California Trees Not Keeping Up With CO2

Forests aren’t absorbing as much carbon dioxide as in the past, and fire suppression might be to blame. Fire suppression in forest encourages the growth of smaller trees and, as a result, significantly reduces a forest's
overall ability to store carbon, according to a new study by
scientists at the University of California at Irvine.

The researchers, studying forests in California, found that while the
number of trees per acre increased in the sixty year period between
1930 and 1990, carbon storage actually declined about 26 percent.
This change in the nature of the forests, with greater numbers of
smaller trees at the expense of large trees, seems to have been
caused by the assiduous suppression of fires by human intervention,
the researchers said.

Using detailed records, the scientists, compare forests as they were in the 1930s with forests in the 1990s and found that the "stem density" of the forests had increased, which would seem to enhance a forest's ability to store carbon. In fact, the smaller-tree factor outweighs the denser-forest factor because large trees retain a disproportionate amount of carbon, the
researchers concluded.

Climate change, or at least the vast increase in carbon dioxide
launched into the atmosphere by the combustion of fossil fuels
during the industrial era, has focused scientific attention on the
ability of plants, especially trees, to take up and store the added
CO2. Trees are not the only carbon sinks (the oceans store vast
amounts of CO2), but they are often cited as a key indicator in the
fight to stabilize the buildup of greenhouse gases in the atmosphere.

This study, published last month in the journal Geophysical Research
Letters, pertains to California only, but Aaron Fellows, one of the
study's authors, believes it will apply to other dry conifer
(evergreen) forests in the U.S. western region.