Nearly two decades of research on the 2000-ha old-growth landscape of the Big Reed Forest Reserve in northern Maine has yielded numerous insights into the natural disturbance dynamics of forest types distributed across northern New England. The topographic relief extending from lowland ponds and wetlands to peaks almost 600 m in elevation supports a corresponding gradient of deciduous and coniferous forest types, all typically dominated by mixes of shade-tolerant tree species, including Picea rubens, Abies balsamea, Thuja occidentalis, Acer saccharum, and Fagus grandifolia. Applying dendroecological methods to the tree-ring records of over 6000 trees in 50+ stands, research has utilized the landscape diversity of the BRFR to examine the historic variability in the temporal (rates and frequency) and spatial patterns (gap sizes and distributions) of disturbances in the associated forest types and topographic settings.
Results/Conclusions
Disturbance rates reconstructed for the last 150+ years have averaged <10% of the area being disturbed per decade. Small, single-tree gaps with areas of <50 m2 have prevailed, regardless of forest composition. Episodic disturbances have opened 20-30% of the canopy during at least one decade at many sites. Increased numbers of small gaps have been the common response to such events, favoring the advance regeneration of the shade-tolerant species. However, a few larger gaps (>100 m2) have also resulted, most often on slopes and in exposed settings, and may have been critical for the maintenance of tree species of intermediate shade tolerance (e.g., Betula alleghaniensis) in the compositional mix. Moderate severity disturbances (opening >30% of the area during a decade) have been rare regardless of forest type, and work to date has revealed no evidence of stand-replacing events in the BRFR. Pollen and charcoal analyses of sediments from localized organic depressions have provided stand-level vegetation histories and extended the temporal depth of the tree ring records. Limited compositional change and minimal charcoal in the pollen-based vegetation histories suggest that the disturbance patterns reconstructed for the last 150+ years from tree rings are representative of at least the last 500 years. To more fully characterize the forest disturbance dynamics at the northeastern limit of the Eastern Deciduous Forest, additional work is required to capture the temporal element of the interaction between climate and disturbance and to examine patterns in forest types not represented in the BRFR.