Fire history and vegetation dynamics of a Chamaecyparis thyoides wetland on Cape Cod, Massachusetts

Fire history and vegetation change over the past millennium and modern successional trends in a Chamaecyparis thyoides (Atlantic white cedar) wetland on Cape Cod, Massachusetts were investigated using fine-resolution pollen analysis and stand age-structure analyses. Before European settlement (c. 1650 AD) low cedar pollen percentages correspond with abundant charcoal, whereas cedar dominates when charcoal values are low. Five fires occurred at 100-200-year intervals in prehistoric time. Since settlement, fires have been rare and cedar dominates the pollen profile. During the past two centuries timber cutting has become a significant factor in the vegetation dynamics of this system. In the nineteenth century intensive cutting resulted in the establishment of cedar. During the first half of the twentieth century, light timber thinnings favoured Acer rubrum (red maple) regeneration. In the past few decades, neither cedar nor its principal associate, red maple, have regenerated beneath the undisturbed cedar overstorey. Our results indicate that, at this site, vegetation composition and successional trends have largely been controlled by allogenic factors in both pre- and post-settlement times. Vegetation changes resulting from autogenic factors are not evident during the 1000-year study period. Age-structure analyses of modern stands in combination with fine-resolution pollen analyses are useful in comparing current vegetation dynamics with those of earlier times. In the 600-800 years before establishment of the current mature stand, cedar did not persist for more than 100-200 years without stand-regenerating fires. Thus the survival of the current stand much beyond its present age of c. 150 years would be atypical compared to the centuries prior to settlement. The present lack, of cedar centuries prior to settlement. The present lack, of cedar regeneration suggests that a management policy excluding disturbance would eventually lead to a decline in the importance of cedar. Our results suggest that an understanding of processes that influence community composition and structure over long periods of time may indicate conservation objectives and management guidelines different from those directed at the preservation of communities that, at a given point in time, appear to be unique on the landscape.