Meteorological forcing of day-to-day stem radius variations of beech is highly synchronic on opposing aspects of a valley

Projected changes in climate highlight the need for a better understanding of the effects of forest meteorological factors on the growth of Central European forests. In this study, we used automatic point dendrometers to investigate day-to-day stem radius variations of 24 European beech trees (Fagus sylvatica L.) in relation to daily forest meteorological conditions. Study trees were located at opposing north-east (NE) and south-west (SW) exposed slopes of a valley in southwestern Germany, and monitored over a six-year period (2001–2006). Seasonal courses of day-to-day stem radius variation (SRV) were analyzed in hierarchical mixed models based on first-order derivatives of cumulative Weibull functions. Responses of SRV to weather conditions were found to be remarkably synchronic within and between the NE and SW aspect. This latter finding suggests that trees at both slopes may have adapted to prevailing environmental conditions. Further, responses were found to be mostly linear within the range of forest meteorological conditions encountered in this study. Highly distinct effects of forest meteorological fluctuations were observed when daily lags were considered. The daily parameters mean air temperature at lag1 (=one day lag), maximum air temperature and soil water content at lag1 were found to explain 59% of the variance in day-to-day stem radius variations. We discuss the complex responses of SRV to lagged and current-day weather variables in relation to stem hydraulics and growth, varying time scales of tree physiological processes, and pre-conditioning of tree water status.