Download Rainforests Round the Globe

Rainforests
Tropical Rainforests
Tropical rainforests are characterized in two words: warm and wet. Mean monthly temperatures exceed 18 °C
(64 °F) during all months of the year. Average annual rainfall is no less than 168 cm (66 inches) and can exceed
1,000 cm (390 inches) although it typically lies between 175 cm (69 inches) and 200 cm (79 inches).This high
level of precipitation (rain)ften results in poor soils due to leaching of soluble nutrients. Rainforests protect 40
to 70% of biotic spiecies.
History
Tropical rainforests have existed on Earth for hundreds of millions of years.
Types of Rainforests
 Lowland equatorial evergreen rain forests are forests which receive high rainfall (more than 2000
mm, or 80 inches, annually) throughout the year. These forests occur in a belt around the equator, with
the largest areas in the Amazon Basin of South America, the Congo Basin of Central Africa, Indonesia,
and New Guinea.
 Moist deciduous and semi-evergreen seasonal forests, receive high overall rainfall with a warm
summer wet season and a cooler winter dry season. Some trees in these forests drop some or all of their
leaves during the winter dry season. These forests are found in parts of South America, in Central
America and around the Caribbean, in coastal West Africa, parts of the Indian subcontinent, and across
much of Indochina.
 Montane rain forests, some of which are known as cloud forests, are found in cooler-climate mountain
areas. Depending on latitude, the lower limit of montane rainforests on large mountains is generally
between 1500 and 2500 m while the upper limit is usually from 2400 to 3300 m.
Forest Structure
Rainforests are divided into different strata, or layers, with vegetation organized into a vertical pattern
from the top of the soil to the canopy. Each layer is a unique biotic community containing different
plants and animals adapted for life in that particular strata. Only the emergent layer is unique to
tropical rainforests, while the others are also found in temperate rainforests.
Forest Floor
The forest floor, the bottom-most layer, receives only 2% of the sunlight. Only plants adapted to low light can
grow in this region. Away from riverbanks, swamps and clearings, where dense undergrowth is found, the
forest floor is relatively clear of vegetation because of the low sunlight penetration. This more open quality
permits the easy movement of larger animals such as: ungulates like the okapi , tapir , Sumatran rhinoceros ,
and apes like the western lowland gorilla , as well as many species of reptiles, amphibians, and insects. The
understory also contains decaying plant and animal matter, which disappears quickly, because the warm, humid
conditions promote rapid decay. Many forms of fungi growing here help decay the animal and plant waste.
Understory Layer
The understory layer lies between the canopy and the forest floor. The understory is home to a number of
birds, small mammals, insects, reptiles, and predators. Examples include leopard , poison dart frogs ring-tailed
coati , boa constrictor , and many species of Coleoptera. The vegetation at this layer generally consists of
shade-tolerant shrubs, herbs, small trees, and large woody vines which climb into the trees to capture sunlight.
Only about 5% of sunlight breaches the canopy to arrive at the understory causing true understory plants to
seldom grow to 3 m (10 feet). As an adaptation to these low light levels, understory plants have often evolved
much larger leaves.
The Canopy Layer
The canopy is the primary layer of the forest forming a roof over the two remaining layers. It contains the
majority of the largest trees, typically 30–45 m in height. Tall, broad-leaved evergreen trees are the dominant
plants. The densest areas of biodiversity are found in the forest canopy, as it often supports a rich flora of
epiphytes, including orchids, bromeliads, mosses, and lichens. These epiphytic plants attach to trunks and
branches and obtain water and minerals from rain and debris that collects on the supporting plants. The fauna is
similar to that found in the emergent layer, but more diverse. It is suggested that the total arthropod species
richness of the tropical canopy might be as high as 20 million. Other species habituating this layer include
many avian species such as the yellow-casqued wattled hornbill, collared sunbird , African gray parrot , keelbilled toucan, scarlet macaw as well as other animals like the spider monkey , African giant swallowtail ,
three-toed sloth , kinkajou , and tamandua.
Emergent Layer
The emergent layer contains a small number of very large trees, called emergents, which grow above the
general canopy, reaching heights of 45–55 m, although on occasion a few species will grow to 70–80 m tall.
