Abstract
The importance of long-term observation of the natural environment has long been recognized, and yet 'monitoring' is often dismissed as low-grade science which can contribute little to our understanding. The value of long-term study is assessed within the context of the Environmental Change Network (ECN) which was established in 1992 to provide a minimum of 30 years' data from a network of sites within the UK. Following a description of the ECN programme, there follows an assessment of the value and limitations of long-term study and consideration of alternative approaches. Three examples of long-term study (Coweeta Hydrologic Laboratory; Radcliffe Meteorological Station; and the Slapton Ley catchment study) are described by way of illustration. It is concluded that long-term study provides an invaluable basis for the development of environmental science. Well designed programmes, supported by sustained funding, provide the best conditions for studying processes whose effects can only be identified over long periods of time and for revealing new questions which could not have been anticipated at the time the monitoring began.