黄土高原丘陵区不同生境小叶杨人工林物种多样性及其群落稳定性分析

通过样地调查,对黄土高原丘陵沟壑区处于阴坡、半阴坡、半阳坡、阳坡4种生境条件下,经过30年发育的小叶杨人工林物种多样性,群落结构动态和土壤水分养分效应进行了系统研究,结果表明:(1)不同生境小叶杨人工林总体上物种丰富度、多样性指数和均匀度指数均呈现出阴坡>半阴坡>半阳坡>阳坡的趋势,且林内物种多样性指数表现为:草本层>灌木层;(2)不同生境条件下的小叶杨人工林年龄结构分析表明,尽管阴坡小叶杨长势相对较好,但更新幼苗数量相当有限,很难实现种群的自我更新,不适合作为人工林培育;(3)土壤含水量和养分因坡向不同而呈现出明显的差异,尽管阴坡和半阴坡的水分、养分条件相对较好,但也出现了枯梢、病虫害等衰老特征,因此阴坡、半阴坡的生境对小叶杨来说也不合适.未来应该对现有林地在保护的前提下,间伐衰老个体,补植和引入乡土物种,进行天然化培育.

Species Diversity and Community Stability of Populus simonii Plantations in Different Habitats in Hilly Area of the Loess Plateau

The species diversities,community-structure dynamics,and soil-water and-nutrient effects of 30-year-old Populus simonii plantations,which were located on north-facing slope,half-north-facing,half-south-facing and south-facing slopes in hilly area of the Loess Plateau,were systematically studied.It was shown that(1) the species richness,diversity indexes and evenness indexes of the Populus simonii plantations in the different habitats appeared to differ in the pattern of north-facing slope>half-north-facing slope>half-south-facing slope>south-facing slope,and the species diversity indexes within the plantations appears differ in the pattern of herbaceous layer>shrub layer;(2) Investigation of the age-structures of Populus simonii plantations in the different habitats revealed that although Populus simonii showed better growth on north-facing slope,there appeared limited numbers of the seedlings for plantation renewal on the slope;as a result,the populations were difficult to renew themselves on the slope and the slope was not suitable for the plantations to develop;(3) The contents of soil-water and-nutrients appeared to differ remarkably among different slope aspects,and despite more favorable soil water and nutrients on north-facing and half-north-facing slopes,such senescent symptoms as spike top and pest infestation occurred and consequentially north-facing and halfnorth-facing slopes were not suitable for Populus simonii.In the future,the naturalization of the plantations should be done by inter-felling aged individuals and replanting and introducing landrace species on the basis of conserving the current forestlands.