Legacy effects of former charcoal kiln sites on the forest vegetation of a Mediterranean area

The objective of the reasearch was analysing the long-term effects of the centennial activity of charcoal production on forest ecosystems of the Mediterranean area. The study is structured in order to achieve three main aims: i) evaluating the impact of kiln sites on the forest vegetation (tree, shrubs and herbaceous species) in relation to abiotic factors; ii) examine the effects of the charcoal-enriched kiln site soil on the early life stages of major forest trees; iii) quantifying and characterizing the legacy of such activity at the landscape level, through the analysis of the distribution and morphology of production sites in different environments of central Italy . The research was carried out in three forest types traditionally exploited for wood charcoal production, sclerophyllous maquis, mixed oak forest and beech forest. In a first exploratory study, we examined tree regeneration and understorey vegetation on a sample of 61 kiln sites, abandoned at least 60 years ago, together with the main soil characteristics and light conditions. At the same time, an experimental work was performed by setting up a common garden to compare germination, growth and mortality in three major forest trees (Quercus ilex, Q. cerris, Fagus sylvatica) grown on soil of kiln sites and control sites. Finally, an inventory work was carried out in sample quadrats using field surveys and LIDAR data, to determine the density, size, surface and other morphological parameters of kiln sites in the three forest types. In the first two studies we found a negative effect of kiln sites on tree regeneration and forest recolonization, whereas the understorey vegetation was positively influenced in terms of species diversity, compositional variations and biomass production. These effects are related to variations in the characteristics of soil and light, also influenced by the kiln sites. The common garden experiment showed that the responses of forest trees to kiln site soil are different, in some cases contrasting, or weak. The inventory study showed that, compared to other European countries, kiln sites are denser but smaller and with different morphology, also in terms of soil profile, with some differences between forest types. Such differences are probably due to the different methods of preparation and the different purposes for which they were made. Charcoal kiln sites are one of the most striking legacies left by the millennial human activity in the Mediterranean woodlands. This study shows that such sites have persistent effects on the vegetation via changes in soil and light conditions. Hence, they represent ecological “micro-islands” of anthropic origin that increase the diversity and fine-scale heterogeneity of the forest ecosystem. The relatively high number of these sites and their total area per unit surface suggest that the magnitude of their effects at the forest level may not be negligible.