Modelling the spread of Himantoglossum hircinum (L.) Spreng. at a site in the south of England

A population of Himantoglossum hircinum (L.) Spreng. (lizard orchid) has been monitored since the 1940s at a site in the south-east of Great Britain. A map of the site showing the number and position of flowering plants has been produced in most summers between 1978 and 1994. The maps have been digitized on a 25 times 25 m scale. In the summer of 1995 the whole site was surveyed for habitat suitable for the growth of the orchid and this information was also digitized on to the 25 m grid. The spread of H. hircinum around the site can now be demonstrated with a program, SCATTER. Population biology parameters for SCATTER have been calculated from data from two permanent 10 times 10 m plots. These data were collected annually between 1987 and 1994, and give information on the size and position of all H. hircinum plants within the plots. Two dispersal models were employed and compared with SCATTER. The first was a diffusion model and the second a tilted plume model. The tilted plume model describes the expansion of the population of H. hircinum and also the number of flowering plants in the population more satisfactorily than the diffusion model.