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

Abstract

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 m) and in the "established regeneration" 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.

Effects of charcoal hearth soil on forest regeneration: Evidence from a two-year experiment on tree seedlings

“…While the deciduous oak QC was not significantly affected, neither for germination nor for survival, the evergreen holm oak was apparently favoured on CHS in the first year of the experiment, with a higher germination rate coupled with lower mortality than on COS. This result is consistent with the lack of a negative effect of CHS on the density of young (≤1 yr. old) QI seedlings recently observed in sclerophyllous Italian forests (Carrari et al, 2016b). Similarly, a recent experimental study (Reyes et al, 2015) highlighted the insensitivity of this species to soils added with ash and black carbon, such as those affected by wildfires.…”

“…This was even more evident for the beech, which germinated significantly better on COS (plus 17%). Given the lack of significant differences in the survival rate of this species on the two types of soil material, decreased rate of seed germination may be one of the causes for the lower density of seedlings observed on CHS in the field (Carrari et al, 2016b).…”

“…Regeneration of woody species on old charcoal sites was recently found to be affected in different forest types of the Mediterranean region (Carrari et al, 2016a,b), while contrasting results were found in Germany (Krause and Möseler, 1993;Wittig et al, 1999;Borchard et al, 2014) and North America (Mikan and Abrams, 1995;Young et al, 1996;Hart et al, 2008), possibly due to different soil types (Borchard et al, 2014). In the Mediterranean, positive or neutral effects were observed on the species richness and composition of young seedlings in the understorey (plant height < 1.30 m), depending on the forest type, while a strong decline of older individuals in the "established regeneration" layer (tree height of 1.3-4 m) was evident in all forest types (Carrari et al, 2016b). A similar detrimental influence on woody species was found in the old platforms of mixed oak-beech forests in eastern North America (Mikan and Abrams, 1995;Young et al, 1996).…”

The old charcoal kiln sites in Central Italian forest landscapes

“…Nutrient availability and pH are also often increased, which may lead to compositional differences in the understorey vegetation with respect to the adjacent stands (Wittig et al, 1999;Carrari et al, 2016c). In addition, the altered processes of tree recolonization in kiln sites abandoned since even decades may lead to long-lasting negative effects on forest recovery Abrams, 1995, 1996;Young et al, 1996;Carrari et al, 2016b).…”

High resolution reconstruction of modern charcoal production kilns: An integrated approach combining dendrochronology, micromorphology and anthracology in the French Pyrenees

“…Repeated combustion on one site can lead to relative sterility of the soil, which can take several decades to recover (Acovitsioti-Hameau, 2001b;Carrari et al, 2017) and lead to its abandonment. The abandonment also may be directly related to the management of the surrounding forest resource.…”