Forest Investment Account (FIA) - Forest Science Program
FIA Project Y103232

    Effects of livestock grazing in southern interior wetlands: interactions with amphibians, benthic macroinvertebrates, vegetation, and breeding waterfowl
Project lead: Lauchlan Fraser (Thompson Rivers University)
Author: Thorne, Susan
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Livestock grazing can be a significant human stressor on wetlands. In regions with widespread livestock use, such as the southern interior of BC, understanding how grazing pressure affects wetland function is crucial to effective wetland management. Wetlands in the Thompson-Okanagan and the Chilcotin-Cariboo are important habitat for migratory birds, but they are also recognized for their natural forage production by the cattle industry. British Columbia produces approximately 5% of Canada’s beef cattle, a disproportionate share in relation to B.C.’s human population, and half of B.C.’s beef cattle are produced in the southern interior (20). In addition, it has been estimated that approximately one-half of the grazed forage and stored winter feed is produced on wetlands in this region (20).

Southern Interior wetlands occur primarily within a landscape mosaic of forests and grasslands. Wetlands provide numerous environmental and economic benefits, including wildlife habitat, regulation of water regimes, filtration of polluted water, and production of forage crops (13). The importance of these benefits, especially in semiarid regions, is disproportionate to the extent of wetlands on the landscape. Given the amount of wetland losses over the past century, the importance of remaining wetlands has become even more critical. Previous research has shown that grazing can affect the structure and function of wetland ecosystems. Grazing can alter wetland water quality, biodiversity, and productivity directly, through removal of biomass, soil compaction and trampling, and nutrient inputs, as well as indirectly by changing plant competitive interactions through selective herbivory and nutrient loading (5,8,11,12,15,17). Grazing influences on some taxa, such as waterfowl, may be primarily mediated through changes to vegetation or invertebrates that alter their habitat and food webs. Maintaining the biodiversity and productivity of wetlands (and thereby sustaining their habitat and forage production values) requires understanding how grazing influences these complex interactions.

We had originally proposed two research components for this project: evaluating the effects of grazing on wetland-associated biota by sampling environmentally similar wetlands along an existing grazing disturbance gradient, and monitoring four heavily grazed wetlands over time to evaluate the effects of fencing and offsite water development, singly and in combination, on the recovery of wetland-associated biota (aquatic invertebrates, amphibians, and vegetation) and water quality. Rather than construct new fences, we found that the effects of fencing can be more efficiently evaluated within the framework of our existing field experiment, which includes several fully- and partially-fenced wetlands. In addition, we would like to expand this aspect of the research to explore more directly the mechanisms through which livestock affect wetland biota.

We propose manipulating water level, defoliation, and soil compaction to evaluate the effects of these variables on wetland plant communities in experimental mesocosms. A controlled experiment will allow for greater causal inference of treatments, and using mesocosms will allow us to evaluate effects on plant communities instead of individual species. This will give greater applicability of the results to real wetland systems. Livestock grazing is a complex disturbance that combines herbivory, soil compaction, and nutrient inputs. By partitioning and directly manipulating simulated herbivory and compaction, we hope to better understand the relative contribution of these factors to overall grazing disturbance. Although these effects are obviously inseparable in the field, understanding their effects and relative importance will increase our understanding of how grazing influences vegetation community diversity, stability, and invasibility. This, in turn, will have practical applications for wetland restoration and management.

Other goals of this research are to identify the natural range of variability of response variables associated with minimally disturbed wetlands and to identify thresholds of biotic and physical variables associated with grazing disturbance.

This proposal requests funds to expand an existing multiyear research project funded by Ducks Unlimited Canada (Western Region and the Institute for Wetland and Waterfowl Research). In the first year of the project (2006), we measured vegetation communities and waterfowl use, primarily, and preliminary results show a very strong response of vegetation structure and composition to grazing intensity, including the reduction of biomass, increase in the abundance of weedy species, and decrease in the abundance of tall emergent wetland plants. In turn, vegetation attributes, such as aboveground biomass and the abundance of tall emergent species, were associated with the density of waterfowl breeding pairs and broods. Funds requested from the FIA-FSP would allow us to fully support a PhD student to run the vegetation, amphibian, waterfowl and landscape project, and add a MSc student to incorporate the collection and analysis of the benthic macroinvertebrate community. In addition, FIA-FSP funds would support a manipulative experimental component – riparian fencing to selected cattle ponds. This will enable greater inference about grazing pressure to wetland ecosystems. The results of this research will inform livestock management options regarding wetlands and will better allow provincial and private managers to balance forage production with other wetland values.

*Numbers in parentheses are references, which are listed in uploaded file: ‘FSP Y103232 Continuing Workplan References’.
Related projects:  FSP_Y081232FSP_Y092232


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Updated August 16, 2010 

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