Gap capture in northern hardwoods: patterns of establishment and height growth in four species

Abstract

We sought to determine whether four tree species that commonly coexist—American beech ( Fagus grandifolia Ehrh.), sugar maple ( Acer saccharum Marsh.), red maple ( Acer rubrum L.), and yellow birch ( Betula alleghaniensis Britt.)—differed in their patterns of establishment in gaps and their height growth after gap formation. Fifty-eight canopy trees were sampled in four experimentally created canopy gaps, 44–48 years old, in a northern hardwood forest at the Bartlett Experimental Forest, NH. Using stem analysis, we determined the year of origin of each tree and its pattern of height growth. Over two-thirds of beech and sugar maple canopy trees were advance regeneration, while most yellow birch stems established after gap formation. Red maple was a mixture of the two. Beech had the oldest stems at the time of gap formation (5 out of 18 stems over 20 years of age). No canopy tree established later than four years after gap formation. Species differed in their patterns of height growth, with beech growing more slowly than the others immediately after gap formation. Beech, however, grew at a more constant rate than sugar maple and yellow birch, and approached the heights of these species 30 years after gap formation. Red maple was the tallest and maintained a constant growth rate over the 30-year period. In beech and sugar maple, individuals that established after gap formation eventually grew faster and caught up with those establishing via advance regeneration.