The population dynamics of rare annual plants on the Lizard Peninsula, Cornwall, UK, 2009–2016

The Lizard Peninsula, Cornwall, UK, is one of the richest botanical sites in Britain, in terms of rare plants at least, many of which have more southerly distributions in Europe reaching their northern limits in southwest England. Though much of the coastal habitat has escaped destruction, and most of the sites of the rare plants survive, very little is known of the details and vitality of the individual populations, and the extent to which species are increasing or declining due to changes in management and climate. Annuals are the easiest to monitor, despite their fluctuating yearly populations, if only because of their exclusivity to a highly localised but easily identified habitat and their relatively low numbers of sites as well as smaller populations compared with the perennials. An attempt was made over an 8-year period (2009–2016) to visit and monitor populations of five of the rarest species, all annuals (three Trifolium species and two Juncus species), whose sole or principal sites in Britain and Ireland are on the Lizard, and to count all plants at each site in each year. Apart from one survey for one species there is no evidence that this has ever been done before, and the rationale was partly to test whether current population figures bore any relation to those estimated in the past, and through that to see how they are faring in relation to climate and management and to set a reliable benchmark for future monitoring. Most of the historical sites for these annuals still seem to be in a suitable condition for their re-appearance, but the results showed a marked decline in the number of populations at those sites and a probable even larger decline in the numbers of individual plants. These declines probably arise from gradual cessation of traditional management over the last century, together with the possibility that drier springs are affecting germination, and wetter autumns and winters are encouraging the growth of competing perennials.