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

Chair: Lindsey Rustad + Josep Penuelas

Are there fundamental differences in the response of ecosystems and ecosystem compartments across climatic differences, which ecosystems are most sensitive, which need more attention, is more water/less water the problem, which compartment and processes are most sensitive, which drivers and interactions are most important. What do the models say and what type of studies do we need.

Questions proposed

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

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)

Andreas Ibrom: Which are the fundamental similarities in the response of ecosystems across biomes to drought and how important are these in comparison to the biome or ecosystem specific response features?
How different is the response of ecosystems to drought in a similar climate?

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

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".