Dynamics of jack pine at the southern range boundary in downeast Maine

Great Wass Island in Maine supports a large population of Pinus banksiana Lamb. (jack pine) at its southern range boundary. Nearly monospecific stands occur on outcrops and coastal plateau bogs. In contrast to typical populations of this species, six stands exhibited old trees, multiaged structure, and continuous but pulsed establishment despite a lack of widespread fire. Unfavorable soil conditions appear to explain the presence of self-perpetuating populations in this study area, across the geographic range for P. banksiana, and for similar shade-intolerant pine species. Pinus banksiana stands on outcrops exhibited synchronous age structure peaks and included many trees over 150 years old. In contrast, coastal plateau bog stands were younger, were not synchronized in terms of age structure, and contained few large dead trees, suggesting turn-of-the-20th century invasion of these bogs. Analysis of historical aerial photographs furthermore reveals substantial infilling of bogs by P. banksiana since 1940. Although it appears to be an inconsistent and slow process, coastal plateau bog infilling warrants further investigation because of the regional rarity of this ecosystem type.