The Twin Limit Marsh Model: A Non-equilibrium Approach to Predicting Marsh Vegetation on Shorelines and in Floodplains
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APPLIED WETLAND SCIENCE
The Twin Limit Marsh Model: A Non-equilibrium Approach to Predicting Marsh Vegetation on Shorelines and in Floodplains Paul A. Keddy 1 & Daniel Campbell 2 Received: 12 April 2019 / Accepted: 20 September 2019 # Society of Wetland Scientists 2019
Abstract Vast areas of wetland occur on shorelines of ponds, lakes, and rivers. These wetlands are divided into vegetation zones, including aquatic vegetation, marsh, and swamp. Here, we provide a simple, mechanistic, and non-equilibrium model that explains the occurrence of marsh as a function of past flood pulses. Marshes are sandwiched between two limits, both of which fluctuate with time. The lower limit is set by the tolerance of marsh plants to continuous flooding. The upper limit is set by competion with woody plants, which are killed by extreme high water events. The twin limit marsh model (TLMM) requires long-term waterlevel records and two biological inputs: duration of flooding required to drown marsh plants ( f ) and the duration of dewatering required for woody plants to reinvade once water levels drop (s). In the temperate zone, we suggest that f is ~4 yr and s is ~30 yr. We illustrate the model for the marshes of Lakes Erie and Ontario. High water years that kill woody plants, followed by low water years, produce large expanses of marsh. The regulation of lakes and rivers generally has negative effects on marsh area and diversity. The TLMM can be calibrated for other climates or ecoregions. Keywords Marsh . Shoreline . Floodplain . Flood pulse . Drowning . Succession . Wet meadow . Water-level fluctuations
Introduction The zonation of ecological communities along shoreline elevation gradients is a well-known characteristic of wetlands. For example, the Cowardin classification system (Cowardin et al. 1979) recognizes four vegetation zones along river floodplains: aquatic bed, emergent wetland, scrub/shrub wetland, and forested wetland. It is easy to assume that such zonation is at equilibrium with recent flood duration and controlled simply by the flood tolerance of individual species. Experimental studies, however, show that other biological interactions produce Botanical nomenclature: https://www.itis.gov Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13157-019-01229-9) contains supplementary material, which is available to authorized users. * Paul A. Keddy [email protected] 1
Independent Scholar, 270 Blue Heron Rd, Carleton Place, ON K7C 0C5, Canada
2
Birchbark Environmental Research, 125 Patterson St, Sudbury, ON P3C 2J6, Canada
zonation, and while lower limits of species may be mostly set by flood tolerance, the upper limits of species are determined in part by competition (Grace and Wetzel 1981; Pennings and Callaway 1992; Keddy 2010), particularly from canopyforming woody plants (Keddy and Reznicek 1986). Moreover, the observed vegetation patterns may not be at equilibrium with present conditions but, instead, may be caused by past conditions, with various lag times. For
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