Islandization and species diversity of semi-humid evergreen broad-leaved forests in the Central Yunnan Plateau

Abstract

Aims: This study focuses on the semi-humid evergreen broad-leaved forests (SEBFs) in Central Yunnan Plateau, a zonal vegetation characterized by varying patches sizes and shapes distributed around rural villages. Through remote sensing based vegetation mapping and field vegetation investigation, we aimed to explore the spatial patterns of fragmented SEBF patches, the changes in plant species diversity of SEBFs in relation with its patch size and distance class from villages, and assess the effects of environmental and anthropogenic factors on the species composition of SEBFs communities.Methods: This study investigated the fragmentation features of SEBFs and their impact on species diversity. We conducted spatial analysis and species diversity assessments using the patch and community data from SEBFs. SEBFs' patches were derived from Landsat 8 OLI imageries in combination of supervised classification and visual interpretation. α diversity and β diversity were compared among the plot community types. And the species composition was compared using non-metric multidimensional scaling to indicate the importance of environmental drives. Results:(1) In Central Yunnan Plateau, the existing SEBFs only accounted for 1.5% of their potential, climate-determined distribution range. This area comprised 92 forest patches covering a space greater than 100 ha, whereas forest patches covering an area of < 10 ha accounted for 54.6% of the total patch number but only 7.8% of the total area. This highlighted the significant shrinking and fragmenting of this vegetation type's area. (2) Remarkably, 99% of forest patches were within 3 km from rural villages. A trend emerged where patches farther away from villages had larger area, but the species α diversity did not show significant changes except for species evenness. For sample plots in patches with different area classes, α diversity only showed significant changes in species richness; larger patches exceeding 100 ha exhibited higher species richness. In contrast, the closer a patch was to a village, the more simplified and more homogeneous its species composition tended to be.(3) β diversity among plot communities was primarily driven by species replacement. Forest islanding was a key factor influencing changes in species composition of SEBFs communities. Moreover, the impact of human interference on species composition was significantly greater than that of local habitat heterogeneity (water conditions) and regional climate gradients (low temperature limitations). Conclusion:The SEBFs in the Central Yunnan Plateau are abundant near villages with fragmented small patches, and these areas are experiencing notable degradation due to human interference. This situation is urgent and demands attention and the implementation of necessary protective measures.