Traditional fire use impact in the aboveground carbon stock of the chestnut forests of Central Spain and its implications for prescribed burning

Highlights: • Traditional cultural fire use is essential for the conservation of chestnut forest ecosystems • Traditionally managed chestnut forest stands accumulate on average 2.6 times more carbon than unmanaged sites • Traditionally managed chestnut forest stands present 4.4 times more understory species that unmanaged sites • Due to land use changes, fire exclusion policies and rural demographic trends traditional fire use is declining. • Surrogate prescribed burning plans based on traditional fire use should be developed to offset this decline. Chestnut forest ecosystems have a complex fire ecology; a result of centuries of co-evolution with pre-industrial era, cultural fire use by local communities based on Traditional Ecological Knowledge (TEK). As the "forest transition" unfolds throughout Europe however, and the traditional role of chestnut forest ecosystems as producers of edible nuts and firewood declines, chestnut forest resilience may be endangered due to disturbance regime changes driven by transformations in land use linked to the rural exodus, state fire exclusion policies and climate change. In this study we compared the aboveground carbon stocks of two chestnut forests located in Central Spain which can be considered representative of divergent Europe-wide management trends. In the first site of Casillas traditional understory burning is still widespread and its impacts on forest stand structure can be characterized as maintaining "open canopy", low density stands dominated by old growth chestnut trees. In the second site of Rozas de Puerto Real traditional fire use has declined and natural ecological succession processes have resumed resulting in high density, "closed canopy" stands dominated by young chestnut tree saplings and increasing pine, oak and shrub encroachment. For both sites we used in-the-field monitoring methods to estimate aerial carbon stock using allometric equations. Our results suggest that carbon sequestration and species richness is greater in the traditionally managed chestnut forest stands. Since present demographic trends present difficulties for the maintenance of traditional fire use by local communities, we argue that future fire management of unmanaged chestnut stands and maintenance of traditional forest stands ought to be implemented through surrogate prescribed burning plans that replicate the seasonal timing and ecological effects of TEK based controlled burning.