How fast can trees migrate?

The forests in the south will go first. Seedlings will wither, the understory plants will be replaced. And over the next century or so, many now-abundant trees will go extinct across much of the United States. Such are the predictions of Margaret Davis, one of handful of ecologists looking at the effects of the much discussed greenhouse warming on North American forests. As Davis and others who make these predictions readily admit, they are riddled with uncertainties. Data are scarce and have been cobbled together from fossil records, theoretical models, and experiments in controlled environments. Few long-term field studies have been done. The critical question to Davis and a colleague, Catherine Zabinski, is how quickly trees can migrate, for the fate of numberous species in North America will depend on whether they can shift north to cooler climates when their current range becomes uninhabitable.