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Int J Biometeorol. 2019 Jul;63(7):963-972. doi: 10.1007/s00484-019-01710-4. Epub 2019 Mar 22.

Frost controls spring phenology of juvenile Smith fir along elevational gradients on the southeastern Tibetan Plateau.

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Key Laboratory of Alpine Ecology, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100085, China.
School of Science, Auckland University of Technology, Private Bag 92006, Auckland, 1142, New Zealand.
Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555, Boulevard de I'Université, Chicoutimi, QC, G7H2B1, Canada.
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
Central Department of Hydrology and Meteorology, Tribhuvan University, Kathmandu, Nepal.
Key Laboratory of Alpine Ecology, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100085, China.
CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, 100101, China.
Harvard Forest, Harvard University, 324 North Main St, Petersham, MA, 01366, USA.


Impacts of climatic means on spring phenology are well documented, whereas the role of climatic variance, such as occurrence of spring frosts, has long been neglected. A large elevational gradient of forests on the southeastern Tibetan Plateau provides an ideal platform to explore correlates of spring phenology and environmental factors. We tested the hypothesis that spring frost was a major factor regulating the timing of bud-leaf phenology by combining 5 years of in situ phenological observations of Abies georgei var. smithii with concurrent air temperature data along two altitudinal gradients. Mean lapse rate for the onset of bud swelling and leaf unfolding was 3.1 ± 0.5 days/100 m and 3.0 ± 0.6 days/100 m, respectively. Random forest analysis and conditional inference trees revealed that the frequency of freezing events was a critical factor in determining the timing of bud swelling, independent of topographic differences, varying accumulation of chilling days, and degree-days. In contrast, the onset of leaf unfolding was primarily controlled by the bud swelling onset. Thus, the timing of bud swelling and leaf unfolding appear to be controlled directly and indirectly, respectively, by spring frost. Using space-for-time substitution, the frequency of spring freezing events decreased by 7.1 days with 1 °C of warming. This study provides evidence for impacts of late spring frosts on spring phenology, which have been underappreciated in research on phenological sensitivity to climate but should be included in phenology models. Fewer spring freezing events with warming have important implications for the upward migration of alpine forests and treelines.


Abies georgei var. smithii; Altitudinal gradient; Bud swelling; Conifer; Leaf unfolding; Spring frost; Spring phenology


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