Tropical Forests – Unique and Diverse
Impenetrable green. Heavy rain and the secret eyes of the jaguar – what we connect with the term “tropical forests” represents mostly just a very small part of the real picture. Reality often looks totally different: totally different – but also much more exciting and varied than in our imagination!
In Summer and in Winter: Always Comfortably Warm!
In the tropical regions around the equator, there are no seasons as we know them in Central Europe. A day lasts – whether in the summer or in winter – always about 12 hours. The seasonal temperature variations are often less than those between day and night. One refers to the so-called “diurnal climate”. Here, the amount and frequency of the precipitation determine the frequency of activity of plants and animals – totally different from what we have here, with temperatures and photoperiods being decisive factors.
Tropical rainforests exist in Middle and South America, Africa, Southeast Asia, and in Australia. Although they differ in the variety of species, the structure of the forests and the ecology is similar in all regions. The typical tropical rainforest can only be encountered up to an altitude of roughly six hundred to one thousand meters above sea level. Beyond that, it is replaced by mountain rainforests and cloud forest formations.
Different Vegetation Types
Not everywhere in the tropics will one encounter dense forests! In case of low annual rainfall, savannas, thorn-forests, grasslands, or deserts will spread instead. In areas with a pronounced change between rainy and dry seasons, trees and bushes will shed their leaves during long periods of drought.
These so-called dry or monsoon forests originally made up one-third of all tropical forests. Although they look similar to the typical tropical rainforests with their lianas and herbaceous epiphytes, the unfavorable water balance, however, is evident in shorter tree trunks, thicker bark, and smaller leaves. The biomass and productivity of the tropical dry forests is well below that of tropical rain forests.
In tropical rainforests, the rain falls abundantly and frequently; long dry seasons do not occur. Evergreen plants from a wide range of families compete for light and nutrients here. On average, sixty to one hundred tree species can be found on one hectare – in Central Europe there are barely twelve!
This mosaic of trees, epiphytes, and climbing palm trees, vines, dense moss, and drooping lichens creates a biotope which is so rich in ecological niches unlike any other on this earth – that is the prerequisite for its unique diversity of species.
Unsurpassed Richness in Species
Of all terrestrial biomes the tropical rainforest possesses the largest variety of species and is home to perhaps as many plant and animal species as in all other terrestrial biomes, altogether. The reason for this high species diversity is seen in the complexity of its vegetation. Shrubs and trees appear to be arranged on numerous different levels. Especially in the treetops of these giant rain forest trees, a lot of inhabitants of the tropical rainforest feel especially comfortable.
According to scientific investigations, the diversity of the tropical rainforests diminishes the further one leaves their central area and moves to the periphery. The level of diversity differs from continent to continent. The highest species richness was registered in the Amazonian rain forest while Africa featured the lowest species richness of tropical rainforests.
Certainly, history is important, too, for the formation of this richness in species. Many rainforests of this planet have already existed for millions of years, while others are considerably younger. In places where glaciation occurred, the rainforests contracted and expanded later, when meteorological conditions during interglacial periods were more favorable. The ensuing isolation in insular forest regions contributed to the evolution of differing species.
The Tropical Rainforest – A Sensitive System
About one half of the amount of precipitation in the rainforests evaporates immediately on the large leaves of this hungry-for-sun vegetation. The water returns as water vapor to the atmosphere, only to be released again soon as strong rain showers. In the case of deforestation, this water cycle is severely disturbed. Without the closed and very productive vegetation cover, much less rain evaporates than before. The rainfalls abate or become erratic. Due to the concentration of roots in surface soils, the trees are dependent on frequent rain and cannot endure long periods of drought. A decline of the tropical rainforests would ensue – even though individual tracts of the forest would be spared from direct destruction by logging.
Especially in the humid tropics, the forest differs from those in the northern temperate zones. In regions with cold seasons, a large part of the organic matter and available nutrients accumulate in the soils and sediments. In the warm tropics, most of the organic matter and nutrients are contained in the living biomass, i.e. above ground in the biomass of plants. In tropical ecosystems, decomposition occurs quickly, and nutrients are rapidly reassimilated into living biomass.
Optimal Use of Limited Nutrients
The root network of the tropical rainforest is extremely dense and shallow. As such, the trees can directly absorb the few available nutrients which are released due to the fast decomposition of dead organic matter. Tropical rainforests rely on the soil to a lesser extent for their mineral nutrition, as we know it in our latitudes, but hey do depend on the soil for structural support. The mighty buttress roots of some of the giant rainforest trees testify to that…
Impact of Destruction
If a forest in a temperate zone is cleared, the soil mostly retains its nutrients and structures and can be cultivated for many years. The winter frost helps to shape nutrients and to prevent diseases and parasites. On the other hand, deforestation in the tropical forests destroys the ability of the soil to cling to nutrients and to combat pathogens. The existing nutrients are lost very quickly due to leaching and erosion. Therefore, agricultural cultivation methods involving annual plants in tropical regions are often completely inappropriate and unsustainable.
Invisible Richness in Species?
Slim stand density
If you have the opportunity to visit a tropical forest, you are often disappointed at first: As far as the eyes can see, there is no sign of the much heralded abundance of species. Hardly a colored bird and only with a lot of luck a dangerous snake or a larger mammal can be discovered. The only plentiful things one can find are ants or termites.
How is that possible? Diversity of species does not necessarily mean high stand density. In a large area, many plant and animal species are only present in small quantities. If you want to see more, you have to venture into the tops of the tree crowns, since a large proportion of animals spend their lives in the upper layers of the vegetation.
Researchers try to explain the phenomenon of the slim stand density of animal and plant species in tropical rainforests by referring to the few freely available nutrients. Indeed, this could be a reason why, despite ideal climatic conditions, many animals of the tropical forests require some years to reach their adult stage and thus sexual maturity. At the same time, and as opposed to their relatives in more temperate zones, they often have a very low reproduction rate.
Why Protect Tropical Forests?
High species richness, an abundance of different types of assimilation, and – at the same time – rareness, are all characteristic for the inhabitants of the tropical forests. One reason for this could be the scant and inaccessible supply of resources; many nutrients are linked with the lush vegetation. If the delicate equilibrium of these woods is disrupted at one location, this will have disastrous consequences for the entire system. A reforestation is often difficult.
Originally, about twelve percent of the world’s land area was covered with tropical rainforest. In the meantime, much more than one-half thereof has been destroyed by mankind. Especially tragic is the accompanying loss of biological diversity. The tropical forests are destroyed faster than the inhabitants can be recorded taxonomically and ecologically.
Along with these forests, we are probably destroying important existing and potential resources for medication and food. We are wiping out a genetic pool of wild plants and animals which could sustain and improve our cultural profiles. Last but not least, the large-scale destruction of tropical vegetation can contribute to global climate change.
For thousands of years, people have traditionally lived in tropical forests and have appreciated and used its resources, and thereby usually also contributed to its conservation. Through their traditional knowledge, the local human population has recognized the values and used options of a vast diversity of plants and animals for food, medicine, fibre, flavour, construction, and clothing. Since the beginning of the 20th century, however, tropical forests have been put under a different scale of threat as larger-scale economic interests and needs have started to predominate the development. As such, it is important to always provide the people living on this land with an alternative perspective.
TROPICA VERDE’s Commitment:
Since 1989, TROPICA VERDE e.V. has been successfully involved in the protection of tropical habitats. In doing so, special emphasis is put on the close cooperation with local environmental groups in the partner country Costa Rica. Through this cooperation, numerous projects for the conservation of the unique Central American flora and fauna have been accomplished, always at the same time to the benefit of the indigenous population.
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