Limitations and future directions
Using the ‘pulse’ and ‘press’ traits to describe the environmental stressors helped to introduce the mechanisms, and highlight the similarities, that may result in biodiversity change, regardless of the GC they are associated with. However, the lack of consistency in results may be due to the simplistic nature of using just a single trait for each stressor. Indeed, proposed 30 different traits to characterize environmental stressors, a classification scheme that they found worked well when applied to a soil microbial experiment. further stated that stressors should not only be classified based on their traits but also sources, temporal overlap, mode of action, and co-tolerance to determine their similarities and aid predictions. Unfortunately, there is currently no classification scheme that assigns environmental stressors to such a wide range of different traits, which would be needed to fully realise the benefits of this approach.
As not all GCs and environmental stressors had enough data to enable in depth investigation, further questions remain as to the specific impacts of habitat fragmentation and invasive species on soil fauna. It would be expected that both habitat fragmentation and invasive species alter the soil enough to impact many soil organisms . Alternatively, more moderators may be needed to capture the heterogeneity (e.g., habitat type; ), and/or more complex interactions between the moderators .
The breadth of this meta-analysis provides us with insight and comparisons that have previously not been possible. However, it also reduces our ability to ‘zoom’ into specific effects, such as different doses of GCs (stressor concentrations, amounts), temporal aspects or community composition shifts. Therefore, further experimental work is needed to elucidate variations in exposure to different GCs and their influences on soil biodiversity, as well as more specific meta-analyses. Although this meta-analysis contained a large number of data points, there still was a lack of data for specific questions, for example, habitat fragmentation and invasive species as discussed above, different pollutant types, and better representation of taxonomic groups. An additional focus on additional diversity indices, such as community composition and beta diversity metrics, may also be insightful. We hope that by highlighting the relative lack of data, these gaps may be overcome in the future with additional studies.
One aspect of the study of global change that is being highlighted in the scientific literature as an important avenue of research is the potential impact of two or more GCs simultaneously . Many meta-analyses that looked at the additive and interactive effects of GCs on biodiversity have found that the interactions between GCs are important . Although it might be anticipated that the interaction between GCs may result in greater negative impacts than expected based on the singular GCs , there is the potential for the presence of two GCs to result in less of a negative impact than expected . Given the changing world that we are in, and that GCs rarely act singularly on biodiversity , this would be the most important avenue to study further, and is indeed possible within a meta-analysis framework when factorial data are present .