基于结构方程模型分析森林草原带草本物种丰富度对景观因子的响应

受损景观是由不同比例的植被斑块组成的镶嵌体,阐明植被斑块的景观结构特征对物种多样性的影响,有助于提高受损景观物种多样性保护。在塞罕坝自然保护区选取38个天然植被斑块,其中包括12个草地、11个灌木林和15个天然次生林。根据光合作用的不同途径将草本物种划分为C_3和C_4功能群。选取斑块面积、形状指数、隔离度指数及每个斑块500 m缓冲区内的森林和草地比例作为景观因子。通过结构方程模型探讨C_3、C_4草本物种丰富度与景观因子的相互关系。斑块面积(2.18—74.06 hm~2)与C_3、C_4草本及总物种丰富度分布格局均具有显著的正相关关系(P0.05),且对C_3草本的影响最大;形状指数(1.06—3.11)、隔离度指数(33.51—327.65)对C_3、C_4草本及总物种丰富度影响不显著(P0.05);C_3、C_4草本及总物种丰富度与毗邻斑块草地比例(4.20%—64.95%)呈正相关,而与森林比例(35.05%—95.80%)呈负相关。研究区斑块面积和毗邻斑块植被构成是影响C_3、C_4草本植物的主要因素。在破碎化景观中保存面积大的天然植被斑块及提高毗邻斑块草地比例是保护关键C_3、C_4草本植物物种的有效途径。

Structural equation modeling analysis of theresponse of herbaceous species richness to landscape factors in a forest-steppe zone

Fragmented landscapes are mosaics of vegetation patches with differing proportions. A more comprehensive understanding of the effect of landscape structure characteristics on species diversity is necessary to improve conservation strategies for species diversity in fragmented landscapes. Sampling plots were established in 38 natural vegetation patches within the Saihanba Nature Reserve, including 12 herbs, 11 shrubs, and 15 natural forest vegetation fragments. Herbaceous plant species were divided into C₃ and C₄ functional groups according to their photosynthetic carbon-assimilating pathway. The patch area, shape index, isolation index, and percentage of forest and grassland within a 500 m radius from the boundary of each sampling patch were selected as the landscape factors. A structural equation model (SEM) was adopted to explore the relationships between species richness of functional groups (C₃ and C₄) and landscape factors. Patch area (2.18-74.06 hm²) had a significant positive effect on C₃, C₄ herbs, and total species richness (P < 0.05), and the effect on C₃ herbs was the highest; the shape (1.06-3.11) and isolation (33.51-327.65) indexes had no significant effect on C₃, C₄ herbs and total species richness (P > 0.05); the species richness of C₃, C₄ and all herbs increased with increasing grassland proportions (4.20%-64.95%) in the surrounding matrix, whereas the percentage of forest (35.05%-95.80%) in the surrounding matrix did not have a direct effect. Patch area and vegetation composition of adjacent patches were the main factors affecting the C₃ and C₄ herbs in Saihanba Nature Reserve. Preserving the large natural vegetation patch and improving the proportion of grassland in the surrounding matrix could effectively conserve key C₃ and C₄ herbaceous plant species.