Former charcoal platforms in Mediterranean forest areas: a hostile microhabitat for the recolonization by woody species

Production of wood charcoal is a traditional form of forest use that lasted for millennia in the Mediterranean countries. Following their almost complete abandonment in the last century, thousands of old charcoal platforms remain in present-day forest landscapes. These sites are characterized by peculiar ecological conditions, whose effects on the recolonization by woody plants are still unknown. We examined 61 platforms in evergreen sclerophyllous woodlands and deciduous broadleaf forests with oaks and beech, spread over a wide geographic range in Tuscany (Italy). At each site, one kiln plot (on charcoal platform) and one control plot (in the adjacent stand) were established, and soil, light conditions and herb cover were measured. We examined species richness and composition of trees and shrubs in the understorey layer ( 1.3-4 m). In the latter, structural parameters such as number of stools, dbh, mean height and number of stems were compared. The density of seedlings of dominant tree species in the understorey was also measured in a subsample of sites per forest type. In the understorey, a general positive effect of kiln platforms was found on species richness at both the habitat and plot-scale level, as well as on species composition, especially in oak forests. Increased light availability, total C content and soil pH were positively related with species richness, while N content was a negative predictor. Density of seedlings was not substantially affected. Contrastingly, woody species richness in the established regeneration layer was considerably lower in the kiln plots of all three forest types. In sclerophyllous forests, all species in this layer were taller, denser and with a higher basal area compared to control plots, while regeneration was completely lacking on platforms of the two other forest types. Soil N content had a positive influence on structural parameters, while total C content resulting from charcoal accumulation had a negative influence. We conclude that charcoal platforms are a favorable microhabitat only in the first regeneration stages of woody species, as their further growth is hindered by long-term effects that should be investigated with an experimental approach.