the Amazon basin is a continuous block, the
abundance of elements of given botanical families of woody plant species
varies from area to area. For instance, Fabaceae and Moraceae are the most
important families in the Ecuadorian Amazon, while Moraceae and
Myristicaceae are predominant in the Bolivian Amazon, and Lecythidaceae
and Moraceae are well represented in Central Amazon forest. On the other
hand, comparisons between the elements of the woody flora of the Amazon
Forest and the Atlantic Forest reveal that many individual species co-occur in
both floristic domains. This can be explained, at least in part, by the migration
of these species across the dendritic drainage of gallery forests that establishes
connection between these two blocks of rain forests.
4. Biodiversity
4.1. Tropical Rain Forests are generally Rich in Species and Endemism
Within the 10 million species that possibly exist on Earth, half or more are
found in tropical forests. However, all this biodiversity is distributed in
different ways between rain forests and dry forests. Thus, rain forests are
generally richer in species than dry forests. Such characteristic seems to be
related to environmental factors, mainly water availability. In fact, tropical
forests of high diversity are distributed throughout all tropical zones, but they
tend to concentrate in low areas that receive regular and abundant rain
throughout the year. In Malaysia, the lowland forests of the Lambir Hills
National Park and the Pasoh Forest Reserve are examples of this situation (see
number of tree species in Table 2).
Table 2. Data of tropical rain forests that compose the network of the forest
dynamics plots organized by the Center for Tropical Forest Science /
Smithsonian Tropical Research Institute.
Another common pattern is that the diversity found in African rain forest is
often lower than the diversity of American and Indo-Malayan rain forests. In
mainland Africa there are about sixty species of palms, although in
Madagascar there are about 170, most of which are endemics. In both tropical
America and Malaysia there are over 1,000 species of palms. In addition, the
Ituri Forest, in Democratic Republic of Congo, and the Korup National Park,
in Cameroon, are between the African forests with highest richness, but they
have less tree species than areas of Asia and Latin America (see Table 2).
The lower diversity of African forests has been related to the uplifting of its
land surface in the Tertiary, which caused a desiccation of the climate, and a
reduced availability of large areas for the occurrence of refuges in those arid
periods. One of the few large areas of endemism in mainland Africa is
between Nigeria and the Democratic Republic of Congo (the Cross RiverMayombe Pleistocene Refuge). Outside the continent, Madagascar has one of
the highest levels of endemics of the Earth, but the surface of the island is not
exclusively covered by tropical moist forest. Of the nearly 12,000 species of
plants, between 70 and 80% are endemic. Ten families and 260 genera of
plants are endemics there; only Australia has more endemic plant species. Of
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the 8 species of baobab found in the world, six are endemic to Madagascar.
The northwest of the South America (ecological region of Chocó-Darién) and
the coast of Brazil possess the higher levels of diversity and endemism of the
world. The ecological region of Chocó-Darién, with 196,400 km², initiates in
the province of Darién, in the Canal of Panama, and spreads southwards
passing by the Pacific coast of Colombia until Cabo Pasado, in the province
of Manabí, North Ecuador. Annual precipitation varies from North to South
and in the Chocó-Darién, one of the most humid places of the world; it
reaches 4,000-9,000 mm. The moist forests cover about 90% of the ecological
region, from sea level to altitudes of 2,700 m, and the lowland moist forests
are the most significant, with higher biodiversity. Estimates suggest that the
flora of Chocó-Darién has 9,000 vascular plant species (with 25% of
endemism). For vertebrates, for instance, endemism is also high (total 1,625
species of which 418 are endemic). The Yasuní National Park is in ChocóDarién and has over 1,000 tree species (see Table 2).
Despite controversies regarding the definition of the Atlantic Forest, data
available for the broadest definition (1,300,000 km² that encloses moist
forests of the Brazilian coast and continental semi-deciduous forests) indicate
the existence of 2,330 species of vertebrates (732 endemics), and about
20,000 species of plants (8,000 endemics).
4.2. The Diversity in Local Scale
Alpha diversity - or the wealth of species in a local scale - in the tropical
forests is often higher than most terrestrial ecosystems as a result of the sparse
distribution of individuals of the majority of the populations. Thus, in a given
area many species (called rare) are represented by small populations, whereas
a reduced number of species (called dominant) is endowed with populations
with many individuals, constituting what is called an "oligarchy". In
phytosociological studies, the registering of species with only one or two
individuals per hectare is rather common. For example, in the Atlantic Forest
of the Santa Lúcia Biological Station, in southeast Brazil, approximately 45%
of the 384 registered trees species in a 1-hectare forest inventory are
represented by 1 or 2 trees/ha, whereas the ten most representative species
accumulate 26% of the trees.
