High elevation treeline
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 rate of tree growth, but not the actual position of the treeline.
The worldwide treeline temperature assessment ended by 2001, when year-round data from ca. 30 different treeline sites around the globe became 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 hence the regional tree limit does not represent biologically the life form limit, as can be shown by the successional establishment of exotic tree taxa of higher elevation (e.g. Hawaii).
We see no decline of reserves as one approaches the existential limit of trees, in fact, carbohydrate and lipid stores reach a maximum at the tree limit. Thus, it seems unlikely that carbon limitation is a cause of treeline formation.
Hoch G, Körner C (2012) Global patterns of mobile carbon stores in trees at the high-elevation tree line. Global Ecol Biogeogr 21:861-871
- Paulsen J, Körner C (2014) A climate-based model to predict potential treeline position around the globe. Alp Bot 124:1-12
- 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
- Lenz A, Hoch G, Körner C (2013) Early season temperature controls cambial activity and total tree ring width at the alpine treeline. Plant Ecology and Diversity 6: 364-375
- Hoch G, Körner C (2012) Global patterns of mobile carbon stores in trees at the high-elevation tree line. Global Ecology and Biogeography 21:861-871
- Körner C (2012) Alpine treelines. Springer, Basel, ISBN 978-3-0348-0395-3
- Alvarez-Uria P, Körner C (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 C (2009) Nitrogen status of conifer needles at the alpine treeline. Plant Ecol Divers 2(3):233-241
- Hoch G, Körner C (2009) Growth and carbon relations of treeline forming conifers at constant vs. variable low temperatures. Journal of Ecology 97:57-66
- Shi P, Hoch G, Körner C (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
- Körner C (2007) Climatic treelines: conventions, global patterns, causes. Erdkunde 61:316-324
- Hoch G, Körner C (2005) Growth, demography and carbon relations of Polylepis trees at the world’s highest treeline. Functional Ecology 19: 941-951
- Körner Ch, Paulsen J 2004: A world-wide study of high altitude treeline temperatures. J. Biogeogr. 31:713-732
- Hoch G, Körner C (2003) The carbon charging of pines at the climatic treeline: a global comparison. Oecologia 135:10-21
- Li MH, Hoch G, Körner C (2002) Source/sink removal affects mobile carbohydrates in Pinus cembra at the Swiss treeline. Trees 16:331-337
- Paulsen J, Körner C (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 C (2000) Tree growth near treeline: abrupt or gradual reduction with altitude? Arct Antarct Alp Res 32(1):14-20
- Körner C (1998) A re-assessment of high elevation treeline positions and their explanation. Oecologia 115:445-459