Fire-induced changes in northern Patagonian landscapes

Abstract

In northern Patagonia, Argentina we quantify changes in fire frequency along a gradient from mesic Nothofagus dombeyi forest to xeric woodlands of Austrocedrus chilensis at the steppe ecotone, and we examine patterns of vegetation change coincident with the changes in fire regimes across a range of spatial scales. At a regional scale changes in land cover types are documented by comparing 1:250 000 scale cover type maps from 1913 and 1985. Changes in landscape structure are analyzed by comparing vegetation patterns on 1:24 000 scale aerial photographs taken in 1940 and 1970. Fire frequency peaked in the late nineteenth-century due to widespread burning and clearing of forests by European settlers late in the century. Subsequently, fire frequency declined dramatically about 1910 due to the cessation of intentional fires and has remained low due to increasingly effective fire exclusion. At a regional scale there has been a dramatic increase during the twentieth century in the proportion of forest cover relative to areas mapped as recent burns or shrublands in 1913. Remnant forest patches that survived the widespread late-nineteenth century burning have coalesced to form more continuous forest covers, and formerly continuous areas of shrublands have become dissected by forest. Under reduced fire frequency there has been a shift in dominance from short-lived resprouting species (mostly shrubs) towards longer-lived species and obligate seed-dispersers such as Austrocedrus chilensis and Nothofagus dombeyi. Due to limited seed dispersal of these tree species, the spatial configuration of remnant forest patches plays a key role in subsequent changes in landscape pattern.