- Understory characteristics
- Forest plant structure
- Weather
- Adaptations
- Nutrients
- Understory dynamics
- Flora
- Rainforest or humid tropical forest
- Temperate forest
- Boreal forest or taiga
- Fauna
- Tropical rainforest
- Temperate forest
- Boreal forest or taiga
- References
The understory 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).
Understory. Source: Manuel Francisco Parrilla Cabezas. / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)
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. Similarly, snakes are mainly from the understory, although some species can climb to the upper strata.
Understory characteristics
The understory, depending on the type of forest or jungle, develops from ground level to about 4 or 5 m high. It is formed by herbs of different sizes, shrubs, small trees, as well as various species of ferns, mosses, lichens and fungi.
Forest plant structure
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 undergrowth has different biotypes such as lichens, mosses, low and medium grasses, giant grasses and tree ferns.
Understory of a tropical forest. Source: Thomas Schoch / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.5)
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. On the other hand, 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, moss, herbs and shrubs.
Weather
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.
Adaptations
The climatic conditions of the understory promote the development of fungi, mosses, lichens and ferns in the soil. Similarly, the plants that grow there have 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. In 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 through.
Nutrients
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 through 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.
Understory dynamics
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.
Understory of the boreal forest. Source: DenisStPierre / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)
In this case, secondary plant succession processes begin, where first pioneer plants adapted to this greater solar radiation emerge. Then, little by little, the original condition of the understory and the upper canopy is restored.
Flora
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.
Rainforest or humid tropical forest
These forests present a very diverse understory with abundant grasses, shrubs and small trees. In the forests or jungles of tropical America, heliconia, araceae, zingiberaceae and marantaceae are abundant, 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 solanaceae. Some cultivated plants originated in the American tropical understory, such as cacao (Theobroma cacao) and cassava (Manihot esculenta).
Flora of the tropical understory. Source: Rafaga08 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)
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 and Bowenia (underground stem palm-like gymnosperms) are common.
Temperate forest
There are also abundant herbs of low to medium size and shrubs such as barberry (Berberis vulgaris) that can reach up to 3 m in height. The holly (Ilex aquifolium), boxwood (Buxus sempervirens) and lonchite fern (Blechnum spicant) are found in the oak and beech undergrowth.
Likewise, species that have been domesticated as spices such as rosemary (Salvia rosmarinus) and mint (Mentha piperita) are common. Bamboo (Chusquea spp.) Undergrowths are found in the Andean temperate forests of the southern American cone.
Boreal forest or taiga
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.
Fauna
Most of the mammals, reptiles, insects, amphibians and mollusks of the forests 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.
Tropical rainforest
The big cats of the forests such as the jaguar (Panthera onca) or the Bengal tiger (Panthera tigris) are inhabitants of the understory. Likewise, 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.
Jaguar (Panthera onca). Source: Bjørn Christian Tørrissen / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)
Some birds feed on the forest floor such as cracids, where curassow and turkeys are found.
Temperate forest
Ursus americanus. Source: Rafael M. Marrero Reiley
Wolves (Canis lupus), bears (Ursus arctos, Ursus americanus) and lynx (Felis lynx) are found in the understory of these ecosystems. In addition, there are wild boars (S us scrofa), deer (Cervus elaphus), hares (Lepus spp.), European bison (Bison bonasus) and birds such as grouse (Tetrao urogallus) and partridge (Perdix perdix).
Boreal forest or taiga
The sparse and cold understory of the taiga is inhabited by reindeer (Rangifer tarandus), bears, wolf and elk (Alces alces). In addition to hares, and ermines (Mustela erminea), and among the birds is the ptarmigan (Lagopus muta and Lagopus lagopus).
References
- Calow, P. (Ed.) (1998). The encyclopedia of ecology and environmental management.
- Espinoza-Martínez, LA, Rodríguez-Trejo, DA and Zamudio-Sánchez, FJ (2008). Synecology of the understory of Pinus hartwegii two and three years after prescribed burns. Agro-science.
- Hernández-Ramírez, AM and García-Méndez, S. (2014). Diversity, structure and regeneration of the seasonally dry tropical forest of the Yucatan Peninsula, Mexico. Tropical biology.
- Ibarra, JT, Altamirano, TA, Rojas, IM, Honorato, MT, Vermehren, A., Ossa, G., Gálvez, N., Martin, K. and Bonacic, C. (2018). Bamboo understory: essential habitat for the biodiversity of the Andean temperate forest of Chile. La Chiricoca.
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- Rey-Benayas, JM (1995). Patterns of diversity in the strata of boreal montane forest in British Columbia. Journal of Vegetation Science.
- Voigt, CC (2010). Insights into Strata Use of Forest Animals Using the “Canopy Effect.” Biotropic.
- World Wild Life (Viewed on April 20, 2020). Taken from: worldwildlife.org/biomes/