Shifting Spruce: Structural and compositional change over 30 years in central Appalachian Mountains red spruce–northern hardwood ecotones

The distribution of red spruce ( Picea rubens ) in the central Appalachian Mountains in Virginia and West Virginia, USA, was limited during post-Pleistocene warming followed by exploitative logging, wildfire, and other stressors in the early twentieth century. Moreover, future climate projections predict further fragmentation of this globally rare, montane boreal forest type. Ecotones provide a useful framework to identify changes in species distribution associated with environmental change. To evaluate long-term dynamics in unmanaged red spruce–northern hardwood forests, we remeasured 10 ecotonal transects across the central Appalachian Mountains that were established in 1992–1994 to assess post-exploitation recovery or lack thereof. In the tree strata, red spruce significantly increased its importance value, a metric of density and basal area, throughout the transects with gains in both the transitional ecotone and northern hardwood forest zones. Changes in red spruce sapling densities varied among transects, though decreases in sapling densities were correlated with increased trees per hectare. Over the 30-year study period, the red spruce–northern hardwood ecotone continued the compositional shift toward red spruce identified in the first decade of the study, while average annual temperature also increased.