They found that areas where farmland has been abandoned during the last century have early generations of trees that produce higher levels of VOCs than older growth forests. In the South, pine plantations used for their fast-growing supplies of timber have proven to be havens for sweetgum trees, which are major producers of VOCs. Indeed, virtually every tree that grows fast -- a desirable quality for forestry production -- is a heavy emitter of VOCs.
"It's just one of those biological correlations," said Purves. "What you want is a fast-growing tree that doesn't produce a lot of VOCs, but that doesn't seem to exist."
The findings also could raise questions about potential strategies for developing "green" fuels. One idea for cutting greenhouse gas emissions is to create "biofuels" from renewable tree plantations; however, these plantations may lead to increased ozone levels, the authors note.
The findings lend support to proposals among environmentalists to shift attention to regulating NOx, the other main ingredient for ozone. They also underscore the pervasive effect of human activities on the environment, because something as seemingly benign as planting forests can have a substantial impact.
"You can't identify any of these processes as 'natural,'" said Purves. "The idea of natural versus human-caused is disappearing. Ten years from now, woodlands may have more of one species than another, and you could call that natural change. But here in New Jersey, the mix of trees is affected by the population of deer, and they are entirely under our control. In other parts of the country, it is the fire-suppression policies."
Noting President Ronald Reagan's notorious 1980 reference to trees causing pollution (Reagan said: "Approximately 80 percent of our air pollution ste
'"/>
Contact: Steven Schultz
sschultz@princeton.edu
609-258-5729
Princeton University
28-Sep-2004