%0 Journal Article
%T Silver Fir Defoliation Likelihood Is Related to Negative Growth Trends and High Warming Sensitivity at Their Southernmost Distribution Limit
%A Juan Carlos Linares
%A J. Julio Camarero
%J ISRN Forestry
%D 2012
%R 10.5402/2012/437690
%X Changes in radial growth have been used to estimate tree decline probability since they may indicate tree responses to long- and short-term stressors. We used visual assessments of crown defoliation, an indicator of decline, and retrospective tree-ring analyses to determine whether climate-growth sensitivity and tree growth rates may be used as predictors of tree die-off probability in Abies alba (silver fir) at the Spanish Pyrenees. We used climatic data to calculate standardized temperature and precipitation data and drought indexes. Basal area increment was measured for declining (defoliation > 50%) and nondeclining (defoliation < 50%) silver firs in stands with contrasting defoliation. Logistic regressions were applied to predict tree die-off. Since the early 1980s, a synchronised reduction in basal area increment was observed in declining trees. The basal area increment trend correctly classified 64% of declining trees and 94% of nondeclining trees. The growth sensitivity to water deficit, temperature, and a drought index also significantly predicted silver fir decline, but providing underestimated predictions. Our findings underscore the idea that long-term climatic warming seems to be a major driver of growth decline in silver fir. Ongoing growth reduction and enhanced mortality may promote vegetation shifts in declining Pyrenean A. alba forests. 1. Introduction Declining trends of tree radial growth are considered as reliable indicators of long-term stress and may be an additional risk factor for drought-induced mortality [1¨C3]. Individual tree decline and death often occur as a result of the combined effects of different long-and short-term stressors [4, 5]. Radial growth, used here as a proxy of whole plant carbon gain [6], may be used to identify those trees with the highest probabilities of death [3, 7]. Indeed, several studies have shown that mortality rates are to some extent inversely related to radial growth trends [8¨C11]. However, the potential use of both growth trends and climate sensitivity, as surrogates for evaluating the vulnerability of tree species to climate change, has received less attention [3, 12¨C14]. Dendrochronological assessments of changing trends of radial growth may be useful to understand decline processes [15, 16]. Usually, reduced wood formation occurs prior to visual symptoms of decline such as crown defoliation. Thus, dendrochronology may be useful to forecast the impending decline of particular trees and forests [3, 16]. Moreover, tree decline may result of the combined effects of several stressors acting at
%U http://www.hindawi.com/journals/isrn.forestry/2012/437690/