Holocene Vegetation, Hydrology, and Fire in the North-Central Adirondacks of New York

The Adirondack region of New York has an estimated 81,000 hectares of old-growth forest embedded in a matrix of wetlands and second-growth forest. Few paleoecological records exist in the region, although records from adjacent regions indicate that there were several times of abrupt vegetation change during the mid and late Holocene, and the causes of these events are poorly understood. To better understand how Adirondack forests have responded to past changes in climate and disturbance regimes, I developed coupled records of Holocene fire, forest vegetation, and moisture variability using the sediments of Bloomingdale Bog in northern New York. My primary objectives were to 1) develop a high resolution Holocene record of forest vegetation, drought, and fire for the region, and 2) assess the potential causes of abrupt regional forest vegetation change at 500-600 and 5000 years BP. Consistent with other areas of the Northeast, results indicate that the two largest changes in forest vegetation, prior to land clearance, occurred ~550 and 5000 years BP. Comparison of drought, fire, and vegetation records revealed that vegetation changes at 550 year BP were likely driven by drought and fire. The decline of mesic species like Fagus grandifolia was widespread at this time as pollen records from elsewhere in the Northeast also document similar changes. Post-fire succession did not return the forest to its previous structure, and the compositional changes persisted until European land clearance. Vegetation changes 5000 years ago were characterized by the well-documented, range-wide decline in Tsuga canadensis (hemlock) in eastern North America. Comparison of drought, fire, and vegetation records revealed that the decline of hemlock was well underway prior to the occurrence of a large drought, and fires occurred shortly after the vegetation change and drought. Patterns are not consistent with drought as the sole or initial cause for the hemlock decline, and suggest that a pathogen or some other factor was responsible for the decline; however, drought may have suppressed recovery of hemlock populations after their abrupt decline. Fire and drought have not been primary drivers of large-scale forest change during the past century in the Adirondacks, and the long-term perspectives provided by this study highlight the potential vulnerability of the region to future changes in drought and disturbance regimes.