Acta Societatis Botanicorum Poloniae Article ID: 918 DOI: 10.5586/asbp.918 Publication History Received: 2021-08-17 Accepted: 2022-04-25 Published: 2022-08-15 Handling Editor Jan Holeksa; Adam Mickiewicz University in Poznań, Poland; https://orcid.org/0000-0001- 5138-484X Authors’ Contributions FZ designed the study, analyzed data, and cowrote the paper; AS edited and reviewed the manuscript and wrote the initial draft; GZ carried out data visualization and searched scientifc literature; BZ designed the study, acquired funding, supervised the research, and administered the project; XL assisted in the revision phase and validation of models; JT verifed data points and assisted in the revision; FZ, AS, and BZ contributed equally to this research Funding This research was funded by the National Natural Science Foundation of China (41601091) and Integrated Scientifc Investigation of the North-South Transitional Zone of China (2017FY100900) (funders had no role in designing the experiments). Competing Interests No competing interests have been declared. Copyright Notice © The Author(s) 2022. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits redistribution, commercial and noncommercial, provided that the article is properly cited. ORIGINAL RESEARCH PAPER in ECOLOGY A Multivariate Regression Model to Explain the Altitudinal Distribution of Timberlines on the Eurasian Continent Fang Zhao 1,2 , Abdul Shakoor 1,2 , Gul Zaib 3 , Baiping Zhang 4* , Xincan Lan 1 , Jiale Tang 1 1 College of Geography and Environmental Science, Henan University, 475004 Kaifeng, Henan, China 2 Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions (Henan University), Ministry of Education, 475004 Kaifeng, Henan, China 3 Institute of Epigenetics and Epigenomics, Yangzhou University, 225009 Yangzhou, China 4 State Key Laboratory of Resource and Environment Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 100101 Beijing, China * To whom correspondence should be addressed. Email: zhangbp@lreis.ac.cn Abstract e altitude of alpine timberline elevation has been considered to correlate with certain climatic factors. Many related isotherms (e.g., warmest month 10 °C isotherm) have been proposed to explain the altitudinal distribution of alpine timberline at the global scale. However, any climatic index actually has a wide range at the alpine timberline position worldwide. e altitudinal position of the alpine timberline is related to far more than just one climatic factor. erefore, we developed a multivariable model for timberline elevation variability by collecting data from 473 timberline sites on the Eurasian continent. We analyzed 12 climatic variables that potentially account for timberline variation. Principal component and regression analyses were used to mine four climatic variables. e mean temperature of the warmest month (MTWM), mean temperature of the coldest month (MTCM), climatic continentality (K), and annual precipitation (AP) explained 95% of the variability of timberline elevation. MTWM, MTCM, K, and AP contributed 18%, 41.28%, 34.9%, and 5.82%, respectively, to the altitudinal distribution of alpine timberline on the whole continent; 20%, 44%, 28.86%, and 7.14% in the eastern continent; and 17.71%, 39.79%, 40.21%, and 2.29% in the western continent. We showed that MTWM, MTCM, K, and AP are deterministic factors for the altitudinal distribution of alpine timberline in the Eurasian continent. MTCM and K contributed to explaining the altitudinal distribution of timberline both in the entire, eastern, and western parts of the Eurasian continent. Our research highlights the signifcance of MTCM for the altitudinal distribution of timberline. Keywords Eurasia; timberline elevation; climatic variables; climatic continentality; mean temperature of the warmest month; annual precipitation; mean temperature of the coldest month; multivariable model 1. Introduction e vegetation boundary that divides closed forests and nonforest in the high mountain area is referred to as the timberline or treeline (Korner & Paulsen, 2004). Above this line, forest life forms disappear and are replaced by the elfn wood belt, alpine meadow, or other high mountain scenery (Troll, 1973). Timberline elevation is related to climatic factors, topography, and even anthropogenic activities (Holtmeier, 2009). Among these factors, climatic factors, including warm-season temperatures, are deterministic factors and play a vital role in tree growth and survival in the Acta Societatis Botanicorum Poloniae / 2022 / Volume 91 / Article 918 Publisher: Polish Botanical Society 1