Extended tree growth season not as hot as it sounds for New England foresters

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Source: Worldwatch Institute

A century ago, a New England winter averaged 24 degrees Fahrenheit. Now, New Englanders are about three degrees warmer during the cold season, and temperatures are likely to continue rising.

As a result, spring is arriving earlier, snowpack is melting faster, and rivers are flowing at peak levels sooner than ecologists have seen before.The growing season for New England forests has been extended.  Trees are now growing for 10 more days per year than foresters observed before 1970.

That may sound like good news for foresters, but it turns out foresters care about much more than just industrial numbers, or in forester-speak “timber volume.” And the climate change forecast for the rest of New England is not so chipper.  I found this out at the New England Society of American Foresters Winter Meeting last week in Nashua, New Hampshire.  There, a talk by Dave Orwig, forest ecologist at the Harvard Forest, revealed a shocking map of predicted climate change in New Hampshire under low and high emissions scenarios (pictured above).  If high emissions continue, cool New Hampshire could be feeling somewhat like the humid Washington DC area by mid-century!  With New Englanders deeply involved in the culture and seasonal activities of their region, this diagram did not excite many people.

Orwig reported that a warmer New England climate would put native habitats and wildlife at increasing risk and force many species to migrate north in order to survive – something trees can do over time, but not necessarily quick enough for forest ecosystems to remain healthy. Climate change could also threaten non-timber forest products such as maple syrup and ecosystem services such as clean water.

An increase in carbon dioxide (CO2) in the atmosphere is theoretically beneficial for tree growth, but such gains could be offset by expected increases in atmospheric concentrations of air pollutants, while more frequent drought conditions may increase fire risk.  The Intergovernmental Panel on Climate Change asserted in its Fourth Assessment Report that, “New studies suggest that direct CO2 effects on tree growth may be revised to lower values than previously assumed in forest growth models.”

The IPCC report does in fact show net gains in crop and forest growth due to climate change in certain parts of the world, mostly temperate northern latitudes. However, the New England foresters reminded me that as rapid climate change sends shocks through the region’s ecology, the shifts are not likely to benefit business or regional culture.

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