Trees to soak up less CO2 in future
The study, published in Global Change Biology, examined the subalpine
forests of the Front Range, part of the Rocky Mountains in Colorado.
These high-elevation forests make up about 70 per cent of the western USA’s carbon sink.
Previous studies of other ecosystems have suggested that as the climate warms and growing seasons lengthen, the uptake of carbon by plants will increase. However, the researchers – graduate student Jia Hu and Russell Monson, fellow of the university’s Cooperative Institute for Research in Environmental Sciences – found that while a warmer climate led to a decline in spring snow, thus extending the growing season, it also reduced the amount of available water during summer and autumn. This meant that the trees were then less effective in converting CO2 into biomass.
Hu and Monson analysed slight variations in hydrogen and oxygen atoms in the water molecules found in stems and needles collected from subalpine trees to distinguish between water derived from spring snow and summer rain. They discovered that, as late as September and October, 60 per cent of the water could be traced back to spring snowmelt, suggesting that subalpine species depend on water from snow throughout the growing season.
‘Snow is much more effective than rain in delivering water to these forests,’ Monson said. ‘If a warmer climate brings more rain, this won’t offset the carbon-uptake potential being lost due to declining snowpacks.’ He added that drier trees are also more susceptible to beetle infestations and wildfires.
February 2010
These high-elevation forests make up about 70 per cent of the western USA’s carbon sink.
Previous studies of other ecosystems have suggested that as the climate warms and growing seasons lengthen, the uptake of carbon by plants will increase. However, the researchers – graduate student Jia Hu and Russell Monson, fellow of the university’s Cooperative Institute for Research in Environmental Sciences – found that while a warmer climate led to a decline in spring snow, thus extending the growing season, it also reduced the amount of available water during summer and autumn. This meant that the trees were then less effective in converting CO2 into biomass.
Hu and Monson analysed slight variations in hydrogen and oxygen atoms in the water molecules found in stems and needles collected from subalpine trees to distinguish between water derived from spring snow and summer rain. They discovered that, as late as September and October, 60 per cent of the water could be traced back to spring snowmelt, suggesting that subalpine species depend on water from snow throughout the growing season.
‘Snow is much more effective than rain in delivering water to these forests,’ Monson said. ‘If a warmer climate brings more rain, this won’t offset the carbon-uptake potential being lost due to declining snowpacks.’ He added that drier trees are also more susceptible to beetle infestations and wildfires.
February 2010
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