Abstract
Climate warming may enhance the negative effects of droughts on radial growth in areas with severe water deficit, such as Mediterranean mountains under semi-arid conditions. The impacts of drought on growth decline of Mediterranean pines have not been evaluated considering species with different vulnerability and areas with contrasting climates. Dendrochronological methods were used to assess the responses of basal area increment to drought in Pinus pinaster and P. halepensis plantations. We compared growth trends of trees with different defoliation degree in two sites in south-eastern Spain (Sierra de los Filabres and Sierra de Baza) with contrasting climatic conditions. In the more xeric area (Filabres) both pine species showed a sharp growth reduction in response to extreme droughts such as those observed in 1994-1995, 1999 and 2005. The radial growth of both species was enhanced by May and June precipitation of the year of tree-ring formation. P. pinaster showed higher defoliation in the xeric area (Filabres) than in the more mesic area (Baza) but needle loss was not linked to an abrupt growth reduction. Contrastingly, divergent radial growth patterns between trees showing high and low defoliation degrees were found for P. halepensis in the more xeric area, where a negative relationship between recent basal area increment and defoliation was found. Pine plantations in Mediterranean mountains under semi-arid conditions are highly vulnerable to warming-induced droughts. Such marginal stands constitute valuable monitoring systems to assess the negative impacts of drought on tree growth, and to test if management strategies as thinning can mitigate the negative impacts of climate warming on similar drought-stressed forests.
Highlights
Forests are responding to climate warming through changes in growth and vigor acting as monitors of the effects of climate change on terrestrial ecosystems (Bonan, 2008)
We noted a greater divergence in basal area increment (BAI) patterns between P. halepensis with different defoliation degree in Filabres and, to a lower degree, in Baza
No BAI divergence was noted for P. pinaster according to the trees’ defoliation, despite this species showed the highest defoliation degree in the xeric area (Filabres)
Summary
Forests are responding to climate warming through changes in growth and vigor acting as monitors of the effects of climate change on terrestrial ecosystems (Bonan, 2008). Forest dieback and growth decline are usually linked to severe droughts occurrence in areas with pronounced water deficit such as the semi-arid USA (Allen and Breshears, 1998). The negative effects of warming-induced drought might affect negatively the performance of Mediterranean mountain forests, which are mostly drought-prone ecosystems. Droughtinduced dieback, declining radial growth and increased mortality rates have been described for drought-prone forests throughout the world (Allen et al, 2010). These dieback episodes usually show a great spatial variability across geographical gradients (Van Mantgem and Stephenson, 2007; Peñuelas et al, 2008). The responses of forests to warming-induced drought, including growth decline, can vary as a function of species-specific resistance to drought and local climatic conditions (Suárez et al, 2004)
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