Researchers found that increases in rainfall did not make up for decreases in water from spring snowmelt. Photo: Kjell Olsen via flickr.
You still sometimes hear the assertion that as the planet warms longer growing seasons will actually increase CO2 absorption ability of plants and thereby suck more greenhouse gases out of the air. Well, forget about it. At least when it comes to subalpine forests such as those found throughout the Rocky Mountains. That's what new research from University of Colorado, Boulder shows:CU-Boulder's Jia Hu, working with Cooperative Institute for Research in Environmental Sciences fellow Russell Monson, found that smaller spring snowpacks likely to occur with warmer average temperatures did extend the growing season, they also reduced snowmelt to the point that it will reduce the amount of water available to trees later in the season. Hu found that increases in rainfall under warmer climate were unable to make up for the lower water availability caused by decreased spring runoff.
These water-stressed trees are less able to convert CO2 into biomass. Additionally, these trees are more susceptible to forest fire and infestations by beetles.
Spring Snowmelt More Important Than Summer Rains
Interestingly, Hu and Monson found that even as late as September and October, 60% of water in stems and needles of subalpine trees in Colorado's Front Range could be traced back to spring snowmelt.
Will Carbon Storage Increases Elsewhere Be Enough?
Though the researchers did not make calculations as to what this would mean in terms of expected decreases in CO2 storage for the region, they did point out that some 70% of the western United States' carbon sink is subalpine forest.
Considering that other recent research has shown that aspen forests could get a big boost from increased atmospheric CO2, it's an open question whether these increases would offset decreases in subalpine forests' carbon storage ability.
The results of this research will be published in the February edition of Global Change Biology.
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