Factors affecting the establishment of Cytisus scoparius in southern France:: implications for managing both native and exotic populations

1. The ecology of the woody shrub Cytisus scoparius was studied for 4 years in its native range in southern France to investigate how it call become an invasive weed. 2. The proportion of the seed bank that germinated each year was highest in disturbed plots and was correlated with the March rainfall. The seed bank declined at a rate of c. 50% per year when fresh seed rain was excluded, 3. The fate of 2863 seedlings was followed for a variety of treatments. 4. Seedling survival depended on disturbance: none survived their first summer in undisturbed plots; more than 40% survived their first summer and c. 14% survived to flowering age in plots that were initially cultivated. 5. Seedlings flowered first in their fourth year, although only c, 10% set seed. 6. Neither inter- nor intraspecific competition was found to affect significantly seedling survival on cultivated plots. However, some seedlings grown in the absence of interspecific competitors flowered and set seed in their third year. 7. Applications of insecticide, molluscicide or fungicide did not affect significantly seedling survival, growth or minimum age of reproduction on cultivated plots. 8. It is concluded that management strategies should minimize disturbance to competing vegetation, which can inhibit germination and smother emerging seedlings. In many circumstances strategies that target the seed bank, such as burning, are not expected to work. 9. Herbivores and pathogens may prevent stand re-establishment indirectly, by reducing the size, vigour and density of broom plants so that competing vegetation can persist and smother emergent seedlings following the death of the parent stand.