The document discusses the effects of climate change on vegetation responses and forest regeneration bottlenecks in the Central Alps. It notes that vegetation shifts are a function of changes in climate and existing climate type. Models project large changes to species distributions and vegetation under climate change scenarios. Increased disturbances from more frequent windstorms, forest fires, and insect outbreaks will likely create more gaps in forests. Regeneration in gaps may be problematic in some areas of the Alps due to drought, competition, or replacement by non-native species. The document proposes experimental approaches to test how drought limits tree recruitment and how recruitment could be facilitated through soil moisture, seasonal precipitation regimes, nurse vegetation, and mycorrhizal associations.

1. Regeneration bottlenecks in the Central Alps induced by drought Tom Wohlgemuth Barbara Moser, Kipfer, Sarah Richter, Ulrich Wasem, Simon Egli, Jaboury Ghazoul, Andreas Rigling Swiss Federal Research Institute WSL 8903 Birmensdorf, Switzerland

2. Climate change effects: vegetation response by analogy vegetation: Bohn et al. (2003) Map of the natural vegetation of Europe. climate: http://www.globalbioclimatics.org/ (Rivas-Martinez S.) Zurich: atlantic 105 mm; 8.9 °C Conclusion: ∆Vegetation = f(∆climate, climate type) Fagus sylvatica +1,4 ° Geneva Carpinus b. +4,5 ° Bordeaux Pinus pinaster +6 ° Porto Quercus ilex +7,5 ° Genova Quercus ilex Sion: submed/cont (600 mm; 9.2 °C) Pinus sylvestris +2 ° Kerch Stipa pennata

5. 2b. Vegetation response projections (dynamic): gap models Kienast & Kuhn (1989) Vegetatio 79. Mortality Extrinsic growth limits Intrinsic growth limits Growth curves Competition Establishment Gap Recruitment bottleneck

6. Climate change effects: gap producing disturbances

7. Climate change effects: more disturbances, more gaps Usbeck et al. (subm.) Increased windspeeds -> more windthrows Windspeeds in Zürich 1935 1955 1975 1995

8. Climate change effects: more disturbances, more gaps 2003 Summer temperatures shifted by 4.6 °C towards warmer conditions Schär et al. (2004) Nature 427. More heatwaves -> more forest fires

9. Climate change effects: more disturbances, more gaps Ips typographus on Picea in Switzerland More windthrows/heatwaves -> more insect outbreaks Storm VIVIAN 1990 Storm LOTHAR 1999 European heat wave 2003

10. Forest recruitment in gaps: which problems? Lothar windthrow 1999 Forest fire frequency 1900-2000

11. Gap-forming disturbances along the Alpine Arc windthrow forest fire forest fire x x

12. Regeneration problems in gaps x x N-Alps S-Alps Central Alps Windthrow Delayed recruitment competition Forest fire Adapted recruitment or replacement neophytes Forest fire Delayed recruitment drought treeline

13. Forest fire patch ‘Leuk’ “ Spanish Switzerland”

14. broadleaved coniferous oak pine spruce larch 2003 2006 2006 Regeneration after fire 2000 m 1600 m 1200 m 800 m Conclusion Biome shifts in dry regions? Processes to be tested! Steppe ? Forest ?

15. Annual precipitation in continental Sion (Switzerland) 2007 Which processes facilitate forest regeneration? Which processes limit forest regeneration? Trend Regeneration threshold Regeneration processes Oppor- tunity Oppor- tunity Oppor- tunity Bottleneck Bottleneck Bottleneck Bottleneck

16. Experimental approach in the ‘Spanish Switzerland region’ Treatments Soil warmth Precipiation regimes Nurse vegetation Trees Pinus sylvestris Pinus nigra Quercus pubescens