The detection of vegetational change by multitemporal analysis of LANDSAT data: the effects of goose foraging

1 The North American mid-continent population of lesser snow geese now exceeds 3 million birds and the population is increasing in the order of 7% per annum. The foraging activities of the birds on Arctic breeding grounds are leading to loss of vegetation and habitat destruction, particularly in coastal areas bordering the Hudson and James Bays. 2 Multitemporal analysis of LANDSAT data has been carried out to detect vegetational change from 1973 to 1993 at La Perouse Bay and its vicinity, the site of a breeding colony of snow geese. 3 Difference vegetation images (DVI) (difference between infra-red and red images) were prepared from images obtained in late summer in 1973, 1984 and 1993, in order to enhance vegetation density. Pair-wise differences were calculated between these DVI images, which resulted in three, secondary, classified images. Classification of the three secondary images (1973-84, 1984-93, 1973-93) yielded three well-defined classes: water, vegetation decline and no change in vegetation. 4 Histogram counts gave the following values for areas of vegetation decline: 1973-84, 1026 ha; 1984-93, 1428 ha; 1973-93, 2454 ha. 5 The loss of vegetation and the destruction of habitat are discussed in relation to the foraging activities of the expanding goose population.