History and distribution of steepland gullies in response to land use change, East Coast Region, North Island, New Zealand

Abstract

Following the clearance of indigenous forest (~1880s to 1920s) for pastoral use, actively eroding gullies had by the late 1950s become a pervasive form of erosion occupying 0.7% of the 7468km2 of pastoral hill country within the East Coast Region, North Island, New Zealand. Commencing in the early 1960s the primary strategy used to stabilise gully and other associated forms of erosion on degraded pastoral hill country was to establish exotic forest. We compare the status of gully erosion before reforestation commenced with that at the end of a ~40year reforestation period (1957–1997) during which ~1350km2 of exotic forest was planted. Trends in gully area and distribution by land cover (vegetation), but particularly in response to exotic reforestation, are examined for two contrasting geologic terrains. Over this ~40year period, the incidence and extent of gully erosion in areas of hill country that have remained in pastoral use has declined. This was primarily due to the retirement and conversion of extensive areas of gully-prone farmland to exotic forest. Where implemented, the reforestation of this degraded pastoral hill country has proven to be efficient and successful in stabilising existing gullies. However, with the initiation of new gullies and growth of gullies that have remained untreated, the extent of land affected by gully erosion has increased by ~27% to ~0.9% of the regions' hill country area. To reverse this trend, further areas of severely eroding pastoral land will need to be retired with the aim of escalating the rate at which remaining gullies are treated and to prevent new ones developing, primarily through reforestation with exotic tree species or indigenous reversion.