| | Alberta’s Aspen Parkland, which encompasses most of central Alberta, is the breeding grounds for up to two-thirds of the waterfowl in the province. According to recent agriculture census data, this area is also home to approximately 54 percent of all cattle in Alberta.
"Given strong growth in the cattle industry in the Aspen Parkland, Ducks Unlimited needs to understand how we can work with this large landscape level influence," explains Dr. Jonathan Thompson, Senior Biologist with Ducks Unlimited Canada. "We are looking for common ground to work with the grazing community for program delivery." Although the extreme drought conditions the past two years may reverse growth in cattle numbers, experience suggests that a couple of wet years would see the grazing industry in the Aspen Parkland expanding again.
Thompson notes that there is a stark contrast in terms of how ranchers manage their lands in the Aspen Parkland compared to those in the prairies. Prairie ranchers rely primarily on native vegetation and typically manage more from a long-term perspective. In other words, they plan for drought as part of their land management.
"Many parkland ranchers, on the other hand, tend to take a lot of biomass out of their pastures on an annual basis, relying on more reliable precipitation to buffer this high extraction rate," says Thompson. Although there is a range of grazing management practices in the parkland on both native and tame pastures, typical grazing pressure tends to be on the heavy end of the spectrum.
Last year, Thompson initiated two graduate research projects to look at the effects of grazing intensity on upland-nesting duck production and wetland-dependent birds in the Aspen Parkland. To establish grazing intensity, the Robel pole method was used to measure cover height and density. "We’re also using the Alberta Range Assessment procedure so we can translate between our data and what that pasture would look like in terms of a score on the Range Assessment form," says Thompson. This will make it easier to deliver grazing extension programs to parkland ranchers.
These two year studies are being funded by the Institute for Wetland and Waterfowl Research, and the North American Waterfowl Management Plan (NAWMP) partnership in Alberta. "The unexpected drought conditions of the past two years has greatly impacted the number of waterfowl and other wetland-dependent birds nesting in the parkland. However I think we will still end up with good results relative to perhaps the worst case scenario," says Thompson. "In the future, we may conduct similar studies under more average moisture conditions."
The AESA (Alberta Environmentally Sustainable Agriculture) Program staff recently toured the study area to gain a better understanding of grazing management practices and how they relate to Ducks Unlimited management strategies for waterfowl and other wetland dependent birds. "We learned a lot from each other," says Thompson. "One of our greatest opportunities as an organization is to empower those working in extension program delivery so that they can effectively communicate our field-based research results to the grazing community."
AESA staff tour of NAWMP Grazing research site June 2002
Preliminary research results show moderate grazing strategies benefit both grazing managers and birds
Jeff Warren, a graduate student from Montana State University, is leading the grazing project focused on the effects of cattle grazing on upland nesting duck production. Approximately 50 pastures were selected each year of the study. "We’re comparing both nest density (number of nests per acre) and nest success (number of nests successfully hatched) in native and tame pastures grazed at different levels of intensity including lightly, moderately or heavily grazed," explains Warren.
"Preliminary results from last year, and the data we’ve compiled so far this year shows a strong linear trend between nest density and the level of intensity of grazing," says Warren. "As grazing intensity increases, nest density decreases." Although the lightly grazed pastures had the highest density of nests, with five times the number of nests per acre than heavily grazed pastures, it’s the moderately grazed pastures that appear to have the highest nest success. Nest success also differs between native and tame pastures, with higher success in native pastures.
"The moderately grazed pastures are really the well managed pastures that producers try to achieve," says Warren. Moderately grazed pastures actually produce more forage than heavily grazed pastures, which is especially evident during dry years. The litter layer present in moderately grazed pastures helps trap more snow over winter, increases moisture infiltration and reduces soil moisture losses by keeping the soil cool. The same litter cover that benefits a producer’s pasture attracts Mallards and other early nesting duck species each spring.
The second study focuses on the effects of cattle grazing on wetland-dependent birds. Lead by graduate student Robb Stavne from the University of Alberta, this study includes 104 wetlands within the same 50 pastures. "We focused on semi-permanent wetlands ranging from 3 to 10 acres (1 to 4 hectares) in size, equally distributed between low, moderate and heavy grazing intensities in both native and tame pastures," says Stavne. "Within wetland margins, there is complex habitat structure that provides a range of ideal nesting habitat for a variety of birds, everything from sora rails to savannah sparrows."
Preliminary results for nest density and nest success are similar to Warren’s findings. "Based on ‘apparent’ nest success, our preliminary findings show that the highest nest success is on lightly to moderately grazed pastures, whether they are native or tame, with success declining as grazing intensity increases," explains Stavne. "We also conducted a simple amphibian survey to examine the abundance of wood and boreal chorus frogs." Preliminary observations provide evidence that more frogs were present in the lightly grazed pastures, with very few occurring in the heavily grazed areas.
Several species are attracted to the complex habitat of wetlands and conduct their breeding activities there. Cattle also tend to concentrate in these same areas to access water, vegetation or escape the hot sun. "Because wetlands tend to be the first areas to ‘green up’ after the spring melt, cattle tend to go there first, potentially discouraging birds from nesting in the area," says Stavne. Along with their removal of nesting cover, cattle trampling and disturbance can impact bird nesting behavior. Active nests in wetland margins become increasingly vulnerable to predation because of reduced concealment. Using light to moderate grazing management strategies, or where practical, fencing off wetland and riparian areas and providing off-site watering can make a difference in maintaining this habitat for wetland-dependent bird nesting.
"Although preliminary, the results so far are indicating a trend for slightly higher nest success in the moderately grazed areas," says Thompson. This is providing additional support that there is something operating in moderately grazed areas that provide birds with the opportunity to have slightly higher nest success, including waterfowl, shorebirds, song birds and a variety of species. "It also supports what we’ve been trying to point out to producers," says Thompson. "What is likely in their long-term economic interest from a range management standpoint, is likely a level of grazing that can help maintain healthy populations of breeding waterfowl and help general wetland bird communities as well."
For more information, contact:
Dr. Jonathan Thompson
Robb Stavne
Jeff Warren
Alberta Conservation Connection - Issue 18, Fall 2002 |
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