Posts Tagged ‘Wetlands’

The Tolstoy effect

Sunday, December 12th, 2010

In Anna Karenina, Tolstoy reminds us that “happy families are all alike” while “every unhappy family is unhappy in its own way”.

Emilie Stander and Joan Ehrenfeld concluded that the same was true for wetlands. They studied the functioning of wetlands used as (supposedly “pristine”) reference wetlands for wetland mitigation in New Jersey (USA) and found that in this heavily urbanized setting, even reference wetlands were “unhappy”… (pdf here)

This raises issues for using typologies of wetlands in the assessment of wetland states (as in the context of wetland mitigation in the USA).

Identifying reference wetlands on the basis of standard structural indicators is misleading when wetlands are in heavily modified landscapes and watersheds. They suggest that instead, multi-year data on functioning should be used to create appropriate typologies of wetland functioning.

A further step would be to use “theoretical” references for assessing wetland state but this would most likely make in-the-field assessment more difficult.

Setting restoration targets : how specific should they be?

Tuesday, December 7th, 2010

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?