Get reliable science

Mixed grass prairie grasslands of southern Canada historically had little shrub cover. However, wetlands created for the purpose of increasing waterfowl habitat have, in some situations, led to a marked expansion in woody species. This is the case on a significant portion of the University of Alberta Mattheis Research Ranch in SE Alberta, where Shepherdia argentea (thorny buffaloberry) is thought to have expanded considerably after the introduction of irrigation overflow water more than half a century ago. In order to track the spatial extent of shrub expansion coincident with water introduction, we are using a series of archived aerial photographs to map S. argentea coverage at multiple dates between the early 1950's and present day. Aerial photos from each date will be orthorectified, digitized, and classified into cover types, including shrublands, to identify areal coverage. Our ultimate objective is to determine the extent to which S. argentea expansion reflects the introduction of water on the landscape (using a GIS framework), and also to determine whether rates of shrub expansion have slowed, accelerated, or remained the same during this period. These results have implications for identifying the risk of future shrub expansion in these landscapes, including the current urgency of woody control measures. In addition, when combined with supplemental field data examining the impacts of shrub presence on understory composition and productivity, these results have implications for assessing the overall impact of shrub encroachment on livestock carrying capacity in the region.