Abstract
Understanding how climate change influences succession is fundamental for predicting future forest composition. Warming is expected to accelerate species succession at their cold thermal ranges, such as alpine treelines. Here we examined how interactions and successional strategies of the early-successional birch (Betula utilis) and the late-successional fir (Abies spectabilis) affected treeline dynamics by combining plot data with an individual-based treeline model at treelines in the central Himalayas. Fir showed increasing recruitment and a higher upslope shift rate (0.11 ± 0.02 m yr−1) compared with birch (0.06 ± 0.03 m yr−1) over the past 200 years. Spatial analyses indicate strong interspecies competition when trees were young. Model outputs from various climatic scenarios indicate that fir will probably accelerate its upslope movement with warming, while birch recruitment will decline drastically, forming stable or even retreating treelines. Our findings point to accelerating successional dynamics with late-successional species rapidly outcompeting pioneer species, offering insight into future forest succession and its influences on ecosystem services.
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Data availability
The CRU TS v.4.07 climate dataset was obtained from https://crudata.uea.ac.uk/cru/data/hrg/. The SSP scenarios in the Coupled Model Intercomparison Project Phase 6 were downloaded from https://data.isimip.org/. Occurrence data for Himalayan birch and Himalayan fir were retrieved using the Global Biodiversity Information Facility database (https://www.gbif.org/). The data have been archived in the National Tibetan Plateau Data Center at https://doi.org/10.11888/Terre.tpdc.301173. Source data are provided with this paper.
Code availability
Statistical analysis in this study was performed with publicly available packages in R (version 4.3.1)75 and Programita software (version ProgramitaNovember2018.exe) (https://programita.org/)64. The custom code for the analysis of the data and the modified Sygera Treeline Model has been archived in the National Tibetan Plateau Data Center at https://doi.org/10.11888/Terre.tpdc.301173.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (grant nos 42030508 and 41988101) and the Second Tibetan Plateau Scientific Expedition and Research Program (grant no. 2019QZKK0301). J. Peñuelas was supported by the Spanish government grants PID2022-140808NB-I00 and TED2021-132627 B–I00 funded by MCIN, AEI/10.13039/501100011033 European Union Next Generation EU/PRTR, the Fundación ‘Ramón Areces’ grant CIVP20A6621, and the Catalan government grants SGR 2021–1333 and AGAUR2023 CLIMA 00118. J.J.C. acknowledges funding by Spanish Ministry of Science and Innovation projects PID2021-123675OB-C43 and TED2021-129770B-C21. The Department of National Parks and Wildlife Conservation, government of Nepal, is especially acknowledged for granting research permission. We thank S. Rai and S. Chaudhari for their help during the fieldwork and Y. Zhao for data analysis.
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E.L. designed the research. S.R.S. and J. Pandey collected the data. S.R.S. and X.Z. analysed the data. S.R.S. drafted the paper with intensive input from E.L., F.B., J.J.C. and J. Peñuelas. All authors contributed ideas, interpreted the results and were involved in the editing and writing of the paper.
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Extended data
Extended Data Fig. 1 Spatial distribution of fir and birch within three treeline plots.
Points are scaled based on tree ages.
Extended Data Fig. 2 Comparison of temperature and moisture ranges of birch and fir under different climatic conditions.
a, Annual degree-days ( > 0 °C) (Mean uDD, Eq. 1). b, Maximum drought index, the ratio between yearly PET and precipitation. The lower and upper box boundaries represent the lower and upper quartiles, respectively, and the lines inside each box show the medians. The p value is the results of t test.
Extended Data Fig. 3 Simulated density dynamics of birch (cyan lines) and fir (red lines) adults (height > 2.0 m) including projected temperature and precipitation in three SSP scenarios (SSP126, SSP340, and SSP585).
During the first 50 years of spin-up, 200 seeds (100 birches and 100 firs) entered the plot every year and are shown on the left side of the dashed lines. Various biotic and abiotic species-specific variables were considered in the model simulation (see Supplementary Table S2 for detail). The vertical solid lines represent 1901 and 2020 of the real simulation phases. The range of variation in the figure represents means ± standard errors.
Extended Data Fig. 4 Variability in shade tolerance of two species.
The relationships between tree establishment performance (f_shadow) and available light for the two study species.
Extended Data Fig. 5 Photograph showing an alpine treeline (Manang) with different tree species in the central Himalayas.
Birches (brown color) at top are followed by firs (dark green) and pines (light green).
Extended Data Fig. 6 Map showing the locations of the treeline plots.
Map showing the locations of the treeline plots, mountain peaks near the treeline sites and the pyramid meteorological station.
Extended Data Fig. 7 Flow chart of the model processes for the simulation cycle of the treeline model which proceeds in yearly time steps.
All trees experience different stages such as seed production, seed dispersal, establishment, growth and mortality, and processes are influenced by abiotic (temperature and drought) and biotic (intra- and interspecific interaction) factors.
Extended Data Fig. 8 Conceptual framework of the treeline model.
Birch and fir trees are located on a hypothetical mountain slope ranging from closed forest to the alpine treeline ecotone. Individual trees competed with neighbors representing interspecific competition. The slope was subjected to a smooth gradient of temperature, decreasing with increasing elevation. The thermal lapse rate was -0.0065 °C m-1.
Supplementary information
Supplementary Information
Supplementary Figs. 1–7, Tables 1–3 and descriptions for the Sygera Treeline Model modification.
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Sigdel, S.R., Zheng, X., Babst, F. et al. Accelerated succession in Himalayan alpine treelines under climatic warming. Nat. Plants 10, 1909–1918 (2024). https://doi.org/10.1038/s41477-024-01855-0
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DOI: https://doi.org/10.1038/s41477-024-01855-0
