Wetlands Ecology and Management 12: 483–498, 2004. # 2004 Kluwer Academic Publishers. Printed in the Netherlands. 483 Spatial and temporal changes in salt marsh distribution in the Dee estuary, NW England, determined from aerial photographs J.M. Huckle 1 , R.H. Marrs 1, * and J.A. Potter 2 1 Applied Vegetation Dynamics Laboratory, School of Biological Science, University of Liverpool, P.O. Box 147, Liverpool L69 3GS, UK; 2 Environmental Research Group, Biology Department, Chester College of Higher Education, Parkgate Road, Chester, CH1 4BJ, UK; *Author for correspondence (e-mail: calluna@liv.ac.uk; phone: +44-151-794-4752; fax: +44-151-794-4940) Received 20 March 2002; accepted in revised form 27 October 2003 Key words: Aerial photography, Colonisation, Dee estuary, Remote sensing, Salt marsh, Spartina anglica, Vegetation change Abstract Vegetation changes in salt marsh communities of the Dee estuary, northwest England, were analysed with a combination of remote sensing techniques using data dating back to the 1950s. The distribution of commu- nities in 1997 was classified using Airborne Thematic Mapper data and used to develop a methodology for the analysis of black and white photographs of the marsh. These methods were then applied retrogressively to a time sequence of monochrome photographs running from 1955 to 1975. At the apex of the salt marshes on the English shore of the Dee estuary, the marsh expanded dramatically to 1975, and consisted predomi- nantly of pioneer and low marsh vegetation types. Between 1975 and 1997, however, there was only a slight increase in salt marsh area, but with an increase in mid and high marsh vegetation, replacing pioneer marsh. In a second area of the salt marsh on the English shore, a different pattern of salt marsh expansion was observed. The area occupied by marsh continued to increase right up to 1997, with extensive pioneer vegetation suggesting a process of continuing expansion. However, the pattern of marsh colonisation appeared to be different in 1997 compared to 1975. The significance of the changes in salt marsh distribution within the Dee estuary are discussed in relation to the historical pattern of salt marsh colonisation, the importance of Spartina anglica in the process and the implications for strategic management of the estuarine resources. Introduction Increasingly, an integrated approach to coastal management has been adopted to take into account the many issues and activities that affect coas- tal habitats (Imperial and Hennessey 1996). Management of estuarine environments requires an inter-disciplinary approach that co-ordinates anthropogenic and natural issues into strategic programmes that promote the principle of balanced, sustainable use (Fowler 1996). Within such a strategic framework, it is recognised that natural processes of coastal habitat change, such as the colonisation of mudflat with salt marsh vegetation, should continue with the minimum of human intervention (Jemmett 1996). The ability to map the distribution and composition of salt marsh vegetation accurately is therefore essential to the monitoring of changes in salt marsh development over time and the establishment of informed man- agement strategies. Changes in the patterns of zonation of salt marsh vegetation have traditionally been monitored by the use of field survey techniques such as transect