Twenty years of monitoring invertebrates and weeds in cereal fields in Sussex.
Farming methods are in a state of rapid change. Over the past 20 years, the use of fertilizers and pesticides has increased, traditional ley farming and crop rotations have been largely abandoned, minimum cultivation or direct drilling have come and mostly gone again, hedgerows have been removed and fields made larger in response to greater mechanization (Sturrock & Cathie 1980; Davies 1984: Barr et al. 1986; Rands, Hudson & Sotherton 1988). A number of arable farms have changed from a patchwork of small fields in diverse crops to an intensive rnonoculture of winter wheat spanning hundreds of hectares (Pollard, Hooper & Moore 1974). Such dramatic changes must have had many effects upon the distribution and abundance of wild plants and animals - either vertebrate or invertebrate - which coexist with agriculture and, in many ways, have become dependent upon it (Bunyan & Stanley 1983; Chancellor, Fryer & Cussans 1984; Edwards 1984: O'Connor & Shrubb 1986).
In order to detect and quantify such changes, it is necessary to have data collected in the same way over a sufficient number of years to encompass the major phases of agricultural change. The Game Conservancy has monitored levels of invertebrate abundance and various other aspects of the cereal ecosystem, as well as crop management, every year from 1970 onwards in West Sussex (e.g. Potts & Vickerman 1974; Potts 1984). This ongoing study thus now spans exactly 20 years. Based on the monitoring, this paper highlights changes that have taken place in the cereal ecosystem from 1970 to 1989 inclusive; it investigates relationships within the system and the effects of changes in farming techniques.