Barbeta A., Camarero J.J., Sangüesa-Barreda G., Muffler L., Peñuelas J. (2019) Contrasting effects of fog frequency on the radial growth of two tree species in a Mediterranean-temperate ecotone. Agricultural and Forest Meteorology. 264: 297-308.LinkDoi: 10.1016/j.agrformet.2018.10.020
The performance and persistence of rear-edge tree populations are relevant issues for conserving biodiversity because these stands harbor high intraspecific biodiversity and play a key role during periods of climate change. The occurrence of these populations is associated with the influence of heterogeneous topography, creating suitable refugia with regionally rare environmental conditions. Climate is changing at a global-scale, but little is known about the long-term impact on local climatic singularities and the associated taxa. We analyzed tree-ring growth chronologies of the two species (Fagus sylvatica and Quercus ilex) forming the evergreen-deciduous forest ecotone, constitutive of the rear-edge of F. sylvatica distribution. The study area is a coastal range with frequent fog immersion, which has been hypothesized to favor the persistence of F. sylvatica in Mediterranean peninsulas. We analyzed the long-term effect of fog on tree growth along a topographical gradient and the sensitivity of growth to rainfall and temperature. The annual number of foggy days has decreased by 62% over the last four decades, concomitant with increasing temperatures. Fog frequency was a relevant factor determining tree growth; fog during summer had positive effects on F. sylvatica growth mainly through a temperature buffering effect. The positive effect of fog on the growth of Q. ilex, however, was likely caused by a collinearity with rainfall. Q. ilex growth was less sensitive to climate than F. sylvatica, but growth of both species was enhanced by a positive early-summer water balance. Our results indicate that a decrease in fog frequency and an increase in temperature may generally benefit Q. ilex in this forest ecotone. Although future changes in rainfall and temperature matter most for the fate of rear-edge tree populations, local climatic singularities such as fog should also be considered. Those can have complementary effects that can swing the balance in ecotones and rear-edge tree populations such as those studied here. © 2018 Elsevier B.V.
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