Response of crop trees of sugar maple, white ash, and black cherry to release and fertilization

Abstract

In Grey County, southern Ontario, a crop-tree release and fertilization experiment was carried out in 35- to 85-year-old hardwood stands of variable composition. The objective of the treatments was to improve the growth rate of selected high-quality trees. A method is described for the selection and allocation of crop trees to treatments according to a competition index (CI). Release involved thinning to reduce a tree's CI by nominal levels 0, 50, and 75%. Fertilizer was applied within a circular plot equal to 1.5 times the crown radii at rates of N = 295 and 590 kg/ha (ureaform); P = 227 and 454 kg/ha (triple superphosphate). Fertilization resulted in increased foliar concentrations of N and P in sugar maple (Acersaccharum Marsh.), white ash (Fraxinusamericana L.), and black cherry (Prunusserotina Ehrh), but only black cherry responded to N fertilizer with an increase in diameter growth; none responded to P fertilizer. The diameter growth of sugar maple showed a response that was linearly related to the degree of release. Black cherry and white ash showed only small responses to release. It was concluded that P was not limiting to any species on these soils, and N may be limiting only to black cherry. Crop-tree release was an effective treatment for stimulating the growth of sugar maple, but it appeared to be relatively ineffective for white ash or black cherry at this age.