To mark the centennial of the Ecological Society of America, ESA commissioned a set of “centennial papers” that synthesize the current, past and future state of major areas of ecology. Starting last January, this blog hosted an extended discussion of Erle Ellis’ centennial paper on ecology in the Anthropocene. In this post, I’d like to look much more briefly at one of the other centennial papers: “Advances in restoration ecology: rising to the challenges of the coming decades”, published by Michael Perring et al. last year in Ecosphere.
Restoration ecology is the science of restoring “damaged, degraded or destroyed” ecosystems. Defined narrowly, it encompasses the re-establishment or re-introduction of flora or fauna to an ecosystem. Defined more broadly, restoration ecology includes any conservation action undertaken to restore an ecosystem to some prior state (e.g., the removal of heavy metal contaminants or invasive species, or the restoration of degraded habitat). In this broader definition, restoration ecology complements the preservation of wild places, and these two types of actions together are the two main components of modern conservation practice.
Restoration ecology is a relatively young science, and the practice of restoration has developed more or less alongside growing awareness of the dominance of human activities on the Earth’s ecosystems, i.e. the Anthropocene. So, many of the current ideas in restoration ecology should dovetail nicely with the subjects of recent posts on this blog. As a freshwater ecologist interested in the practice of restoration, I was curious to reflect on my own experiences with restoration, and the ways in which the practice of restoration in freshwater ecosystems might differ from that in terrestrial ones.
Many authors distinguish between restoration ecology (the science of restoration) and ecological restoration (the practice and implementation of restoration), though these two fields are usually discussed hand-in-hand. Perring et al. attempt the ambitious task of reviewing the development of restoration ecology over the past 30+ years, and of looking to the future to highlight ongoing challenges and pressing questions for restoration ecologists. This is an ambitious and comprehensive effort that synthesizes both important conceptual and theoretical advances as well as practical issues. The authors focus exclusively on the restoration of plant communities in terrestrial ecosystems, understandably because this reflects both the development of the field and the authors’ expertise. Here, I would like to briefly consider how well the ideas in this paper apply to the restoration of freshwater ecosystems.
The guiding principles of restoration practice apply equally to terrestrial, freshwater and marine systems:
- the need for clear articulation of restoration goals before undertaking any action,
- a growing appreciation of “novel ecosystems” and the challenges associated with restoring some ecosystems to historical states,
- and the need for careful assessment of societal benefits that might be derived from restoration projects.
Indeed, many of the conceptual advances reviewed by Perring et al. apply across ecosystem types. Implementing these ideas effectively is the key challenge of ecological restoration, and Perring et al. argue that this will require “solid ecological foundations on which to build restoration practice.”
What are the conceptual foundations of restoration ecology, and are they different for freshwater and terrestrial systems? Perring et al. give, as Table 1 (p. 5), a list of ecological concepts that are applicable to restoration practice. Many of these concepts are applicable to most ecosystem types. For example, ideas from disturbance ecology inform restoration projects in both terrestrial and freshwater systems (e.g., an important restoration goal in rivers is often to move towards a more historical or natural flow regime, a flow regime which constitutes a disturbance regime to which resident organisms are adapted). Emerging concepts related to alternative stable states and ecosystem resilience are also applicable to freshwater systems. Other ideas emphasized by Perrin et al., for example ideas of succession, seem to have less application to freshwater systems.
The idea of managing for ecosystem resilience is particularly compelling. In an editorial entitled “Rivers of the Anthropocene?” LeRoy Poff argues that managing ecosystems for resilience to anticipated and ongoing environmental change is a key guiding principle for the practice of ecological restoration. Future climate change and continued changes in land cover and land use will alter the large-scale hydrological cycles that drive river flows. A key consequence is “shifting baselines:” the idea that historical river conditions may not be a feasible restoration goal given the large-scale changes that have occurred and will continue to occur in the upstream watershed. This idea of shifting baselines is closely linked with the idea of “novel ecosystems,” i.e. ecosystems that are outside of historical reference conditions and without a historical precedent. For these ecosystems, restoration to some historical condition may not be feasible given available resources. Restoration ecologists can recognize that restoration towards some historical baseline may not be possible, but it may still be possible to manage ecosystems to maximize resilience in the face anticipated future environmental changes.
Many of these same ideas are presented in the Perring et al. synthesis. As recently as 30 years ago, Perring et al. point out, the goal for many restoration projects was “hastening a return to the pre-disturbance equilibrium state.” Most contemporary practitioners have a greater appreciation for “novel ecosystems” and the difficulty of attempting to move current ecosystems towards some historical baseline. As a result, restoration goals and practice are often informed by an appreciation for the many complex and longstanding inter-relationships between human societies, ecosystems and global change. So, another example of concepts of the Anthropocene influencing the practice of conservation on the ground!