Long-term stability of northern hardwoods across a topographic gradient and variations in harvest methods

Increased emphasis on forest complexity, resilience, and biodiversity, has renewed interest in northern hardwood forests. In parallel, there is concern of impacts of traditional, timber-oriented regeneration methods on successional trajectories and tree communities. To ensure compatibility of emerging goals with site biological capacity, assessment of common silvicultural methods across forest conditions is imperative. This work utilizes a long-term dataset of 407 sampling plots from the Bartlett Experimental Forest in New Hampshire, USA, over 70-years. Topographic and meteorological variables were utilized to test the effects of site conditions and silviculture on tree species diversity and composition. Results show a decline in diversity over time that reflect a shift toward dominance of late successional species, which vary with site-specific conditions. The effect of silviculture was not detectable, and differences in tree communities were attributed to pre-existing conditions of site variables prior to installation of experimental treatments. Tree diversity and composition for both 1932 and 2003 measurements were correlated with solar insolation, local windspeed, and hydrologic catchment area. The collective findings highlight the long-term stability of species under past silvicultural regimes, that some areas are more facilitative/limiting to goals of enhancing tree biodiversity, and emerging technologies can capture species-site interactions in northern hardwoods.