Research in 40- to 60-year-old even-aged mixed hardwood stands in southern New England suggests a stratified canopy structure by species, with red oak crowns occupying the uppermost canopy stratum. The basal area growth of individual red oak trees with crowns in this uppermost canopy stratum is negatively related to the basal area of neighboring oaks with crowns in the same stratum. The total basal area of neighboring trees with crowns in this stratum has no effect on individual oak growth. Similarly, the basal area of trees in lower strata has no significant effect on the growth of oaks with crowns in the uppermost canopy stratum. Crown width of individual oaks is negatively related to the basal area of neighboring oaks with crowns in the uppermost canopy stratum. Also, both the total foliar biomass per tree and the efficiency of that foliage in producing basal area increment are negatively related to the quantity of surrounding oaks with crowns in the uppermost canopy stratum. These results imply that basal area increment of individual red oaks in the overstory depends on the species composition of the mixture (i.e., the proportion of red oaks in the mixture) and the resulting competition for growing space in the canopy.
