Figure 2: Change in soil biodiversity in response to global changes (GCs). Hedges’ g was used as the effect size. Negative effect sizes indicate that the GC causes a reduction in biodiversity, and a positive effect size indicates an increase in biodiversity. Error bars indicate 95% confidence intervals. Effect sizes where error bars do not cross the dashed vertical zero line, are significantly different from zero. The values of n indicate the number of cases of each GC in the model, with values in parentheses indicating the number of publications.
Pollution had a significant negative impact on biodiversity (estimate = -0.71; ±95% CIs = -0.92, -0.49; p-value < 0.0001), the largest effect of all the GCs. Land-use intensification (estimate = -0.58; ±95% CIs = -0.77, -0.39; p-value = < 0.0001) and climate change (estimate = -0.28; ±95% CIs = -0.54, -0.04; p-value = 0.01) also had a significant negative effect on biodiversity, whilst habitat fragmentation, invasive species, and nutrient enrichment did not have a significant effect.
When focusing on the environmental stressors model relating to climate change, body size was removed as an effect from the model (both as an interactive effect, and a main effect). The only climate change environmental stressor that had a significant effect on biodiversity was the detrimental impact of drought (estimate = -0.52; ±95% CIs = -0.76, -0.28; p-value <0.0001; Figure 3a). The effects of gas (CO2 and O3) and temperature change, although trending towards a negative impact of biodiversity, were not significant. The impact of increased water (absolute amount, rates, or number of events) through floods trended towards a positive impact on biodiversity but, again, was not significant (although also had the least amount of data, n = 41 cases).