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Osborne, Benjamin Mikal

Botany

2005

MS

Forest vegetation plots initially established in 1964 along elevational gradients on the western slopes of the Green Mountains of Vermont, USA, were resurveyed in 2004 to determine if the distribution of tree species has shifted in response to changing regional climate. In the deciduous-boreal ecotone between the lower elevation, northern hardwood ("deciduous") forest and the upper elevation, spruce-fir ("boreal") forest, the deciduous component has increased, and the boreal component has decreased. Increases in the basal area of deciduous species at their upper range limits have accompanied decreases in the basal area of boreal species at their lower margins. Observed changes in forest composition may have been driven by shifts in regional climate. Temperatures have risen 0.67 - 1.5°C and total annual precipitation has increased by as much as 645 mm over the same 40-year period.