Principles of ecological restoration include climate-adjusted provenancing
Written by Matt Brincka and Eve Beaury, edited by Bethany Bradley
Summary
Due to climate change, many restoration practitioners are already relaxing the traditional approach of sourcing seeds or plants from areas near the restoration site (local provenancing; Prober et al. 2016) . Unfortunately, the degree to which species are locally adapted is likely highly variable depending on species, populations, and habitat. Moreover, in some areas local adaptation may no longer be desirable with climate change. Therefore, restoration actions that seek to increase gene flow and genetic diversity may be paramount for the persistence of some species or populations (e.g., Millar et al. 2007). But when and where to use, or not use, different strategies to increase genetic diversity still remains an open question. Gann et al. (2019) discuss cases when assisted gene flow (sourcing plant material from warmer regions in anticipation of climate change) may be more or less effective, depending on the characteristics of the restoration site and the population structure of the focal plant species.
Local provenancing may still support ecological resilience in large, intact habitats or when restoring with species that have high genetic diversity, long-distance gene flow, and naturally high reproductive and dispersal capabilities. Local provenancing is less likely to support ecological resilience in degraded or fragmented landscapes and where local populations have low genetic diversity (i.e., leading to inbreeding depression) thus reducing the potential for populations to adapt to change. Low genetic diversity could also lead to increased vulnerability to climate change if populations are adapted to historical, cooler climate conditions, and thus are maladapted to climate change.
Local provenancing is unlikely to be successful in areas experiencing rapid climate change and in degraded or fragmented landscapes with low gene flow. In these cases, Gann et al. (2019) suggest collecting plant material from longer distances and including multiple sources in warmer climates (termed ‘climate-adjusted provenancing’; Prober et al. 2016) in order to introduce the genetic diversity needed to build climate resilience. One risk to be aware of with climate-adjusted provenancing is sourcing material from too many populations that are far away from the restoration site. This approach risks outbreeding depression, where breeding between individuals from populations that are too different results in a loss of fitness. This suggests a trade-off in seed provenancing strategies: collecting from multiple sites, including those adapted to future climates, can facilitate species persistence under climate change and can reduce inbreeding depression, but collecting from too many far-away sites risks losing fitness in restoration candidates via outbreeding depression. Gann et al. (2019) recommend 1) using site and species characteristics to select the best provenancing strategy, and 2) recognizing that the ‘reference’ ecosystem (i.e. historical species composition) may no longer be relevant with climate change.
Take home points
The landscape context of the restoration project, and the population dynamics of the candidate species, can help inform which seed provenancing strategy will be most effective.
Current restoration standards recommend incorporating climate change by decreasing reliance on ‘reference’ ecological conditions and potentially incorporating warm-adapted species and genotypes.
Management implications
Local provenancing is likely most effective when restoration sites are large and continuous, are buffered from climate change, and when restoration species have high genetic diversity or high gene flow.
Climate-adjusted provenancing is likely most effective when restoration sites are patchy or degraded, impacted by climate change, and when restoration species have low genetic diversity or low gene flow.
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Keywords: Climate-smart restoration, assisted migration, assisted gene flow, climate adjusted provenancing, forest, managed relocation, plants, restoration