As forests reclaim the land: Latitudinal variations in carbon-biodiversity trade-offs under natural forest expansion in Italy

Abstract

Spontaneous forest expansion following land abandonment can play a key role in achieving European targets for climate-change mitigation and biodiversity conservation. Understanding how biodiversity relates to carbon (C) stocks across successional stages can inform management strategies that simultaneously promote species diversity and C sequestration, thereby optimizing land use for ecosystem multifunctionality. We analysed 16 chronosequences spanning five successional stages, from meadows and pastures to mature forests (up to ∼75 years since abandonment), organized into four clusters along a latitudinal gradient in Italy, encompassing the Alpine, Continental, and Mediterranean biogeographical regions. We quantified vegetation, deadwood, and soil C pools and calculated diversity indices for herbaceous plant species. Linear and generalized linear mixed models were used to assess successional stage and site effects on C stocks and diversity indices. Total ecosystem C increased along succession, driven primarily by tree biomass, reaching 195–289 Mg C ha−1 in late-successional forests. Soil C showed no clear successional trend, with weak or site-specific patterns. Herbaceous species richness and diversity peaked in managed meadows/pastures and early encroachment stages but declined towards closed-canopy forests in three sites. By contrast, a U-shaped pattern emerged in the southernmost site. Consequently, the C–diversity relationship was predominantly negative, except for the non-linear response observed in the Mediterranean site. Overall, spontaneous reforestation promotes C storage but often reduce herbaceous plant diversity, revealing potential trade-offs between climate mitigation and plant diversity. However, under favourable environmental conditions, partial recovery of plant diversity in late-successional forests may occur, suggesting for win-win management policies.

Lorenzo Orzan

PhD candidate in Life and Environment

Antonio Tomao

Assistant professor

Giorgio Alberti

Associate professor in Silviculture and Forest Management

My research interests include ecological issues concerning carbon and nitrogen cycles in agricultural and forestry ecosystems.