The Prairie Pothole Region (Region 10*) forms the core of what was formerly the largest expanse of grassland in the world – the Great Plains of North America. It encompasses some 700,000 km2, stretching from the Peace Lowlands of northwestern Alberta and northeastern BC, southeast to the Tall Grass Prairie of Iowa. When the glaciers from the last ice age receded across this landscape about 10,000 years ago, they left behind millions of shallow depressions that are now wetlands known as prairie potholes. Since that time, these pothole complexes, rich in plant and aquatic invertebrate life, have supported populations of breeding waterfowl unmatched anywhere in the world. In some portions of the region, potholes occur in densities exceeding 70 ponds/km2, creating a wetland community that supports up to 50 breeding duck pairs/km2. Despite wetland drainage and conversion of grasslands, the PPR remains the most important habitat for breeding waterfowl in the world.
The last 125 years have seen a dramatic change in this landscape’s ability to support breeding waterfowl. Settlement by Europeans has brought with it significant impacts on the ecological function of the PPR. The nutrient-rich soils have proven to be highly productive for growing annual crops, and the vast grasslands supported the introduction of millions of grazing livestock. To facilitate agricultural development, pothole wetlands have been subjected to considerable drainage and consolidation. Though variable across the PPR, estimates suggest that on a localized basis anywhere from 50-90% of these potholes have been lost or severely degraded, and this trend continues today. But drainage has not been the only impact on PPR wetlands. Years of cultivation and soil erosion have also resulted in many more potholes being filled, and the cumulative effect of agricultural chemicals have impacted the survival and composition of aquatic plant and invertebrate communities.
In many areas across the PPR, upland habitats have been under even greater siege than the wetlands. Native prairie has been cultivated, and today annual crops dominate much of the region. Recent analysis has revealed that some parts of the PPR have suffered losses of native habitat in excess of 70%. In the PPR of Canada, the cropland base has increased by 30% in the last 25 years alone. This alarming rate of native habitat loss shows no signs of abating. Up to 3% of the remaining native uplands continue to be converted to cultivated lands on an annual basis in some areas of the PPR. Conversion of these upland habitats is not the only threat to the integrity of the habitat for breeding waterfowl. Poor range use and management practices, and increased stocking rates of grazing livestock, have resulted in much of the remaining native grasslands being severely degraded. In addition, fragmentation of critical upland habitats has been shown to have negative impacts on waterfowl production. These changes in the landscape have also had an impact on the predator community to the detriment of breeding waterfowl. In some areas of the PPR, recruitment of waterfowl on an annual basis is unable to keep pace with the mortality caused by predation.
*Region 10 – NABCI Bird Conservation Region 11 with Peace River Parkslands added.
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