Pinus contorta understory vegetation dynamics following clearcutting in west-central Alberta, Canada

A 100-year chronosequence of Pinus contorta clearcut and unmanaged stands differed from a recognized model of natural forest development, due to the lack of a stem exclusion and a subsequent understory reinitiation stage. These differences in development were probably related to the low density of planted trees and the correspondingly open overstory that occurred during the early stages of stand development. Despite these differences, the composition of the understory vegetation within clearcuts appeared to be changing toward that of the unmanaged stands, although the initially more open overstory may have prolonged the presence of early-seral understory species. An overstory cover-based sequence suggests that growth-form cover and composition vary in response to the degree of understory shading. Understory vegetation that developed beneath a 30-70% overstory cover reflected characteristics of a tolerance interaction model, whereas greater overstory cover inhibited the development of ericaceous shrubs. Models of early forest community development should be stratified according to both the amount of overstory cover and the stand age to appropriately represent understory development trends.