Long-term logging residue loadings affect tree growth but not soil nutrients in Pinus contorta Doug. ex Loud. forests

Abstract

The 19-year monitoring study revealed continuously positive and dynamic responses of tree growth to logging residue loadings. However, the lack of changes in soil nutrients suggested that increased growth might result from enhanced nutrient cycling with no net accumulation in the soil. Understanding how logging residue loadings affect soil nutrients and forest growth is critical for designing management strategies for sustaining long-term productivity in forest ecosystems. We aimed to examine the relationships among logging residue loadings, soil nutrients, and tree growth over a long-term field experiment in lodgepole pine (Pinus contorta Doug. ex Loud.) forests. We established a field experiment in 1996 to examine the responses of lodgepole pine growth and soil nutrients to four residue loading treatments in the central interior of British Columbia, Canada. The four treatments were removal of all residues on the forest floor (N, 0 mg ha−1), residues loading similar to whole-tree harvesting (W, 35–45 mg ha−1), residues loading similar to stem-only harvesting (S, 60–70 mg ha−1), and residues loading similar to that found in disease- or insect-killed forests (D, 100–120 mg ha−1). Logging residue loadings had significantly positive and dynamic effects on diameter and height growths. The logging residue loadings did not significantly change soil nutrients in mineral soil pools in the long run, and there was no difference in tree growth between the treatments S and W over the study period. Logging residue loadings significantly improved tree growth. The lack of response of soil nutrients leads to the hypothesis that nutrient fluxes from logging residues might play a more important role in tree growth in lodgepole pine forests. Our results can have important implications for bio-energy production and designing of nature-based practices for sustainable forest productivity.