Changes in spatial distribution of dominant overstory taxa in an old-growth forest over 30 years
The temperate deciduous forests of eastern North America are subject to an array of ecosystem drivers including anthropogenic disturbance, gap dynamics, and both local and regional climate events. An ongoing “mesophication” trend has been observed in many of these forests where communities are shifting from domination by oaks (Quercus spp.) to more mesophytic, shade-tolerant species (Acer spp.). Using a 30-year dataset (1979–2010) collected in Big Everidge Hollow, an old-growth forest with minimal anthropogenic impacts in southeastern Kentucky, we examined decadal distribution patterns of dominant overstory taxa (Quercus spp., Acer spp., Carya spp., and Fagus grandifolia). Overstory stem data were divided into three size classes, small (2.5–10 cm dbh), medium (10–25 cm dbh), and large (> 25 cm dbh) to assess regeneration patterns over time.
Large Quercus spp. stems were widely and consistently distributed (~63% of plots) through time, but small and medium stem frequency decreased from 45% and 52.5% to 20% and 27.5% respectively, becoming more restricted to xeric ridgetop areas. On the contrary, Acer spp. and Fagus grandifolia were more widely distributed within the small (up to 80% and 88.75%) and medium size classes (up to 73.75% and 56.3%), while larger stems occurred less frequently (up to 42.5% and 43.8%). The observed patterns suggest that Quercus species are persisting mainly as mature canopy trees with little recruitment in mesic areas of the study site, while mesophytic species (Acer, Fagus) have historically been restricted to certain habitats (as evidenced by the clustered, limited distribution of mature trees) but are currently recruiting across a broader area of the watershed. This “mesophication” trend is widespread in eastern deciduous forests and commonly attributed to altered fire regimes, which may in part be true for this site, but changes in species-level recruitment may also be driven by large-scale climatic events.