In fact, one of the key questions in ecology of biological communities is how
high levels of alpha diversity are kept in tropical forests. Some hypotheses,
which are often mutually compatible, have suggested mechanisms that
explain this pattern. Amongst the best known, there are the Janzen-Connell
Hypothesis, the Regeneration-Niche Hypothesis and the Hypothesis of Gap
Dynamics. The Janzen-Connell Hypothesis proposes that seedlings next to cospecific adult trees generally suffer greater mortality than seedlings that are
more distant. This is because the aggregation of individuals attracts more
predators and pathogens, increasing mortality and limiting the establishment
of new individuals to more distant areas from the co-specific adult. The
Regeneration-Niche Hypothesis and that of Gap Dynamics are based on the
cycle of development of the forest, where different species present different
requirements for establishment and growth. This results in preference for
certain environments within the mosaic of environments in the forest. The
choice of these environments by the different species is related mainly to the
light levels that reach the forest floor in each phase of development. Thus, a
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great variety of environments allows the existence of diverse niches that will
result in the maintenance of a great number of species (see also Section 5,
next).
4.3. Diversity as a Result of Latitudinal Gradients
The greatest biodiversity of tropical forests (when compared to other climatic
zones of the world) is one of the oldest and most accepted global biodiversity
patterns. However, despite some controversy, latitude is not the determining
factor of variation in regional distribution of biodiversity. Environmental
factors correlated to the latitude are primarily responsible for such a
distribution. It seems reasonable to argue that latitudinal gradients of diversity
result not only of a single factor, but of a set of factors that act synergistically.
In this line, some hypotheses are distinguished that try to explain the relations
between latitudinal diversity gradients:
Climatic stability and favorable environments: environments that are
climatically steady possess one constant supplement of resources and
create favorable conditions for the existence of many species.
Time: diversity increases throughout time because it is a product of
evolutionary processes. Speciation should have been faster and
extinction less sharp in steady tropical environments than in temperate
habitats, since during geological time the tropics had more climatic
stability than temperate zones.
Spatial heterogeneity: the more diverse the physical environment, the
more diversified the inhabiting organisms.
Productivity: in the tropics, light intensity and temperature are higher
and, therefore, productivity is higher. With more available energy, it is
likely that more species should benefit.
Competition: competition between individuals of different species is
higher in the tropics, reducing the size of each niche, but increasing the
number of niches.
Predation: the highest number of predators and parasites in the tropics
reduces the size of the populations of carnivores. Small populations
reduce competition levels and allow species addition, as much of
carnivores as of predators;
Disturbance: the occurrence of perturbation in various scales (e.g.,
climatic changes, hurricanes, landslides, volcanic flooding and
eruptions) delays the process of competitive exclusion and allows the
coexistence of many species. Hence, when disturbances are small, less
competitive species are excluded, and when disturbances are high, even
the highly competitive species might be lost.
4.4. The Paradox of the Monodominant Forests
Nowhere diversity is greater than in the tropics. As seen in the previous
sections of this chapter, the tropics are widely renowned for their spectacular
plant diversity, and the occurrence of one or a few species dominating large
areas of tropical forest was until the mid-1980's considered uncommon.
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However, monodominant rain forests have been found in all regions of the
tropics. They can occur side by side with highly diverse forests and these
monodominant forests are often similar in species composition to the adjacent
mixed forests.
It is interesting that most tropical monodominant forests reported in Africa
and America are dominated by legume trees, mainly Caesalpiniaceae species
(i.e. Cynometra alexandri C. H. Wright, Gilbertiodendron dewevrei (De
Wild.) J. Léonard, Julbernardia seretii Troupin and Talbotiella gentii Hutch.
& Greenway in Africa, and Eperua purpurea Benth, Monopteryx uaucu
Spruce ex Benth, Mora excelsa Benth and Peltogyne gracilipes Ducke in
America), while in Asia they are dominated by dipterocarp trees
(Dipterocarpaceae) such as Shorea curtisii Dyer ex King and Dryobalanops
aromatica C. F. Gaertn.
