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Harvard Forest Symposium Abstract 2018

  • Title: Cambial phenology and xylogenesis of Juniperus przewalskii over a climatic gradient influenced by both temperature and drought
  • Primary Author: Junzhou Zhang (Not specified)
  • Additional Authors: Ross Alexander (Illinois Mathematics and Science Academy); Ruben D. Manzanedo (Harvard Forest); Xiaohua Gou (Lanzhou University); Neil Pederson (Harvard Forest)
  • Abstract:

    While temperature is known to be an important factor determining cambial phenology in cold and humid climates, how it interacts with other factors or the importance of other factors for the onset and end of xylogenesis is still not fully understood. Here, we analyzed phenological traits related to observed cambial activity and xylem formation across six sites that span the entire spatial distribution of Qilian juniper (Juniperus przewalskii Kom.) in the Northeastern Tibetan Plateau (NETP) over the course of two extreme hydroclimatic years. we found that warmer temperature result in an earlier initiation of xylogenesis regardless moisture conditions and an earlier cessation and a lower rate of wood formation, which would make future warming a bit of a double-edged sword for the cambial phenology and xylogenetic dynamics of J. przewalskii in the NETP. Under global warming conditions, unfavorable factors may reduce the growth rate and wood production in this tree species, leading to a potential radial growth decline. However, because J. przewalskii can survive for 1,800 years under the harsh climate of the NETP, these findings do not imply that it will disappear form the region. This observation and our findings suggest that it has a special radial growth strategy and plasticity that would likely allow J. przewalskii trees to persist in the northeastern Tibetan Plateau.
    For the seven years monitoring in eastern Qilian Mountains, the formation of Intra-annual Density Fluctuations (IADFs) were observed in three out five monitoring trees in the 2016 growing season. Formation of IADFs in the annual growth rings of trees is commonly used as an indicator of environmental conditions. We found that the timing of IADFs formation in the three trees occurred in mid-August, when other two trees had ceased their wood production. Meanwhile, the decrease in wood production in these three trees were concomitant with a 16 days gap that without precipitation in the end of July and early August, much later than what is reported in other semi-arid environments. These results indicate that the drought event in early August and subsequent precipitation recovery led to the formation of false rings in J. przewalskii in 2016. Our findings suggest that the formation of false rings in J. przewalskii has the potential to be a drought indicator in the arid northeastern Tibetan Plateau.

  • Research Category: Regional Studies; Physiological Ecology, Population Dynamics, and Species Interactions; International Research Projects; Historical and Retrospective Studies