Published in 2007 by two Russian physicists, the still little-known biotic pump theory postulates that forests create and control ocean-to-land winds, bringing moisture to terrestrial life, reports Rhett Butler at Mongabay. How? Winds tend to blow from areas of high air pressure to low. Air pressure depends on the number of gas molecules present. When water vapor condenses, it disappears as a gas, decreasing the number of gas molecules, and the air pressure falls. This low pressure zone can persist if condensation over land continues. Now, acre for acre, forests evaporate more than oceans, because forest leaves and branches provide far more surface area from which water evaporates. This greater evaporation maintains a stronger low pressure zone through greater condensation, which, as rain, runs off ultimately into oceans, completing the water cycle. The persistently stronger low pressure zone pulls in moist oceanic air, refueling the system. By contrast, tree plantations lack the balance of different plants that, in turn, creates the balance of soil moisture and evaporation needed to keep the water cycle stable. So, forests are good buffers against the extreme weather predicted under climate change — another good reason to preserve them.
New meteorological theory argues that the world’s forests are rainmakers. http://news.mongabay.com/2012/0201-hance_interview_bioticpump.html#ixzz1lYQtKu5j First published in 2007 by two Russian physicists, Victor Gorshkov and Anastassia Makarieva, the still little-known biotic pump theory postulates that forests are the driving force behind precipitation over land masses. Mongabay