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Contrasting growth and mortality responses to climate warming of two pine species in a continental Mediterranean ecosystem

Abstract:

The long lifespan of trees makes them sensitive to climate warming, particularly when abrupt changes in climatic conditions occur and when trees are already growing near to their climatic tolerance thresholds. In many Mediterranean pine forests, drought stress induced by warmer temperatures and increased aridification compromise tree survival, causing growth decline and, eventually, triggering tree mortality. We evaluated the effect of climate on radial growth and mortality comparing dead and living trees of two pine species, Pinus sylvestrisand. Pinus nigrasubsp.salzmannii, in a continental Mediterranean area over a 50-year long period. We used linear mixed models and correlations to evaluate the effect of climate on basal area increment (BAI) and on ring-width indices, respectively. In P. nigra, growth was enhanced by wet and cold conditions, whilst growth increased with temperatures in. P. sylvestris. A gradual BAI reduction was detected in P. nigratrees since the late 1970s, becoming more pronounced in recently dead trees. Contrarily, P. sylvestris growth did not show such decline, whilst death events in this species were linked to severe and punctual droughts. Our findings show that warming and drought stress trigger contrasting responses in functionally and phylogenetically similar tree species, and suggest climate-mediated important changes on competitive dominance in Mediterranean forests.