Growth responses of arctic graminoids following grazing by captive lesser snow geese

Abstract

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0-180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.

Normalized Difference Vegetation Index as an Estimator for Abundance and Quality of Avian Herbivore Forage in Arctic Alaska

“…While local factors like soil properties can affect plot-scale biomass measurements [66], they may have little influence on seasonal nitrogen accumulation. In particular, localized grazing pressure could reduce the standing crop and therefore the NDVI value of any plot, yet previous research suggests that the effect of grazing on tissue nitrogen content in halophytic grazing wetlands is minimal for most of the growing season [67,68].…”

Global net primary production: Combining ecology and remote sensing

“…Herbivory by vertebrates or invertebrates leads to increased plant growth in some cases (McNaughton, 1976) but unchanged (Zellner et al, 1993) or decreased NPP in others (Pastor et al, 1993). Effects of animals on NPP result not only from direct effects of herbivory, but also from the role of animals in regulating plant community composition, through impacts on pollination, seed dispersal, and trampling.…”

The effects of simulated spring goose grazing on the growth rate and protein content of Phleum pratense leaves

“…Central to the concept of plant-herbivore interactions is the question of whether the physical removal of above-ground green material stimulates growth, so that plant production of grazed plants exceeds that of ungrazed plants (McNaughton 1979;termed``over-compensation'' by Belsky 1986;Milchaunas and Lauenroth 1993). In the study of the eects of grazing of monocotyledous plants by arctic geese, overcompensation has been found in some situations (Cargill and Jeeries 1984;Jeeries 1987, 1989;Bazely and Jeeries 1989) explained in some circumstances by enhanced nutrient availability from deposition of goose faeces (Bazely and Jeeries 1985;Hik et al 1991) but not in others (Kotanen and Jeeries 1989;Zellmer et al 1993;Gauthier et al 1995). In addition, there is evidence that grazed graminoids have signi®cantly higher nitrogen concentrations than ungrazed plants (Dyer and Bokhari 1976;Mattson 1980;Cargill and Jeeries 1984;Gauthier et al 1995).…”