Tuesday, August 16, 2011

Forests help to keep our world cool

Forests provide a wide array of important services to society such as clean drinking water, recreational opportunities, carbon sequestration, wildlife habitat, cultural values, and much more. A new study published in the Bulletin of the American Meteorological Society highlights the unique role that forests play in maintaining relatively cool land surface temperatures relative to surrounding native plant communities during hot summer months. This effect is particularly important in areas like the Blue Mountains where the summer dry period is very pronounced and non-forest plant communities “brown-down” during the summer and commensurately exhibit very high surface temperatures. The image below shows satellite based land surface temperature on the left and land cover type on the right and illustrates the much cooler land surface temperatures of the forested areas of the Blue Mountains compared to the surrounding grasslands, shrublands, and barren areas. The map graphically displays that with land surface temperature alone you can outline the location of forest ecosystems relative to drier shrublands and grasslands during the hot, dry, mid- and late summer months, particularly in the semi-arid climate of eastern Oregon and Washington. If you are interested in learning why the land surface temperatures measured by satellite are so much higher than the air temperature everyone is so accustomed to hearing reported by the local TV station, radio, or newspaper, follow the link below to the BAMS paper for a detailed explanation of this interesting temperature distinction.

Figure altered from Mildrexler et al. 2011.

Large portions of the Blue Mountains including the Wallowa and the Elkhorn Mountains have maximum land surface temperatures similar to that of Oregon’s Cascade Mountains and Coastal Ranges. While this might seem surprising, with the exception of deciduous broadleaf forests that shed their leaves to avoid drought stress, all forests ecosystems converge to a similar upper temperature limit of about 100 F. The reason for this has to due with the characteristics that forest ecosystems share such as deep roots to access groundwater, and deep complex canopies that are efficient at shedding heat through interactions with the atmosphere.

Despite the numerous benefits that forests provide to society such as regulating the most extreme maximum temperatures that we experience all year, much of our current forest policies, such as the US National Fire Plan, focus almost exclusively on fuels. Its time we move beyond this overly simplistic approach and explicitly consider the numerous valuable ecosystem services we derive from forests in our overarching policies to managing these incredible ecosystems.

The BAMS study may be accessed here: http://journals.ametsoc.org/doi/pdf/10.1175/2011BAMS3067.1

Post by David Mildrexler, Ecosystem Conservation Coordinator, Hells Canyon Preservation Council and lead author of the study.

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