Editing Tropical rainforest (section)

== Ecology ==
=== Climates ===
[[File:Chiapas Rainforest.jpg|thumb|Rainforest in [[Chiapas]], Mexico]]
[[File:Parc amazonien de Guyane, une balade à Saül.jpg|thumb|[[Guiana Amazonian Park]] in [[French Guiana]]]]
[[File:Swains Island 2.jpg|thumb|Road on Swains Island, [[American Samoa]]]]
[[File:El bosque inundado amazonico-cosmocaixa-2009 (2).JPG|thumb|Artificial tropical rainforest in Barcelona]]
Tropical rainforests are located around and near the equator, therefore having what is called an equatorial climate characterized by three major climatic parameters: temperature, rainfall, and dry season intensity.<ref name="MalhiandWright2004"/> Other parameters that affect 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 moist and dry seasons. Tropical forests are [[Tropical and subtropical moist broadleaf forests|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 [[Holdridge life zones|Holdridge's classification]] of tropical ecosystems, true tropical rainforests have an annual rainfall greater than 2{{nbs}}m and annual temperature greater than 24 degrees Celsius, with a [[potential evapotranspiration]] ratio (PET) value of <0.25. However, most lowland [[tropical forest]]s can be classified as tropical moist or wet forests, which differ in regards to rainfall. Tropical forest ecology- dynamics, composition, and function- are sensitive to changes in climate especially changes in rainfall.<ref name="MalhiandWright2004"/>

=== Soils ===
==== Soil types ====
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 age.<ref name="Aragao2009"/> Most tropical soils are characterized by significant [[leaching (agriculture)|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 aluminium, 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 whereas chemical properties such as available nitrogen and phosphorus control forest growth rates.<ref name=Moreira/> The soils of the eastern and central Amazon as well as the Southeast Asian Rainforest are old and mineral poor whereas 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.<ref name="Aragao2009" /> Additionally, Amazonian soils are 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.<ref>[http://www.mongabay.com/ Environmental news and information]. mongabay.com. Retrieved on 28 March 2013.</ref>

Oxisols, infertile, deeply weathered and severely leached, have developed on the ancient [[Gondwana]]n [[Shield (geology)|shields]]. Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminium oxides by the [[Laterite|laterization]] process gives the oxisols a bright red color and sometimes produces minable deposits (e.g., [[bauxite]]). On younger substrates, especially of volcanic origin, tropical soils may be quite fertile.

==== Nutrient recycling ====
[[File:Cogumelos brancos.jpg|thumb|Fungi play a part in nutrient recycling]]
This high rate of decomposition is the result of phosphorus levels in the soils, precipitation, high temperatures and the extensive microorganism communities.<ref name="Cleveland2006"/> In addition to the bacteria and other microorganisms, there are an abundance of other [[decomposer]]s 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.<ref name="Aragao2009" /> The soil contains microbial organisms such as bacteria, which break down 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.<ref name="Cleveland2006" /> 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.<ref name="Cleveland2006" />

==== Buttress roots ====
[[File:Flickr - ggallice - Ceibo.jpg|thumb|Base of ''[[Ceiba pentandra]]'' in eastern Ecuador]]
A common feature of many tropical rainforests is the distinct [[buttress root]]s of trees. Instead of penetrating to deeper soil layers, buttress roots create a widespread 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.<ref name="Young2010"/> 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.<ref name="Young2010" /> 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.<ref name="Young2010" />

=== Forest succession ===
[[Ecological 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.<ref name="SahneyBentonFerry2010LinksDiversityVertebrates"/> Human land use practices have led to large-scale deforestation. In many tropical countries such as Costa Rica these deforested lands have been abandoned and forests have been allowed to regenerate through ecological succession. These regenerating young successional forests are called secondary forests or second-growth forests.