Regeneration of Scots pine and black pine under changed climate in the Valais, Switzerland (2008-2011)

Rationale and questions

Pine forest (Pfynwald) near Susten (VS) Photo: R. Lässig, WSL

In the upper Rhone valley (canton Valais, Switzerland), tree mortality in Scots pine (Pinus sylvestris) stands increased since the second half of the 1990ies. Several research studies have related the phenomenon with direct and indirect effects of climatic changes. One of the effects concerns the number of warm summer days that has significantly risen during the last 20 years.

In addition to the increased Scots pine mortality, which questions the continuation of these forests, tree regeneration after disturbance effects in that region seems to be markedly reduced. For instance, a survey of post-fire vegetation after a stand-replacing forest fire in Leuk revealed only small numbers of Scots pine saplings four years after the burn in 2003.

In the ongoing PhD study, experiments serve to evaluate the influence of different climate parameters (i.e. summer drought, rain seasonality, start of the growth period) and interspecific competition on germination and early growth of Scots pine and black pine (Pinus nigra). Black pine is known to resist drought better than Scots pine. In details, the following questions are addressed:

• How differ Scots pine and black pine in regard to germination, growth and survival under different water availability and different soil temperatures?
• How vary Swiss and Spanish provenances of Scots pine and black pine in regard to germination, growth, survival and competition?
• How differ Scots pine and black pine in regard to their competitive power (with Quercus pubescens) under different water and light availabilities?
  
  

Forest burn above Leuk (VS) Photo: R. Lässig, WSL	Rock steppe near Leuk (VS) Photo: S. Richter, WSL

Experimental design

All experiments are performed using a mobile rainshelter facility located near Leuk/Susten in the Valais. Rainshelters move automatically controlled over boxes with seedlings as soon as rain starts, and after rain has stopped they move back. Water is given manually according to different treatment requirements.

Rainshelter facility near Leuk/Susten Photo: E. Schnider, WSL	Seedling boxes Photo: T. Wohlgemuth, WSL	Measuring seedlings Photo: E. Schnider, WSL

Terminated experiments:

• Experiment 1 (2009): Germination, growth and survival of two provenances of Pinus sylvestris (Switzerland and Spain) and Pinus nigra (Spain) in regard to different water (dry, dry-moist, moist) and temperature treatments (ambient, +2.5 °C and +5 °C above ambient).
  
• Experiment 2 (2008-2010): Competition effects of pubescent oak (Quercus pubescens) on 2-years-old plants of Pinus sylvestris and Pinus nigra (with provenances of the Valais and Spain, respectively) under different water treatments.
  
  

Scots pine seedling early after germination. Photo: E. Schnider, WSL	Germination experiment: left box with treatment moist/+5 °C soil temperature; right box with moist/ambient soil temperature. Photo: S. Richter, WSL

Publications

Richter S., Kipfer T., Wohlgemut T., Calderón Guerrero C., Ghazoul J., Moser B. (2012) Spring precipitation and genotypic variation may be the key to the persistence of Pinus sylvestris at the forest-steppe ecotone. Oecologia 169: 269-279. DOI: 10.1007/s00442-011-2191-x.

Contact

• Sarah Richter
  

• Thomas Wohlgemuth