Global change at timberline in the Central European Alps G. Wieser, W. Oberhuber, A. Gruber, R. Matyssek Innsbruck / Munich © G. Wieser Photo J. Wagner

The timberline ecotone Krummholz-limit Forest limit Tree-limit AfterTranquillini 1976, 1979 © G. Wieser

What is Global Change?  Climate change  altered atmospheric chemistry  climate warming  Land use change  management, land abandonment © G. Wieser

Climate change air temperature Wieser unpublished © G. Wieser

Climate change air temperature Mean Mean Difference Annual mean Winter Spring Summer Fall3.5 0 Vegetation period Wieser 2007 © G. Wieser

Impacts of climate warming carbon balance – present situation Presently warm growing season temperatures and their effect on ER are the key factors limiting NEP Wieser and Stöhr 2005, Wieser 2007 © G. Wieser

Impacts of climate warming carbon balance – future warmer climate GPP+ 15 % ER+ 10 % NEP+ 5 % Temperature increase 1°C Carbon sequestration may benefit from future climate warming After Wieser and Stöhr 2005 and Wieser 2007 © G. Wieser

Impacts of climate warming carbon gain of trees Soil tempertature also affects carbon gain Havranek 1981 © G. Wieser

Impacts of climate warming soil temperature and tree growth Krummholz limit artificial soil cooling Soil cooling caused a significant decline in stem diameter increment at the krummholz limit Oberhuber, Gruber, Wieser unpublished © G. Wieser

Global change treeline shifts – seedling re-establishment Luzian and Pindur 2007 Seedling re-establishment results from invasion into potential habitats rather than an upward migration due to climate warming © G. Wieser

Land use change carbon balance Wieser and Stöhr 2005, Larcher 1977, Koch et al VegetationNEP [g C m -2 y -1 ] Forest360 Dwarf shrubs Grassland and pastures © G. Wieser

Land use change water balance Matyssek et al. 2008, Wieser 1983, Guggenberger 1980, Kronfuss 1997 Alpine pasture The vegetation type has a significant impact on the carbon and water balance VegetationETI [mm y -1 ] Forest480 Dwarf shrubs350 Grassland and pastures280 © G. Wieser

. Conclusions © G. Wieser  With respect to carbon gain, trees and stands will benefit from future climate warming  Invasion is a consequence of the currently decreasing grazing pressure on pastures, which has suppressed forest up-growth throughout centuries  This kind of habitat re-occupation suggests the tree line in the Central European Alps to behave in a conservative way.

. Conclusions © G. Wieser  Finally, one has to be aware that the alpine timberline in the Central European Alps is more susceptible to human impact such as land use changes and management practices than to expected climate change.  In addition episodic extreme events by e.g. summer and/or frost drought, severe frost during the growing season or biotic stress (by pathogens/herbivores) rather than the gradual temperature increase will control tree population dynamics within the timberline ecotone of the Central European Alps in the future environment.

Thank you for your attention © G. Wieser Photo K-H Häberle Mining area opened 1272 closed 1967