The interactive effects of fire and herbivory on a coastal marsh in Louisiana

Abstract

Both vertebrate herbivores and fire have long been known to have dramatic and important effects on wetland vegetation. However, the interactive effects of burning and herbivory have received less attention. In this study, conducted in the coastal marshes of the Pearl River Basin in Louisiana, USA, both the effects of herbivory and fire as well as the interaction between these effects were examined in three marsh community types: Sagittaria lancifolia, Panicum virgatum, and Spartina patens. At five sites for each of the three cc~mmunity types, the effects of burning and fencing to exclude herbivores were determined over two years.Results showed that total biomass was reduced by burning but increased by fencing, with no interactive effects on total biomass. Species density (the number of species per unit area) was enhanced in plots that were both burned and fenced. Spartina patens was an important component in all three communities. Cover estimates indicated that S. patens responded to burning and fencing differently from the other dominant species. In the Panicum virgatum community, P. virgatum cover was enhanced by burning and fencing while S. patens cover was reduced. In the Sagittaria lancifolia community, S. lancifolia and Vigna luteola were enhanced by burning and fencing while S. patens was reduced. In the S. patens community, Scirpus americanus was enhanced by fencing, but burning had no significant effect on cover of either dominant species. These and other data are generally consistent with the hypothesis that herbivory favors S. patens while burning favors other dominant species. Thus, the relative effects of fire and herbivory have an influence (along with other factors such as salinity) on the dominance of S. patens in coastal marshes.

The effects of landscape position on plant species density: Evidence of past environmental effects in a coastal wetland

“…Experimental studies of the effects of salinity on marsh plants indicate that effects on plant communities are driven by both long-term average effects and short-term extreme events (Grace & Ford, 1996;Howard & Mendelssohn, 1998. Previous studies of the relationship between salinity regimes and plant communities provide support for the hypothesis that periodic saltwater intrusions produced by storms act to leave lasting effects on the plant communities (McKee & Mendelssohn, 1989;Brewer & Grace, 1990;Taylor, Grace & Marx, 1997;Ford & Grace, 1998b). Typically, saltwater pulses act both as stresses for plant growth and as a filter for the elimination of intolerant species, with characteristic reductions in species diversity (Howard, 1995).…”

Recovery of a northern New England salt marsh plant community from winter icing

“…Many of these physical factors can strongly affect the ability of species to colonize and/or survive in a given habitat (Bertness et al 1992;Bertness and Shumway 1993). Salt marsh disturbances (e.g., terrestrial runoff, wrack, ice, deposition of sand and mud, herbivory and even fire), commonly act over a number of spatial scales, affecting a number of different species within a marsh (Miller and Egler 1950;Bertness and Ellison 1987;Hik et al 1992;Ford and Grace 1998;Pennings and Bertness 2001). Many of these disturbances, such as sand deposition from storm overwash and grazing by waterfowl may also require amelioration of harsh abiotic factors in order for recovery to occur (Smith and Odum 1981;Jefferies 1988;Hik et al 1992;Gough and Grace 1998).…”

Effects of prescribed burning on marsh-elevation change and the risk of wetland loss

“…Biological agents that damage or remove vegetation include grazers such as geese, nutria, muskrat, and snails (Gauthier and others, 1995;Ford and Grace, 1998;Silliman and others, 2005). Physical processes include sediment or wrack burial, erosion or scouring, and fire (Guntenspergen and others, 1995;Nyman and Chabreck, 1995).…”

“…Prescribed burning is a common management practice used in coastal marshes to reduce hazardous buildup of fuel, enhance wildlife habitat or food sources, and promote rare or endangered species (Nyman and Chabreck, 1995). Burning may stimulate marsh productivity through release of nutrients or may alternatively cause a net loss of organic matter through direct combustion of peat and/or a change in the species composition or plant tissue chemistry, which affects community production or decomposition rates (Hackney and De La Cruz, 1977;Schmalzer and others, 1991;Nyman and Chabreck, 1995;Ford and Grace, 1998;Gabrey and Afton, 2001;Smith and others, 2001;Ponzio and others, 2004). Burning not only removes aboveground biomass but may also remove upper layers of peat that may have accumulated over long periods of time (Nyman and Chabreck 1995).…”