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Historical vegetation reconstruction of a degraded sub-arctic coastal marsh using Landsat imagery and ancillary data

Abstract In recent decades, increasing numbers of Lesser Snow Geese have severely damaged the sub-arctic coastal marshes on which they feed in summer. Because the geese are an economic, aesthetic and visible species, plans for population control via increased harvest are controversial, and accurate vegetation maps are needed both for management decision-making and for public education. Documentation of the extent, pattern, and timing of habitat damage over large spatial and temporal scales requires reconstruction of the previously-existing vegetation. Satellite imagery is increasingly used for mapping and monitoring vegetation change over large areas, and archives of Landsat imagery provide consistent, spatially-extensive historical data. Previously-existing vegetation at La Pérouse Bay, Manitoba, was mapped using unsupervised classification of a 1984 Landsat TM image and ancillary information. Using a commercial clustering algorithm, sixty-three spectral clusters were produced and subsequently identified using a combination of historical and current aerial photos, current vegetation data, and knowledge of local vegetation trajectories in time. These initial clusters were then aggregated into 14 classes, resulting in a detailed map of vegetation as it was before degradation by the geese. The map was compared to earlier results documenting change in the study area. Vegetation degradation between 1973 and 1993 occurred earliest and most extensively in the salt marsh and other classes containing salt marsh vegetation. Map accuracy was assessed with current vegetation data collected independently at a number of precisely located points.