基于结构方程模型的天然白桦次生林林下生态功能评价OACHSSCD

As a crucial pioneer species in the alpine region of Qinghai,Betula platyphylla(BP)natural secondary forests play an irreplaceable ecological role in water conservation,soil protection,and biodiversity conservation.Therefore,scientifically assessing the understory ecological functions of BP is essential for regional ecological security.This study examined 45 plots of BP natural secondary forests with different stand densities ranging from 150 to 1000 trees/hm2 in Baoku Forest Farm,systematically analyzing differences in soil nutrients,understory vegetation diversity,and water-holding capacity under different density regimes.A structural equation model(SEM)was employed to quantitatively evaluate the comprehensive ecological functions,aiming to identify the optimal stand density range for maximizing ecological benefits.Results showed that water-holding capacity contributed most to the comprehensive ecological function(weight 0.3252),followed by soil nutrients(0.2602),shrub diversity(0.2358),and herb diversity(0.1789).In this alpine region with limited annual precipitation(520 mm),hydrological regulation was the key factor in maintaining ecosystem stability.The ecological function evaluation across density gradients demonstrated that ecological functions exhibited significant fluctuations with changes in stand density,with the medium-high density group(600-800 trees/hm2)scoring highest(0.66±0.13,Grade Ⅳ),significantly outperforming the high-density group(＞800 trees/hm2,0.49±0.11).Therefore,it was recommended that BP forest management in Qinghai's alpine regions maintain stand density within the optimal range of 600-800 trees/hm2,avoiding excessive density that would intensify resource competition and deteriorate the microenvironment,or excessive sparseness that would reduce ecological benefits,thereby maximizing the understory ecological functions of BP forests and achieving ecosystem stability and sustainable development.