Abstract
The genetic structure of ten Abies alba populations at the western rear edge in the Spanish Pyrenees was characterized and compared with two German populations, looking for the role of climatic factors in the fir decline. Growth, defoliation, aridity and cumulative summer water deficit summer were also characterized. Spanish populations show a lower genetic diversity and a high genetic differentiation than German ones, mainly established by an East (higher diversity)-West (lower diversity) gradient. The three defoliated populations are the western ones, with higher summer aridity. Contrastingly, the southern population (Guara) shows climatic variables close to western sites but without defoliation and with a higher genetic diversity, indicating a possible adaptation to the sub-Mediterranean conditions. Silver fir in the Spanish Pyrenees constitutes a “stable” rear edge because of their isolation, small sized and small genetic diversity. Western Pyrenean sites subjected to dryer conditions and presenting lower genetic diversity are prone to drought-induced mortality in the context of global warming.
Highlights
Tree populations are facing new and rapidly changing selective pressures such as more frequent extreme droughts which threat the conservation of forests and related ecosystem services (Lindner et al, 2010)
One of the major research gaps identified by Allen et al (2010) is a better knowledge on within-species genetic variability as related to forest decline which may allow understanding the differential responses of rear-edge tree populations to drought stress
Rear edge tree populations inhabiting the southernmots margins of the species distribution range may act as an important reserve of genetic diversity in changing climates because they have often been longisolated and lack gene flow, display strong differentiation, and may exhibit local adaptation in response to strong selective pressures such as drought stress (Hampe & Petit, 2005; Parisod & Joost, 2010; Gugger et al, 2011)
Summary
Tree populations are facing new and rapidly changing selective pressures such as more frequent extreme droughts which threat the conservation of forests and related ecosystem services (Lindner et al, 2010). Drought-induced forest decline is a major emerging threat for forests in drought-prone areas (Allen et al, 2010) and in mesic temperate forests (van Mantgem & Stephenson, 2007). One of the major research gaps identified by Allen et al (2010) is a better knowledge on within-species genetic variability as related to forest decline which may allow understanding the differential responses of rear-edge tree populations to drought stress. Rear-edge tree populations living near the species xeric distribution limit may have adapted to drought stress and represent genetic reservoirs of drought-resistant genotypes. Selection of drought-resistant genotypes may lead to populations of a high adaptive value in a warmer and dryer climatic scenario
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