Growth of Douglas Fir and Red Alder on Coal Spoils in Western Washington

Abstract

Responsible conservation ethic calls for restoration of mined forest land to its former level of productivity. This study was conducted to determine the effectiveness of reclamation of spoils from a large coal mine in western Washington in achieving that goal. Potential productivity of spoils was evaluated by comparing tree performance, rooting depth, and substrate properties on mined areas with conditions on nearby unmined areas, some of which were in plantations (termed reference plantations) of similar ages to the trees planted on the spoils. Mean site index (50 y) of young Douglas fir, Pseudotsuga menziesii (Mirb.) Franco, on spoils was not significantly lower (mean 38 ± 3 m) than on unmined soils (40 ± 2 m), whereas mean site index of young red alder, Alnus rubra Bong., (20 ± 1 m) was significantly lower on spoils than in older stands on natural soils (29 ± 1 m). Maximum rooting depth of the Douglas fir was significantly less in spoils (0.6 ± 0.1 m) than in natural soils (0.9 ± 0.1 m), whereas rooting depths of the alder (0.7-1.0 m) were not significantly different between spoils and natural soils. Bulk densities were generally higher in spoils than in natural soils. Nitrogen status of spoils was less than half that in natural soils (both concentration and content in the profile) and foliar N concentration in Douglas fir was less on spoils. Consequently, N fertilization may be needed in the future to prevent a decline in growth relative to natural stands. Problem areas on spoils where trees were absent or growth was severely restricted showed a variety of substrate problems. Care in placing spoils is needed to minimize such problems.