Intra-annual stem growth dynamics of Lebanon Cedar along climatic gradients

Abstract

Onset of cambial activity in Lebanon Cedar is triggered by stem temperature but may be delayed by high site-LAI. Higher growth rates and tree-ring widths were observed under better water and light availability. Daily stem radius variations were sensitive to humid conditions. Studies on intra-annual dynamics of stem growth provide useful information on tree growth responses to environmental conditions, but are fragmentary for species from Mediterranean Mountain ranges. Lebanon Cedar is a frost and drought tolerant species, growing between 1000 and 2000 m a.s.l in the Taurus Mountains (Turkey). Foresters see it as a potential candidate for plantation in Central European forests facing global warming. To describe the natural variability of Lebanon Cedar growth dynamics, five study sites were established: four along an altitudinal gradient at a natural site in SW-Turkey and one in a Lebanon Cedar plantation in Central Germany. Two stem growth monitoring methods were used: (1) bi-weekly microcoring during 2013 growing season and (2) point dendrometers during 2013 and 2014. Histological analyses were used to calibrate dendrometer records and to describe cambium phenology. Seasonal dynamics of xylem and stem radial increments were modelled by Gompertz functions. Onset of cambial activity was observed 1–2 weeks after stem temperatures reached a threshold of 5 °C but could be delayed by high site-LAI. Cedars growing under better light and water availability showed higher growth rates and wider tree rings. Daily stem radius variations (dSRV) extracted from dendrometer records were negatively related to vapor pressure deficit and global radiation; multiple linear regressions explained 30–52% of dSRV variance being dominated by relative humidity, precipitation, and soil water content. Best growth performance was observed at the German site, likely for a continuous water supply throughout the year, underlining the potential of Lebanon Cedar for Central European Forestry.