Response of western hemlock (Tsugaheterophylla) and early huckleberry (Vacciniumovalifolium) seedlings to forest windthrow

Abstract

Seedlings of western hemlock (Tsugaheterophylla (Raf.) Sarg.) and early huckleberry (Vacciniumovalifolium Smith) were studied for 5 years following windthrow in a dense 45-year-old forest to better understand the contrasting reproductive and growth stategies of woody shrubs and trees to small natural disturbances in temperate rain forest environments. Seedlings of both species responded to the disturbance with increased growth and increased recruitment. Tsuga seedling establishment and Vaccinium seedling density increased after the disturbance. Tsuga height growth, number of branches, and biomass were linearly related to solar radiation transmission in all 3 years. Vaccinium exhibited an exponential shoot growth pattern characterized by an initial delay of 3–4 years, whereas Tsuga increased productivity within months of the disturbance and continued to increase its growth exponentially throughout the study. Vaccinium increased rate of branching, total biomass, and allocation of biomass to roots following the windthrow, but did not significantly increase twig elongation rates until the fourth growing season. No significant difference in soil or air temperatures was detected between the forest and open windthrown areas, but litter temperatures increased by as much as 1 °C in the windthrow during the summer. Infrequent opening of dense second-growth conifer canopies whether by thinning or by small-scale disturbances is likely to result in dense secondary canopies of shade-tolerant trees and in little understory vegetation or forage for wildlife.