Development of Cytisus scoparius L. at stand and individual level in a mid-elevation mountain of the French Massif Central

Cytisus scoparius (L.) is a common native species of the Chaîne des Puys, a mid-elevation volcanic mountain range of the French Massif Central. Widely used in the former traditional agricultural system, broom has now become an invasive species colonising open areas after grazing abandonment. This study quantifies variation in size as a function of age and local competition at both stand and individual level. Eleven monospecific stands free of grazing were sampled according to an age gradient from young and recently established to old senescent populations. Density, age, mean dimensions and individual biomasses were measured. Intraspecific competition was assessed for 4–year-old broom plants by recording the number and size of neighboring broom within a fixed competitive radius. Age at which senescence occurred was also quantified. Results showed that the age distribution exhibited a clear peak in all stages, whereas diameter distribution shifted from a reversed J shape at the young stage to a broad range distribution at the terminal stage. Density decreased exponentially with time, while stand mean dimensions increased linearly for height, or followed a power model for stem diameter and crown width. On the individual scale, biomass was accurately predicted by stem diameter. Biomass, stem diameter and crown width increased with age without any asymptote, whereas height followed a sigmoid relation. However, at a given age, broom plant main dimensions were significantly reduced by competition that was quantified as the sum of the neighboring broom stem sections. The senescent terminal stage was characterized by a low density of individuals, a lack of seedling recruitment and age at senescence followed a normal distribution. Lastly, we replaced the above aerial development patterns by distinguishing three main stages of stand dynamics: stand initiation, stem exclusion and senescent stages. © 2003 Elsevier SAS. All rights reserved.