A large number of studies has been published on the mechanisms maintaining
high diversity among the canopy trees, such as compensatory mechanisms,
predation and herbivory, disturbance and neutral theory of tropical forest
dynamics. On the other hand, little attention has been paid to low-diversity
communities and only by the end of the 1980s attempts were made to explain
the mechanisms that produce or maintain low-diversity among the canopy
trees of tropical forests. Many abiotic and biotic factors have been cited to
lead dominance in a community, such as soil moisture regime or water-table
level, soil nutrient concentrations, wildfire, seed predation and herbivory,
allelopathy or ectomycorrhizas. In some of these cases, the occurrence of
monodominance in a community seems to be related to a single
environmental stress. However, monodominant forests also occur on welldrained soils and adjacent to species-rich forests where soils show similar
characteristics. According to Connell & Lowman (1989) monodominant
forests on well-drained soils can be produced by two ways:
The most common species produces abundant seeds and disperse them
into a large open patch during the short period available before canopy
closure;
The most common species gradually invades an existing diverse rain
forest by tree-by-tree replacement.
Therefore, a monodominant species is likely to be the species most tolerant of
adverse conditions and also the most efficient competitor for resources such
as light, water or soil nutrients. We can recognize two types of monodominant
forest:
Type I: with a persistent dominant that, once established, persists
because of its abundant regeneration or its superior ability to exploit
resources;
Type II: with a temporary dominant that does not persist beyond one
generation and shows poor recruitment in the understory because its
seedlings cannot establish and survive after canopy closure. This type is
related to an early successional process.
Other authors also recognized these two types and similar mechanisms to
those proposed by Connell and Lowman for the maintenance of the
dominance. However, the hypotheses for the origin of the dominance were
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different. While some authors emphasized the importance of the
ectomycorrhizal association in promoting type I dominance, others considered
the disturbance (or successional stage) the key factor. According to Hart and
collaborators, type I forests occur where disturbance is infrequent and slight
(late succession). In this case, the dominant species has lower seed predation
and herbivory than the other species. Type II dominance occurs where
disturbance is frequent and large (early succession) and so the dominant
species shows poor recruitment in the understorey. In the case of intermediate
disturbance (mid succession) a species-rich forest is expected, with greater
abundance of tree falls and shade-intolerant species.
More recently, the ‘suite of traits’ hypothesis was proposed by Torti and
collaborators in 2001, where adults of monodominant species have a number
of traits that alter the understory environment in such a way that inhibits
recruitment by other tree species. Seedlings and saplings of monodominants,
in turn, are thought to possess a number of traits that allow them to tolerate
the stressful environment created by the adults. Although the suite of traits
hypothesis (Table 3) seems well-supported for the Gilbertiodendron system,
does the hypothesis apply to other monodominant species as well? An
analysis based on available data for tropical monodominant species provides
initial support for this hypothesis (Table 4). Monodominant species, in
general, have similar traits, although they did not possess all traits considered
as potentially important.
Table 3. Proposed suite of traits necessary for a plant to be a tropical
monodominant. Plants do not have to possess all traits, but the possession of
just a few does not result in monodominance. (from Torti et al. 2001)
Table 4. A comparison of traits of tropical monodominant species (> 60%
dominance) in lowland, tropical rain forest on well-drained soils (modified
from Torti et al. 2001).
An interesting case study is that of Peltogyne gracilipes that forms the only
monodominant forest that has been described in the Amazon Basin (Figure 3).
Large Peltogyne forests exist in and around Maraca Island, a protected
ecological reserve with an established biological station (3° 15’N and 61°
22’W) in Boa Vista district, Roraima State, northern Brazil. The island is 60
km long and 15-25 km wide, with a total area of approximately 100,000 ha.
Annual rainfall on the island is 1750-2000 mm, with a distinct dry season
from December-February. Previous research shows that soils on Maraca
Island are generally poor and that the only difference between soils in the
Peltogyne forest and those in forests without Peltogyne is that the Peltogyne
forest soils are rich in magnesium and therefore exhibit a high Mg/Ca ratio.
Because this forest has high soil and foliar Mg concentrations, and Mg is
known to be toxic to plant growth at high concentrations, the monodominance
of Peltogyne was related to its deciduousness and faster leaf-decomposition in
the dry season, which coincides with a large leaf fall. Magnesium is lost
quickly from the Peltogyne leaves and the resultant pulses of Mg into the soil
during the heavy rains at the beginning of the wet season may be deleterious
for other species which are not adapted to high solution Mg concentrations.
Therefore, Peltogyne dominance seems also related to the pattern of its
nutrient cycling and the seasonal pulses of toxic Mg.
