This research will provide a regional assessment of the impacts of past droughts for use as potential future scenarios; provide a chronology of eolian activity for the Yukon; and paleo-wind, paleo-environmental and paleo-drought data for regional use in the National Paleo- environments Synthesis. Methodologies include field work at selected eolian deposit sites in the Western Interior to target effects of Mid-Holocene and late Holocene environmental change. Data pertaining to chronology, circulation patterns, and environmental change derived from eolian deposits in the Western Interior of Canada will be incorporated into existing ESS databases.

Stephen Wolfe
Project Leader

Drought has historically been the main climatic concern on the prairies, causing impacts on multiple economic sectors and land use. Severe droughts have occurred recently (1987-88, and 2001-02), historically (1961 and 1930s), and in the geologic past. Geological studies of dune fields on the prairies have helped to determine the timing and impact of past droughts, and the potential severity of impacts from future climate change.

Holocene drought and dune activity:

Optical dating of sand dunes (Lian et al., 2002) conducted across the Canadian prairie provinces has determined when dune activity and stability occurred in the geologic past. Most of these dune fields are derived from glaciofluvial and glaciolacustrine deposits reworked by wind after the retreat of the Laurentide ice sheet. Most stabilized dune fields, occurring in the boreal forest regions of Alberta and Saskatchewan, are relict features that first formed in ice-proximal tundra settings between 16 to 13 ka (Wolfe et al., in review). Dune continued to be active in areas of central Alberta, between 13 to 11 ka under parkland and grassland settings, but were subsequently stabilized by a moderating climate associated with the Pacific air mass. Also beginning at 13 ka, dune-forming winds along the margins of the retreating Laurentide ice sheet were influenced by anticylconic winds from the southeast, that were maintained until about 9 ka. Dune activity in central and northern regions of Saskatchewan terminated between 11 and 9 ka, in a time-transgressive manner, with the establishment of boreal forest cover and reduced wind strength.

Distribution of dune fields in Alberta, Saskatchewan and Manitoba, showing active dune fields (red dots) and air circulation patterns (green arrows) between 17 and 13 ka. White areas are glacial ice and blue areas are glacial lakes.

Mid and late Holocene droughts have had a significant impact on the landscape of the central and southern Canadian prairies, indicating that droughts were potentially widespread and long-lived in the past. Dune fields in the present-day prairie parkland and southern boreal forest margins of central Saskatchewan were reactivated during the mid-Holocene, between 7.5 and 4.5 ka. This activity was likely related to a period of increased aridity, and associated reduction in vegetation cover via a northward migration of grassland and parkland biomes. Dune fields throughout the southern Canadian prairies were likely active during the mid-Holocene, and have been repeatedly active during the late Holocene (Wolfe et al., 2002a and b).

Active sand dunes in the Great Sand Hills, southwestern Saskatchewan

Recent drought and dune activity:

Geological investigations in the Great Sand Hills region have determined that widespread dune activity last occurred around AD 1800 and continued, at levels higher than any time in the 20th century, for a period of about 80 years. Additional data from tree-ring records indicate that below-average precipitation during much of the 1700s, culminating in drought in the 1790s, triggered widespread dune activity (Wolfe et al., 2001).

Historically, sand dunes have been stabilizing across the Canadian prairies. This trend in decreased dune activity is a response to recent climate variations, particularly decadal-scale changes in aridity, which are superimposed on a longer trend towards stabilization, possibly established since the late 1700s. These observations show that dune recovery on the Canadian prairies is prolonged well after an initial disturbance, causing higher than predicted levels of dune activity for extended periods (Hugenholtz and Wolfe, 2005a).

A conceptual model for the activity of dune systems on the Canadian prairies has been developed that incorporates vegetation growth theory and geomorphic system theory (Hugenholtz and Wolfe, 2005b). Dune activity is modelled as a cyclic phenomenon, alternating between active and stable states. Activation results from climatic perturbation, such as drought, which decreases vegetation cover. Stabilization is described using a logistic growth model of vegetation growth. The model shows that small perturbations (frequent but minor droughts) can prolong the duration of recovery, enabling dunes to remain activity well after the initial perturbation.

Area of active dune sands (in hectares) for successive years in the Brandon Sand Hills. An example of the historical trend in stabilization that has occurred across the prairies.

Impacts of future climate change:

Outputs from multiple global circulation models (GCMs) predict that due to increased greenhouse gas concentrations the prairies may experience the greatest increases in temperature in southern Canada, resulting in widespread changes and the need to develop appropriate adaptation responses by society. The projected climate change in focus areas on the Canadian prairies by the 2050s may include: an increase in average temperatures on the order of 2.5 to 5.0 °C, with warming occuring in all seasons; a small increase in annual precipitation (scenarios vary from essentially no change to an increase of about 50 mm); a decrease in moisture availability. The ratio of precipatation to evaporatranspiration will decrease more markedly in the moister areas and less so in the drier ones (Wolfe and Thorpe, 2005).

