Following her recently published Review, Links between community ecology theory and ecological restoration are on the rise, author Claire E. Wainright discusses taking a global perspective on restoration ecology.
Community ecology and restoration ecology are often considered complementary fields. Ecologists recognize that the science of ecology provides solid conceptual foundations on which to construct hypothesis-driven restoration research. By extension, restoration offers unique opportunities to empirically test those foundations while simultaneously addressing urgent environmental issues.
It’s currently an introspective time for both disciplines. The past year has seen advances in theoretical organization and articulation of the most essential concepts in community ecology, including Vellend 2016 and Reiners et al. 2017. Restoration ecology is witnessing a similar age of reflection on its intellectual foundations. For example, the most recent Special Feature in this journal emphasized the role that ecology theory should play in making restoration ecology a more predictive science, thereby helping practitioners better manage variation in restoration outcomes. This endeavour to better “bridge theory and practice” has gained particular momentum over the last two decades. Out of this enterprise, restoration ecologists have outlined the potential restoration applications of a suite of community ecology concepts, encouraging the possibility of more tractable and biologically interpretable results.
We decided to systematically review the literature for these applications in real-world restoration scenarios across the globe from 1995 to 2015 as a means of quantifying the bridging of theory and practice. We assessed over 1000 peer-reviewed studies directly relevant to restoration programs focused on multi-species communities, the majority of which described outcomes of in situ restoration experiments. We scored the prevalence of a selection of ecological concepts derived from theoretical ecology, many of which have been explicitly suggested for use in restoration. Of these studies, we asked: how often do community ecology theories or concepts appear? Which theories or concepts do practitioners use when designing restoration experiments and interpreting the outcomes?
Our results confirmed that the incorporation of our set of ecological concepts has increased slowly but steadily over time. The most highly-cited concepts and theories are mainstays of community ecology: assembly rules, succession, and multispecies coexistence (including niche theory). These mechanistic concepts related to where species establish, how communities change over time, and why they coexist (or don’t) have been used to understand restoration dynamics in ecosystems ranging from old fields to coral reefs. Interestingly, we found that succession theory (both in a classical sense and including the concept of alternate stable states) appears to be gradually declining in use relative to other concepts, perhaps reflecting a shifting vocabulary to newer terms that describe compositional change such as community “reassembly”.
In addition to concepts that have remained tried-and-true, we found a significant uptake of elements of evolutionary theory in recent years. Sources of genotypic variation are an important consideration in single-species restoration programs due to the importance of local adaptation to site conditions and, more recently emphasized, population-level resilience to future climate change. Over the past decade, practitioners have more frequently explored the implications of local provenance for whole-community dynamics over shorter timescales typical of restoration programs. For example, Weißhuhn et al. examined community-level outcomes of European grassland restoration, including diversity and provisioning of ecosystem services, as a function of the provenance of constituent species. Community performance indicated regional superiority (as opposed to foreign), and was only partially explained by species-level responses, possibly indicative of greater resource partitioning in restoration assemblages containing more recently co-evolved species. By contrast, Hancock et al. found a much weaker relationship between provenance and plant-herbivore interaction outcomes in restoration plantings in a temperate eucalypt woodland ecosystem in Australia. The contextual nature of interspecific interactions mediated by source population choice as well as the possibility of eco-evolutionary feedbacks in restored communities makes this an exciting new realm of exploration.
These applications indicate significant progress in bridging theory and practice. In moving forward, it’s always worth stepping back to view this progress holistically. The prevalence of ecological concepts assessed in published restoration results in English-language, peer-reviewed journals is undoubtedly inflated compared to restoration applications globally, including those in the grey literature. In fact, according to our pool of studies, studies that incorporate theory are disproportionately authored by academic practitioners of grassland restoration in the United States. While not inherently negative, we should be aware of how these biases might influence paradigm development in restoration ecology. Effectively bridging the theory-practice gap will require the exchange of ideas with practitioners from a variety of ecosystems and professional perspectives. We hope our review will inspire greater cross-pollination not only between fundamental ecology and restoration ecology, but restoration cultures as well.