Abstract:

Extensive fragmentation has led to the original desert steppe soils of hard sierozem to become isolated in the desertified lands, forming the so-called “soil islands”. We aimed to reveal the effect of fragmentation on the co-existence of plant species within “soil islands” habitat. To this end, we characterized the plant communities on three large (200-300 m²), medium (about 100 m²) and small (about 50 m²) soil islands each, in the Wanjigou Village of Yanchi County in Ningxia Hui Autonomous Region of China. We analyzed the similarity of plant community within and outside those soil islands, the breadth and overlap of plant ecological niche, the species co-existence pattern and its influencing factors using Jaccard similarity coefficient, niche overlapping degree formula, null model analysis, and meta-analysis. Our results showed that: (1) with increased fragmentation, plant diversity within the soil island decreased, and the dominant plant species changed from Stipa breviflora to a combination of Artemisia scoparia and S. breviflora, and the plant communities within soil islands became more similar to communities outside; (2) most species showed relatively small ecological niche overlap between within and outside soil islands, with the overlap showing concentrated distribution within soil islands but scattered distribution outside the islands; (3) environmental filtering was the main driver of species co-existence patterns. As soil islands became larger, the effect of environmental factors on species co-existence decreased, and the key environmental factor that explained species composition changed from clay and fine sand to coarse sand. Notably, a competition was a key driver of co-existence patterns within small “soil islands”. In summary, “soil islands” provide an important habitat for representative plant species in the desert steppe and environmental factors influenced species co-existence patterns. Both processes were disrupted by fragmentation. Maintaining soil islands larger than 200 m² would be critical for restoring representative plant species and preserving plant diversity of the desert steppe ecosystems.

Key words: habitat fragmentation, soil islands, niche overlap, species co-existence, desert steppe