Forest soils are only 'fertile' for one type of sustainable land use, that is; forestry.
Several writers on the contested give away of Mabira forest have not given the public: obvious, basic knowledge, and facts about the soil ecology of rain forests.
Mabira is a rain forest whose soils are very poor and cannot support agricultural production as it may seem. This is a fact that people often overlook. A basic understanding of forest soils, nutrient deposits locations, the root systems, tree adaptations and the traditional agricultural systems could help one understand why there are problems with clearing rainforest lands for agriculture.
We, the scholars of forestry and related ecology consider 75% of the world's rainforests, including Mabira forest, as "wet-deserts". This implies that such soils on which the rainforests grow are actually deficient of nutrients since they are deeply leached laterites that are equally very acidic. In addition, these soils are not only very old numerically, but have spent equally the same amount of time without replenishment from volcanic activity, a common source of nutrients. The soils are weathered and much leached due filtration of precipitation through the porous humus and peaty surface.
One would actually wonder how such very poor soils can support such green and flourishing plants and trees, and a flourishing beautiful jungle that is often too thick to penetrate. The explanation for this is very simple;
a) The thick, but shallow humus and peaty layer
The forest base has a thick humus layer that may be termed as 'un-true' soil. This layer supports a lot of below ground diversity including flora and fauna both micro and macro. The interactions of these organisms helps to decompose the falling debris from the forest canopy at very fast rates so that they avail nutrients to the standing and higher plants timely. Specifically, if one tries to plough at six inches (1ft) of the forest base, one will find a maze and thick network of tree roots, competing to explore these surface nutrients. This actually explains why most rain forest trees have no tap roots and will fall easily in a storm. Of course tree falling is another healthy phenomenon in a rain forest for another day's discussion.
Therefore, it is the ecology of the top 6 inches of the forest base that supports the beauty seen outside. To a common man, it is this beauty that makes one think that clearing the forest would provide good arable land. This is not true and is misleading. It misled the early European colonialists in the Amazon (a rain forest like Mabira) who cleared the rain forest areas but could not sustain optimal agricultural production for more than two seasons. This means that one will need more fertiliser application than they expected. This often frustrates many in the short run and they often abandon such projects, a very bad precedent, since there is loss of both forest cover and the agricultural business due to poor yields. This is the very reason why our great grandparents practiced burnt patch/shifting cultivation. This was so because soils under rainforest cannot sustain crop production. They would clear forest land, grow crops for one or two seasons, and then shift to another patch of forest because they previous one has lost fertility quickly.
Given such known facts, why would such a wonderful agriculturalist as Sugar Corporation of Uganda Ltd (SCOUL)opt for such very poor land, that is very expensive in the long-run (after the first season)? Are there are other undisclosed interests?
b) Nutrient storage
In a rainforest ecosystem, majority of the carbon and many other nutrients are stored above the ground. This is so much to the extreme, such that nutrients can only be accessed when recycled into the soil after the rotation or life time of the tree. This means that if a tree will die and fall after 80 years, such nutrients are locked in the standing tree for 80 years, and are not available to the soil. Imagine the number of trees in Mabira forest and their ages; use this to imagine the amount of nutrients drained from the soil where the trees stand and how long it takes to have them recycled back to the ground for agricultural production. This clearly shows how rainforest soils are poor and should not be an option for natural-fertility-led agriculture.
c) Adaptation evidences
The way the forest trees physically appear should not be taken for granted. It is evidence of adaptation to such poor nutrient soils. The buttresses ,lack of tap roots, aerial roots and the symbiotic mycorrhiza fungi are all adaptation for trees to manage and survive in the 'wet desert'. The buttresses provide alternative support because there is no tap root (since there is no business deep ground), feed from the surface that can easily be lost within one season of arable land use. The aerial roots held in suspense supplement nutrient supplies from the immediate micro climate and the symbiotic mycorrhiza, a fungi, that helps the tree root systems access and imbibe nutrients from the immediate micro-environment.
In a nut shell, it is the unique forest ecosystem that can support such flourishing vegetation that is mouth watering for anyone who thinks that it is fertile land. When one removes the forest environment, this ecosystems falls short of its complex functions and then gives you the typical experience of a wet desert that cannot support agriculture for more than a season. Therefore, forest land is only 'fertlile' for itself and no other land use. Say no to the 'give away', 'sale away', 'lease away' whatever you call it of Mabira forest and other rain forests like Budongo and others.
Owen E. Sseremba is from the Department of Forest products Engineering, Makerere University