Assessing regional scale habitat area with a three dimensional measure

Abstract A method of measuring the three-dimensional (3D) area of habitats across a regionally complex cultural landscape is described. It is based on overlaying field mapped habitats from sample grid squares onto a digital terrain model of topography constructed using triangulated irregular networks to calculate a terrain corrected area (3D area). The method is suitable for regional-scale ecological studies and has the potential to be used to determine habitat metrics other than area that are sensitive to dimensionality. It is pragmatic with currently available software. The extent to which the area of habitats is underestimated by a two-dimensional (2D) area measure, compared with a 3D measure, is assessed. There was a significantly greater 3D area of all habitat types. The 2D to 3D area increase was especially large in specific seminatural habitats associated with topographic complexity and agricultural land use constraints. They included European Priority Habitats of high conservation value such as dry heath and calcareous grassland. This is of direct relevance for assessing area-based biodiversity evaluation criteria. The economic consequences of 3D area adjustments to production subsidies for agricultural habitats and agri-environment scheme payments were large if applied at a regional scale, especially in marginal upland and upland farms.