An index of weed size for assessing the soil productivity of ancient crop fields

A method is presented for generating data on archaeological weed species relevant to soil productivity and consequently crop husbandry. Three plant attributes (maximum canopy height, maximum canopy spread and maximum dry leaf weight per node) which are functionally related to habitat productivity were measured for 161 British annual species. These three attributes were combined to produce an index of weed size. Index values were found to differ significantly between character species of phytosociological classes from fertile and infertile habitats and to provide an objective assessment of CSR (Competitor/Stress-tolerator/Ruderal) strategy sensu Grime (1974, 1979). Further work is required, however, to distinguish 'medium-sized' species that exploit highly disturbed and productive habitats from those of less disturbed and less productive situations.