The Ecology and Conservation of Rare Arable Weed Species and Communities.

Abstract

Since 1940, considerable changes have occurred in both arable farming practices and arable weed floras in Britain. The aim of this project was to investigate the ecology of a range of annual weed species in relation to farming practices, in order to suggest some reasons for the decline in frequency of some species, and to propose some methods by which populations may be conserved.

A survey of the sites at which eight uncommon species are still found, demonstrated the strong association of the weed communities and the presence of individual species, with the cropping history and soil characteristics of fields. Climatic factors and the long-term histories of sites were also found to be important. Another survey demonstrated the tendency for the seed-banks of most weed species to be greatest at the extreme edge of fields.

Four herbicides were tested against ten weed species, and the effects of levels of nitrogen application on 18 weed species were investigated. It is believed that herbicide use and the high levels of nitrogen applied to modern crop varieties have favoured their growth at the expense of weeds.
The type of crop sown and the date of sowing also had a great influence on the development of the weed flora. Some species rely on a post-harvest stubble in order to set seed.

Changes in arable weed communities and the status of rare species is thought to be a result of changes in the farming practices described above in addition to others not investigated. Management guidelines based on the experimental investigations are proposed.