The natural succession of species is the vehicle through which life flows in time and space.
The Earth and the sun complement each other. The vegetation and animal life of our planet Earth convert the energy from the sun into organic compounds. Each living being has a unique function that contributes either directly to this process through plant, bacteria and green algae photosynthesis and chemosynthesis, or, indirectly, through successive transformation, intermediation, transport, optimisation, and acceleration processes. Excessive solar energy transformed into organic compounds is deposited in swamps (in time becoming carbon compounds) and in tropical oceans (with time forming hydrocarbons and gas).
E. Götsch explains that life is organized in systems everywhere. As time progresses life increases and becomes more complex resulting in more elaborate systems (synthroptic processes) that are not static; on the contrary, they are very dynamic.
The “colonizers” which can be found in soils that have been destroyed, cliffs and overexploited sites, take the first step. For example, the first to colonize barren rocks are bacteria that create the necessary conditions for the development of moss and lichens. In turn, when they have created the conditions that favour the development of other more demanding species, pioneer plants start to develop, initiating the next stage, the first Accumulation Systems.
Accumulation Systems are characterized by including plant species with a wide carbon/nitrogen ratio. The lignin content of the organic matter is high and; consequently, the decomposition of organic matter such as leaves and ligneous parts is slow (accumulation of energy – organic matter).
The fruits produced by trees found in the lignin system are not edible by men or large animals. They are home to insects noxious to human beings, small animals such as mice, poisonous snakes and small birds. As living conditions are improved through the dynamics of life itself (succession processes), other species that form part of the following Accumulation Systems begin to appear.
It’s easier for life to reach this state in soils which originated from young granite rocks or basalt. Living conditions in the intermediary system are better, given the closer Nitrogen/Carbon relation, the improved fruits and seeds and the medium sized animals.
Abundance Systems are found at the peak of the complexity chain. Normally, they are found in cilia and alluvial forests, in riverbeds and hydrographical basins. These systems are the habitat of large animals and its vegetation is characterized for the close Carbon/Nitrogen links.
The species found in the Abundance Systems are characterized for their large fruits, rich in carbohydrates, fat and protein that are able to support large animals. In order to survive, mankind, being a large animal, needs the conditions prevalent in abundance systems.
Transformation processes in these abundance systems are intensive and the flow of carbon is very high (greater activity of micro-organisms). Within each of the systems described before there is a sequence regarding the dominance of the different consortiums of species.
The consortiums that characterize the different stages are the following:
The degree of development each system achieves is characterized by the development stage of the predominant species considered in the natural succession. Thus, each system has its own consortium of pioneer, secondaries and primary organisms, that are also subject to variations depending on the ecological characteristics of the site.
The principles of natural succession are, however, the same for all ecosystems.
Understanding the principles of natural succession and the species associated to them in each stage and in each ecosystem is the key to achieving a successful management of dynamic and stratified agricultural and forest systems.
1. Pioneers (up to 6 month)
After eliminating the primary layer of vegetation (as a result of slash and burn practices, or when an emerging tree falls, leaving an empty space) many pioneer plants and other species corresponding to the next succession, begin to grow.
The majority of our short cycle crops belong to the pioneer group of the Abundance System: Corn, Rice, Sweet Potatoes, Soybean, Beans, Squashes, Tomatoes, Watermelon.
2. Secondary I (six month up to two years), II (two years up to 15 years)
The secondary vegetation is born along with the pioneers, dominating the latter after one or two years. The secondary vegetation includes species with different life cycles (two, fifteen, eighty years, approximately).
The most renowned species of secondary species with a short life cycle (two to 15 years) in the Alto Beni Region of Bolivia are the following: Manioc, Pineapple, Sugar Cane, Banana, Cecropias, Balsa wood, Ingas ssp., Cardamomo, Passion Fruit, Morera, Curcucma, Toco (Schizolobium amazónicum), and others.
3. Secondary III with long life cycle (15 years up to 80 years)
Some of the species that form part of forests in process of becoming primary forests are presented below – what we call a primary forest is also a system who is in transition and subject to change.
Asaí (Euterpe ssp.), Pejibeye (Bactris gassipaes), Motacú (Scheelea princeps) Oranges and other citric plants, Jacaratia cf. digitata, Eritrina ssp., Guazuma ulmifolia, Jackfruit (Artocarpis altilis, Artocarpis heterophylla), Guanabano – Tree, Soursop (Anona muricata), Lime, native mandarin, Avocado (Persea americana).
4. Primary (> 80 years)
The primary consortium is composed by species of the “primary forest” that dominate the secondary III species. Eventually, they become the upper stratums and the trees emerging from the forest. The pioneers and the different secundary species are born along with the primary species. For the primaries to prosper they must be raised by the first.
Some examples of species found in a primary forest and of primary crops of the Abundance System in Alto Beni are the following: Cocoa, Copuazú (Theobroma grandiflora), Achachairú (Rheedia ssp.), Coffee, Cashew, Mahogany (Swietenia macrophylla), Ceiba (Ceiba ccp.), Ochóo (Hura crepitans), Ficus ssp., Rubber (Hevea brasiliensis), Brazil nut (Bertholletia excelsa), Garlic tree (Gallesia integrifolia), etc.
Within a succession, in order to achieve a primary forest, none of the stages of the natural succession can be left out. However, even if none of the stages can be skipped, a proper intervention can accelerate some of these processes.
In order to guarantee a successful and productive agroforestry system, all species that form part of the system – at a given place, at a given moment – should be planted.
Not respecting the natural succession process has consequences
Currently, we slash and burn primary forests in order to create adequate conditions for our “pioneers”. When we are no longer able to grow these pioneers the land is left to rest, favouring the development of species characteristic of the secondary forest. After 5 or 7 years the secondary forest is slashed and burned and, once again, we grow species that belong to the pioneer consortium. Depending on the soil and climate conditions and as a consequence of this practice, the Abundance System is degraded into an Advanced Accumulation or even worse, a Poor Accumulation System. Pioneer species of Abundance Systems are not able to grow in Accumulation Systems. For a while, then, we insist in growing these crops in adverse conditions, using chemicals and pesticides that simulate the conditions prevalent in abundance systems, until the ecosystem is so degraded that no crop of interest to us will be successful.
At this stage, many farmers plant pioneers of a secundary system such as grasses. In the end they are expelled by pioneers of the lower secundary Systems (e.i.: sujo – Imperata spp.). When this point is reached the soil can no longer sustain cattle. As a consequence of the degradation of the soils and ecosystems, natural disasters such as droughts, floods and hurricanes begin to occur.
