August 27, 2012
Despite Drought, West African Forests Experience Biomass Increase
redOrbit Staff & Wire Reports - Your Universe Online
Even in the midst of a four decade long drought, protected forests in West Africa have somehow experienced an increase in their carbon storage capacity in recent years, a team of researchers from Ghana and the UK have discovered.
According to BBC News Environmental Reporter Mark Kinver, previous studies had suggested that a lack of precipitation in Ghana and the surrounding region resulted "in less carbon being stored as vegetation died."
However, the new study, which has been published in the journal Ecology Letters, now suggests that not only was no biomass lost in those areas, but that there had actually been biomass gains over the 40-year period.
"Biomass is a vital component in the global carbon cycle. When plants grow, they absorb carbon dioxide and water in the photosynthesis process," Kinver explained in an August 25 report. "While oxygen is released into the atmosphere as a waste product of this process, the absorbed carbon primarily remains locked in the plant until it dies."
When asked what could be the cause of the biomass increase, co-author Sophie Fauset of the University of Leeds suggested that it was a shift in the types of species inhabiting the region. Because the environmental changes occurred over a prolonged period of time, she said that it was possible for the composition to "reshuffle" to some degree, meaning that species that can thrive in the new conditions to become dominant in the ecosystem and lessening the negative effects of the extremely dry conditions.
For their study, Fauset and colleagues from University College London, the University of Aberdeen, the Ghana Forestry Commission and the Forestry Research Institute of Ghana, tracked changes in the plant biomass and functional composition in 19 plots of different types of forests over a 20-year span. Kinver added that they analyzed more than 10,000 trees throughout West Africa between 1990 and 2010.
They discovered "a consistent increase in dry forest, deciduous, canopy species with intermediate light demand and a concomitant decrease in wet forest, evergreen, sub-canopy and shade-tolerant species," they wrote, adding that those changes were also accompanied by "an increase in above-ground biomass. Our results indicate that by altering composition in favor of drought-tolerant species, the biomass stocks of these forests may be more resilient to longer term drought than short-term studies of severe individual droughts suggest."
"It is generally thought that if you have droughts then you are going to see a decrease in biomass. Certainly, studies that have looked at short-term, quite extreme droughts do seem to show biomass loss," Fauset told BBC News.
"It could be that the increase in biomass (recorded in this study) could be the result of something else, but we think that the maintenance of the forest structure, despite the drought conditions, is a result of a change in species composition," she added. "This basically means that you cannot take those short-term studies of extreme droughts and extrapolate the findings to a long-term event with different kinds of precipitation changes."