Effects of climate on diameter growth of co-occurring Fagus sylvatica and Abies alba along an altitudinal gradient

Abstract

In high-elevation forests, growth is limited by low temperatures, while in Mediterranean climates drought and high temperatures are the main limiting factors. Consequently, the climate-growth relationships on Mont Ventoux, a mountain in the Mediterranean area, are influenced by both factors. Two co-occurring species were studied: silver fir (Abies alba Mill.) and common beech (Fagus sylvatica L.), whose geographical distribution depends on their low tolerance to summer drought at low altitude/latitude, and low temperatures (late frost and short length of the growing season) at high altitude/latitude. Firs and beeches distributed along an elevational gradient were investigated using dendroecological methods. Silver fir growth was found to be more sensitive to summer water stress than beech. On the other hand, beech growth was more impacted by extreme events such as the 2003 heat wave, and negatively related to earlier budburst, which suggests a higher sensitivity to late frost. These results are confirmed by the different altitudinal effects observed in both species. Beech growth decreases with altitude whereas an optimum of growth potential was observed at intermediate elevations for silver fir. Recent global warming has caused a significant upward shift of these optima. As found for the period 2000–2006, rising temperatures and decreasing rainfall may restrain growth of silver fir. If these trends continue in the future beech might be favored at low altitudes. The species will have a reduced capacity to migrate to higher altitudes due to its sensitivity to late frosts, although an upward shift of silver fir is likely.