The understory It is the lower level of the forest, formed by the plants that live under the tree strata. It is made up of herbs, shrubs, small trees and juveniles of species typical of the upper strata.
The floristic composition (species present) and structural complexity of the understory depends on the type of vegetation where it is found. Thus, the understory is more complex in tropical forests than in temperate forests and in these more than in the boreal forest (taiga).
There are environmental differences between the understory and the upper canopy of the forest or jungle. The upper canopy exerts a covering influence on the understory, restricting the quantity and quality of solar radiation that can reach it..
On the other hand, the trunks of the trees in the upper canopy are a barrier that protects the smaller plants from the winds. All this creates a particular microclimate in the understory with a higher relative humidity than in the upper canopy, while the temperature and evapotranspiration are lower..
The flora of the understory varies with the type of forest and the latitude where it develops, and the same occurs with the fauna. The latter, given its mobility, is divided into species exclusive to the understory and occasional or transit species..
For example, big cats are typical understory animals, while most monkeys rarely descend from the upper strata. In the same way, snakes are mainly from the understory, although some species can climb to the upper strata.
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The understory, depending on the type of forest or jungle, develops from ground level to about 4 or 5 m high. It is made up of herbs of different sizes, shrubs, small trees, as well as various species of ferns, mosses, lichens and fungi..
Forests have a structure defined in horizontal and vertical dimensions, the latter being determined by the number of strata that are formed. The number of strata in a forest will depend on its complexity, diversity and lushness..
The plant formations with the greatest structural complexity and diversity are the rainforests or humid tropical forests, with an understory plus 4 or 5 arboreal strata. In these, the understory presents different biotypes such as lichens, mosses, low and medium grasses, giant grasses and tree ferns..
In addition, in these understory there are shrubs of various sizes, small trees (including juveniles of the upper canopy species), as well as abundant climbers and epiphytes. For its part, in the taiga (boreal forest) there are one or two arboreal strata and the understory is poorly developed with some herbs, shrubs, mosses and lichens.
In an intermediate position are temperate forests, which depending on the particular type range from two to three strata. In these, the understory is rich in species of fungi, lichens, mosses, herbs and shrubs..
The position of the understory under the tree canopy of the forest creates a different microclimate than the environmental conditions of the upper canopy. The understory foliage is shaded, affecting variables such as light, temperature, relative humidity and evapotranspiration..
The determining factor is the least amount of solar radiation that reaches the lower level of the forest, after being filtered by the upper canopy. Therefore, understory plants generally have less solar energy to carry out photosynthesis..
In addition, large trees are a barrier against the wind, and their canopies reduce the escape of heat from the ground to the atmosphere outside the forest. Thus, the interior of the forest maintains a somewhat higher thermal sensation than the exterior, as well as a higher relative humidity due to internal condensation..
The climatic conditions of the understory promote the development of fungi, mosses, lichens and ferns in the soil. In the same way, the plants that grow there present forms adapted to these conditions and in extreme cases develop particular metabolisms..
For example, in temperate deciduous forests, many of the understory species in the spring form new leaves earlier than those in the upper canopy. This way they can take better advantage of solar radiation for a short period of two to three weeks..
In the case of humid tropical forests, where environmental humidity is very high, many understory species develop the guttation mechanism. This consists of expelling the water in liquid form through the margins of the leaves, through special structures called hydátodes..
Another characteristic difference between upper canopy plants and understory plants is the size of the leaf blades. The understory leaves tend to be wider and thinner, to expose more area and capture the light that manages to filter.
The understory receives a shower of organic matter from the upper canopies including flowers, fruits, leaves and even fallen trees. As well as all the organic matter from the forest fauna in the different strata, either due to excreta or deaths.
This is a contribution of nutrients for plants and part of the fauna of the understory, such as decomposers and some species of insects..
The periodic falls of the trees of the upper canopy upset the balance in the understory, destroying large areas of the forest. This produces clearings through which more solar radiation penetrates, modifying the local microclimate..
In this case, processes of secondary plant succession begin, where pioneer plants adapted to this greater solar radiation first emerge. Then little by little the original condition of the understory and the upper canopy is restored.
The flora of the understory varies depending on the type of forest, which is given by the latitude and altitude at which the forest grows..
These forests present a very diverse understory with abundant grasses, shrubs and small trees. In the forests or jungles of tropical America there are abundant Heliconias, Araceae, Zingiberaceae and Marantaceae which are giant herbs with large and broad leaves..
Among the shrubs and small trees are various species of Croton, as well as palms, rubiaceae, piperáceas and solanaceas. Some cultivated plants originated in the American tropical understory, such as cacao (Theobroma cacao) and cassava or manioc (Manihot esculenta).
Tree ferns up to 5 m high, of the Dicksoniaceae and Cyatheaceae families, are found in the understory of the world's tropical forests. On the other hand, in the humid and warm tropical forests of the South in Australia, genera such as Lepidozamia Y Bowenia (underground stem palm-like gymnosperms).
Also abundant are herbs of low to medium size and shrubs such as barberry (Berberis vulgaris) that reaches up to 3 m in height. While holly (Ilex aquifolium), boxwood (Buxus sempervirens) and the lonchite fern (Blechnum spicant).
Similarly, species that have been domesticated as spices such as rosemary (Salvia rosmarinus) and mint (Mentha piperita). In the Andean temperate forests of the southern American cone, there are bamboo undergrowths (Chusquea spp.).
The understory of the boreal forest is among the least complex both structurally and in terms of species composition. Basically there are lichens (Cladonia spp., Cetraria spp.), mosses (Sphagnum spp.) and some herbs and shrubs.
Most forest mammals, reptiles, insects, amphibians, and mollusks live in the understory. In this area the presence of birds is much more restricted, in any case only occasionally or those with a terrestrial habit..
The big cats of the jungles like the jaguar (Panthera onca) or the Bengal tiger (Panthera tigris) are inhabitants of the understory. Similarly, the jungle elephant (Loxodonta cyclotis) and the jungle gorilla (Gorilla beringei) in Africa and the different species of tapir (Tapirus spp.) in America and Asia.
Some birds feed on the forest floor such as cracids, where curassow and turkeys are found..
Wolves (Canis lupus), Bears (Ursus arctos, Ursus americanus) and lynxes (Felis lynx). In addition, wild boars (Sus scrofa), deer (Cervus elaphus), hares (Lepus spp.), European bison (Bison bonasus) and birds such as grouse (Tetraus urogallus) and the partridge (Perdix lost).
The thin and cold undergrowth of the taiga is inhabited by reindeer (Rangifer tarandus), the bears, the wolf and the elk (Moose moose). Besides hares, and stoats (Mustela erminea), and among the birds is the ptarmigan (Lagopus muta Y Lagopus lagopus).
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