Abstract
We conducted floristic and community analyses to compare the floristic composition, forest structure, taxonomic richness, and species diversity between two tiankeng (large doline, or sinkhole) habitats and two outside-tiankeng habitats of forest fragments in a degraded karst area in southwestern China. We found remarkably higher taxonomic richness in the tiankeng habitats than in the outside-tiankeng habitats at the species, generic, and familial levels. The inside-tiankeng habitats had higher floristic diversity but lower dominance. The remarkably higher uniqueness at all taxonomic levels and the much larger tree size in the two tiankeng habitats than in the outside-tiankeng habitats demonstrated the old-growth and isolated nature of the tiankeng flora. Plot-scale species richness, Shannon-Wiener index, Pielou’s evenness, and Berger-Parker dominance significantly differed across habitats. Heterogeneity in floristic composition at the species, generic, and familial levels was extremely significant across habitats. In pairwise comparisons, except for the Chuandong Tiankeng-Shenmu Tiankeng pair, all the pairs showed significant between-habitat heterogeneity in floristic composition. Our results suggest that as oases amidst the degraded karst landscape, tiankengs serve as modern refugia that preserve old-growth forest communities with their rich floristic diversity, and can provide a model for habitat conservation and forest restoration in that area.
Highlights
Biodiversity loss, habitat fragmentation, and land degradation characterised by soil erosion, lower fertility, and rocky desertification are the typical features of mountainous karst landscapes[1,2,3]
For tree stems ≥ 10 cm diameter at breast height (DBH), we recorded a total of 933 tree individuals of 96 species from 66 genera and 38 families in all four habitats (Supplementary Table 1; see the Methods section for the definition of the four habitats.)
Restoring the vegetation in the degraded karst areas is a major challenge for biodiversity conservation and regional development[30, 31], since these areas have undergone longtime environmental degradation and biodiversity loss due to geological and climatic processes, as well as intense human activities[32, 33]
Summary
Biodiversity loss, habitat fragmentation, and land degradation characterised by soil erosion, lower fertility, and rocky desertification are the typical features of mountainous karst landscapes[1,2,3]. Limited, investigations from excursions to this area have revealed that the tiankengs contain pristine old-growth forest[8, 13], making them oases amidst the degraded karst landscape. We hypothesised that these tiankengs might serve as refugia for the once rich biotic diversity in this area. We aimed to reveal the floristic composition and community structure of the tiankeng pristine forest compared to those of the outside-tiankeng forest fragments To achieve this goal, we compared the floristic composition, taxonomic richness, tree size, and species diversity between two tiankeng habitats and two outside-tiankeng habitats in forest fragments of a degraded karst area in southwestern China
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