Some examples of emergents include: Balizia elegans, Dipteryx panamensis, Hieronyma alchorneoides,
Hymenolobium mesoamericanum, Lecythis ampla and Terminalia oblonga.These trees need to be able to
withstand the hot temperatures and strong winds that occur above the canopy in some areas. Several unique
faunal species inhabit this layer such as the crowned eagle (, the king colobus , and the large flying fox .
However, stratification is not always clear. Rainforests are dynamic and many changes affect the structure of
the forest. Emergent or canopy trees collapse, for example, causing gaps to form. Openings in the forest
canopy are widely recognized as important for the establishment and growth of rainforest trees. It’s estimated
that perhaps 75% of the tree species at La Selva Biological Station, Costa Rica are dependent on canopy
opening for seed germination or for growth beyond sapling size.
Ecology
Climate
Most tropical rainforests are located around or near the equator, therefore having what is called an equatorial
climate characterized by three major climatic parameters: temperature, rainfall, and dry season intensity. Other
parameters that effect tropical rainforests are carbon dioxide concentrations, solar radiation, and nitrogen
availability. In general, climatic patterns consist of warm temperatures and high annual rainfall. However, the
abundance of rainfall changes throughout the year creating distinct wet and dry seasons. Rainforests are
classified by the amount of rainfall received each year, which has allowed ecologists to define differences in
these forests that look so similar in structure. According to Holdbridge’s classification of tropical ecosystems,
true tropical rainforests have an annual rainfall greater than 800 cm and annual temperature greater than 24
degrees Celsius. However, most lowland tropical rainforests can be classified as tropical moist or wet forests,
which differ in regards to rainfall. Tropical rainforest ecology- dynamics, composition, and function- are
sensitive to changes in climate especially changes in rainfall.The climate of these forests is controlled by a
band of clouds called the Intertropical Convergence Zone located near the equator and created by the
convergence of the trade winds from the northern and southern hemispheres. The position of the band varies
seasonally, moving north in the northern summer and south in the northern winter, and ultimately controlling
the wet and dry seasons in the tropics These regions have experienced strong warming at a mean rate of 0.26
degrees Celsius per decade which coincides with a global rise in temperature resulting from the anthropogenic
inputs of greenhouse gases into the atmosphere. Studies have also found that precipitation has declined and
tropical Asia has experienced an increase in dry season intensity where as Amazonia has no significant pattern
change in precipitation or dry season. Additionally, El Niño-Southern Oscillation events drive the interannual
climatic variability in temperature and precipitation and result in drought and increased intensity of the dry
season. As anthropogenic warming increases the intensity and frequency of ENSO will increase, leaving
tropical rainforest regions susceptible to stress and increased mortality
of tree.
Soils
Soil types are highly variable in the tropics and are the result of a combination of several variables such as
climate, vegetation, topographic position, parent material, and soil ageMost tropical soils are characterized by
significant leaching and poor nutrients; however there are some areas that contain fertile soils. Soils throughout
the tropical rainforests fall into two classifications which include the ultisols and oxisols. Ultisols are known as
well weathered, acidic red clay soils, deficient in major nutrients such as calcium and potassium. Similarly,
oxisols are acidic, old, typically reddish, highly weathered and leached, however are well drained compared to
ultisols. The clay content of ultisols is high, making it difficult for water to penetrate and flow through. The
reddish color of both soils is the result of heavy heat and moisture forming oxides of iron and aluminum, which
are insoluble in water and not taken up readily by plants.
Soil chemical and physical characteristics are strongly related to above ground productivity and forest structure
and dynamics. The physical properties of soil control the tree turnover rates where as chemical properties such
as available nitrogen and phosphorus control forest growth rates. The soils of the eastern and central Amazon
as well as the Southeast Asian Rainforest are old and mineral poor where as the soils of the western Amazon
(Ecuador and Peru) and volcanic areas of Costa Rica are young and mineral rich. Primary productivity or wood
production is highest in western Amazon and lowest in eastern Amazon which contains heavily weathered soils
classified as oxisols. Additionally, Amazonian soils greatly weathered, making them devoid of minerals like
phosphorus, potassium, calcium, and magnesium, which come from rock sources. However, not all tropical
rainforests occur on nutrient poor soils, but on nutrient rich floodplains and volcanic soils located in the
Andean foothills, and volcanic areas of Southeast Asia, Africa, and Central America.
