Soil indicators of plant diversity for global ecoregions: Implications for management practices

Environmental indicators have been developed widely to promote biodiversity conservation, ecological restoration, and nature resource management from local to global scales. Ecoregions are effective tools for global conservation of plant diversity, and soil conditions can affect the plant diversity within ecoregions. Hence, soil indicators of plant diversity have substantial potential as tools for effectively understanding global ecoregions. Here, we used plant diversity data from 361 ecoregions and seven soil variables in a regression analysis to explore the relationships between soil and ecoregional plant diversity (EPD). We found that soil means and heterogeneity were significantly related to EPD. EPD decreased curvilinearly as both mean cation exchange capacity and mean soil pH increased, while mean soil organic carbon stock was negatively related to EPD (P < 0.05). EPD increased curvilinearly with mean soil texture clay fraction and mean soil texture silt fraction (P < 0.05). Heterogeneity of bulk density, cation exchange capacity, and soil pH had positive relationships with EPD (P < 0.05). EPD had a negative, unimodal response to soil organic carbon stock heterogeneity, with an opposite trend in heterogeneity of soil texture clay fraction (P < 0.05). Furthermore, such relationships may depend on the vulnerability of ecoregions of interest. Specially, means of soil texture clay fraction and heterogeneity of bulk density were useful indicators of EPD for relatively stable or intact and vulnerable ecoregions (P < 0.05), and mean cation exchange capacity and heterogeneity of soil organic carbon stock were useful indicators of EPD in critical or endangered ecoregions (P < 0.05). Hence, monitoring soil conditions should be conducted for plant diversity at broad scales, and conservation efforts should focus on soil diversity, with a particular emphasis on relatively stable or intact ecoregions worldwide.