Abstract
The species richness–climate relationship is a significant concept in determining the richness patterns and predicting the cause of its distribution. The distribution range of species and climatic variables along elevation have been used in evaluating the elevational diversity gradients (EDG). However, the species richness of gymnosperms along elevation and its driving factors in large geographic areas are still unknown. Here, we aimed at evaluating the EDG of gymnosperms in the ecoregions of China. We divided the geographical region of China into 34 ecoregions and determine the richness pattern of gymnosperm taxa along elevation gradients. We demonstrated the richness patterns of the 237-gymnosperm (219 threatened, 112 endemic, 189 trees, and 48 shrubs) taxa, roughly distributed between 0 and 5,300 m (above sea level) in China. As possible determinants of richness patterns, annual mean temperature (TEMP), annual precipitation (PPT), potential evapotranspiration (PET), net primary productivity (SNPP), aridity index (AI), temperature seasonality (TS), and precipitation seasonality (PS) are the major predictor variables driving the EDG in plants. We used the species interpolation method to determine the species richness at each elevation band. To evaluate the richness pattern of gymnosperms in an ecoregion, generalized additive modeling and structural equation modeling were performed. The ecoregions in the southern part of China are rich in gymnosperm species, where three distinct richness patterns—(i) hump-shaped, (ii) monotonic increase, and (iii) monotonic decline—were noticed in China. All climatic variables have a significant effect on the richness pattern of gymnosperms; however, TEMP, SNPP, TS, and PS explained the highest deviance in diversity-rich ecoregions of China. Our results suggests that the highest number of gymnosperms species was found in the southwestern and Taiwan regions of China distributed at the 1,600- and 2,800-m elevation bands. These regions could be under severe stress in the near future due to expected changes in precipitation pattern and increase of temperature due to climate change. Thus, our study provided evidence of the species–climate relationship that can support the understanding of future conservation planning of gymnosperms.
Highlights
Species are not randomly distributed on the earth’s surface; instead, they form a distinct distribution pattern (Lomolino, 2001)
Endemic species accounts for 47.25% (112) of the total gymnosperms of China and formed a unimodal distribution pattern (R2 = 0.942, p < 0.005)
Distribution of Gymnosperms Along Elevation Gradients The patterns of all studied forms of gymnosperm species richness in response to elevation gradients in China were consistent, showing a unimodal distribution pattern
Summary
Species are not randomly distributed on the earth’s surface; instead, they form a distinct distribution pattern (Lomolino, 2001). The distributions of plants along elevation were extensively used to determine the richness pattern and to formulate the future conservation planning (Kluge et al, 2017; Paudel et al, 2018; Vetaas et al, 2019). One of the most interesting features is that species richness follows common patterns in the distribution along the elevations (i.e., the EDG pattern) (Rahbek, 1995; McCain, 2004). Lomolino (2001) reviewed and summarized the studies linking the elevational distribution of species richness, and identified the further need for comparing the richness patterns and the factors that determine EDG. Most researches have explained a significant role of EDG in defining the diversity patterns of plants (Rahbek, 1995; Lomolino, 2001; Bhattarai and Vetaas, 2003; Bhattarai et al, 2004; Wang et al, 2007; Gao et al, 2017; Kluge et al, 2017; Gao and Liu, 2018; Subedi et al, 2019; Pandey et al, 2020b). Lomolino (2001) reviewed and summarized the studies linking the elevational distribution of species richness, and identified the further need for comparing the richness patterns and the factors that determine EDG. Lomolino (2001) prioritized understanding the richness of different conservation groups (e.g., threatened and endemic) and life forms (e.g., tree, shrub, herbs, etc.) in varied climatic and vegetation-rich ecological regions (hereafter ecoregion)
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