Spatial and temporal patterns of tree regeneration in the Acadian Forest of central Maine

Abstract

Relatively few studies of forest regeneration have attempted to integrate the analysis of spatial and temporal pattern. In order to fill this gap in our understanding of forest regeneration, I used data from two long-term silviculture studies on the Penobscot Experimental Forest (PEF) in Bradley, ME. Multivariate analysis was used to retrace compositional development of permanent sample plots in a USDA Forest Service silviculture experiment over five decades (1953-2005) based on both pre-treatment forest composition (i.e., plot-level tree composition when the experiment was established) and harvest disturbance history. This study revealed that different harvest treatments initiated an array of developmental pathways at the plot level that were linked to both factors. Hardwood dominance increased in plots with a history of heavy and infrequent cutting, while pre-treatment composition largely was maintained in plots where cutting was lighter and more frequent. Balsam fir dominance was maintained across a wide range of harvest intensities, which contrasted with the ubiquitous decline in cedar importance over the experiment. The Acadian Forest Ecosystem Research Program (AFERP) experiment was used to evaluate spatial responses of forest regeneration to gap harvesting and variability in local biotic and abiotic conditions. First, spatial pattern analysis was used to describe the spatial patterns within stands containing harvest gaps of various sizes (0.01 to 0.22 ha) and over a range of spatial scales. This study indicated that stands that have received gap-harvest treatments have unique spatial patterns in understory tree density and canopy openness, and supported the hypothesis that gap harvesting created a coarse-grained spatial pattern in both factors. Second, spatial and non-spatial models were developed to identify plot-level factors affecting the species richness of tree regeneration. Negative associations were found between: (1) richness of small regeneration (≥ 0.1 m and < 0.75 m tall) and balsam fir regeneration density and (2) richness of large regeneration (≥ 0.75 m and < 1.4 m tall) and overstory basal area. Both small and large regeneration richness were positively associated with percent canopy openness. Collectively, the findings of this investigation highlighted the importance of local environmental and historical factors (i.e., neighborhood-scale factors) in determining the spatial and temporal patterns of natural regeneration in the Acadian Forest.