Individual study: Conservation headlands for conservation of arable plant communities in the Breckland Environmetally Sensitive Area, Norfolk and Suffolk, England
Hodkinson D.J., Critchley C.N.R. & Sherwood A.J. (1997) A botanical survey of conservation headlands in Breckland Environmentally Sensistive Area, UK. The Brighton Crop Protection Conference – Weeds, Brighton, 979-984.
With the increase in agricultural intensification in recent decades, the value of arable field margins for the conservation of arable plant communities is now recognised. The most important arable communities in Britain perhaps occur in the Brecklands of East Anglia, southeast England. Here, some component species are long-established weeds of cultivation and some are associated with dry summers and low soil nutrient availability, which are consequences of the light soils and semi-continental climate of the area. The Breckland Environmentally Sensitive Area scheme allows management of arable field margins as conservation headlands. These are cereal headlands in which pesticide and herbicide inputs are restricted and as such may act as refugia for some less-herbicide resistant species. To elucidate the benefits to plant conservation, if any, botanical surveys of conservation headlands and adjoining cultivated areas were undertaken.
A botanical survey was carried out during 17 May to 10 June 1993. All farms with Environmentally Sensitive Area agreements for conservation headlands at the time of the survey were included. Of these, nine farms had both conservation headlands and normally sprayed cereal headlands. Within each of these farms, three conservation headlands and one normally sprayed headland were randomly selected. A number of farms had conservation headlands but no normally sprayed headlands. From these, an additional 17 sites were randomly selected, making a total of 44 conservation headlands surveyed.
Within each headland a 100 m long section was located randomly. In each section, three transects, each 50 m apart, were established. The transects were positioned at right angles to the field boundary and three 0.5 x 0.5 m quadrats were placed at 1, 3 and 5 m from the field boundary in 6 m wide headlands, and 2, 6 and 10 m in 12 m wide headlands. The number of individuals of all plants rooted in a quadrat was recorded to give a plant density. For grasses, the number of tillers were also counted. Vascular plants were identified to species or subspecies, occasionally when this was not possible they were identified to genus. Mosses and liverworts were recorded collectively with no species separation.
Comparisons were then made between the plant communities on conservation headlands and those of the normally sprayed headlands.
On the conservation headlands insecticide applications are prohibited between 1 January to 31 August. Permissible herbicide application at any time, is restricted to five chemicals; tri-allate, diclofop-methyl, difenzoquat, flamprop-m-isopropyl and fenoxaprop-ethyl. Glyphosate can only be applied pre or post-havest and fluroxypr applied by spot treatment for control of cleavers Galium aparine. Other herbicides are only permissible subject to approval by (the then) Ministry of Agriculture, Fisheries and Food (now Department for Environment, Food and Rural Affairs).
A total of 44 species were recorded from both headland types; 41 were recorded in the conservation headlands; 27 in the normally sprayed headlands. As well as supporting more species overall, the frequency of occurrence of the majority of species was also greater in the conservation headlands and they also supported a greater proportion of annuals and biennials (see Table 1, attached).
There were no significant differences in plant density, average number of species/quadrat or number of grass tillers. However, the conservation headlands had a higher dicotyledon to monocotyledon ratio (0.78:1) as opposed to the normally sprayed headlands (0.65:1).
Conclusions: The fact that the conservation headlands supported a higher proportion of annuals and dicotyledons is important in conservation terms. It is generally annual dicotyledons which have declined most in arable fields and the current widespread practice of direct drilling and minimal cultivation may favour perennial species. The conservation headlands within the Breckland Environmentally Sensitive Area have thus provided opportunities for the otherwise declining annual dicotyledonous species, to prosper.
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