Grasslands

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Grassland health

In addition to direct loss, the remaining grasslands in Canada are under stress. Natural disturbance regimes that historically maintained grasslands have been altered; in particular, the suppression of fire and replacement of free-ranging bison with confined cattle have modified the structure and composition of native grasslands. Also, many of the richest soils have been cultivated,2, 19 leaving remaining grasslands on less productive soils. Other threats to grassland health include invasive non-native species, overgrazing, forest encroachment, continued fragmentation from development, and intensification of agriculture. Overall results from two studies investigating rangeland health in Alberta and Saskatchewan in 2008 showed that 49% were healthy, 8% unhealthy, and 43% healthy with problems.20, 21 In the Okanagan Valley, between 19 and 69% of rangelands were in poor condition in the 1990s.13 In Manitoba, 14% of remnant tallgrass prairie patches were so severely degraded by non-native species between 1987 and 2006 that patches could no longer be recognized as tallgrass prairie. Patch quality declined significantly over the time period and few are likely self-sustaining.5

Canadian grassland birds

Breeding Bird Survey Abundance Index, 1967 to 2006
Graph: abundance of Canadian grassland birds. Click for graphic description (new window).
Long Description for Canadian grassland birds

This line graph shows the trend in breeding grassland bird populations in Canada from 1967 to 2006. Each point represents the annual index of abundance based on all grassland species. While fluctuating slightly annually, the graph shows a significant, steady, steep decline from a peak of 89 on the abundance index in 1969 to a low point of 43 in 2002. Although increasing since 2002 to 50, in 2006 the overall trend remains a significant steep decline.

 

Source: adapted from Breeding Bird Survey22 by Downes et al., 201023

 

Grassland birds are showing steep and widespread declines throughout North America.24, 25 In Canada, there has been an overall loss of 44% of the populations of grassland species since the 1970s, with individual species showing significant declines of up to 87%.23

Photo: grasshopper sparrow © iStock.com/WilliamShermanGrasshopper sparrow, declined by 78% since the 1970s23

Grazing and grassland health

Degree of alteration
of Saskatchewan grasslands due to grazing
Percent, 2007
Graph: degree of alteration of Saskatchewan grasslands due to grazing. Click for graphic description (new window).
Long Description for Degree of alteration of Saskatchewan grasslands due to grazing

This bar graph shows the degree to which Saskatchewan grasslands had been altered as a result of grazing by 2007. Twelve percent were severely altered, 35% were moderately altered, and 29% had only minor alterations.

 

Source: Thorpe, 200927
 

Large areas of intact grasslands are used as rangelands for livestock grazing. The relationship between grazing and grassland health is complex. Most grasslandsevolved with grazing by herbivores. Maintaining a range of grazing intensities is important for biodiversity as habitats with different grazing intensities support different species. Although improvements in land management practices have been made in some areas, for example community pastures and other stewardship initiatives in the Prairies,4, 21, 26 livestock grazing can affect grassland health. Using data on species composition to indicate change, Thorpe27 found almost 50% of plots in the Aspen Parkland and Mixed Grassland regions of Saskatchewan had, by 2007, been moderately or severely altered by livestock grazing. In B.C., about 90% of grasslands are now grazed by domestic livestock,11 resulting in grasslands that are in early stages of succession, with many invasive species.13, 28-30

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