Editing Tropical rainforest (section)

== 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.<ref name="Golley"/> 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 rainforest]]s.<ref>{{cite journal |title=A Physiognomic Classification of Australian Rain Forests|first1=Len|last1=Webb| author-link=Leonard Webb (academic) | journal = Journal of Ecology| publisher=British Ecological Society : Journal of Ecology Vol. 47, No. 3, pp. 551–570|date=1 October 1959|volume = 47|issue = 3|pages = 551–570|doi = 10.2307/2257290|jstor = 2257290|bibcode=1959JEcol..47..551W }}</ref>

=== Forest floor ===
[[File:Gorilla gorilla04.jpg|thumb|Western lowland gorilla]]
The [[forest floor]], the bottom-most layer, receives only 2% of the sunlight. Only plants [[Adaptation|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]] (''Okapia johnstoni''), [[tapir]] (''Tapirus'' sp.), [[Sumatran rhinoceros]] (''Dicerorhinus sumatrensis''), and apes like the [[western lowland gorilla]] (''Gorilla gorilla''), as well as many species of reptiles, amphibians, and insects. The forest floor also contains [[decomposition|decaying]] plant and animal matter, which disappears quickly, because the warm, humid conditions promote rapid decay. Many forms of [[Fungus|fungi]] growing here help decay the animal and plant waste.

=== Understory layer ===
{{Main|Understory}}
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]] (''Panthera pardus''), [[poison dart frog]]s (''Dendrobates'' sp.), [[South American coati|ring-tailed coati]] (''Nasua nasua''), [[boa constrictor]] (''Boa constrictor''), and many species of [[beetle|Coleoptera]].<ref name="Newman, Arnold 2002"/> 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{{nbs}}feet). As an adaptation to these low light levels, understory plants have often evolved much larger leaves. Many seedlings that will grow to the canopy level are in the understory.

[[File:FRIM canopy.JPG|thumb|The canopy at the [[Forest Research Institute Malaysia]]]]

=== Canopy layer ===
{{Main|Canopy (ecology)}}
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.<ref name=Erwin/> Other species inhabiting this layer include many avian species such as the [[yellow-casqued wattled hornbill]] (''Ceratogymna elata''), [[collared sunbird]] (''Anthreptes collaris''), [[grey parrot]] (''Psitacus erithacus''), [[keel-billed toucan]] (''Ramphastos sulfuratus''), [[scarlet macaw]] (''Ara macao'') as well as other animals like the [[spider monkey]] (''Ateles'' sp.), African giant swallowtail (''[[Papilio antimachus]]''), [[three-toed sloth]] (''Bradypus tridactylus''), [[kinkajou]] (''Potos flavus''), and [[tamandua]] (''Tamandua tetradactyla'').<ref name="Newman, Arnold 2002" />

=== Emergent layer ===
[[File:Forest dominated by Gilbertiodendron dewevrei 02.jpg|thumb|[[Congolian rainforests|Congolian rainforest]] dominated by ''[[Gilbertiodendron dewevrei]]'', near [[Isiro]]]]
The emergent layer contains a small number of very large [[trees]], called ''emergents'', which grow above the general [[Canopy (forest)|canopy]], reaching heights of 45–55{{nbs}}m, although on occasion a few species will grow to 70–80{{nbs}}m tall.<ref name="Golley">{{cite book |last= Bourgeron |first= Patrick S.|editor= Frank B. Golley |title=Tropical Rain Forest Ecosystems. Structure and Function |year= 1983 |edition= 14A|series= Ecosystems of the World |publisher= Elsevier Scientific |isbn= 0-444-41986-1 |pages= 29–47 |chapter= Spatial Aspects of Vegetation Structure}}</ref><ref>{{cite web | url = http://www.nativetreesociety.org/worldtrees/sea_ei/malaysia/sabah2005.htm | title = Sabah | publisher = [[Eastern Native Tree Society]] | access-date= 14 November 2007}}</ref> Some examples of emergents include: ''[[Hydrochorea elegans]]'', ''[[Dipteryx panamensis]]'', ''[[Hieronyma alchorneoides]]'', ''[[Hymenolobium mesoamericanum]]'', ''[[Lecythis ampla]]'' and ''[[Terminalia oblonga]]''.<ref name=King/> 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]] (''Stephanoaetus coronatus''), the [[king colobus]] (''Colobus polykomos''), and the [[large flying fox]] (''Pteropus vampyrus'').<ref name="Newman, Arnold 2002" />

However, [[stratification (vegetation)|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 is 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, for example.<ref name="Denslow"/>