Characterising windthrown gaps from fine spatial resolution remotely sensed data

This paper evaluates the potential of fine spatial resolution remotely sens ed data for the identification and characterisation of windthrown gaps. The study site was Cwm Berwyn Forest, in central Wales, a planted forest of pr edominantly Sitka spruce (Picea sitchensis (Bong.) Carr.) containing windth rown gaps ranging in size from 50 to 3000 m(2). The remotely sensed data us ed were acquired by an 11 waveband airborne thematic mapper (ATM) sensor wi th a spatial resolution of approximate to 4 m. This resolution is finer tha n the gaps on the site and comparable to that of future satellite sensors. A three class (gap, forest canopy and moorland) thematic land cover map was produced using a conventional maximum-likelihood classification of the dat a and provided an accurate representation of the classes (>90% of the pixel s allocated correctly). This classification provided an accurate means of i dentifying windthrown gaps and was capable of identifying a greater number of gaps, than manual interpretation of temporally coincident aerial photogr aphs. In addition, the magnitude and spatial distribution of class membersh ip probabilities derived from the classification provided information on va rious gap properties, such as exposed soil and living, windthrown tree cano pies. This may enable other properties such as windthrow direction to be in ferred. (C) 2000 Elsevier Science B.V. All rights reserved.