By: Dave Coyle, Southern Regional Extension Forestry and UGA – D.B. Warnell School of Forestry and Natural Resources. Find Dave on Twitter @drdavecoyle, and check out his website: http://southernforesthealth.net/
Mac Callaham, USDA Forest Service – Southern Research Station. See more about Mac at https://www.srs.fs.usda.gov/staff/447
Soil fauna are central to the field of soil ecology. For a generation, scientific giants Drs. Dave Coleman, Dac Crossley, and Paul Hendrix at the University of Georgia - Odum School of Ecology taught a course on soil biology and ecology largely centered on fauna, training numerous ecologists and taxonomists. After these three retired from UGA, however, the class went on a multi-year hiatus. In 2013, Dr. Mac Callaham, a soil ecologist with the USDA Forest Service, and Dr. David Coyle, a forest health specialist with Southern Regional Extension Forestry and the University of Georgia, teamed up to bring the course back. As part of the course, students from the Warnell School of Forestry and Natural Resources, Odum School of Ecology, and departments of Plant Sciences and Crop and Soil Sciences, conducted a literature review on the impacts of various land disturbance factors on soil biota and wrote term papers synthesizing their findings. Student papers were combined and edited into the first-of-its-kind review on the impacts of disturbances on soil fauna, and was published in the journal Soil Biology and Biochemistry (http://www.sciencedirect.com/science/article/pii/S0038071717301530).
Mac is well-known for his work with earthworms, and other macroinvertebrates, and in particular their responses to land-management activities. Dave’s PhD research examined the impacts of a suite of non-native root-feeding weevils in the Upper Peninsula of Michigan. Together, we have often lamented the fact that soil fauna – especially macrofauna – rarely get the attention they deserve (our opinion, obviously). But, in researching this paper, we found that publishing trends confirm this notion (see right). In recent years, there has been a disproportionate increase in papers dealing with soil microbes compared to soil fauna. Anecdotally, with the exception of earthworms, ants, and a select few economically important taxa (think crop pests like corn rootworm, or citrus root weevil), soil fauna are somewhat ignored. And for those of us who work on soil fauna, that isn’t cool. Sure, we know that microbes are important actors in soil ecosystems, but they don’t act alone, and the soil ecology research community has amassed years of scholarship indicating that macrofauna can have big influences on the biomass, composition, and activity of soil microbes.
So, we acted like any good scientists and we wrote about it (and it was peer-reviewed, even!). We synthesized what was known (and unknown) about the impacts of natural and anthropogenic disturbances on soil fauna. For some taxa, there was very little information (published or otherwise) available. For others, information was plentiful. We know there are a LOT of complex interactions between organisms, disturbances, and their environments - especially when dealing with multiple scales (see below). One of our challenges was capturing this heterogeneity and adequately conveying what it meant, in some cases, when information was only available from one scale. Fortunately, there are some really good long-term studies in existence (e.g. Luquillo LTER: http://luq.lternet.edu/) that were great sources of information. We examined natural disturbances like wind damage, flooding and water stress, drought, and fire; invasive plants and invasive invertebrates; and fire. In each case we reviewed the impact of these factors on fauna in different parts of the soil (i.e. epigeic and endogeic/anecic).
In what may hardly be considered groundbreaking to anyone who does research below the soil surface, the take home message was “it depends,” and it depends on a lot of different things. A lot. The impacts of particular disturbances vary depending on the specific fauna in question. It also matters at what scale – you may see fine-level impacts (e.g. in a plot) but at the watershed scale there is no discernable impact on fauna communities. Short time duration versus long time duration also matters, as certain taxa are much better at “rebounding” after a disturbance than others. Additionally, the issue of giving an accurate name to the organism under study (i.e. taxonomy) is important. Most studies of soil fauna do not identify organisms to the species level, which makes interpretation of results incredibly difficult (not to mention complicating the comparison of data across studies).
Our review reaffirmed some things we already knew: belowground ecology is hard, scale is important, and there isn’t enough taxonomy in the world. It also highlighted some things we didn’t know: the pace of publishing work on soil microbes is much greater than that dealing with soil fauna. As one would expect, there are some significant gaps in the knowledge. But that’s why we’re all here working and reading this blog, in the hopes of filling those gaps.