Foliage-Height Profiles and Succession in Northern Hardwood Forests

Leaf area index (LAI) and foliage-height profiles were determined for 13 northern hardwood stands ranging from 3 to 57 yr since clearcutting and for 1 uncut stand. Leaf litter collection and stratified clipping were used to measure LAI which showed no relationship to total canopy height or foliage-height distribution, and recovered quickly to near mature forest levels following cutting. A camera and telephoto lens were used to measure the distribution of heights to lowest leaf in the 12 oldest stands (7 / yr). Distributions were converted to foliage-height profiles using equations from MacArthur and Horn (1969). Profiles in the 2 youngest stands (3 and 4 yr) were determined by stratified clipping. Total canopy height varies predictably with age and is the major determinant of foliage-height diversity calculated using data in 1-m intervals by height. The concentration of foliage into a definable stratum occurs early in succession and persists through year 30. An associated lack of understory in this period results in a reduced foliage-height diversity using data normalized to a 4 strata per profile. Beyond year 30, canopy structure is variable but mature stands generally have leaves evenly distributed by height.