Effects of herbivory on arrowgrass: Interactions between geese, neighboring plants, and abiotic factors
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Authors: C. P. H. Mulder, and R. W. Ruess
Date: 1998
Journal: Ecological Monographs
Volume: 68
Number: 2
Pages: 275-293
Summary of Methods: The direct and indirect effects of herbivory by Brant geese (Branta bernicla nigricans) including selective foraging on growth, abundance, and distribution of arrowgrass (Triglochin palustris), in a subarctic salt marsh near Tutakoke River Black Brant were investigated in June and July for two years on the Yukon-Kuskokwim Delta, Alaska (61° 5' N, 165° 30' W). Three individual experiments (grazing, clipping, and gosling) were conducted. The grazing experiment had three treatments (exclosure-no grazing, fecal removal, and control). The clipping experiment had three levels of feces deposition (none, single load, and double load), two levels of arrowgrass clipping (not clip and clipped), and two levels of neighbor clipping (not clipped and clipped). In the gosling experiment, hand-reared goslings were placed on pre-manipulated plots from the clipping experiment for 28 minutes of active feeding or searching for food. Treatments were applied 4 times in the first year and 3 times during the second year.
Article Summary / Main Points: Arrowgrass was negatively affected in both the clipping and grazing experiments due to increased feces deposition and limited light availability caused by neighboring plants in the clipping trial. In the grazing experiment individual arrowgrass plant vigor was negatively impacted biomass and percent cover by the increase in grazing pressure and competition from other species (Potentilla egedei, Chrysanthemum arcticum, Carex spp., Salix spp.). Feces deposition reduced bulb mass, percent biomass in bulbs and roots and increased percent biomass in leaves of unclipped plants and no had effect on leaf biomass of clipped plants. Unclipped arrowgrass root and stolon mass increased when neighbors were clipped. Vegetative reproduction of clipped and unclipped arrowgrass plants increased when neighbors were clipped, but was not affected when neighbors were unclipped with feces deposition. Plants were larger in exclosures and had higher C and N concentrations than plant outside the exclosure. As percent cover and biomass of neighboring species increased the probably of an individual arrowgrass plant to be grazed decreased.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: 238 Yukon-Kuskokwin Coastal Plain
Agrovoc Control Words: Riparian zones Grazing Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: alaska, associational resistance, biomass allocation, brant geese, branta bernicla nigricans, selective herbivory, stoloniferous perennial, subarctic salt marsh, triglochin palustris, vegetative reproduction
Annotation: The results of this replicated, two-year study are applicable to salt marsh areas with arrowgrass. As is true for all grazing research, the results are most directly applicable to areas with similar landscapes, species, level and season of use, and weather conditions. There is very limited little applicability to most rangeland grazing scenarios. These results do illustrated the complexity of interactions between geese, neighboring plants and abiotic factors in subarctic salt marsh and their effects on establishment and growth of individual marsh plants. Mulder and Ruess (1998, Can J Bot 76:2164-2176) found that as size increased (bulb size) so did survival and vegetative reproduction of arrowgrass following goose herbivory. In 2001, Mulder and Ruess (J Ecol, 89:406-417) used a cellular automata model to predict the long-term effects of goose grazing on arrowgrass communities and found both large- and small-scale grazing behavior is needed to accurately predict the effects of grazing. Both of these articles are available in the RSIS database.
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