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

Chair: Yiqi Luo + Claus Beier

Are there fundamental differences in the response of ecosystems and ecosystem compartments to changes in the timing of water inputs, are wet and dry ecosystems equally sensitive to changes in timing, are there particular interactions with other drivers which becomes important if timing changes, is it just the change in timing that matters or is it the severity of extreme events, which are the most sensitive processes affected by changes in timing, will the effects be driven by changes in ecosystem structure and functioning, are there particular problems related to amounts and timing in snowmelt, how big change does it take to make a difference, 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

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

Filip Moldan: Potential of time for space substitution in assessing the effects of increased/decreased precipitation

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)

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

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

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