They don't just turn pretty colors; they also affect the regional climate.
When environmental scientists look at a tree, they don’t see an inert, immovable object, rooted in the ground and subject to external events. They see a living organism that reacts to and affects the environment around it even as it shapes that environment. One focus of Associate Professor Jose D. Fuentes’ research is how volatile organic compounds that trees emit affect the regional climate. “This is a complex issue,” Fuentes notes, “that touches on a variety of fields, including hydrology, ecology, and atmospheric science.”
For instance, Fuentes has traced what happens when some of these compounds are oxidized to form aerosols. Water molecules condense on these particles, forming haze layers and affecting cloud formation, which in turn reduce the solar energy reaching the Earth’s surface. This may have a cooling effect on the surface, countering to some degree the rise in temperature from the greenhouse effect.
At the same time, the energy that does reach the Earth does so as diffuse, rather than direct, sunlight. Because diffuse light reaches more deeply into forest canopies, it allows more foliage to consume carbon dioxide, producing additional growth and, in the process, reducing the presence of greenhouse gases and mitigating global warming. “It is only by sorting out these relationships and others like them that we can begin to understand the mechanisms of climate change and the role of plants in this process,” he says.
Making this work even more difficult, the amount of volatile organic compounds entering the atmosphere is changing. For instance, in precolonial times, hickory and chestnut trees, two species that release only trace amounts of reactive hydrocarbons, dominated the forests in eastern North America. At the turn of the 18th century, forests disappeared as settlers cleared the land to support agriculture and other activities. In the last 70 years, the region has become reforested, not with hickory and chestnut but with oaks, sweet gums, and conifers, species that emit more hydrocarbons. It is possible, therefore, that these second- and third-growth forests are to some extent mitigating the effects of climate change and sequestering carbon, providing at least a temporary stay against global warming.
“U.Va. is a great place to study such issues,” Fuentes asserts. “There is nowhere else in the country where I can get the insight and guidance I need just by walking down the hall.” Proximity also leads to collaboration. Fuentes has embarked on a project with fellow department members Greg Okin, Michael E. Mann, and Paolo D’Odorico to understand the influence of the increased emission of biogenic hydrocarbons in eastern forests on the regional climate.
As part of this team project, Fuentes is developing and applying models to quantify rates of hydrocarbon produced from forested landscapes, assessing the subsequent production of aerosols, and estimating the light scattered and absorbed by particles. Okin is tracking the spatial distribution of hydrocarbon-emitting tree species throughout North America using satellite images. Mann is investigating the influence of reduced surface insulation caused by aerosols on climate. And D’Odorico is studying the ways in which the hydrologic cycle is being slowed by the decrease of available energy at the Earth’s surface. “It’s only by combining our efforts that we gain a complete picture of the entire system,” Fuentes says.
This article originally appeared in the Fall 2004 issue of Explorations.