Nutrient Recycling
The soils of tropical rainforests are characterized by rapid recycling of fallen leaves and other organic matter
due to the large biomass of the rainforest. This high rate of decomposition is the result of phosphorus levels in
the soils, precipitation, high temperatures and the extensive microorganism communities In addition to the
bacteria and other microorganisms, there are an abundance of other decomposers such as fungi and termites
that aid in the process as well. Nutrient recycling is important because below ground resource availability
controls the above ground biomass and community structure of tropical rainforests. These soils are typically
phosphorus limited, which inhibits net primary productivity or the uptake of carbon.The soil contains tiny
microbial organisms such as bacteria, which breakdown leaf litter and other organic matter into inorganic
forms of carbon usable by plants through a process called decomposition. During the decomposition process
the microbial community is respiring, taking up oxygen and releasing carbon dioxide. The decomposition rate
can be evaluated by measuring the uptake of oxygen. High temperatures and precipitation increase
decomposition rate, which allows plant litter to rapidly decay in tropical regions, releasing nutrients that are
immediately taken up by plants through surface or ground waters. The seasonal patterns in respiration are
controlled by leaf litter fall and precipitation, the driving force moving the decomposable carbon from the litter
to the soil. Respiration rates are highest early in the wet season because the recent dry season results in a large
percentage of leaf litter and thus a higher percentage of organic matter being leached into the soil.
Buttress Roots
A common feature of many tropical rainforests is the distinct buttress roots of trees. Instead of penetrating to
deeper soil layers, buttress roots create a wide spread root network at the surface for more efficient uptake of
nutrients in a very nutrient poor and competitive environment. Most of the nutrients within the soil of a tropical
rainforest occur near the surface because of the rapid turnover time and decomposition of organisms and
leaves.Because of this, the buttress roots occur at the surface so the trees can maximize uptake and actively
compete with the rapid uptake of other trees. These roots also aid in water uptake and storage, increase surface
area for gas exchange, and collect leaf litter for added nutrition. Additionally, these roots reduce soil erosion
and maximize nutrient acquisition during heavy rains by diverting nutrient rich water flowing down the trunk
into several smaller flows while also acting as a barrier to ground flow. Also, the large surface areas these roots
create provide support and stability to rainforests trees, which commonly grow to significant heights. This
added stability allows these trees to withstand the impacts of severe storms, thus reducing the occurrence of
fallen trees.
Carbon flux
Carbon flux can be defined as the exchange of carbon dioxide between the atmosphere and a sink. Net primary
productivity, an important ecological concept, can be defined as the amount of carbon retained in plant biomass
over time. It is also the difference between gross primary productivity and autotrophic respiration and is used
to measure the amount of carbon within a rainforest. The importance of rainforests in the carbon cycle depends
on the above and below ground (root systems and soil organic matter) biomass, amount of carbon stored, and
the rate at which it is fixed by plants through photosynthesis.Compared to other forest types, tropical
rainforests are known to be significant carbon sinks, absorbing 4.8 billion tons of carbon dioxide every year.
The rainforests of Amazonia contain between 14 and 40 kilograms of carbon per square meter and the soils
contain 27% of the carbon in roots, microorganisms, soil fungi and plants.
Forest Succession
Succession is an ecological process that changes the biotic community structure over time towards a more
stable, diverse community structure after an initial disturbance to the community. The initial disturbance is
often a natural phenomenon or human caused event. Natural disturbances include hurricanes, volcanic
eruptions, river movements or an event as small as a fallen tree that creates gaps in the forest. In tropical
rainforests, these same natural disturbances have been well documented in the fossil record, and are credited
with encouraging speciation and endemism.
Rainforests Round the Globe
South and Central America
 Amazon Rainforest
 Atlantic Forest
 Central American Atlantic Moist Forest
Africa
 Atlantic Equatorial Coastal Forest
 Ituri Rainforest
 Kilum-Ijim Forest
 Madagascar lowland forests
Asia
 Sulawesi Lowland Rainforest
 Borneo Lowland Rainforest
 Palawan Rainforest
 Harapan Rainforest
Australasia/Oceania
 Daintree Rainforest
 Huon Peninsula Montane Rainforest
 Hawaiian Tropical Rainforest
By
Kieran Anders Ray