Flora of Ashdown Forest - Botanical Society of the British Isles

19The frequencies with which species have been recorded in 1-10,11-20, etc., squares is shown in Figure8. 194 (21.2%) species have been recorded in only one square, or 129 species (17.6%) excludingthose with known recording bias. 34 (3.7%) species have been recorded in every square, This graphfollows the reverse-J pattern as expected (Jaccard 1908) I with many rare species and relatively fewerintermediate ones, and then a few more very common ones.Figure 8. Number of species recorded in 1-10 squares, 11-20 squares, etc.600500400Frequency 300.AII speciesm Species excluding criticals200100o10 20 30 40 50 60 70Number of squares3. Comparison of the environment, recording and species dataThe data were first investigated for systematic recording bias. Rich & Woodruff (1990) assessedrecording quality by assuming that ~lluares relatively poorly recorded would have below averageproportions of grasses, common species and critical taxa recorded; the maps for these groups forAshdown Forest are shown below:Below average proportionof grassesBelow average proportionof common speciesBelow average proportionof critical taxaThese measures of recording quality can then be combined to indicate squares relatively poorly-recordedand well-recorded. The squares with two or more measures of under-recording (i .e. relatively poorlyrecorded),and the converse (i.e. relatively well-recorded), are shown below.Squares relatively poorly-recorded.Squares relatively well-recorded