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

We sought to determine whether four tree species that commonly coexist-Amer ican 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 growt h after gap formation. Fifty-eight canopy trees were sampled in four experi mentally created canopy gaps, 44-48 years old, in a northern hardwood fores t at the Bartlett Experimental Forest, NH. Using stem analysis, we determin ed the year of origin of each tree and its pattern of height growth. Over t wo-thirds of beech and sugar maple canopy trees were advance regeneration, while most yellow birch stems established after gap formation. Red maple wa s a mixture of the two. Beech had the oldest stems at the time of gap forma tion (5 out of 18 stems over 20 years of age). No canopy tree established l ater than four years after gap formation. Species differed in their pattern s of height growth, with beech growing more slowly than the others immediat ely after gap formation. Beech, however, grew at a more constant rate than sugar maple and yellow birch, and approached the heights of these species 3 0 years after gap formation. Red maple was the tallest and maintained a con stant growth rate over the 30-year period. In beech and sugar maple, indivi duals that established after gap formation eventually grew faster and caugh t up with those establishing via advance regeneration. (C) 2000 Elsevier Sc ience B.V. All rights reserved.