Tree-ring width and vessel characteristics of oriental beech (Fagus Orientalis) along an altitudinal gradient in the caspian forests, northern iran

Abstract

Vessel features of broadleaf trees may contain information about both spatial and temporal variations of environmental conditions. We report quantitative data about annual vessel characteristics for Oriental beech (Fagus orientalis Lipsky) in the Caspian forest in the Alborz Mountains, northern Iran. Time series of tree-ring width and of various vessel variables were constructed over a 50-year period for three sites along an altitudinal gradient from 1260 to 2200 m a.s.l. We evaluated the dependencies between ring width and vessel variables and estimated the influence of altitude and climate on these variables. Mean ring width and average vessel-lumen area decreased towards the high-elevation site whereas total vessel-lumen area was independent from altitude, and vessel density increased. Above-average warm summer and autumn seasons in the year prior to growth were negatively correlated with ring width and average vessel-lumen area whereas precipitation in the current June showed a positive association; vessel density responded exactly opposite to these climatic variables. Total vessel-lumen area was the only variable that reacted differently from site to site, mainly positively to temperature at 1200 m a.s.l. and negatively at 2000 and 2200 m a.s.l., whereas a consistent response to precipitation was lacking. The results indicate that vessel variables are meaningful indicators of changes in dynamics of wood formation in relation to climate along an altitudinal gradient in the Caspian mountains. As for climate reconstruction, we have to conclude that for our study area, vessel variables do not add much to information derived from ring width.