Today, March 21, is the international day of forests . There are a large number of definitions of “forest”, most could be divided into three types: those that define an administrative unit, those that define a type of land use, and those that are defined by coverage. However, from a scientific perspective, the most objective definitions and those that best fit what we understand by “forest” are those that are stated from the perspective of ecology. In other words, a forest is, after all, an ecosystem.
As an ecosystem, a forest is a complex community of living beings that live in a space and are related to its physical and chemical factors. The forest ecosystem extends vertically from the subsoil , where roots hold the soil together and interact with water and mineral salts, to the atmosphere, beyond the canopy of trees , where birds fly, water floats pollen and dissipates the water vapor evapotranspired by plants.
A forest is also a refuge for biodiversity . Apart from the species of trees —one or several—, the forest has a complex plant community , made up of numerous species of shrubs and herbaceous plants, and a no less rich community of animals and microorganisms that inhabit it. Even its soil has its own characteristics.
Forests can be classified in different ways. For example, if we look at the climate, there are tropical, subtropical, temperate, Mediterranean and boreal forests. If we look at the type of tree that dominates, we usually differentiate between leafy forests —which can be evergreen or deciduous— or coniferous. However, among the most relevant classifications is natural history.
The origin of the forest
A primary forest has its own history in which the human hand has not intervened or has done so in a minimal way. Ecological succession is the natural evolution of an ecosystem, as a product of its own internal dynamics. Starting from bare soil, it begins with the colonization of the first microorganisms and pioneer plants, and over time, the ecosystem becomes more and more complex. The primary forest is , in this evolutionary process, the climax community, the final stage of that natural succession.
This type of forest has, therefore, a unique natural history , which explains the enormous complexity that we can find in its intrinsic relationships. A forest has the ability to preserve itself against normal disturbances in the area it occupies, although a very strong disturbance or one that comes from outside and to which the forest is not adapted can cause a problem.
Secondary forest is usually defined as that which has had, in one way or another, interaction with the human hand. Unfortunately that definition, today, is very vague: practically all the world’s forests have suffered anthropogenic interaction in one way or another.
A secondary forest is generally considered to be one that has recovered —on its own, or with human assistance, by replanting the same species— after massive logging . Some authors extend the name of secondary forest to those that come from the natural regeneration of a primary forest previously destroyed by natural causes, such as the passage of a hurricane or a flood. There are even authors who consider secondary forest to be one that has suffered, for example, a serious impact on the fauna such as the disappearance of predators , something that alters the ecological succession.
A secondary forest can, of course, become primary if the ecological succession process follows its normal course and reaches the climax community again. It is considered recovered if it manages to reach the level of self-maintenance and adaptation to normal disturbances that characterizes them and loses all scars of the disturbances —anthropic or natural— that gripped it in the past.
What is not a forest
In all the types of community compiled so far, certain features stand out; a natural history that a community of plants, animals and microorganisms maintain in common, throughout what we have called ecological succession. But what if in a completely deforested land, where the plants no longer exist, the microorganisms have disappeared and the animals have died or have left, we plant a large number of trees, perfectly ordered, all of the same species?
That is not a forest. That is a forest plantation . And from an ecological point of view it has enormous differences. Forests have an internal dynamic between plants, animals and microorganisms, which we do not find in plantations. It is true that, frequently, some herbaceous plants, fungi, microorganisms and even a handful of animal species are installed in a plantation. However, this flora, fauna and microbiota are not typical of that ecosystem. They are not part of natural succession ; there has been no natural succession. And the biodiversity found in plantations is at very low levels when compared to the biodiversity of primary forests.
The ecological relationships that occur in a plantation are simple , and remain constantly interrupted by the human hand, which extracts and replants without stopping, without allowing the ecosystem to advance in its ecological succession. A forest plantation has neither the natural history nor its own identity that the forest has.
Of course, the wood with which we build our furniture and the paper on which we print our books, the oranges and apples we eat, all have to come from somewhere. And to plant those trees, land had to be taken from the natural environment, in many cases forests. Our standard of living requires that today forests have to coexist with forest plantations. Regulating the area that is used and how the landscape is managed is in the hands of the human being. But in doing so, we must not forget that forests are a refuge for biodiversity at levels that forest plantations cannot reach. And we still need them.
REFERENCES:
Barlow, J. et al. 2007. Quantifying the biodiversity value of tropical primary,secondary, and plantation forests. Proceedings of the National Academy of Sciences, 104(47), 18555-18560. DOI: 10.1073/pnas.0703333104Corlett, R. T. 1994. What is secondary forest? Journal of Tropical Ecology, 10(3), 445-447. DOI: 10.1017/S0266467400008129Lund, G. 2002. When Is a Forest Not a Forest? Journal of Forestry, 100, 21-28.Waring, R. H. et al. 2007. Forest Ecosystem Analysis at Multiple Time and Space Scales. En Forest Ecosystems (pp. 1-16). Elsevier. DOI: 10.1016/B978-012370605-8.50005-0
