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Proactive disclosure Print version   | |  Sand Dune & Climate Change Studies in the Prairie Provinces Historical Changes in Land-Cover
Vegetation cover on the prairies has changed considerably since European settlement of the region. The introduction of agriculture transformed much of the grasslands into cropland, while less productive lands such as dune soils are commonly used as rangeland. Land-cover in dune areas has also changed dramatically over the last century, with most dunes showing increased vegetation cover and, consequently, decreased areas of bare active sand. Early explorers accounts, survey records, aerial photography and satellite imagery provide documentation of these changes in dune areas across the prairies. Middle Sand Hills, Alberta The Middle Sand Hills are located about 50 km north of Medicine Hat, on the west side of the South Saskatchewan River. This dune field covers an area of nearly 400 km2, most of which lies within the Suffield Military Reserve. The remainder is private or leased rangeland. The photographs to the right show identical areas of the Middle Sand Hills along the South Saskatchewan River. In 1937, active sand dunes were migrating towards the river. By 1998, all of the dunes, except for a very small portion near the river, were vegetated and stabilized. This illustrates how land-cover on these dune areas can change dramatically over a relatively short time period. Source: Great Sand Hills, Saskatchewan The Great Sand Hills region is located near the centre of the Palliser Triangle, approximately 100 km northwest of Swift Current, Saskatchewan. It is the largest dune area in the southern prairies, comprising over 2000 km2. It is used almost exclusively for grazing, with some recreational use and oil and gas development. Due to the sensitivity of the environment, development in the Great Sand Hills is controlled by a regional planning commission and development plan. Oil and gas development is presently restricted or prohibited across most dune areas. Land surveys from the late 1800s show that over 260 sections of the Great Sand Hills region, or about one-third of the sand hills, had some bare blowing sand. This is likely an underestimate, as some areas were not well-surveyed. Between then and the late 1980s, the number of sections with bare blowing sand decreased by more than 60%, to about 100 sections. Diligent management practices have contributed to the reduction in bare blowing sand, and to the increase in vegetation cover in sensitive dune areas. Even after more than 100 years, however, there are still areas with bare blowing sand, indicating that it requires considerable time for some dune areas to stabilize once they have become active. Numerous questions arise from these observations. For example, why were dunes very active in the 1880s, prior to European settlement? Was it because of drought or climate change, natural disturbance by bison, fires started by lightning or native people, or some combination of these?
Source: Spirit Sand Hills, Manitoba The Spirit Sand Hills represent an active portion of the Carberry Sand Hills east of Brandon, Manitoba. Most of the sand dunes in the larger region are stabilized by forest vegetation including white spruce, aspen, balsam poplar, bur oak and larch. The primary land uses in the dune areas include the Shilo Military Reserve, Spirit Sands Provincial Park, and cattle rangeland. As with the Middle and Great Sand Hills, the bare sandy areas of the Spirit Sand Hills have become progressively more vegetated since the earliest airphoto observations were made in the late 1920s (figure to right). Since about the 1960s, however, there has been very little change in the overall area of active sand. Early explorers also described this area in the 1800s. For example, on July 12, 1806 Alexander Henry wrote: this "ridge of barren sandy hills, is a body of sand several miles in length ... several miles in circumference, and level on top, where no kind of vegetation grows ... westward lies a sandy waste for three miles, where nothing grows but a few stunted epinettes (spruce trees), that tumble down when the sand are blown from about their roots." From this account, it is clear that these dunes were more active in the early 1880s, than at any time between the 1920s and today.
Source: Summary of Historical Changes In summary, most active dunes fields in southern Alberta, Saskatchewan and Manitoba have become more stable throughout the last century. Many active dune areas have vegetated at a rate of 10% to 20% per decade, and some have nearly completely stabilized over the last century. This has occurred in spite of droughts in the 1930s, 1960s, and 1980s. While these droughts imposed major impacts in agricultural areas, they appear to have had only minor impacts in dune areas, with the exception of the Great Sand Hills, where activity increased in some parts of the sand hills following droughts in the 1980s (graph to right). These observations suggest that most sand dune areas on the southern prairies were more active prior to European settlement than they are today. This can be viewed as a positive trend since it suggests that dune areas can withstand the impacts of several drought years without being re-activated. However, this raises the question as to whether these historical changes have been due to changes in land use activities and the frequency of natural disturbances, or due to changes in climatic conditions on the prairies over the last century.
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