People impact biodiversity through a myriad of pathways (e.g., through changes in climate and land use, hereafter, global change drivers). Due to the large amount of data published on this topic, there are many opportunities to perform meta-analytical analyses to generalise the patterns and magnitude of changes that are occurring. However, previous meta-analyses investigating the impact of different global change drivers on biodiversity have often been focussed on aboveground biodiversity and have omitted soil biodiversity. Not only is soil biodiversity incredibly important to many ecosystem functions and services, but by using soil biodiversity data we are able to look at effects of additional global change drivers that are often lacking data (e.g., pollution). We conducted a meta-analysis focussed on six global change drivers (land use intensification, habitat fragmentation, climate change, nutrient enrichment, invasive species and pollution) on soil fauna. Based on previous synthesis work, we expected land use intensity and climate change to have the largest impact on soil fauna. In addition, we expected the body size of the organism to influence their response to the driver.
In total, we analysed 3193 effect sizes, from 626 publications. Land use intensification and pollution had the largest negative impact on soil fauna communities. Land use intensity impacts were expected based on previous work, however the extremely negative impact of pollution is particularly worrying due to continually increasing levels of pollution, and the fact that pollution is understudied relative to other drivers. Not all drivers were detrimental. For example, nutrient enrichment increased soil fauna, mostly due to the addition of structure to the soil (e.g., through manure and soil amendment applications). On the whole, climate change had minimal impact on soil fauna. The reduction of water, through drought, was the only climate change driver that was associated with significant declines in soil fauna communities. The impact of the global change drivers did not vary with organism body size. Overall, this work shows the importance of including soil biodiversity in large-scale analyses as soil organisms often do not show the same responses as organisms above-ground. It is important that we understand how soil organisms may respond to continuing human pressures, due to their importance in many of the services and functions that we rely on for our survival.