Thinning promotes the nitrogen and phosphorous cycling in forest soils

Abstract

Thinning, a major practice of even-aged forest management, notably affects the stand structure and microclimates and thus in turn soil nitrogen (N) and phosphorous (P) cycling. However, the magnitude and direction of these effects remain uncertain. We performed a meta-analysis of 1228 observations from 115 studies worldwide to explore the effects of thinning on forest soil N and P processes. The results showed that thinning increased the concentrations of soil nitrate, total P, and available P by 11.7%, 6.1%, and 11.4%, respectively, but had no effect on the concentrations of soil total N and ammonium. Thinning stimulated soil microbial activities regulating soil N and P cycling, evidenced by the increased microbial biomass N and the activities of N- and P-acquiring extracellular enzymes. Thinning also increased net N mineralization and nitrification rates, but did not significantly affect N2O emission. However, these thinning effects varied with climates and forest biomes. The effect sizes of N-cycling processes were significantly correlated with mean annual precipitation or mean annual temperature, implying that these N fluxes are more sensitive to thinning in warm and humid regions. Collectively, our meta-analysis indicates that thinning promotes forest soil N and P cycling and increases the soil fertility, which are conducive to improving forest ecosystem functions.