Importance of big old trees for carbon sequestration recognized in a new study

martedì 28 gennaio 2014
   

Contrary to the general belief that young trees absorb more carbon than old ones due to their more vigorous growth, a new analysis suggests that the rate of tree carbon accumulation increases with tree age and size.
This is the main result of research led by Nathan L. Stephenson, an ecologist from the US Geological Survey, published in the journal Nature on 15th January.
Everybody agrees on the essential role of forests as carbon sinks and their contribution in combating global warming: between 2005 and 2010, the average annual sequestration of carbon in forest biomass reached 870 million tons for the European region, about 10 percent of the greenhouse gas emissions.
However, contrary to the general belief that young trees absorb more carbon than old ones due to their more vigorous growth, a new analysis suggests that the rate of tree carbon accumulation increases with tree age and size.
This is the main result of research led by Nathan L. Stephenson, an ecologist from the US Geological Survey, published in the journal Nature on 15th January and based on the measurements of more than 600,000 trees belonging to 403 different temperate and tropical tree species from all around the world.
According to the outcomes of this study, tree mass grows (and, therefore, also carbon sequestration) as trees increase in age and size.
This happens even though the productivity of individual leaves decreases with the tree's age.  This is because, although individual leaves in old trees are less efficient at absorbing carbon, older trees have more of them, so compensating for their lower productivity.
It should be noted that young forests have a higher density of trees, while in older ones there are fewer, larger trees and that when old trees die and decompose, the carbon stored in their trunks, limbs and leaves is returned into the atmosphere.  In other words, if we compare the level of carbon sequestration at a forest (not an individual tree) level, it would not be accurate to say that old trees capture more carbon overall than young ones.
The findings of this analysis resolve the apparent contradiction between the traditional view that faster growing younger trees sequester more carbon and the new result stating that old trees do.
These conclusions also confirm the importance of conserving old trees in forests, not only because they are carbon reservoirs but also because they actually and actively fix larger amounts of carbon than smaller trees.
 
 

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