Within-year variation in the vegetative spread of five temperate grasses

Questions: Do species planted outdoors in native soil differ in the timing of their period of vegetative spread during the growing season? Location: Cleish Hills, Fife, Scotland, UK. Methods: Patches (20 cm × 20 cm) of Agrostis capillaris, Festuca rubra, Holcus lanatus, Lolium perenne and Poa trivialis were arranged in plots so that every species patch had all the remaining species as neighbours. The plots were cut every 14 days at 3 cm and photographed monthly from above. The photographs of species boundaries were traced and digi-tised. Measurements were made on the digitised images of the distances each species spread and of the area occupied by each species. Results: Fitting some simple models to the data indicated firstly that species varied in their vegetative competitive ability, with A. capillaris and P. trivialis being the most and least competitive respectively, and secondly that the ability of a species to colonize can differ from its ability to resist colonization, the most discrepant species being H. lanatus. Our analysis also indicated statistically significant variation in the data over and above the simple models, providing evidence of additional, genuine, complexity in the seasonal patterns of spread. Conclusion: This study provides evidence to support the hypothesis that clonal grass species do not spread vegetatively at the same times within a growing season. Since sward height is known to affect species spread, there is some opportunity for the manipulation of species composition simply through temporal control of sward height. Nomenclature: Stace (1991). Abbreviations: s.e.d. =standard error of difference.