Table of Contents
ISRN Forestry
Volume 2012, Article ID 437690, 8 pages
http://dx.doi.org/10.5402/2012/437690
Research Article

Silver Fir Defoliation Likelihood Is Related to Negative Growth Trends and High Warming Sensitivity at Their Southernmost Distribution Limit

1Área de Ecología, Universidad Pablo de Olavide, Ctra. de Utrera Km 1, 41002 Sevilla, Spain
2Departamento Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. de Utrera Km 1, 41013 Sevilla, Spain
3ARAID, Instituto Pirenaico de Ecología (CSIC), Avenida Montañana 1005, 50192 Zaragoza, Spain

Received 30 August 2012; Accepted 16 October 2012

Academic Editors: J. F. Negron, S. Sun, A. M. Vettraino, and M. Vitale

Copyright © 2012 Juan Carlos Linares and J. Julio Camarero. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

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.