CAS Workshop on Ecosystem Succession Theory and Practice of Ecological Restoration 

 Abstract: Succession theory, as the basis for prediction of wetland restoration, plays an important role in wetland restoration ecology.  Indeed, ecological restoration has been considered as acceleration of succession.  Wetlands have been fertile ground for studies of ecological succession over the last century.  Most of these empirical studies on community dynamics in wetlands yield evidences that are considered in support of the Gleasonian and not the Clementsian succession theory.  The contrasting views of the Clementsian and Gleasonian also have been involved often in the discussion of the theories of ecological restoration.  This paper attempts to examine the linkage between historical succession theories and current schools of thoughts in wetland restoration ecology and discuss the need and directions to broaden the theoretical framework for the development of wetland restoration ecology.

There have been two major schools of thoughts on wetland restoration ecology, self-design vs. designer-design.  The self-design approach takes more an ecosystem approach and emphasize that the nature of the environment (including the disturbance regimes) and the ecosystem processes dictates the composition and spatial pattern of plants in wetlands. Self-designers question the necessity and long-term effectiveness of the human intervention of designed planting in hydrologically open wetland systems and believe plant species will be sort out spatially when prorogues are available. They stress that the development of ecosystem functions may take considerable time and human intervention can help accelerate their development.  The designer-design approach takes more a reductionist, population-level approach and emphasizes the importance of designed planting based on sound understanding of life history attributes of the species involved.  Designer proponents believe, because the lack of sufficient seed bank and limited dispersal, as well as the strong influence of initial floristic composition in many cases, human intervention is critical in determine the eventual outcome of restored wetlands. 

Some scholars have argued that the self-design and designer theories are simply restatements of the Clementsian and Gleasonian succession theories.  This characterization, however, is not quite accurate.  Although influenced by Odum’s ecosystem ecology, the self-design theory does not include some of the basic elements of Clementsian theory, such as a predictable, orderly process toward a stable climatic climax.  Its strong emphasis on the role of the physical environment and disturbance regime in sorting the composition and spatial distribution of species actually appears more Gleasonian than Clementsian.  The emphasis of the designer approach on population-level processes as mechanisms of community dynamics is Gleasonian and is essential to the understanding and development of wetland restoration.  Gleasonian emphasis on the role of chance events, however, can be for or against the key element of designer theory, designed planting; planting can prevent the development of unwanted structure due to chance event such as preemption of undesirable species, but the long-term effects of planting can be reduced or overridden by disturbances that are stochastic in nature.

The different emphases of the self-design and designer theories are influenced to a degree by different goals of wetland restoration, self-design tends to focus more on ecosystem function and less on biodiversity than designer.  The goal setting of self-design tends to focus on longer temporal scale than that of designer as well.  Experiences with different wetland ecosystem of the proponents of the two theories may have also played a role.  The designer thoughts are strongly linked to studies of prairie potholes where seed bank is a key element of the wetland dynamics and dispersal is often limited in the agriculture landscape with low connectivity among wetlands.  The self-design thoughts are strongly linked to studies of hydrologically open wetlands such as riparian systems where availability and dispersal of prorogues are not limiting.

Neither self-design nor designer theory appears have expanded sufficiently beyond the traditional succession theories and explicitly incorporated some of the contemporary views of vegetation dynamics.  A more comprehensive conceptual framework that integrates key elements of both self-design and designer theories and explicitly anchors on contemporary theories of vegetation dynamics is needed for the development of wetland restoration ecology.  Several theoretical issues key to the development of wetland restoration ecology include the following.  (1) Adopt the view that continuous change in vegetation is the norm (similar to Cowles’ view of succession) and that multiple steady states exist in ecosystem dynamics.  This may require fundamental modifications of our concepts of reference conditions (e.g., multiple reference states and contingency/redundancy) and restoration designs.  (2) Explicitly address spatial and temporal scales of disturbance regimes and the development of different ecosystem structures and functions.  Development of some ecosystem attributes, such as soil development and nutrient cycle, are critical factors influencing community development but can take considerable amount of time.  This may not only affect expected timeframe for restoration but also the specificity of goals of restoration given the stochastic nature of disturbances events and other long-term (e.g., climatic) changes.  (3) Emphasize the landscape context for wetland restoration.  More than those in other areas of ecological restoration, wetland restorationists appreciate the importance of landscape context likely due to their awareness of the inherently critical importance of hydrologic regimes and plant dispersal to wetland restoration; a stronger emphasis, however, is the need on quantitative assessment of landscape setting and dynamics and their influence to the dynamics and long-term fate of restored wetlands, as well as the expected distribution and function of the wetlands in the watershed.  (4) Recognize the potential limitations of succession theories and empirical knowledge for restoration applications because the significant differences between restoration and natural succession.  Restoration starts with an unnatural setting with often sudden changes in the environmental conditions and artificially synchronized introduction of vegetation, which likely invoke spatial and temporal patterns of interactions and processes different from those operate in natural succession; in addition, some of the basic processes, such as hydrology/flooding regime in urbanized watersheds, have been fundamentally altered by human disturbances, which may result in novel settings that can induce new patterns and mechanisms of ecosystem dynamics.  (5) Promote the incorporation of large-scale experiments into restoration projects.  This may allow testing and developing new succession and restoration theories, which is essential to the development of the science and practice of restoration ecology.

Key words: wetland restoration ecology; succession theory; self-design vs.designer-design

Affiliation Links
©1988-2002, All rights reserved by Sino-Eco.  Last modified at 11/20/02  Web Statistics