Under these projected changes, there are likely to be significant influences to sand dune areas in the Canadian prairies. These impacts may include changes in grassland species composition and productivity, reduction in forest productivity, and potential increases in the susceptibility of dune fields to erosion. These physical and biological impacts, in turn, may have social and economic consequences that will require society to alter its behaviour and respond with adaptive strategies that minimize the negative economic and environmental consequences with climate change.

Management planning and practices in most sand hills areas are clearly more protective and conservation-oriented than in other parts of the prairies. Progress on land-use planning is also comparatively advanced (especially in Great and Manito Lake Sand Hills). This situation should facilitate adaptation to climate change. However, detailed biophysical inventories should be completed for all areas to obtain a baseline for monitoring. Land use plans should be developed for all areas and should consider the impacts of climate change on future land uses. Land use plans should incorporate mechanisms for adaptive management (i.e. monitoring, scheduled plan review and revision). Communication with managers of rangelands, forest, parks and other stakeholders should continue to increase awareness of climate change impacts and adaptation. Vegetation monitoring programs should be designed to include indicators of climate change impacts such as decadal-scale changes in grassland productivity and species composition measured in a network of fenced range benchmark sites. Repeat time-series aerial photography or satellite imagery can be used to monitor changes in the woodland/grassland mosaic over large areas.

As the Boreal Transition ecozone is susceptible to change, forest monitoring programs in areas such as the Nisbet and Fort à la Corne Sand Hills should be designed to include indicators of climate change impacts. Such indicators may include changes in tree growth rates, drought-related tree mortality, incidence of insects and diseases (e.g. forest tent caterpillar (Malacosoma disstria), spruce budworm (Choristoneura fumiferana), dwarf mistletoe (Arceuthobium americanum), and changes in plantation survival.

Sand dunes covered by emergent forest vegetation (in foreground) in the Fort à la Corne Sand Hills of central Saskatchewan, following a fire in 1995. Unburned lowlands are occupied by white spruce (Picea glauca) and trembling aspen (Populus tremuloides).

Acknowledgements:

This research has been conducted jointly with researchers from the universities of Mount Allison, Calgary, Simon Fraser, and Okanagan College of the Fraser Valley, and through collaboration with the Saskatchewan Research Council. We are indebted to Bowies Ltd. and Martin Grazing Co-op for their continued support and access to field sites in the Great Sand Hills.

References:

Hugenholtz, C.H. and Wolfe, S.A. 2005a. Recent stabilization of active sand dunes on the Canadian prairie and relation to recent climate variations. Geomorphology, 68: 131-147.

Hugenholtz, C.H. and Wolfe, S.A. 2005b. Biogeomorphic model of dunefield activation and stabilization on the northern Great Plains. Geomorphology. In press.

Lian, O.B., Huntley, D.J. and Wolfe, S.A. 2002. Optical dating of eolian dune sand from the Canadian prairies. Géographie physique et Quaternaire, 56: 191-202.

Wolfe, S.A. and Thorpe, J. 2005. Shifting sands: climate change impacts on sand hills in the Canadian prairies and implications for land use management. Prairie Forum, 30: 123-142.

Wolfe, S.A., Huntley, D.J. and Ollerhead, J. In review. Relict late Wisconsinan dune fields of the northern Great Plains, Canada. Géographie physique et Quaternaire.

Wolfe, S.A., Ollerhead, J., Huntley, D.J. and Lian, O.B. In press. Holocene dune activity and environmental change in the prairie parkland and boreal forest, central Saskatchewan, Canada. The Holocene.

Wolfe, S.A., Huntley, D.J. and Ollerhead, J. 2002a. Optical dating of modern and late Holocene dune sands in the Brandon Sand Hills, southwestern Manitoba. Géographie physique et Quaternaire, 56: 203-214.

Wolfe, S.A., Ollerhead, J. and Lian, O.B. 2002b. Holocene eolian activity in south-central Saskatchewan and the southern Canadian prairies. Géographie physique et Quaternaire, 56: 215-227.

Wolfe, S.A. Huntley, D.J., David, P.P., Ollerhead, J., Sauchyn, D.J. and MacDonald, G.M. 2001. Late 18th century drought-induced sand dune activity, Great Sand Hills, Saskatchewan. Canadian Journal of Earth Science, 38: 105-117.