Peltogyne has a number of traits thought to be important in the suite of traits
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hypothesis (Table 4). Peltogyne is a mast fruiting species, producing seeds
every 2-4 years. Juveniles are slow growers, shade tolerant, and appear to
suffer low damage by herbivores. Unlike Gilbertiodendron, Peltogyne does
not form ectomycorrhizae. Also, unlike Gilbertiodendron, adult Peltogyne
trees are deciduous during the dry season, but juveniles do not lose their
leaves. Peltogyne do not have poor quality leaf litter, although the high
amounts of Mg they release may create a chemical barrier to the
establishment of other species. Also, while Peltogyne leaf litter decomposes
slowly, most of the nutrients are quickly mobilized from its decomposing
leaves. Thus, the unique suites of traits possessed by adult and juvenile
Peltogyne individuals couple together to favor monodominance in this
system.
Figure 3. Aerial view of the Peltogyne monodominant forest and mixed forest
boundary on Maracá Island, Roraima, Brazil. The pale areas are Peltogyne
forest.
5. Tropical Rain Forests are Dynamic
Plant communities are called "climaxes" when they have structure and
composition in equilibrium. But, contrary to what the word "equilibrium"
might suggest, stability here is of a dynamic nature. Thus, these communities
are not "static" throughout time.
The process of regeneration in tropical forests is more complex than in
temperate forests and the equilibrium is guaranteed by the incorporation of
new components in substitution to what had been lost. This balance between
losses and gain is based on the cyclical behavior of the forests, where three
phases of development are recognized: mature (mature), open area (gap) and
regeneration or construction (building). The mature phase shows trees in
several layers and a closed canopy. Eventually trees of the canopy die or are
damaged, knocking down lesser surrounding areas and forming bare places.
These bare places are quickly filled by herbs, lianas and young trees. Some of
these plants arise from banks of seeds and seedlings, while others simply burst
from exposed roots and trunks broken. The regeneration phase corresponds to
the growth of these components until the formation of a new canopy many
years later, reestablishing the mature-phase stage. Interestingly, all these
phases generally coexist in forest patches, resulting in a forest mosaic,
resulting in a heterogeneous environment.
In this context, mortality, recruitment and growth of trees play an important
role in the maintenance of the structure and diversity and in the processes of
nutrient cycling in forests (more details in Section 6). The mortality of trees in
tropical forests is the result of the combination of different biotic and abiotic
factors. Four main causes of tree mortality can be defined, each one with its
own spatial scale, regularity and frequency. The first one is related to
endogenous processes of genetic origin that provoke a set of gradual
physiological and metabolic alterations ultimately leading to death, known as
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senescence. The second one refers to the sudden or gradual action of toxic
substances, pathogens, parasites and consumers, in an individual or
population context. The third cause is related to changes in abiotic factors,
such as edaphic (soil) conditions, light intensity and natural flood regimes,
causing an essential reduction in the energy availability and materials. The
last possible cause is associated to the occurrence of catastrophic natural
disturbance such as strong winds, uncommon storms, hurricanes, landslides,
flooding, droughts and fires that can provoke irreversible damages to the
trees.
In general, in tropical forest stands where only natural disturbance of small
scale operate, mortality is highest for the youngest plants (i.e. seedlings), of
any given population, which are often times numerous. However, curves of
individual distribution in size classes often have a "reversed-J" shape, which
means that smaller size classes have higher number of plants despite high
mortality.
The recruitment is a spare mechanism of trees in forests that depends directly
on the fecundity rates, the growth and the survival of young individuals of
diverse species. Therefore, recruits emerge from seed bank, bank of seedlings
or young trees, whose development is often enhanced by higher light
availability provoked by gaps in the forest canopy. Recruitment substitutes
dead trees and also contributes for the replacement of the live material in the
forest. Thus, for forests in dynamic balance, the addition of the increase in
biomass of surviving trees via growth to the increment of biomass of the new
trees recruited must be approximately equal to the total of lost live material
due to the fall of vegetative organs, such as leaves and branches, and for the
death of trees.
6. Nutrient Cycling
6.1 An Overview
The often unseen processes that underlie most mechanisms of diversity
distribution and patterns described in this chapter may be related to nutrient
cycling as plant nutrient cycling and allocation patterns may alter the
community biology and ecology of plants and animals in tropical forests.
Chemical fertility and soil moisture are among the factors which have been
considered important determinants of species richness in tropical forests.
Early studies associated low species diversity with low soil nutrient
availability, but no confirmation to this pattern has been found yet. The
available data on soil-nutrients and tree species-richness are conflicting.
These relations encompass nutrient cycling process in tropical forests
described from now on in this chapter.
The term nutrient cycling involves geochemical, biogeochemical and
biochemical pathways of the essential elements required to plants, mainly N,
P, K, Ca, and Mg, which are most likely to limit primary production and other
ecosystems functions, denominated nutrients. It is interesting the view that
nutrient cycling encompasses a wide range of processes co-occurring on
different timescale from minutes or days, as the turnover of available nutrients
in soil solution, to millions of years, as the development of tropical soils.
