Filling the gaps: Remote sensing meets woodland ecology

Natural disturbance has considerable ecological significance, and within woodlands tree-falls significantly change environmental conditions. The spatial characteristics of canopy gaps influence regeneration dynamics, and species diversity and distribution. In this study imagery from a Compact Airborne Spectrographic Imager (CASI) was analysed to produce a vegetation cover map for a range of types of deciduous woodlands. This map was used to delineate canopy gaps in these areas. A raster-based GIS was used to derive a range of measures to describe the spatial characteristics of canopy gaps, in order to infer the relative ecological status of different types of deciduous woodland. For the study sites, spatial characteristics have been used to derive information on: (1) gap creation mechanisms: large gaps are created by progressive enlargement rather than instantaneously by a catastrophic event; (2) regeneration dynamics: pioneer invasion and small gaps for climax regeneration, plantations have only small gaps; (3) species diversity and distribution: semi-natural woodlands have high potential genetic variability, high probability of persistence of gap species, and a high potential to support 'edge' species, the opposite is the case for plantations. The combination of airborne remotely sensed data and GIS technology holds great potential for ecological studies of woodlands. This approach provides a spatial framework on which to base future pattern-process studies, and the GIS-based output is valuable for environmental management purposes. The analysis of multi-date imagery in this way should provide a basis for monitoring woodland dynamics.