Setting restoration targets : how specific should they be?

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In a recent paper published in the journal Wetlands, Diane De Steven and her colleagues present a 5 year restoration experiment where they tried to pilot restored coastal depressional wetlands in South Carolina to either herbaceous wetlands or wet forests. They failed!

Well, they didn’t fail overall. In fact, they generate a whole suite of restored wetlands that are well within the range of preserved wetlands in the region in terms of hydrology and plant communities. What they failed to do was to correctly predict which one of the 16 wetlands they restored would (likely) evolve into either a herbaceous wetland or a wet forest. This is because they could not predict the restored hydrology of each wetland (restored by plugging drains) which is the main determinant of tree establishment, ahead of planting tree seedlings into the wetlands targeted to become wet forests.

Diane De Steven and her colleagues draw several conclusions from this outcome :

  • There are high stakes in evaluating ecological restoration success in wetlands because of the requirements for mitigating wetland losses
  • Restoration success is rarely a simple yes / no outcome
  • Specifying, in advance, a specific plant community as a target for restoration ignores the variability of ecological (and community) dynamics and under-appreciates the multiple possible states of natural wetlands
  • More flexible restoration targets, based on a spectrum of reference communities (“natural” or otherwise) is more fitting to an adaptative management approach to restoration.
  • The spectrum could be defined in terms of wetland functioning, plant communities or even functional groups or functional traits (thereby recognizing that different plant assemblages can provide similar functions).
  • These are interesting ideas to keep in mind when discussing restoration (of course!) but also in designing assessment methods for wetland mitigation : with which metrics and against which targets should losses and gains in wetland condition be assessed?

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