Three principal processes are measured in tropical forests: (i) inputs and
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outputs from the forest, which includes throughfall and stemflow; (ii) internal
pools and cycles within the forest ecosystem, which includes the feedback of
nutrients from soil-plant (e.g. litterfall, decomposition, Figure 4), comprising
most data; (iii) internal distribution of mobile elements (retranslocation).
Those processes are interactive, controlling the availability, cycling and
limitation of nutrients in tropical forests, and in terrestrial systems as a whole,
despite their differences in timescale.
Figure 4. A litter trap in an Atlantic forest underground at the União
Biological Reserve, Brazil, used to collect and measure the amount of litterfall
mass and nutrient input in forested ecosystems.
There is a "popular view" of the occurrence of primary and old secondary rain
forests in infertile soils, having most of their nutrients in the above-ground
living matter, maintaining high production by rapid and efficient nutrient
cycling, having closed and tight nutrient cycles, since the first studies on
nutrient cycling in tropical forest ecosystems in Ghana and in the Brazilian
Amazon around the 1960s. However this view has been criticized and much
more studies are needed to hold those assumptions as the pattern of nutrient
cycling in tropical forests are diverse, and as Vitousek & Sanford in 1986
pointed out "it makes no more sense to describe a ‘typical’ tropical forest than
a ‘typical’ temperate forest", although some patterns may be found.
Another ‘paradigm’ relates the occurrence of tropical forests on poor soils
with specific features and strategies of plants, such as root mats or small
sclerophyllous leaves. This assumption has been challenged, as some
Amazonian rain forests do not present those characteristics. Nevertheless they
are neither unproductive with a low nutrient demand, nor are particularly
efficient in nutrient use or have a rapid nutrient recycling, as expected. It
raised questions on the functional strategies of the tropical forests, which
show no evidence of nutrient limitation, contradicting several generalizations
about rain-forest nutrition.
6.2. Environmental Conditions Which Drive Nutrient Cycling in the Rain
Forests
Some environmental conditions may drive nutrient cycling in the tropical
forests such as climate, soils, species composition and sucessional stage.
Litterfall seasonality is one of the processes strongly related to rainfall in
moist and seasonally dry forest in opposite way. While in moist tropical
forests as those in Australia, Brazil, New Guinea, Sarawak, Zaire the peak
litterfall is in the wet season, in seasonally dry forests the peak of litterfall
mass and nutrient input is in the dry season, as in some Amazon and Atlantic
forest in Brazil, in secondary forest in Nigeria and elsewhere in the tropics.
But even in some evergreen moist forests, the litter may fall in the dry season.
This common pattern of tropical forests suggests that water deficit is one of
the main factors of leaf-fall in those ecosystems. Nevertheless, quantities of
litterfall is not determined only by climate, as moist or dry tropical forest
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produce annually about 7 to 13 t/ha, a variation that may be driven also by
other factors as floristic composition, sucessional stage or soil type.
Climate may also interfere with litter decomposition process, a critical step in
nutrient cycling, which is the responsible for the transference of nutrients
from the litter layer to the soil. Dry-season retardation of decomposition has
been observed in moist and dry tropical forests. The faster decomposition
process in the wet season is attributed to an increase in the activity of microdecomposers and macro-fauna, and in some forests to a greater growth of fine
roots. Rapid decomposition rate is a result of the initial rains stimulating mass
loss and nutrient release after dry spells resulting in pulses of nutrients. Pulses
of nutrients are known to be important regulators in tropical forests
functioning.
The higher stock of nutrients in the small litter layer in the dry season in many
forests may be a consequence of the high input and low litter decomposition
rate during this season. However, although differences among sites may
influence decomposition, the effects of substrate quality and soil fauna can be
crucial in this process in tropical forests.
Altitude is also a factor that may interfere in rain forests structure,
productivity, nutrient limitation and cycling. Most studies have been shown
that tropical rain forests decrease in stature, above-ground biomass and net
primary productivity, litterfall nutrient input, decomposition rate, and soils
nitrogen concentration, with increasing elevation mainly in response to
temperature decrease. In-situ fertilization experiments in montane forests have
indicated that growth and litter production, are limited by N or N and P.
However, the conclusions in relation to the effect of soils nutrient limitation
and reduction of plant nutrients with altitude are not consistent, as it may be
influenced by air temperature directly.
