DEMOGRAPHIC PROPERTIES OF AN OUTLIER POPULATION OF ORCHIS-MILITARIS L. (ORCHIDACEAE) IN ENGLAND

Orchis militaris L. underwent a catastrophic decline in range and plan t numbers in the British Isles around the end of the nineteenth centur y, and was long thought to be nationally extinct. A small number of co lonies have been discovered since then, including one in Buckinghamshi re, which has been recorded annually almost every year since its disco very in 1947. This paper presents an analysis of the demography and be haviour of this population using census data which have been collected annually from 1977 to 1995. Yew trees which shaded the site occupied by the orchids were removed in 1984 and 1989, and the growth of the he rb layer has been strongly constrained by active management since 1989 . Since the start of this period of intensive management, the annual g ains and losses of plants in the population have become more pronounce d, but in most years there has been a net gain in the number of plants . The number and proportion of the emergent plants which flower each y ear has increased considerably since 1986, and the age structure, whic h was dominated by older plants prior to 1984, has since become domina ted by younger plants, resecting the increased rate of recruitment and lack of a corresponding increase in mortality. Analyses are presented to show changes in behaviour in consecutive years between the pre-198 4 and post-1986 management eras. (C) 1998 The Linnean Society of Londo n.