Post-fire Mediterranean vegetation dynamics and diversity: A discussion of succession models

Abstract

Post-fire vegetation dynamics is examined over an extended timescale, to investigate the long-term effects of fire on plant diversity and to verify if a succession model, such as Clements’ “relay floristic” or Egler's “initial floristic” models, applies to post-fire dynamics in Mediterranean communities. In the Alpilles massif, Provence, southern France, 20 plots were sampled at each of six sites; five that had been burned by wildfires within the last 30 years (1977, 1983, 1989, 1999 and 2003), and a control site not burned for at least 80 years. Temporal variations in relative species density are modelled by regression curves. The structure of diversity is analysed based on mean species richness ( α), beta diversity ( β w), Shannon diversity index ( H) and relative equitability index ( E h), knowing that the Egler's model leads to the prediction that richness should be highest immediately following disturbance. No significant differences in species richness were detected between sites, and species diversity is not related to time since the last fire except 2 years after fire that shows the highest β w-diversity resulting from an elevated list of species per site (γ-diversity) immediately after fire. Instead, an effect of site location on species diversity is detected. The observed post-fire dynamics show a progressive transition between three stages, from initial, through transitional to mature. Each stage is characterized by different relative species density. Furthermore, several plant species can be considered as early, intermediate or late successional species with regards to their density at different times after burning. In conclusion, initial floristic composition model (Egler's model) applies to this ecosystem, with all species present at the early post-fire dynamics, and the diversity shows the highest γ-diversity 2 years after fire. In the long term (>50 years), a successional pathway can be discerned. The growth rates and longevity of main species influence the post-fire dynamics.