Huge percentages of forests are destroyed each year as a result of hurricanes, insect outbreaks and wildfire, but scientists are only just beginning to get a handle on what this does to the overall carbon intake of a forest.
A new study published in the journal Global Change Biology by researchers from the Oregon State University has focused on the effect such forest destruction has on the overall albedo effect – the amount of sunlight reflected back into space – of the remaining forest.
Albedo is a measure of the radiation reflected off the surface, in this case, planet Earth. Lighter colours such as snow reflect more light, whereas darker colours absorb the heat and allow for localised warming as a result.
In theory, destroy a forest, and you expect the carbon dioxide entering the atmosphere to increase local warming with no counter. But if the region in which the forest has been felled is home to a large amount of snow cover, then the albedo of the region may actually increase, countering the increase in carbon dioxide.
This is obviously not something that is common in more tropical climates, but for boreal forests throughout Canada and Russia, it’s more than likely.
“On a global scale, warming caused by increased carbon dioxide still trumps everything else,” said Beverly Law, a professor in the Department of Forest Ecosystems and Society at Oregon State University. “On a smaller or local scale, however, changes in albedo can be fairly important, especially in areas with significant amounts of snow, such as high latitudes or higher elevations.”
“This decreased absorption of heat by the land surface is a local atmospheric cooling effect,” said Tom O’Halloran, a recent postdoctoral research at OSU who is now with the Department of Environmental Studies at Sweet Briar College. “This was clear in one case we studied of trees killed by mountain pine beetles in British Columbia.
“In areas with substantial snow cover, we found that canopy removal due to either fire or insect attack increased reflected radiation and approximately offset the warming that would be caused by increased release of carbon dioxide,” O’Halloran said. “However, we haven’t been able to measure the full impact from the current beetle outbreak, which could take decades to complete.”
Subsequently, while a forest felled to reveal more snow may increase reflectivity in the northern latitudes, move further south and suffer a similar destruction of your forest and you may end up revealing a darker surface than the tree canopy had been.
For example, when Hurricane Wilma swept through the Florida Everglades in 2005 and defoliated more than 2,400 square kilometres of mangrove forest, the underlying surface was darker than the forests canopy had been, thus increasing the amount of heat absorbed rather then reflected.
Given that the forces focused on in this study – hurricanes, insect outbreaks and wildfire – are likely to increase in severity and extent with a warmer world, understanding now what could happen is vital.