High elevation treeline

Central Alps, near Davos, Switzerland, treeline at 2200 m
Mexico, Pico di Orizaba, treeline at 4000 m

If one considers the high elevation treeline as a global phenomenon, many local drivers, which dominated the debate in the past, become less significant, they become modulators of a more fundamental, common cause. Our working hypothesis is that the major driver of treeline formation is the ability to form new structures, rather than the provision of raw materials for these structures. In other words, we suggest that the treeline is a sink (growth) rather then a source (photosynthesis) driven phenomenon, with temperature representing the single most important determinant. We do not question the influence of other factors, but we consider them to represent a suite of regional peculiarities, which may affect the actual position by not more then 100 m in elevation. A detailed discussion of the treeline issue can be found in:
Our activities go in several directions. They include treering studies across the treeline ecotone (see ref. below), microclimate measurements at various latitudes and an assessment of the carbohydrate supply status at the tree limit.

The worldwide treeline temperature assessment nears its end by 2001, when year-round data from ca. 30 different treeline sites around the globe will be available. As a standard procedure we measure root-zone temperature at 10 cm depth in the shade of tree crowns at the treeline using Tidbit (Onset Corp.) data loggers. Currently available data from 90 % of the stations average at seasonal mean ground temperatures of ca 6.5 C, with very little site to site variation, irrespective of latitude (minimum of 5.5 C on Mexican volcanos at 4000 m and maximum at some maritime temperate zone treelines of ca 7.5 C). The seasonal mean proved to be a better predictor of treeline position than warmest month temperatures or a suite of thermal sums tested. There are regions with no suitable treeline taxa where natural treelines occure at lower elevations (higher temperatures; e.g. Hawaii).

In a work on carbohydrate pools we compare treelines in Mexico, the central Alps and in N-Sweden (Abisko). We see no decline of reserves as one approaches the existential limit of trees, in fact, carbohydrate and lipid stores reach a maximum at tree limit. Thus, it seems unlikely that carbon limitation is a cause of treeline formation.



Alvarez-Uria P, Körner Ch 2011: Fine root traits in adult trees of evergreen and deciduous taxa from low and high elevation in the Alps. Alpine Botany 121:107-112

Birmann K, Körner Ch 2009: Nitrogen status of conifer needles at the alpine treeline. Plant Ecol Divers 2(3):233-241

Fajardo A, Piper FI, Pfund L, Körner Ch, Hoch G 2012: Variation of mobile carbon reserves in trees at the alpine treeline ecotone is under environmental control. New Phytologist 195:794-802

Hoch, G. (2013) Reciprocal root-shoot cooling and soil fertilization effects on the seasonal growth of two treeline conifer species. Plant Ecology & Diversity, 6, 21–30

Hoch G, Körner Ch 2012: Global patterns of mobile carbon stores in trees at the high-elevation tree line. Global Ecology and Biogeography 21:861-871

Hoch G, Körner Ch 2009: Growth and carbon relations of treeline forming conifers at constant vs. variable low temperatures. Journal of Ecology 97:57-66

Hoch G, Körner Ch 2005: Growth, demography and carbon relations of Polylepis trees at the world’s highest treeline. Functional Ecology 19: 941-951   

Hoch G, Körner Ch 2003: The carbon charging of pines at the climatic treeline: a global comparison. Oecologia 135:10-21   

Hoch G, Popp M, Körner Ch 2002: Altitudinal increase of mobile carbon pools in Pinus cembra suggests sink limitation of growth at the Swiss treeline. Oikos 98:361-374   

Hoch G, Richter A, Körner Ch 2003: Non-structural carbon compounds in temperate forest trees. Plant Cell Environ 26:1067-1081

Körner Ch 2012: Alpine treelines. Springer, Basel, ISBN 978-3-0348-0395-3   

Körner Ch 2008: Alpine ecosystems and the high-elevation treeline. In: Jørgensen SE, Fath BD (eds) Ecosystems, Vol 1 of Encyclopedia of Ecology. Elsevier, Oxford, pp 138-144   

Körner Ch 2007: Climatic treelines: conventions, global patterns, causes. Erdkunde 61:316-324   

Körner Ch 2007: The use of “altitude” in ecological research. TREE 22:569-574   

Körner Ch 2003: Alpine plant life. 2nd edition Springer, Heidelberg [Chapter 7]   

Körner Ch 1998: A re-assessment of high elevation treeline positions and their explanation. Oecologia 115:445-459

Körner Ch, Paulsen J 2004: A world-wide study of high altitude treeline temperatures. J. Biogeogr. 31:713-732

Lenz A, Hoch G, Körner Ch 2013: Early season temperature controls cambial activity and total tree ring width at the alpine treeline. Plant Ecology and Diversity 6: 364-375   

Li MH, Hoch G, Körner Ch 2002: Source/sink removal affects mobile carbohydrates in Pinus cembra at the Swiss treeline. Trees 16:331-337   

Li MH, Hoch G, Körner Ch 2001: Spatial variability of mobile carbohydrates within Pinus cembra trees at the alpine treeline. Phyton 41: 203-213       

Paulsen J, Körner Ch 2001: GIS-analysis of tree-line elevation in the Swiss Alps suggest no exposure effect. J Veg Sci 12:817-824   

Paulsen J, Weber UM, Körner Ch 2000: Tree growth near treeline: abrupt or gradual reduction with altitude? Arct Antarct Alp Res 32(1):14-20   

Shi P, Hoch G, Körner Ch 2008: A test of the growth-limitation theory for alpine treeline formation in evergreen and deciduous taxa of the Eastern Himalayas. Funct Ecol 22:213-220   

Shi P, Körner Ch, Hoch G. 2006: End of season carbon supply status of woody species near the treeline in western China. Basic and Applied Ecology 7:370-377