Vascular and Cryptogam Richness in the World's Highest Alpine Zone, Tibet

Abstract

This study explores the elevational richness patterns of vascular and cryptogam species in the highest alpine zone in the world, the Tibet/Xizang Autonomous Region (78°25′–99°06′E, 26°50′–36°53′N). The data are based on the published flora for vascular plants, bryophytes, and lichens. Elevational ranges have been interpolated for each species recorded in the flora at altitudes between 4500 and 6000 m into 16 elevational bands of 100 m each. A species is assumed to be present at all elevational bands between its lower and upper limits as recorded in the flora. Total richness has been further subcategorized into richness of different functional groups and some dominant angiosperm families. Generalized linear models (GLMs) up to 3 orders are applied to assess the relationship between species richness and elevation and the statistically most appropriate model based on the highest F value among the significant models is selected. A total of 1585 species, 385 genera, and 111 families are recorded in the flora from this part of the alpine zone. Flowering plants are represented by 1328 species, 261 genera, and 54 families. A significant decreasing quadratic relation with increasing elevation is the most common pattern among most of the functional groups. Bryophytes, lichens, and their functional groups show a linear declining pattern except for a quadratic relation in foliose lichen richness. A significant unimodal relation is found with some angiosperm families. The patterns found are both similar and dissimilar to published results from studies using interpolation or direct observations. Scale, environmental heterogeneities, stress, disturbance, and tolerance by individual species are the likely causes for these patterns.