The relationship between soil fertility and nutrient cycling in rain forests has
demonstrated that patterns of the cycles of nutrients differ in forests on
different soils. It has been shown that moderately fertile soils support
productive forests that cycle large quantities of nutrients, contrasting with
forests on medium to low fertile soils that efficiently cycle smaller quantities
of phosphorus and calcium, although they seems to be not limited by nitrogen,
while forests on very low fertile soils cycle small quantities of N and P, with a
high root/shoot ratio. Nevertheless, we may reinforce the position prior raised
by Proctor in 1995 that rain forest soils are rarely critically evaluated and hard
facts about relationship between rain forests and their soils are still relatively
few, what causes a number of widely accepted ideas up to that moment about
rain forest and their soils, including those relating to the proportions of
nutrients in biomass and soils, the efficient cycling of nutrients and the
importance of mycorrhizas, which are shown to be oversimplifications and
based on slender evidences.
6.3. Floristic Composition, Diversity, Nutrient Cycling and Rain Forest
Management
It is known that species create positive feedbacks to the patterns of nutrient
cycling in natural ecosystems, further reducing nutrient availability in lownutrient sites and in opposite way enhancing nutrient availability in highnutrient ones. In fact, species effects have been found to be many times more
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important than abiotic factors in controlling ecosystem fertility. Different
studies in the tropics and elsewhere have been raised questions on the
influence of specialist species which dominates some specific ecosystems on
their function. It has been discussed that it might be true that ecosystems in
regions with more diverse flora could function differently due to a greater
diversity of species within sites, because members of an array of species could
have complementary patterns of resource use or of responsiveness to
disturbance.
Some studies have shown that key species, which represent dominant trees
have a great influence on nutrient cycling through their litter in tropical
ecosystems, for example the Peltogyne gracilipes in a monodominant
Amazon forest (see above, Figure 5), Metrodorea nigra in seasonally dry
Atlantic forest, or even nurse-plants such as Clusia hilariana in sand dune
vegetation thickets in Brazil. The opposite also happens as nutrient
availability and cycling may drive species dominance as seems the case for
the forest type dominated by Peltogyne gracilipes described earlier in this
chapter, and for some monodominant ectomycorrhizal tropical forests as those
in Africa, which are related mainly to P control which is particularly
important on highly weathered tropical soils.
Figure 5. Leaf litter layer composed mainly by Peltogyne leaves in the
Peltogyne monodominant Amazon forest on Maracá Island, Brazil, at the end
of the dry season (March).
Nutrient cycling studies also help elucidate environment changes related to
vegetation succession, as well as nutrient cycling and allocation patterns may
also influence those processes. In general, there is an increase in biomass and
nutrient accumulation in the tropical forests with successional stage, and
secondary forests may present higher values than the stable mature forests.
The knowledge of roles of richness and composition is essential for
understanding the function of preserved ecosystems as species are gained or
lost. It is also true for degraded forests as there is a general trend of reducing
tree diversity and changing in composition with the disturbance intensity. A
less diverse and more disturbed (open) forest tends to have a rapid nutrient
release from decomposing leaf-litter and it has been suggested that the
successes of the system is more dependent of its capacity to retain nutrients.
It is already a general consensus that the understanding of nutrient cycling
processes is fundamental to the management of natural and disturbed
vegetation growing on tropical soils of low fertility. The deleterious effects of
a variety of disturbances as deforestation, fire, selective logging and
fragmentation on biomass, litter production, decomposition and nutrient
dynamics were shown for a sort of African, Asian, central and south
American rain forests.
The results from deforestation may vary with factors such as tree species,
period and type of logging, rainfall pattern and soil properties. Although
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relatively few trees are cut per hectare in a selective logging operation, the
effects on ecosystem structure due to loss of nutrients may be underestimated.
Fragmentation is one of the main consequences of deforestation in the rain
forests (Figure 6) causing a variety of abiotic and biotic changes in the
community, which may also alter litterfall and nutrient dynamics. There are
still few and sometimes contrasting data on the effects of rain forest
fragmentation on those processes, however the possible synergism between
forest fragmentation and fires has been shown in the beginning of this century
(2004) for the Amazon, amplifying the risk of threatening the rain forests
elsewhere in the globe, as fragmentation process is already a fate for the
tropics (Figure 7). The role of nutrients in regulating organic matter
decomposition has also been discussed in the present decade for tropical rain
forests and its consequence on global carbon cycle stressed as tropical forests
contain up to 40 % of terrestrial carbon biomass and account for one-third of
annual biosphere-atmosphere CO2 exchange.
