Coordinating Editor: M. Partel.
Tree recruitment above the treeline and potential for climate-driven treeline change
Article first published online: 9 SEP 2009
© 2009 International Association for Vegetation Science
Journal of Vegetation Science
Volume 20, Issue 6, pages 1133–1144, December 2009
How to Cite
Hofgaard, A., Dalen, L. and Hytteborn, H. (2009), Tree recruitment above the treeline and potential for climate-driven treeline change. Journal of Vegetation Science, 20: 1133–1144. doi: 10.1111/j.1654-1103.2009.01114.x
- Issue published online: 26 OCT 2009
- Article first published online: 9 SEP 2009
- Received 14 July 2009; Accepted 18 July 2009.
- Alpine zone;
- Climate change;
- Mountain birch;
- Treeline dynamics
Questions: How do population structure and recruitment characteristics of Betula saplings beyond the treeline vary among climatic regions, and what is the potential for development into tree-sized individuals with interacting grazing pressure?
Location: Scandes Mountains.
Methods: Sapling characteristics of Betula pubescens subsp. tortuosa, their topographic position above the treeline, growth habitat and evidence of recent grazing was investigated in three areas with a long continuous grazing history, along a latitudinal gradient (62-69°N).
Results: Saplings were common up to 100 m above the treeline in all areas. The northern areas were characterised by small (<30 cm) and young (mean 14 years old) saplings in exposed micro-topographic locations unfavourable to long-term survival. In the southern area, broad height (2-183 cm) and age (4-95 years; mean 32 years) distributions were found in sheltered locations. Age declined with altitude in all areas. Sapling growth rate varied within and between areas, and the age × height interaction was significant only in the southern area. Growth rates decreased from south to north and indicated a considerable time required to reach tree size under prevailing conditions.
Conclusions: Regional differences can be attributed to climatic differences, however, interacting biotic and abiotic factors such as micro-topography, climate and herbivory, mutually affect the characteristics of birch saplings. In view of the long time needed to reach tree size, the generally expected evident and fast treeline advance in response to climate warming may not be a likely short-term scenario. The sapling pool in the southern region possesses strongest potential for treeline advance.