林分密度对杉木人工林林下植被和土壤性质的影响

以杉木人工林为研究对象，探究4种林分密度（A：650株/hm²；B：1100株/hm²；C：1250株/hm²；CK：1650株/hm²）林下物种多样性、生物量以及土壤理化性质及其之间的相关性。结果表明：（1）灌木层Shannon-Wiener指数、Patrick丰富度指数及草本层中Shannon-Wiener指数、Simpson指数、Patrick丰富度指数随林分密度的增加均呈现出双峰型变化趋势，在密度A和C处均出现峰值；灌木层Simpson指数、Pielou均匀度指数随林分密度升高而降低，且灌、草层4种多样性指数最小值均出现在密度CK处。（2）草本层生物量比灌木层高。草本层总生物量（地上+地下）随密度的增大而减少，凋落物的量则随密度的增大而增大。（3）土壤养分含量和林下植物多样性指数随林分密度增大的变化趋势大致相同，且有机质含量在密度A取得最大值。（4）灌木层Shannon-Wiener指数、Patrick丰富度指数与全氮、水解氮、有效磷、有机质呈显著正相关；草本层植被物种多样性与土壤理化性质无显著相关性。（5）各指数与灌木层生物量的相关性较强。综上所述，密度A （650株/hm²）能够促进杉木林林下植被发育，增加林下植被物种多样性、生物量和有机质，可提升维持地力的能力，有利于杉木林稳定持续发展。

Effects of stand density on understory vegetation and soil properties of Cunninghamia lanceolata plantation

We used a typical sampling to study the impact of four types of stand densities (A: 650 trees/hm²; B: 1100 trees/hm²; C: 1250 trees/hm²; and CK: 1650 trees/hm²) on the species diversity, biomass and soil physicochemical properties of understory plant and their correlation in Cunninghamia lanceolata plantations. The results were as follows. (1) The Shannon-Wiener index, Patrick richness index of the shrub layer, and the Shannon-Wiener index, Simpson index, Patrick richness index of the herb layer showed a double-peak distribution: initially decreased, then increased, and then finally decreased again. The turning point appeared at densities of both A and C. The Simpson index and Pielou evenness index of the shrub layer decreased with stand density. The minimum values of the four diversity indexes of shrub layer and herb layer appeared at the density CK. (2) The herb layer had more biomass than the shrub layer. The total biomass of herb layer decreased with the increase of stand density, and the amount of litter increased with the increase of density. (3) The trends of the relationship between both diversity and soil physiochemical characteristics and tree density were similar. The organic matter decreased with the increase of density, with the maximum value presented at the density of A. (4) The Shannon-Wiener index, Patrick richness index of the shrub layer were positively correlated with the total nitrogen, hydrolyzable nitrogen, available phosphorus and organic matter contents of topsoil. There was no significant correlation between species diversity of the herb layer with the physicochemical property. (5) The correlation between the indexes and biomass of shrub layer was strong. In conclusion, density of 650 trees/hm² could promote the growth of undergrowth vegetation, increase the species diversity, biomass and organic matter of undergrowth vegetation, improve the ability to maintain soil fertility, and contribute to the stable and sustainable development of cunninghama lanceolata forest.