Estimating dark diversity and regional species pool in the high-altitude Himalayan habitats

Several species of the regional pool rarely become part of local communities. Such a considerable fraction of the species pool which remains absent but have potential to establish is referred to as dark diversity, and has till now remained understudied. In this study, we aimed to estimate the dark diversity, site-specific species pool, community completeness and species co-occurrence patterns in the Himalaya. Following a globally standardised sampling protocol, we delineated a circle of radius 10 km in the high-altitudes habitats of Kashmir Himalaya and selected two major habitat types: temperate coniferous forest and alpine grassland. Within each habitat type, we laid two 10-m core and two 50-m surrounding plots at natural and disturbed sites, and also thirty 10-m co-occurrence plots. The size of dark diversity was found higher at the disturbed sites (grassland: 23.43, forest: 29.07) in comparison to the natural ones (grassland: 21.52, forest: 26.08). Conversely, the site-specific species pool size was higher in the natural sites (grassland: 44.53, forest: 51.08) as compared to the disturbed ones (grassland: 35.43, forest: 45.07), and a similar trend was observed for the community completeness index at both the habitats. The majority of the species co-occurrences in both the habitats were truly random, therby indicating possibly least role of biotic and abiotic factors. Our study provides empirical estimates of dark diversity and quantifies how they differ in natural and disturbed sites in Kashmir Himalaya. These findings have immediate implications in guiding site-specific biodiversity conservation and ecosystem restoration in the study region, and also hold promise to be upscaled at much larger spatial scales.