Elevational seed plants richness patterns in Bhutan, Eastern Himalaya

Aim We used published data of the floristic and elevational distribution of seed plants of Bhutan to test the contribution of climatic, topographical and biogeographical variables to shape elevational species richness and endemism patterns. Location Bhutan. Methods We compiled data of seed plant species distributions from the Flora of Bhutan and related them to energy, humidity, and topographically related variables and biogeographical distributions. We used multiple regression models to identify most predictive independent variables by multi-model-inference based on AICc. Results We find highest species richness at mid elevations (1500–2000 m), while endemic richness peaks markedly higher at 4500 m. Separated for life forms, the peak of richness shifts upward along the elevational gradient in the order of trees – shrubs – herbs – graminoids. Elevational richness peaks of temperate taxa were centred at high and of tropical taxa at low elevations. Temperature was identified as most influential for species richness patterns and showed a humped relationship to richness patterns. Main conclusions The humped patterns of species richness in Bhutan correspond to results from other studies in low latitude mountains, and the correlation of these patterns to energy driven variables, especially temperature, can be confirmed. The humped relationship of temperature (including water regimes driven by temperature) to richness indicates elevation zones of moderate temperatures with absence of temperature extremes as predicting species richness, and the high elevation peak of endemism may be related to mountain terrain configuration and climatic history. The different elevations of richness peaks of tropical and temperate taxa underlines the notion of a transition zone between temperate and tropical realms, thus the intermingling of different evolutionary histories. For further research, we require fine scale local data for detailed taxa distributions in order to infer issues from evolutionary processes in landscape development to identify target regions for conservation purposes.