Effects of temperature and photoperiod on xylogenesis at the timberline

Abstract

Timings and dynamics of xylogenesis in cold forest ecosystems are crucial aspects for understanding climate changes because they represent the time window in which environmental factors directly affect growth. Cambium phenology and xylem cell differentiation were monitored from 1996 to 2004 in larch, stone pine and Norway spruce at the Alpine timberline using automatic dendrometers and cell analyses. Cell division occurred from May to August while the last developing cells were detected in October. All the species showed similar dynamics of wood formation, indeed cell production was concentrated in the first part of the growing season, while cambial activity, synchronized with photoperiod, with the maximum rates of wood production during summer solstice. Threshold temperatures for maintaining xylogenesis varied between 5.6 and 8.5°C and attested the existence of thermal limits in cell production. These studies represent the first attempt to connect growth with weather factors in timberline areas at both annual and intra-annual level in order to better understand mechanisms of growth processes in plants of cold environments.