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Saturday, February 16, 2013

Climate good news, bad news

Spring Leaves Expected to Sprout Sooner in North American Forests
From: Allison Winter, 

This year the spring equinox falls on March 20th, marking the first day of spring. But regardless of the date, it feels like spring when the temperature warms and we start to see new green leaves and flowers bloom after a dormant winter. 

According to new research, trees in the continental U.S. could send out new spring leaves up to 17 days earlier than expected in the coming century as global temperatures start to rise. Researchers at Princeton University suggest that these climate-driven changes could lead to composition changes of northeastern forests and give a boost to their ability to take up carbon dioxide.

Trees absorb and store carbon dioxide in their wood, roots, and leaves. This is important as carbon dioxide is a global warming suspect and by storing this carbon, the trees are locking-up the process of turning the pollutant into an available "greenhouse" gas. The date of spring bud­burst (the sprouting of new plant growth after months of winter dormancy) will affect how much carbon dioxide is taken up each year.

Researchers led by David Medvigy, assistant professor in Princeton's department of geosciences, evaluated predictions of spring bud­burst from models that predict how carbon emissions will impact global temperatures.

The Princeton model, which was published in the Journal of Geophysical Research, relies on warming temperatures and the decline in the number of cold days in order to predict spring bud-bursts.

In a recent paper published online in Geophysical Research Letters, Medvigy and his colleagues tested the model against a broader set of observations collected by the USA National Phenology Network, a nation-wide tree ecology monitoring network consisting of federal agencies, educational institutions and citizen scientists.

As a result, the team estimated that, compared to the late 20th century, red maple bud­burst will occur 8 to 40 days earlier, depending on the part of the country, by the year 2100.

Researchers also found that early bud­burst may give deciduous trees a competitive advantage over evergreen trees because as deciduous trees grow for longer periods of the year, they may begin to outstrip growth of evergreens, leading to lasting changes in forest make-up.

According to Medvigy, bud­burst causes an abrupt change in the exchange of energy, water and pollutants between the land and the atmosphere. Once leaves start to sprout, energy from the sun is increasingly used to evaporate water from the leaves rather than to heat up the surface. This can lead to changes in daily temperature ranges, surface humidity, stream­flow, and even nutrient loss from ecosystems.

Read more at the Princeton Journal Watch.