ORIGINAL PAPER Phenological variation in height growth and needle unfolding of Smith fir along an altitudinal gradient on the southeastern Tibetan Plateau Yafeng Wang • Xiaoxia Li • Binod Dawadi • Dieter Eckstein • Eryuan Liang Received: 17 March 2012 / Revised: 3 October 2012 / Accepted: 8 October 2012 / Published online: 18 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012 Abstract Little is known about variations in tree phe- nology and their driving forces on the Tibetan Plateau. Herein, we monitored shoot growth and needle unfolding of Smith fir (Abies georgei var. smithii) between 3,800 and 4,360 m a.s.l. in the Sygera Mountains, southeastern Tibe- tan Plateau. The trees were 0.45–1.48 m high and 12–39 years old. Their phenology was observed every week between May 5 and August 26, 2011. With increasing ele- vation, shoot growth and needle unfolding started increas- ingly later, thus indicating a thermal driving force. Although the weekly shoot increment was decreasing with increasing elevation, height growth at various elevations ended in the same week, implying other factors than tem- perature being responsible for the end of height growth. The accumulated heat sum for the onset of shoot growth appeared to be lower between 4,200 and 4,360 m than between 3,800 and 4,000 m. The anticipated spring warm- ing will likely induce an earlier onset of shoot growth, whereas shoot growth will apparently not benefit from autumn warming. However, the lack of long-term data records precluded a robust statistical test of the underlying cause-and-effect relationships involved in the phenological variations of height growth and needle unfolding. Keywords Phenology Á Smith fir Á Height growth Á Leaf unfolding Á Accumulated temperature sum Á Altitudinal gradient Á Tibetan Plateau Introduction Tree phenology (e.g., bud burst, shoot elongation, and needle unfolding) plays an important role for the distribu- tion range of a tree species as well as for the growth and survival of trees (Keeling et al. 1996; Chuine and Beaubien 2001). As tree phenology is impacted by constraints such as wind abrasion, low temperature, and persistence of snow cover at high altitudes and latitudes (Ko ¨rner 2007), it is a sensitive ecological indicator for climate change (Parmesan and Yohe 2003; Walther 2003; Menzel et al. 2006). Compelling lines of evidence indicated that the amount of precipitation and the length of the photoperiod affect tree phenology (Badeck et al. 2004; Zheng et al. 2006; Rossi et al. 2009). Temperature, however, is considered to be the major driving force (Pen ˜uelas and Filella 2001; Chen et al. 2005; Salminen and Jalkanen 2007; Vitasse et al. 2009; C ˇ ufar et al. 2012). Thus, tree phenology and its response to climate at high elevations, such as on the Tibetan Plateau, could be an interesting research target. The highest treeline on the northern hemisphere was found on the southeastern Tibetan Plateau (Miehe et al. 2007) where Communicated by A. Braeuning. Special topic: Dendroecology in Asia. Y. Wang Á X. Li Á B. Dawadi Á E. Liang (&) Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese, Academy of Sciences, PO Box 2871, Beijing 100101, China e-mail: liangey@itpcas.ac.cn Y. Wang Á X. Li Á B. Dawadi University of Chinese Academy of Sciences, Beijing 100049, China B. Dawadi Central Department of Hydrology and Meteorology, Tribhuvan University, Kathmandu, Nepal D. Eckstein Department of Wood Science, University of Hamburg, Leuschnerstrasse 91, 21031 Hamburg, Germany 123 Trees (2013) 27:401–407 DOI 10.1007/s00468-012-0793-5