DOI: 10.5061/dryad.7sqv9s4t2
title: Key roles for the freezing line and disturbance in driving the low plant species richness of temperate regions

description: Aim: At the macroscale, climate strongly correlates with species richness
 gradients, resulting from differences in in-situ diversification and
 dispersal. One historical explanation for the pattern is that regions
 spanning temperate climates contain few species because past disturbances
 have generated high extinction rates, and species from tropical regions
 are unable to easily colonize temperate regions. We test these postulates
 for Himalayan plants, which span subtropical to temperate climates over
 steep elevational gradients. Location: Himalaya Time period: Present day
 Major taxa studied: Angiosperms Methods: We use a comprehensive survey of
 31 floras to document the elevational and geographical distributions of
 native Himalayan plants, augmented by field studies of trees in both the
 east and west Himalaya. We use grade of membership models to cluster
 species according to locations shared and phylogenetic analysis to
 evaluate diversification rates. Results: Species fall into four cohesive
 biotas, organized by climate. Points of turnover between biotas occur
 where the mean minimum temperature of the coldest month is approximately
 0oC (2,000 m - 2,500 m), and at the point of occasional annual freezing
 (1,000 m - 1,500 m); these boundaries run the length of the Himalaya. The
 patterns are retained when we consider whole clades rather than species.
 All plants (and the subsets trees, herbs and shrubs) belonging to the
 biota above the 2,000 m - 2,500 m line have higher recent speciation rates
 than those lower down. Main conclusions: We attribute the high rate of
 recent speciation in temperate climates to high rates of turnover,
 creating ecological and geographical opportunity. The high elevation biota
 has few species, but spans the largest area, implying species numbers are
 far from any carrying capacity, at least with respect to accumulation of
 allopatric forms. This study thus links climatic restrictions of clades to
 differences in diversification rates, and by inference species numbers.
description: We compiled the elevational and distribution ranges of 8765
 species of angiosperms reported from the Himalayas in 31 floras published
 either for an individual country (Nepal, Bhutan), states, or smaller local
 regions. Data S1 shows the list of 8765 species with
 the lowest and highest elevational limit, mid-point of the elevational
 range, average values of climatic parameters, presence and elevational
 ranges within states, climatic affinities, diversification rate and mean
 family age of the species. Data S2 represents the field
 sampling data of trees along an elevational gradient in the western
 Himalaya showing the number of individual trees of each species and the
 location of the sampling sites at seven elevational zones.
 Data S3 shows the top 100 contributing angiosperm species in each
 of the four biogeographic regions (Motifs) with additional information
 diversification rate, mean family age etc.  Data S4
 shows the top contributing tree species in each of the four biogeographic
 regions (Motifs) with associated information.