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Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2016-559
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
06 Jan 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Tree growth and its climate signal along latitudinal and altitudinal gradients: comparison of tree rings between Finland and Tibetan Plateau
Lixin Lyu1, Susanne Suvanto2, Pekka Nöjd2, Helena M. Henttonen3, Harri Mäkinen2, and Qi-Bin Zhang1 1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China
2Natural Resources Institute Finland, Bio-Based Business and Industry, Jokiniemenkuja 1, 01370 Vantaa, Finland
3Natural Resources Institute Finland, Economics and Society, PO Box 2, 00791 Helsinki, Finland
Abstract. Latitudinal and altitudinal gradients can be utilized to forecast the impacts of climate changes on forests. To improve the understanding of forest dynamics on these gradients, we tested two hypotheses: (1) the change in the tree growth-climate relationship is similar along both latitudinal and altitudinal gradients, and (2) the time periods during which climate affects growth the most occur later towards higher latitudes and altitudes. We used tree-ring data from a latitudinal gradient in Finland and two altitudinal gradients on the Tibetan Plateau. We analysed the latitudinal and altitudinal growth patterns in tree-rings and investigated the growth-climate relationships of trees by correlating ring-width index chronologies with climate variables calculated with flexible time-windows, using daily-resolution climate data. The high latitude and altitude plots showed higher correlations between the tree-ring chronologies and growing season temperature. However, the effects of winter temperature showed differing patterns for the gradients. The timing of highest correlation with summer temperatures in southern sites was approximately one month ahead of the northern sites in the latitudinal gradient. In one out of the two altitudinal gradients the timing of strongest negative correlation with summer temperatures at low altitude sites was ahead of the treeline sites, possibly due to differences in moisture limitation. Mean values and the standard deviation of tree-ring width was found to increase with increasing mean summer temperatures on both types of gradients. Our results showed similarities of tree growth responses to growing season temperature between latitudinal and altitudinal gradients. However, differences in climate-growth relationships were also found between the gradients, due to differences in other factors, such as moisture conditions. Changes in the timing of the most critical climate variables demonstrated the need to use daily resolution climate data in studies on environmental gradients.

Citation: Lyu, L., Suvanto, S., Nöjd, P., Henttonen, H. M., Mäkinen, H., and Zhang, Q.-B.: Tree growth and its climate signal along latitudinal and altitudinal gradients: comparison of tree rings between Finland and Tibetan Plateau, Biogeosciences Discuss., doi:10.5194/bg-2016-559, in review, 2017.
Lixin Lyu et al.
Lixin Lyu et al.

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L. Lyu, S. Suvanto, P. Nöjd, H. M. Henttonen, H. Mäkinen, and Q.-B. Zhang
doi:10.6084/m9.figshare.4522928
Lixin Lyu et al.

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Short summary
Our results reveal that the change in tree growth-climate relationship is similar along latitudinal and altitudinal gradients, especially during growing seasons. Moreover, the critical periods for climatic effects on tree radial growth occurred earlier at lower latitudes and altitudes than at the cold ends of the gradients. We further demonstrate the use of daily climate data, as for it may disclose more precise gradient patterns that could not be detected if monthly climate data is used.
Our results reveal that the change in tree growth-climate relationship is similar along...
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