A primer on choosing goals and indicators to evaluate ecological restoration success

Abstract

We discuss aspects of one of the most important issues in ecological restoration: how to evaluate restoration success. This first requires clearly stated and justified restoration goals and targets; this may seem “obvious” but in our experience, this step is often elided. Indicators or proxy variables are the typical vehicle for monitoring; these must be justified in the context of goals and targets and ultimately compared against those to allow for an evaluation of outcome (e.g. success or failure). The monitoring phase is critical in that a project must consider how the monitoring frequency and overall design will allow the postrestoration trajectories of indicators to be analyzed. This allows for real‐time management adjustments—adaptive management (sensu lato)—to be implemented if the trajectories are diverging from the targets. However, as there may be large variation in early postrestoration stages or complicated (nonlinear) trajectory, caution is needed before committing to management adjustments. Ideally, there is not only a goal and target but also a model of the expected trajectory—that only can occur if there are sufficient data and enough knowledge about the ecosystem or site being restored. With so many possible decision points, we focus readers' attention on one critical step—how to choose indicators. We distinguish generalizable and specific indicators which can be qualitative, semiquantitative, or quantitative. The generalizable indicators can be used for meta‐analyses. There are many options of indicators but making them more uniform would help mutual comparisons among restoration projects.

Three Invasive Tree Species Change Soil Chemistry in Guam Forests

“…Third, restoration projects vary in the form of interventions from passive approaches to full-scale reclamation approaches [54], and the integration of habitat restoration and species-targeted conservation may take on many forms [55]. One annoying issue with conservation and restoration programs is how to select the goals and indicators that meaningfully prove success [56]. When projects are funded with public funds, taxpayers need to know that the best available science is employed to define success.…”

Harnessing knowledge of animal behavior to improve habitat restoration outcomes

“…Behavioral knowledge can help inform all of the three broad phases of restoration (i.e., planning, doing, and evaluating; Prach et al 2019). During planning, knowledge of behavior can help identify which habitat elements should be targeted.…”

“…We can use behavioral information, in particular knowledge of the habitat elements that are either used as cues or determine fitness, to select sites to restore (i.e., in the doing phase; Prach et al 2019). Sites can be targeted that have some of these elements already, so restoration focuses on supplementing these, which may be more cost-effective than rebuilding much degraded habitats.…”

“…Restoration is an iterative process that involves periods of assessment of success, often within an adaptive management framework (Holling 1978, Prach et al 2019. For simplicity, our decision tool presents information as a linear process.…”

“…For each step, we outline reasons why restoration can fail (Fig. 2 S1-S5) and suggest solutions, building on previous studies that have described the steps in successful restoration (Bond and Lake 2003b, Miller and Hobbs 2007, Hale and Swearer 2017, Prach et al 2019. While the structure of our decision tree is reactive in that we identify causes for failure and we propose solutions, the information we highlight about habitat selection and its consequences should also guide the design of restoration projects (i.e., in steps 1 and 2 in Fig.…”