Residual Densities Affect Growth of Overstory Trees and Planted Douglas-Fir, Western Hemlock, and Western Redcedar: Results from the First Decade

Abstract

•In recent years, interest has increased in silvicultural systems and harvest cuts that retain partial overstories, but there are few data available on the growth of the understory trees in such stands. We studied the response of overstory trees and underplanted seedlings, Douglas-fir (Pseudofsugo menziesii), western hemlock (Tsuga heferaphylla), and western redcedar (Thuja plicafa), to a range of residual overstory densities. Forty to 70-year-old Douglas-fir stands in western Washington were harvested, leaving retention levels of 0, 8, 16, 24, 32, and 40% of full stocking. The 9-year response of the understory seedlings was species-dependent wnh Douglas-fir the largest in diameter (mean diameter 6.4 cm and mean height 3.8 m), western hemlock the tallest (mean diameter 5.5 cm and mean height 5.4 m), and redcedar the smallest (mean diameter 1.5 cm and mean height 1.5 m), in port because it was heavily browsed. Douglas-fir and western redcedar showed the greatest growth in the lowest retention levels (0 and 8%), and western hemlock responded best at the middle retention levels (8 and 16%).