While much of the alarm over global deforestation centres on the Amazon rainforest, which continues at a shocking rate, African rainforests receive relatively little attention. Yet a study published today in Nature demonstrates the increasing size of the carbon sink these forests contain: similar to Amazonian forests in per unit area terms.
A large international team of scientists, headed up by Simon Lewis at the University of Leeds, found that across 79 plots in ten African countries, the above-ground carbon storage increased by 0.63 Mg C per hectare per year, between 1968 and 2007. Scaling up to include unmeasured material — roots, small trees, rotting trees and so on — brings the continental increase in carbon storage to 0.34 Pg C (that’s 340 million tonnes of carbon) per year.
The reason for the increase, which mirrors similar findings in the Amazon, is not known, but is likely to be one or both of the following explanations. First, increased atmospheric carbon dioxide levels are effectively fertilising the forests, boosting growth rates and thus increasing the size of the carbon sink. The alternative explanation is that these supposedly pristine forests aren’t quite so ancient as supposed. Past disturbance, whether human mediated or otherwise, would mean that the “intact” forests are in a state of recovery: trees could be growing larger and dying later. How long this process will continue for is for now an open question.
The study highlights the value of the world’s tropical rainforests in soaking up our carbon emissions. The size of the sink dwarfs the greenhouse gases produced from fossil fuel use in the African tropics. Unfortunately, it only just matches the scale of emissions arising from deforestation.
So here’s a thought. The UK Trade statistics show that, of the 50 thousand tonnes or so of charcoal imported in 2008, more than 25 thousand tonnes appear to have originated from sub-Saharan Africa. It takes four tonnes of air dried wood to produce one tonne of high quality charcoal, so round 100 thousand tonnes of African wood were used up last year just to keep our barbecues burning.
Whilst there is much merit in using woodfuel — especially when the alternative is foosil fuel, such as gas — harvesting must be sustainable. UK-produced charcoal is increasingly available, and is widely recognised for its superior burning attributes.
So here’s the easy way to help preserve the tropical forest carbon sinks — when (or if!) the sun shines and you fire up the barbie, make sure you’re cooking on British charcoal!
Source: Lewis SL et al (2009) Increasing carbon storage in intact African tropical forests. Nature doi: 10.1038/nature07771