Fire recurrence effects on the abundance of plants grouped by traits in Quercus suber L. woodlands and maquis

Disturbances such as fire profoundly affect plants, but their effects are strongly dependant on species’ biological and life-history traits. Thus, in Mediterranean-type ecosystems (MTEs), where the frequencies and intensities of fires are increasing in association with ongoing land use and climate changes, the composition and diversity of plant communities may change at both species and trait levels. Fire–plant trait interactions have rarely been examined in MTEs on acidic soils. Therefore, we have explored the responses of classes of plants with differing characteristic traits, focusing on easily discernible traits (life forms, dispersal mode, Grime’s strategies and regenerative traits), to fire recurrence in a mosaic of Mediterranean cork-oak woodlands and maquis shrublands on acidic soils in south-eastern France. Stands of several fire recurrence classes (0 to 3–4 fires since 1959, with different time intervals and times since the last fire) were surveyed. The results indicate that these fire variables are both influenced by plant traits (e.g. fire recurrence was positively correlated with cover of the main structural species, Erica arborea (Nomenclature: Nomenclature of species follows the numerical referencing of Brisse and Kerguelen (1994)) which negatively affects the diversity of plant traits in high maquis) and influence the composition and diversity of the traits. The abundance of ruderal stress-tolerant species, therophytes and wind-dispersed species was positively associated with recent and/or recurrent fires. Conversely, resprouters were suppressed at sites with high fire frequencies (3–4 fires during the last 50 years), indicating that fire intervals shorter than 10–15 years are insufficient for them to build reserves and that this represents a resilience threshold for the studied communities, as observed in other Mediterranean ecosystems.

► Recent and/or recurrent fires significantly affect plant trait distributions and diversity.
► Fire recurrence favours ruderal, wind-dispersed species, therophytes and seeders.
► Diversity indices decrease with high fire recurrence.
► A structural resilience threshold of 3-4 fires per 50 years is identified.
► Erica arborea cover negatively affects functional diversity in high maquis.