Development of mixed-oak forests in southeastern Ohio: a comparison of second-growth and old-growth forests

Abstract

Traditionally, studies of forest development have independently focused on the compositional and structural differences of second-growth and old-growth forests. However, few studies have attempted to use current old-growth forest ecosystems as a benchmark with which to compare the composition, structure, and dynamics of a surrounding matrix of sequentially aged second-growth forests. In order to examine the development of mixed-oak forests we compared the composition, structure, and stand dynamics of seventeen relatively undisturbed second-growth forests (70–149 years old) with four old-growth forests (at least 150 years old) on south-facing ecological landtypes (ELTs) in southeastern Ohio. All living and dead trees over 10.0 cm dbh and coarse woody debris over 10.0 cm mid-diameter were inventoried on 500-m2 plots. Saplings and seedlings were sampled on nested 100-m2 and 2-m2 subplots, respectively. Principal components analysis (PCA) was used to support the assumption that study sites had similar soils and physiography.Overstory species richness was greatest in the younger second-growth stands, and significantly differed among age classes. Five species of oaks (Quercus spp.) dominated the overstories of all stands. However, white oak (Quercus alba L.) canopy importance value (IV) ((relative dominance + relative density)/2) significantly differed among stands; it ranged from 35.5% in stands 70–89 years old to 86.1% in stands 130–149 years old, while it comprised 46.5% of the old-growth canopies. Pignut hickory (Carya glabra (Mill.) Sweet.) canopy IV tended to be less in the second-growth than in the old-growth stands. Whereas oaks dominated the overstories of the second-growth and old-growth stands, they were almost absent from the sapling layer of all stands (less than 5% of the total densities). The sapling layers of all age classes were comprised of shade-tolerant species. For example, American beech (Fagus grandifolia Ehrh.) sapling relative density significantly differed between the 70–89 year old stands (6.3%) and the stands at least 150 years old (23.9%). Even though densities of oak saplings were low, the relative densities of oak seedlings were much greater, suggesting adequate oak advance regeneration. Few significant differences in stand structure (e.g. basal area, density, mean diameter, canopy closure) or standing and fallen coarse woody debris were detected between the second-growth and old-growth forests. Detrended correspondence analyses (DCA) appeared to represent a gradient of increasing white oak IV with age. Although indices of old-growth attributes have proven successful in discriminating between second-growth and old-growth ecosystems in other regions of North America, our results suggest that such an index would not work well in mixed-oak forests. Canopies dominated by a mixture of oaks, in conjunction with a majority of canopy individuals at least 150 years old, may be the best indicators of old-growth conditions on south-facing landtypes in southeastern Ohio.