The values shown on this page are based on PLANTATT and refer to the distributions mapped in the New Atlas of the British & Irish Flora (2002). The diagrams show the distribution of values for all British and Irish species in blue and the value for the species in question in red.
The counts of 10km squares in Great Britain, Ireland and the Channel Islands refer to all records, irrespective of date.
The Atlas Change Index is a measure of the change in the number of 10-km squares in which the species was recorded in Great Britain between 1930–69 and 1987–99. The change is relative to the average species, so that positive values indicate that the number of squares increased relative to the average species and negative values that it decreased. The reasons for the change vary (some species were overlooked in the past, for example, whereas others have spread). The changes are interpreted in the Trends paragraph on the Summary page. For details of the calculation of the index, see the New Atlas and Telfer et al. (2002).
Preston, C. D., Pearman, D. A. & Dines, T. D. (ed.) (2002) New Atlas of the British and Irish flora. Oxford: Oxford University Press.
Telfer, M. G., Preston, C. D. & Rothery, P. (2002) A general method for the calculation of relative change in range size from biological atlas data. Biological Conservation 107: 99-109.