Tree growth patterns associated with extreme longevity: Implications for the ecology and conservation of primeval trees in Mediterranean mountains

This study analyzed with dendrochronology 177 Heldreich's pines growing on the Pollino Massif in southern Italy for understanding climatic and human impacts on old trees. Most of the large-diameter trees currently living became established in the late Medieval to Renaissance periods under a snowy wet climate and low anthropic influence. Millennium-old (i.e., > 900 years of age) trees in remote sites escaped Medieval human impacts, then a wave of pine stands established in the late 14th and 16th centuries following recurrent human plague epidemics. Stem growth histories showed that both millennium-old and the majority of century-old trees grew along similar trajectories. These old trees have survived long-lasting climatic reversals, clearly a sign of their resilience to extreme events. Cliff habitats played a strategic environmental role for tree conservation during periods of land exploitation; such biodiversity refugia may serve as stepping stones for rewilding mountain landscapes. In recent decades, land abandonment following the collapse of sheep-herding, together with climate warming, have led to a new pulse of tree recruitment. Since 1850, low-frequency variability (50-70-year periods) in tree growth has been in synchrony with the Atlantic Multidecadal Oscillation. Recently observed growth increases counter widespread reports of tree and forest decline in Mediterranean environments, and suggest that extreme longevity does not necessarily reduce stem increment. Discovering, studying, and preserving primeval trees in forest landscapes remains a priority for biodiversity conservation in the Anthropocene. Heldreich's pine resilience to current global changes bodes well for sustainable development in the Mediterranean mountains they inhabit, and similar studies are needed for threatened habitats and iconic trees of other ecoregions in order to assess their probable survival into the future. (C) 2019 Elsevier Ltd. All rights reserved.