such as "Introduction", "Conclusion"..etc
Tropical forests hold more living biomass than any other terrestrial ecosystem. A new report in the journal Nature
by Lewis et al. shows that not only do trees in intact African tropical
forests hold a lot of carbon, they hold more carbon now than they did
40 years ago--a hopeful sign that tropical forests could help to
mitigate global warming.
In a companion article, Helene Muller-Landau, staff scientist at the
Smithsonian Tropical Research Institute, says that understanding the
causes of this African forest carbon sink and projecting its future is
anything but straightforward.
Growing trees absorb carbon. Dead, decomposing trees release carbon.
Researchers expect growth and death to approximately balance each other
out in mature, undisturbed forests, and thus for total tree carbon
stocks, the carbon held by the trees, to remain approximately constant.
Yet Lewis and colleagues discovered that on average each hectare (100 x
100 meters, or 2.2 acres) of apparently mature, undisturbed African
forest was increasing in tree carbon stocks by an amount equal to the
weight of a small car each year. Previous studies have shown that
Amazonian forests also take up carbon, although at somewhat lower rates.
"If you assume that these forests should be in equilibrium, then the
best way to explain why trees are growing bigger is anthropogenic
global change – the extra carbon dioxide in the atmosphere could
essentially be acting as fertilizer." says Muller-Landau, "But it's
also possible that tropical forests are still growing back following
past clearing or fire or other disturbance. Given increasing evidence
that tropical forests have a long history of human occupation, recovery
from past disturbance is almost certainly part of the reason these
forests are taking up carbon today."
Muller-Landau, who directs a project to monitor carbon budgets in
forest study sites worldwide as part of the Smithsonian's Center for
Tropical Forest Science and the HSBC Climate Partnership, advises that
this newfound sink shouldn't be taken for granted, or presumed to
continue indefinitely. "While we still can't explain exactly what is
behind this carbon sink, one thing we know for sure is that it can't be
a sink forever. Trees and forests just can't keep getting bigger.
Tropical forests are buying us a bit more time right now, but we can't
count on them to continue to offset our carbon emissions in the future."
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