Abstract
Tree growth takes place at different time scales ranging from hours to days. To understand growth responses to climate, continuous high-resolution measurements of tree diameter variations are needed, which are usually obtained with automatic dendrometers. Here, we monitored stem diameter increment of Quercus faginea Lambert growing in central Portugal to determine the effect of climate on daily and seasonal growth dynamics during the 2013 growing season. Stem diameter variation presented a unimodal seasonal pattern characterized by an exponential phase in spring followed by a plateau during summer, interrupted by an abrupt increase in autumn caused by rainfall. Stem diameter increment started in March when the temperature was above 10 °C. Stem diameter variation showed a double climatic constrain, with temperature limiting growth in spring and precipitation in summer. The amplitude of the daily cycles of stem variation was higher in summer, as well as the expansion phase length, meaning that trees needed longer to replenish the water lost through transpiration during the day. The absence of a pronounced stem shrinkage during the summer suggests that Q. faginea has access to water over the whole growing season. Our results indicate that this species relies on deep soil water reserves and can be physiologically active during summer drought.
Highlights
Tree secondary growth is probably the most studied process in forest science, often relying on tree-ring-based methods that investigate the effect of climatic forcing on tree growth in correlative approaches using monthly climate data together with annual tree-ring parameters [1]
Xylogenesis studies are based on-weekly observations of the cambium and developing xylem and have significantly improved the time resolution of tree growth studies and our understanding of the effect of climatic forcing on wood formation [2,3,4,5]
When considering lagged effects of environmental conditions on stem dynamics, we found that current-day climatic conditions were more important for stem diameter variation than the conditions of the previous 1, 2 and 5 days (Supplementary Material, Figure S2)
Summary
Tree secondary growth is probably the most studied process in forest science, often relying on tree-ring-based methods that investigate the effect of climatic forcing on tree growth in correlative approaches using monthly climate data together with annual tree-ring parameters [1]. Cambial activity and wood formation take place at different time scales, from hours to days, highlighting a different resolution between tree growth and the analysis of climate forcing To bridge this gap, studies on the intra-annual dynamics of wood formation are necessary. Xylogenesis studies are based on (bi)-weekly observations of the cambium and developing xylem and have significantly improved the time resolution of tree growth studies and our understanding of the effect of climatic forcing on wood formation [2,3,4,5] Another method frequently used to monitor intra-annual wood formation is monitoring stem variation using dendrometers [6,7,8,9]. Due to its dual nature, it is difficult to estimate cambial activity and to precisely
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