Thinning promotes litter decomposition and nutrient release in poplar plantations via altering the microclimate and understory plant diversity
Yu Wang, Senxian Hong, Shengzuo Fang, Guangcai Cui
Abstract
Thinning is widely employed in forest management to improve productivity,protect forest biodiversity and maintain ecosystem functions. Here a thinning experimentwith four treatments (unthinned, CK; 30% tree removal from below, MB; 50% treeremoval by interlaced thinning, HI; and 50% tree removal from below, HB ) was set upin the poplar plantation, while a followed decomposition experiment with four litter typeswas conducted under the poplar plantations of undergoing four thinning treatments usingthe litterbag technique. Thinning affected the microclimate, but only the heavy thinning(HI and HB) significantly enhanced photosynthetic photon flux density (PPFD) and soilmoisture in the plantations during the growing season. Thinning promoted understoryvegetation biomass and vegetation diversity via modifying the microclimate parameters.Pearson correlation analysis showed that PPFD and understory herbaceous biomass weresignificantly correlated to Shannon-Weiner diversity index. Both thinning intensity andlitter type significantly affected the litter remaining mass over times. Overall, increasingthinning intensity and litter complexity enhanced decay rate, while reduced half live (t0.5)and t0.95 values. Correlation analysis showed that air relative humidity, soil temperature,air temperature and soil moisture significantly influenced the litter mass loss rates. Nonadditive(synergistic) effects were observed when different litters were mixed, but the nonadditiveeffect was most pronounced when more herbaceous species litter were mixedwith poplar leaves and 50% thinning intensity was applied. Dynamics of nutrient releasefrom different litter types were similar to those on the litter mass lose, depending on thelitter quality and microclimatic conditions. Our results suggest that a thinning operationwith 50% tree removal from below (HB) would maintain the structural and functionalfeatures of the poplar plantations at the similar sites.