Now we have discussed the causes of deforestation in the Amazon and its consequences, I shall take a look at how the Amazon can support so much life. The answer may surprise you; the Amazon really ISN’T all that fertile and I shall explain why below.
The majority of soil in the Amazon is in fact very thin and acidic,and to be technical is called latosol. Due to high rainfall any nutrients are quickly washed away. 1 So the question is, how can an infertile soil support the high biodiversity found in the rainforest? There are several reasons:
- Plant matter and dead animals decompose quickly due to high humidity and the ability of the decomposers to recycle them back into the ecosystem.
- This ability to recycle also means nutrients rarely leave the rainforest ecosystem unless disturbed.
- Most of the trees are short rooted so can take up nutrients in the top layer of soul quickly They also require buttress roots to hold them up, which are an iconic image of rainforests.
So really the fertility is all down to really efficient nutrient cycling! 2 This means that when people start to farm in the Amazon, they find that the soil very quickly becomes infertile. The nutrient cycling simply becomes nutrient depletion, as all the crops do is take from the soil. Exposure to the sun also saps the soil of moisture turning it into a hard clay. 3
However, there are areas of the forest that are very fertile. The reason for this is ‘terra preta’, a different type of lathosol. 4 Terra preta is a very dark earth found in the Amazon and is entirely man made and very old. The soil was created by burying animal bones, manure, charcoal and pottery shards to creat biochar. Most importantly, compared to the few centimetres depth of the lathosol type above, terra preta can be up to 2 metres in depth.
The depth and high density of carbon in the soil is what makes it fertile, the charcoal preserving organic matter to keep nutrients in the soil for use at a later date. Our ancestors used their waste in order to provide a highly fertile soil where they could grow crops. Or do they? Most think that it’s too convenient for them to have thought about creating this soil on purpose. Instead terra preta is simply the remains of kitchen rubbish, with charcoal used to fertilise soils they used for growing crops. This crop growing soil is called terra mulata. 5 Nonetheless areas from 20 hectares to 360 hectares of terra preta have been reported, and my cover up to 10% of the Amazon. 6 7 Maybe we could use these findings to help us create more fertile soil elsewhere? Thoughts and knowledge about terra preta are still in their early stages. More reading about terra preta can be found here:
This post concludes the last of three on the Amazon. They aren’t all encompassing, but they do give an insight into how the Amazon rainforest functions, what problems it faces and why.