岷江上游油松造林密度对油松生长和群落结构的影响

DENSITY EFFECTS ON TREE GROWTH AND COMMUNITY STRUCTURE OF CHINESE PINE PLANTATIONS IN THE UPPER REACHES OF THE MIN RIVER, CHINA

调查了岷江上游20 a龄油松人工林样方17个(20 m × 20 m),测定了油松生长参数、林下植被的植物物种多样性和盖度,以分析油松生长和群落结构变化的密度效应.结果发现:油松高度生长随密度增大而增加,在密度2 500～3 500 hm-2时达最大,随后下降;胸径生长在2 200～2 800 hm-2时达到最大,随后下降.油松单位面积生物量由低及高,在3 500～4 000 hm-2达到最大,随后稍有下降;而个体平均生物量约在2 500 hm-2时最大.随着油松盖度的上升,灌木层盖度开始下降,林下散射光增加,导致草本层盖度上升,中等密度时(2 500～3 500 hm-2)油松林乔灌草层次盖度配置较为合理;物种丰富度与油松密度呈显著负相关,但不同密度油松林的物种多样性指数变化无一定规律.因此,如果不以追求生物量最大化为单一目标,中等密度(2 500 ～3 500 hm-2)的油松林具有较好的群落结构配置、较高水平的物种多样性和种群更新能力,符合可持续林业发展的要求. 图3

Seventeen plots (20 m×20 m) of 20-year-old Chinese pine (Pinus tabulaeformis) plantations were investigated for tree growth parameters, plant species diversity, and coverage of shrub and herbaceous layers in the upper reaches of the Min River in southwestern China. The plant height and diameter at breast height (DBH) increased with plant density increasing and peaked at the density of about 2 500~3 500 hm -2 and 2 200~2 800 hm -2, respectively, and subsequently declined with plant density increasing. The aboveground biomass per unit area increased with density increasing and peaked when the density was 2 500~4 000 hm -2, while mean individual biomass peaked at the density of 2 500 hm -2. The tree DBH varied most at the mid-density, indicating high capacity of population regeneration at this density range. With tree density increasing, the coverage of shrub layer decreased and the coverage of herbaceous layer increased, and community structure seemed appropriate at mid-density 2 500~3 500 hm2 of the pine plantation. Plant species richness was found negatively related to pine density, but there was no obvious pattern observed for the variation in plant species diversity indexes under different tree densities. Therefore, based on the data presented in this study, the mid-density (2 500~3 500 hm -2) pine plantations performed better in both plant growth parameters and community structure, matching the strategy of sustainable forestry. Fig 3, Ref 19