Disciplinary perspectives on timescales of ecosystem formation, degradation, and recovery in wetlands in drylands: What is the natural reference state?

Michael Grenfell

Publication Date:

One of the defining characteristics of southern African wetlands is the limited to non-existent imprint of recent Quaternary glaciation, such that these systems have much longer morphodynamic histories than those in cool-humid regions. This complicates the definition and assessment of a wetland present ecological state (PES), which serves as a measure of ecosystem degradation relative to some definition of the natural reference conditions. It is argued here that the underlying assumptions inherent in defining natural reference conditions and assessing PES differ by discipline, primarily due to differences in the appreciation and conceptualisation of time. The introduction of deeper-time concepts into an assessment of PES may be viewed as an inconvenience for assessors of ecosystem components that measure controls over short timescales (e.g. hydrology, physico-chemistry), but it is sacrosanct to geomorphologists. For geomorphology, more so than for any other component, the evaluation of natural reference conditions is complicated by the dimensionality of geomorphic investigation (a nested hierarchy of 3D space and time); geomorphologists are compelled to recognise that their subject of study is a product of both the recent and long-distant (geological) past. As such, the PES cannot be evaluated apart from this context. This paper presents a meta-analysis of timescales and rates of wetland morphological change extracted from a large body of literature on southern African wetlands to interrogate the idea of a natural reference state, and to provide a framework through which the value of such context may be better demonstrated to multi-disciplinary teams working on wetland restoration activities.

Resource Type:
Audio/Video, Conference Presentation, SER2019

Pre-approved for CECs under SER's CERP program

Society for Ecological Restoration