Everyone has heard the cliché of the rainforests being the “lungs of the Earth”, its all over the news with the ongoing climate summit in Paris. As an ecologist, this has bugged me for a while now. I never gave it much thought until now, but it just felt off. The statement infers that the rainforests produce the oxygen in the atmosphere which helps us and all other aerobic organisms live. This seems to make sense since plants produce oxygen through photosynthesis and we use that oxygen in our respiration. However, it glosses over the other product of photosynthesis. Plants do not photosynthesize to make our oxygen, they do so to produce carbon compounds which they use to respire themselves and grow. On top of that; the multitude of animals in rainforests together with the abundance of (still mostly unknown) micro-organisms live off the plant material and each other while respiring as well. All this respiration is also boosted by the year round high temperatures since increased temperature leads to increased metabolism in coldblooded organisms. If we tally all this up, it turns out that a rainforest is a balanced system with hardly any oxygen surplus. Another thing is the carbon production during photosynthesis. If rainforests produced excess oxygen for us to breath, there should also be excess carbon produced. This carbon should then build up as litter on the forest floor, not being eaten by anything and if the forests would contribute substantially to the world’s oxygen reserves, this build up should be pretty massive. We in fact find the opposite with high decomposition rates quickly removing litter from the forest floor all the while consuming oxygen in the process. The only way there could be a net excess of oxygen is when the plant material was sealed off from the air in, for example, peat swamp forests where a layer of peat builds up over time.
These peat swamp forests are currently at the center of a major environmental disaster happening in Indonesia. Massive forest fires along Indonesia’s 5000 km length are releasing as much carbon dioxide in three weeks as Germany releases per year. This of course besides the danger to human health and massive destruction of key rainforest habitats for innumerable animals for which the orangutans are the poster boys/girls as long as they are still around.
Sadly enough, rain forests in other parts of the world are facing similar threats, a key example being the Amazon which is being burned to clear land for cattle pastures. The burning of our rainforests is actually doing the opposite of lungs: using oxygen for the transformation of plants to carbon dioxide. But don’t worry, there is far more oxygen in the atmosphere (21%) than we can consume by burning all our forests. The problem comes from the carbon dioxide being released. Since there is far less carbon dioxide in the atmosphere (0.04%), all this burning does have a major effect on its atmospheric levels. It is estimated that the carbon dioxide released by deforestation through burning exceeds that of all cars and trucks in the world, leading to increased global warming.
So, although it paints a pretty image, the tropical rainforests are not the lungs of the earth. We are, however, destroying them at an unprecedented rate, leading to death and habitat loss for vast numbers of plants and wildlife, serious health issues for local people, and an increase in climate change, something we could really do without right now.