Some Quantitative Methods of Assessing the Conservation Value of Ecologically Similar Sites

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Abstract
Data on the vascular plant flora of 23 small woods in south Bedfordshire [England, UK] were used to examine how 2 criteria-number of species and their local rarity-may be used to assess objectively the conservation value of ecologically similar sites. Locally rare (selected) species, defined as those recorded in less than 128 of the 371 tetrads (units of area 2 .times. 2 km) in Bedfordshire, were given rarity scores reflecting their frequency of occurrence in the county. Three measures of species quantity and/or quality (total number of species, proportion of selected species, and the sum of rarity scores for all selected species present) were used to calculate assessment values for each site based on deviations from the regression line best describing the relationship between each measure and site area. All 3 assessments identified the richest and poorest woods, but results for other sites sometimes differed considerably. A method of incorporating species richness and rarity into a single index of conservation value was suggested. The interpretation of the results and their implications regarding the suitability of sites as nature reserves are discussed.