Discussion group 2
Major factors regulating/controlling the effects of precipitation change on ecosystems: Our current state of understanding.

Chair: Rich Norby + Christian Körner

What are the key factors and processes regulating the effects of interactions among climate change drivers and among other drivers, which processes are most sensitive, what are the major adaptation strategies (species and community level)?What do the models say and what type of studies do we need.

Questions proposed

Martyn Futter: The effects of changes in snow accumulation and melt rates on ecosystem function

Olevi Kull: How much air humidity will influence directly plant growth and ecosystem processes

David Briske: Role of competitive interactions in mediating ecosystem responses to climate change and response of plant traits/functional types to climate change

Norbert Lamersdorf: New challenge for forest ecosystems/trees: Recent de-acidification, still high N-input, enhanced CO₂ - may lead to enhanced growth rates but may also increase future susceptibility of trees to droughts

Franco Miglietta: GPP and Transpiration coupling: do we really understand the process? - In temperate climates, high air temperature events are often accompanied by reduced precipitation leading to drought in forests and agricultural ecosystems. Water stress can reduce photosynthesis under those circumstances through stomatal limitations. Thus, a close coupling between photosynthesis and transpiration or a constant ecosystem water use efficiency (WUE, the ratio between primary productivity and transpiration) can be maintained even under stressful conditions. But heat stress can also directly cause photosynthetic inhibition in the leaves through a series of biochemical mechanisms. This has been neglected when considering environmental stress effects at the landscape scale. In climatic zones, where the vegetation is not specifically acclimated to heat stress, short duration high temperature episodes can actually cause a substantial decrease in carbon uptake of terrestrial ecosystems, even in the absence of drought.

José M. Moreno: Interactions among disturbances (i.e, fire) and post-disturbance precipitation patterns in determining plant composition/structure

Inger Kappel Schmidt: Rooting depth in response to climate change – consequences for measurements

Bridget Emmett: Interactions with other environmental changes

John Grace: What are the critical experiments to be done in order to settle the uncertainties?

Markus Reichstein: Detecting current changes in water balance at larges scales (remote sensing etc)

Andreas Ibrom: “What can the models say?” Which models do exist that can realistically predict changes in ecosystem functioning through changing precipitation? What are minimum model requirements to be useful in this respect?
What is the current understanding on how to describe stomatal functioning?
What is the current understanding on how to describe plant structural adaptation to drought, e.g., fine root production, root-shoot relationships, LAI?

Discussion group 1
Contrasting ecosystem responses to precipitation change at different climatic conditions (wet/dry & cold/warm).

Discussion group 3
Contrasting effects of changes in precipitation amounts and distribution patterns.

Discussion group 4
Uncertainties, thresholds, time lags, and climate and ecological "surprises".