Projected impacts of climate change on regional capacities for global plant species richness

Abstract

Climate change represents a major challenge to the maintenance of global biodiversity. To date, the direction and magnitude of net changes in the global distribution of plant diversity remain elusive. We use the empirical multi-variate relationships between contemporary water-energy dynamics and other non-climatic predictor variables to model the regional capacity for plant species richness (CSR) and its projected future changes. We find that across all analysed Intergovernmental Panel on Climate Change emission scenarios, relative changes in CSR increase with increased projected temperature rise. Between now and 2100, global average CSR is projected to remain similar to today (+0.3%) under the optimistic B1/+1.8 degrees C scenario, but to decrease significantly (-9.4%) under the 'business as usual' A1FI/+4.0 degrees C scenario. Across all modelled scenarios, the magnitude and direction of CSR change are geographically highly non-uniform. While in most temperate and arctic regions, a CSR increase is expected, the projections indicate a strong decline in most tropical and subtropical regions. Countries least responsible for past and present greenhouse gas emissions are likely to incur disproportionately large future losses in CSR, whereas industrialized countries have projected moderate increases. Independent of direction, we infer that all changes in regional CSR will probably induce on-site species turnover and thereby be a threat to native floras.

Figure 1.

(a) Observed current effects of temperature on plant species richness in 1032 geographical units worldwide. Residuals from the species–area relationship (log–log) are plotted against log₁₀ transformed mean annual temperature (in K) for three different classes of water balance (in mm yr⁻¹) calculated as annual precipitation minus annual potential evapotranspiration per 110 × 110 km² grid cell to illustrate the interaction effect between water balance and temperature. Regression lines with 95% confidence intervals are displayed for all three classes. (b–d) Global patterns of water balance. (b) Observed current patterns, (c) projected patterns under +1.8°C/B1 scenario for 2100, and (d) projected patterns under +4.0°C/A1FI scenario for 2100. Displayed are mean values for the CGCM2, CSIRO2, HadCM3 and PCM general circulation models (GCMs).

Figure 2.

Modelled current global patterns of the capacity for species richness (CSR; species number per 110 × 110 km²) and future changes. (a) Modelled current patterns of CSR, (b) change in CSR under +1.8°C/B1 scenario for 2100, and (c) change in CSR under +4.0°C/A1FI scenario for 2100. CSR changes are counted in species numbers per 110 × 110 km² grid cell and represent mean values for the CGCM2, CSIRO2, HadCM3 and PCM GCMs. Colour classes represent steps of 50 species. (d) Congruence in the direction of change (either increase in CSR or decrease in CSR, independent from the magnitude of change) between present and future CSR for all 18 available combinations of five GCMs (CGCM2, CSIRO2, ECHAM4 A2/B2, HadCM3 and PCM) and the four major IPCC scenarios (A1FI, A1, B1, B2). The dark green colour stands for 100% congruence across all 18 models that CSR is going to increase, whereas dark red indicates 100% congruence across models that CSR will decrease in the respective area. Yellow areas are subject to oppositional predictions of the direction of change across the models.

Figure 3.

Modelled changes in the capacity for species richness (CSR; species number per 110 × 110 km²) between today and the year 2100 under the +1.8°C/B1 scenario (blue) and the +4.0°C/A1FI scenario (red). (a) Global average CSR change as mean values for the CGCM2, CSIRO2, HadCM3 and PCM GCMs, and for each GCM individually. (b) CSR change for the industrialized Kyoto protocol Annex B countries when compared with Non-Annex B countries. (c) CSR change across all 13 terrestrial biomes. Percentage values reflect the change in CSR for the respective subset of 110 × 110 km² equal area grid cells. Bold lines indicate the mean value, boxes indicate second and third quartiles and whiskers indicate 10th and 90th percentiles.