Landscape cover change in the Peace-Athabasca Delta, 1927–2001

Abstract

This study examined landscape change in the Peace-Athabasca Delta, northern Alberta, Canada. The proportion of the landscape covered by ten habitat types was determined for five vintages of air photos (1945–2001) from 24 randomly chosen study areas. To test for reproducibility, three vintages were analyzed by two independent teams, neither of which knew the dates or locations of air photos. Their results were highly correlated. Comparison with another air photo study focused in the southeastern delta revealed good agreement. Analysis of oblique air photos extended the reconstruction back to 1927. Of four cover types (water, marshes, willows, forests), only water differed significantly in area between vintages. Cover trends for the most general of types (wet communities and dry communities) indicated drying from 1927 to 2001. This trend may be due to multidecadal geomorphic evolution and climate change. Currently, the changes are statistically non-significant, but nevertheless may inform about the long-term future of the ecosystem. Large spatial and temporal variation in landscape cover is characteristic of the system. The types and ranges of change in the delta’s vegetation post-Bennett Dam (1968) do not appear unusual relative to pre-Bennett Dam change. A multi-decadal perspective is necessary to encompass normal oscillations in abundance. Key to understanding change in the delta is to think at multiple scales and to remain aware that trends or patterns are scale-dependent. The delta may not be predictable on the meso-scales relevant to society and management.