A retrospective analysis of land cover change using a polygon shape index

Aim This study tests the hypothesis that the propensity of land cover patches to change is related to their shape and geometric complexity. Location The analysis is based on a 1000-km(2) area of the Cairngorms in Scotland, incorporating part of Speyside and the high plateau area within the Grampian Mountains. Methods A combined dataset was created by intersecting 1964 land cover data (derived from archive aerial photography) and 1988 land cover data (from the Land Cover of Scotland dataset). A shape index was calculated for each land cover polygon inside a GIS. Information on land cover change was analysed with reference to land cover class and the polygon shape index using a regression analysis. Results For upland seminatural land cover classes, subject to low levels of management, change is related to polygon shape, such that the more complex patches were found to be more susceptible to change. This relationship breaks down where classes are more intensively managed or have been aggregated into mosaic classes. Conclusions Propensity to change was related to shape index for seminatural land cover classes. This implies that at least some landscape processes, such as anthropogenic disturbance of seminatural land covers, can be linked to ecological theory via measurements of spatial pattern. The study also highlighted some of the cartographic issues involved in estimating changes between land cover classes: there are advantages in replacing the 'cartographic paradigm' of comparing two derived datasets (in this case land cover maps) with direct comparison of the digital data - air photographs or satellite imagery. Such a direct approach avoids the compounding of errors introduced by the approximation of each successive air photo as a thematic map.