Figure 6. Aerial view of a rain forest fragment of Atlantic forest at União
Biological Reserve, Brazil. Note that different types of border surround the
fragment.
Figure 7. Border of an Atlantic forest fragment at Guaxindiba Biological
Station, Brazil, just after a fire. Note the invaders grasses at the fragment
border, which may facilitate and amplify the fire risk.
The advantage of more structural diversity ecosystem, as the conservation of
soil condition and nutrient dynamics and the control of intensity and
amplitude of disturbance have been demonstrated all over the tropics in
different aspects of nutrients maintenance and cycling. Although some
managed systems promote natural regeneration, by altering but not
interrupting the basic structure and functioning of the forest, the impacts of
the different types of disturbances on nutrients stocks and dynamics must be
considered important in tropical forests and their effects need to be evaluated
carefully and in long-term studies. The use of key species as indicators of
disturbance is regarded as useful in monitoring and managing some tropical
forests.
7. Conclusion and Outlook
Despite the importance of the world’s tropical rain forest, our knowledge
concerning its flora is still limited and based on relatively few inventories. It
is important to highlight that although the number of floristic inventories in
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tropical rain forests has increased, only few studies cover large geographical
areas, especially in Amazon forest, with most of them concentrated inside or
nearby Conservation Units such as Barro Colorado, Cocha Cashu, La Selva
and Reserva Ducke. Moreover, although a pool of information has been
obtained in those last four decades on nutrient cycling that provided answers
to questions about their stock and function in tropical forests, many processes
and mechanisms are still poorly known to make a more consistent and general
conclusion on its nutrient limitation, dynamics and cycling specially
considering the great diversity of rain forests and its importance to an
increasingly changing world. So, the scarcity of field data in tropical rain
forests still limits our understanding on patterns of species richness, species
distribution and functioning.
Another important point is that most available data on floristic composition
are based on quantitative plant inventories that only include large trees (plants
with a stem diameter greater than 10 cm at breast height), with few samples of
other life forms such as lianes, epiphytes, and herbs. These inventories have
about 20-30% of the tree species sample as unidentified species or
morphospecies. A morphospecies can be a new species or, as in most cases, a
described species that has not yet been identified. This factor means that our
knowledge of the tropical flora is still poor and efforts are needed to improve
it. The annual area deforested in the tropics is very large, and several papers
have shown the relationship between deforestation and species loss. Thus,
attention should be paid to geographical areas that are poorly collected and/or
are suffering high deforestation rates, since good floristic data are important
not just for plant systematic, phytogeographic and evolution studies but also
for conservation and management of the tropical vegetation.
Related Chapters
Click Here To View The Related Chapters
Glossary
Allelopathy
Biomass
Biochemical
cycles
Biogeochemical
cycles
Continental drift
Dendritic
drainage
Decomposition
: Is a chemical process of inhibition of growth of a plant
due to biomolecules released by another.
: The weight of a living organism, or of all the organisms
in an ecosystem or in a habitat.
: Encompass internal transfers or translocation of
nutrients within plants.
: Encompass the recycling of nutrients between the soil
and plants and heterotrophs.
: The hypothetical tendency or ability of continents to
drift on the earth'
s surface because of weakness of the
sub-oceanic crust. Today, scientists believe that 200
million years ago the Earth'
s continents were joined
together to form one gigantic supercontinent, called
Pangaea.
: Is the pattern formed by the streams, rivers, and lakes
in a particular drainage basin.
: Is the natural process carried out by invertebrates, fungi
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and bacteria which a dead plant or animal tissue is
broken down, resulting into nutrients which return to the
soil.
Early succession : The initial stage of a succession process.
Ectomycorrhizas : EcM, typically form between the roots of woody plants
and fungi belonging to the divisions Basidiomycota,
Ascomycota, or Zygomycota.These are external
mycorrhizae which form a loose sheet of hyphae around
tree roots and a branching hyphal network (Hartig net)
inside the root.
Fragmentation
: Is a form of habitat fragmentation occurring when
forests are cut down in a manner that leaves relatively
small, isolated patches of forest known as forest
fragments or forest remnants.
Gallery forest
: A forest along a river or stream.
Genetic diversity : Is a level of biodiversity that refers to the total number
of genetic characteristics in the genetic makeup of a
species.
Geochemical
: Encompass inputs and losses of nutrients to the large
abiotic environment.
cycles
Ice ages
: Is a period of long-term reduction in the temperature of
the Earth'
s surface and atmosphere, resulting in an
expansion of continental ice sheets, polar ice sheets and
alpine glaciers.
Late succession
: The final stage of the succession process.
