Forest carbon storage 'depends on diversity'
The ability of tropical forests to store large amounts of carbon and so help curb future climate change depends heavily on the tree species growing in them, say scientists.
This, in turn, is determined by logging and reforestation practices as well as environmental factors such as drought.
The researchers, led by Daniel Bunker of Columbia University, United States, publish their findings today (20 October) in Science online.
They simulated scenarios where tree species in a forest in Panama became extinct and were replaced by others.
Each scenario simulated how the amount of stored carbon would change if a different set of trees — such as the largest, most common, or least drought-tolerant — disappeared from the forest first.
The researchers found that depending on the scenario, the total carbon stored in the trees varied by more than 600 per cent.
"Species that store more carbon will have a high wood density, large diameters on average, and be relatively tall for a given diameter," says Bunker.
He explains that the most likely way to boost the forests' carbon storage capacity would be to manage the forests in such a way that these traits are maximised.
The research suggests that selective logging, in which a small number of valuable timber species are removed, will lead to declines in stored carbon.
By contrast, converting forests into plantations of species with high wood density would increase the amount of carbon stored above ground by up to 75 per cent — as long as the trees are not harvested.
"Carbon storage is not the only service that forests provide," says Bunker.
"The species that store the most carbon are not likely to be the best at providing other services, such as flood control, water quality or fruit production. Any effort to manage forests must consider all of the services that we require from them."
Bunker admits that his team only considered carbon stored "above ground" (in trunks, branches and leaves). He says any forest management plans will also have to take storage capacity "below ground" (in roots and soil) into account.
Maintaining high diversity in tropical forests is like buying "biological insurance" against future events, says Bunker; the more diverse a forest is, the more resilient it is to change.
"It is similar to the effect of a diversified investment portfolio, where having many stocks leads to lower overall variability."
He adds, "Having a diversity of species increases the likelihood that, in the face of climate change, species capable of adapting to those changes are present."
Read the full article in Science