Researchers assess impact of livestock use on intermountain wetlands, vegetation, biodiversity and waterfowl.
In the intermountain west and prairie pothole regions, freshwater depressional wetlands are dispersed throughout rangelands. These wetlands are very important for forage production, seasonal flooding, water quality management and wildlife habitat, especially for breeding waterfowl and amphibians. Researchers at the Thompson Rivers University in Kamploops BC wanted to better understand the effects of livestock grazing on freshwater wetlands in the southern interior of the province. In riparian and wetland areas, cattle can cause disturbance by forage removal, trampling, soil compaction and altering microtopography and soil nutrient status.
“We started this project about nine years ago, building on ongoing research work by Ducks Unlimited Canada and the Canadian Wildlife Service,” explains Dr. Lauchlan Fraser, Professor and Canada Research Chair in Community and Ecosystem Ecology. “They had been monitoring hundreds of ponds in BC across the province for over 20 years, counting pairs of breeding birds. We designed this project to add another layer of information to this valuable set of long term data.”
Of the many ponds monitored, Fraser selected 36 for the project that spanned a range of cattle use from heavily grazed to excluded. The objectives were to determine how grazing affects vegetation, breeding and brooding waterfowl and biodiversity in the marsh and wet meadow zones. Fraser notes that understanding how grazing affects vegetation is an important step in determining tradeoffs between the ecological and economic services of wetlands and maintaining their biodiversity and productivity.
An ecosystem approach was used for the research, assessing differences in vegetation in the marsh and wet meadow zones, surveying aquatic invertebrates and counting breeding and brooding pairs. “Counting breeding pairs is a good indicator, but counting brooding pairs as well provides more information about the ongoing productivity of the wetland for raising the young in the pond,” says Fraser. “It is a little trickier and takes more effort to track brooding pairs and requires multiple trips back to the research sites.” Field research and innovative computer modelling were used in the project.
Researchers have finished collecting information for the study, but are still in the process of analyzing the results. “Generally we did find that there does seem to be a relationship with cattle use and some of the parameters of these wetland systems,” explains Fraser. “The vegetation diversity and quality was strongly associated with grazing intensity. Increased livestock grazing showed a reduction of biomass, an increase in the abundance of weedy species, and a decrease in the abundance of tall emergent wetland plants. The grazing effects were greater in the marsh than in the wet meadow areas.”
As well, the density of waterfowl breeding pairs and broods were affected by the aboveground biomass and the abundance of tall emergent species. Results showed a general pattern that breeding bird pairs decline with increased cattle use. Livestock grazing also impacted the population of aquatic invertebrates, which provide food for waterfowl, amphibians and other wildlife.
Management Strategies for Grazing, Waterfowl and Biodiversity
“Our recommendation is not necessarily that cattle be excluded from the entire wetland, but we think that efforts to protect important parts of wetlands and these depressional ponds is important,” says Fraser. “Our results show a strong relationship between vegetation cover and macro invertebrates in the ponds. If we can protect certain areas and enough area of a wetland that it can provide food sources for waterflow, then there can be synergy between grazing and wetlands. Low intensity grazing is much more likely to be compatible with the management of these wetlands for conservation values. However, further work is needed to link the observed grazing intensity gradient with stocking rates and seasonality of livestock use.”
Other research has shown that cattle will use a designated access point to a pond if it is easily accessible and erosion resistant, without having to fence off the area. Providing offsite watering and ensuring access to good quality upland grazing areas are other options to reduce the impacts of cattle on riparian areas and ponds. Minimizing trails and roads near these areas is also important. Where practical, fencing of sensitive areas may be an option, either with temporary electric fencing or permanent fencing.
“We are also working on a project that is looking at transferring some of our research results using constructed wetlands for the treatment of water to the treatment of these ponds in rangelands,” says Fraser. “Certain wetland plants are more efficient at reducing nutrient loads than other plants, so we may be able to design areas of these wetlands, such as outflow areas, to filter water quality.”
Fraser is also looking at other related projects including the impact of climate change and other factors on wetlands. “Over the past decade the water levels in many of these depressional wetlands have been declining, probably as a result of changing precipitation levels and groundwater issues,” explains Fraser. “Lowered water levels will not only constrict wetland plant communities, it will potentially change aquatic and soil salt concentrations. We are looking at whether these shifts in salinity will impact the plant community structure and the forage opportunities for livestock and wildlife.”
“Maintaining the biodiversity and productivity of wetlands, which will also sustain their habitat and forage production value, requires understanding how grazing influences these complex interactions,” says Dr. Lauchlan Fraser.
Dr. Lauchlan Fraser
http://www.env.gov.bc.ca/wld/documents/bmp/wetlandways2009/Wetland Ways Ch 3 Agriculture.pdf- 2437.7KB