Wood volume increment in thinned, 50- to 55-year-old, mixed species Allegheny hardwoods

A thinning study in 50- to 55-year-old, even-aged, mixed species Allegheny hardwoods produced highly variable merchantable stemwood volume increment responses. Regression equations relating parameters of stand growth (ingrowth, mortality, survivor growth, net growth, and gross growth) to relative stand density had R(2) values ranging from 0.07 to 0.48. When study plots with similar pretreatment species composition were cluster analysis, R(2) values were increased to 0.94-0.99. There were significant differences in the relationships between relative stand density and growth response variables among all plot groups. At all densities, plots with a high percentage of black cherry (Prunus serotina Ehrh.) had the highest volume increment. Plots with a high percentage of black cherry and a low percentage of sugar maple (Acer saccharum Marsh.) showed a decrease in volume increment, relatively high ingrowth, and relatively low mortality with a decrease in relative stand density. Plots with a high percentage of sugar maple and low percentage of black cherry showed an increase in volume increment, relatively low ingrowth, and relatively high mortality with decrease in relative stand density. Guidelines for thinning Allegheny hardwoods recommend a residual relative stand density of 60%. These guidelines may need to be revised to incorporate considerations of species composition. Stands of pole-size to small sawtimber-size trees dominated by black cherry may require a residual density higher than 60% to maximize the volume increment of merchantable stemwood. The volume increment in similarly structured stands dominated by sugar maple might be maximized at densities lower than 60%.