Declines in soil biodiversity as a result of global changes
By Dr. Helen Phillips
Assistant Professor, Ecological Data Science, University of Helsinki
It has been well established that humans have an impact on global biodiversity, through human-caused global changes (GCs) such as climate change, land use intensity, and pollution. Additionally, the consequences of these GCs (stressors) (e.g., drought, harvesting of aboveground biomass, and pesticide use) have an impact on biodiversity. However, there is still debate on the magnitude and direction of that impact. Although experiments can inform scientists on how GCs affect biodiversity on a small-scale, the results may not be applicable for other taxa or globally. To assess patterns at a global scale, scientists often use meta-analyses, which use existing published research to collect and analyze data from across the globe to uncover broad-scale patterns. Although meta-analyses have previously been conducted on GC impacts on biodiversity they have typically been limited in scope, either by excluding soil biodiversity (soil fauna communities), or by limiting the range of GCs studied. Soil biodiversity fills a critical role in ecosystems, but have been largely understudied even though they harbor 59% of Earth’s species (Anthony et al. 2023). To fill these knowledge gaps, we undertook a meta-analysis focused on six GCs (climate change, land-use intensification, pollution, nutrient enrichment, invasive species and habitat fragmentation) and their stressors on soil fauna communities specifically. Following a comprehensive literature search, we extracted data from 624 papers, resulting in 3161 comparisons between soil fauna in un-impacted sites and impacted sites.
Through our meta-analysis, we found that pollution had the strongest negative impact on soil fauna communities. These results are particularly alarming, since most meta-analyses do not include pollution as a GC and the rate of pollution is increasing faster than other GCs. We were only able to collect data from two pollution stressors (metals and pesticides) and found that metal pollution had the strongest negative impact, although the impact of pesticides was still significantly negative.
Our study found that climate change had a negative impact on soil fauna communities, which was predominantly driven by drought, land use intensification, and is in line with the findings of similar studies. And whilst there was no overall effect of nutrient enrichment, when we looked at individual stressors, we found that many of the organic-based additions, such as the addition of manure, or mulch, resulted in an increase of abundance of soil fauna communities. We had expected there to be some context-dependency to the impact of each of the GCs, but rarely found this to be the case. For example, there was no difference in GC impact based on soil faunal body size, except for land use intensification impacts where micro-fauna tended to be less negatively impacted than larger fauna groups.
Overall, we found that many GCs and their stressors reduced soil fauna biodiversity, and that these responses differed from previous analyses measuring above-ground biodiversity. Once again this highlighted the need to explicitly include soil biodiversity (particularly soil fauna) into large-scale global change research, whilst also ensuring that we adequately study a range of different global change impacts.
