Document: JAN-3-69-19

Historical relationships between terrain, land-use and vegetation pattern in a grassland-forest ecotone in the Rocky Mountains foothills of southwestern Alberta.

SIMONSON, J.T* ^1,2 and E.AJOHNSON ¹

University of Calgary, Calgary AB T2N 1N4 Canada ¹
Alberta Environment, Calgary AB T3B 5K3 Canada ²

Abstract:
Using archival data we mapped land-use and vegetation in an ecotone over a 1000-km² area. Prior to settlement the Dominion Lands Act of 1879 established a forest reserve dividing agricultural from non-agricultural land along a boundary that attempted to follow the lower limit of closed coniferous forest. We were able to confirm that the actual boundary followed this limit by overlaying the boundary with pre-settlement land survey data. While vegetation patterns in the forest reserve have not significantly changed, those in the settlement area have. Pre-settlement vegetation varied along an east-west elevational gradient and was strongly influenced by aspect. At lower elevations closed aspen stands occupied north-facing aspects, while fescue grasslands occupied south-facing aspects. Aspen-fescue parkland covered the remainder of the area. At higher elevations on glacial till, closed white spruce and aspen-spruce forests dominated on northward aspects, while grassland dominated on south-facing slopes. Aspen occupied west-facing aspects, while lodgepole pine and mixed stands of aspen and pine occupied the tops of ridges. Aspen and willow occupied wide valley bottoms underlain by glacio-lacustrine deposits. Agricultural land-use now also varies along the elevational gradient and reflects the pre-settlement vegetation pattern. At lower elevations, the steepest north and south-facing slopes have not been cleared or ploughed and still support aspen and grassland. The bottoms of slopes have been ploughed, regardless of aspect. The remainder of the parkland has been ploughed. At higher elevations the steepest slopes have not been cleared or ploughed and still support white spruce, aspen and grassland. Valley bottoms and gentler slopes that supported willow and aspen have been ploughed, while sites occupied by lodgepole pine have not been cleared. Our results suggest that the arrangement of suitable agricultural land determines vegetation pattern.

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This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY