Growing-Space Relationships in Young Even-Aged Northern Hardwood Stands Based on Individual-Tree and Plot-Level Measurements

The amount of growing space occupied by trees of given sizes and species is traditionally assessed on a plot basis, using observations from groups of trees growing within an area of fixed size. Our study combines individual-tree with plot-based observations of upper-canopy trees representing a range of shade tolerance (Fagus grandifolia >= Acer saccharum > Betula alleghaniensis >= fraxinus americana) in three young, fully stocked, even-aged northern hardwood stands. The amount of canopy growing space used by a stem of given size was described by the ratios of crown projection area and crown surface area to stem basal area. These variables were related to species, stand, and relative basal area using analysis of covariance. Both ratios were generally highest in the youngest (19 years) stand, intermediate in the mid-aged stand (24 years), and lowest in the oldest stand (29 years). A few differences were detected among species, with shade-tolerants having larger ratios. Allometric models were used in conjunction with plot density data to estimate canopy cover at the stand level. Considerable crown overlap was indicated among upper-canopy trees in all three stands. Estimates from tree-centered plots suggested that crowns occupied 1.81 +/- 0.02 times the ground area in the youngest stand and 1.45 +/- 0.03 times in the mid-aged and oldest stands; when corrected for sampling bias, these ratios were at least 1.30 and 0.96, respectively. Combining individual-tree with plot-level measurements afforded a comprehensive assessment of trends in growing-space occupancy not possible using either technique alone.