Litterfall
: Consists of leaves, flowers and fruits, woody and trash
(very small parts from a variety of origins) that fall to the
soil floor.
Mid succession
: The intermediate stage of a succession process.
Mast fruiting
: Is the intermittent and synchronous production of large
fruits.
Monodominant
: A forest in which a single late successional tree species
forest
comprises 60% of the canopy trees or of the total basal
area.
Neotropical
: Refers to occurrence in the tropical regions of the New
World, i.e. the Americas.
Pantropical
: Terms used to define an area of geographical
occurrence of an organism, or group of organisms. When
the distribution of a taxon is pantropical, it means that
the taxon occurs in the tropical regions of all of the
major continents.
Phytophysiognomy : The characteristic appearance of a plant community by
which it can be recognized at a distance.
Phytosociology
: Is the study of the characteristics, classification,
relationships, and distribution of plant communities.
Primary
or : Vegetation which has not been disturbed or changed by
mature forest
man.
Retranslocation
: Is the nutrient removal from plant tissue into the
perennial part of the plant prior to senescence, which
occurs primarily from leaves.
Seed bank
: All dormant but viable seeds in the soil.
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Seedling
Shade tolerant
Stemflow
: A young plant growing from its seed.
: Plant adapted to growth under low irradiance.
: The flow of rain water down the trunk or stem of a
plant.
Successional stage : A phase of the succession process is a change in plants
and animals which occurs periodically in all
communities.
Throughfall
: Describes the process of rain water passing through the
plant canopy.
Well-drained soils : Are soils that water is removed from readily (but not
rapidly) and they are not wet for significant periods of
time.
Bibliography
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mechanisms for their existence. American Naturalist 134: 88-119. [This work provides a
general view on the mechanisms for monodominance in tropical forests.]
Hart, T. B.; Hart, J. A. and Murphy, P. G. (1989). Monodominant and species-rich forests of
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Jordan. C. F. (1985). Nutrient Cycling in Tropical Forest Ecosystems: Principles and their
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coexistence. Oecologia 130: 1-14. [Important review on plant species coexistence in hyperdiverse communities.]
Biographical Sketches
Felipe Zamborlini Saiter is Analyst for the Environment at the Management of Natural
Resources of the Instituto Estadual de Meio Ambiente e Recursos Hídricos, Espírito Santo,
Brazil, and Professor of Ecology of the Escola Superior São Francisco de Assis, Espírito
Santo, Brazil. He works in government projects for the conservation of natural resources and
his present research interests are dynamics of plant communities and phytogeography.
Tânia Wendt is Professor of Plant Taxonomy at the Botany Department of the Universidade
Federal do Rio de Janeiro, Brazil. She has a career-commitment to research on plant
systematics especially within Bromeliaceae, a keystone family within the Atlantic tropical
rain forest biome, and its unique ecological adaptations.
Dora M. Villela is an Associate Professor at the Universidade Estadual do Norte Fluminense
Darcy Ribeiro (UENF), Rio de Janeiro, Brazil. Her research interests emphasize nutrient
cycling of forested systems. She has been working for over two decades on cerrado
vegetation and monodominant forests in the Amazon. More recently, her main interest has
been on Atlantic forest ecosystems and the effects of fragmentation on nutrient cycling.
Marcelo T. Nascimento is an Associate Professor and Curator of the Herbarium at the
Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF), Rio de Janeiro. For the
last 15 years, his research has focused on plant communities, including phytosociological
studies, herbivory, and plant population dynamics.
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RAIN FORESTS: FLORISTICS
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To cite this chapter
F. Z. Saiter, T. Wendt, D. M. Villela, M. T. Nascimento ,(2008),RAIN FORESTS:
FLORISTICS, in International Commission on Tropical Biology and Natural Resources,
[Eds. Kleber Del Claro,Paulo S. Oliveira,Victor Rico-Gray,Ana Angelica Almeida
Barbosa,Arturo Bonet,Fabio Rubio Scarano,Francisco Jose Morales Garzon,Gloria Carrion
Villarnovo,Lisias Coelho,Marcus Vinicius Sampaio,Mauricio Quesada,Molly
R.Morris,Nelson Ramirez,Oswaldo Marcal Junior,Regina Helena Ferraz Macedo,Robert
J.Marquis,Rogerio Parentoni Martins,Silvio Carlos Rodrigues,Ulrich Luttge], in
Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the
UNESCO, Eolss Publishers,Oxford,UK, [http://www.eolss.net] [Retrieved May 18, 2009]
©UNESCO-EOLSS
Encyclopedia of Life Support Systems
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