Obj1. To examine the coupling between tree and ecosystem metrics over the recent decades across European forests.
Key open questions are: (Q1.1) Is the increase in WUE (both at tree and ecosystem scale) consistent across the large environmental gradient? Which are the physiological mechanisms underpinning changes in WUE? (Q1.2) Are tree and ecosystem metrics significantly correlated along a large environmental gradient? Is the strength of the relationship (slope) affected by global change factors? (Q1.3) Can we detect changes in N dynamics (retention vs. saturation) at the two levels of Ndep? (Q1.4) How do climate extremes and atmospheric Ndep interact and affect the sensitivity of tree and ecosystem to increasing Ca?
Obj2. To elucidate physiological strategies adopted by different species in response to climate extremes along the latitudinal gradient and how they determine the ecosystem response.
Key questions are: (Q2.1) Can we observe a divergence (among species) and convergence across sites (for a given species), in the physiological mechanisms underpinning tree responses to climate extremes? (Q2.2) Are tree and ecosystem response decoupled during an extreme events? (Q2.3) How quickly tree species recover from the disturbance and how this is reflected in carbon and water fluxes at the ecosystem scale? (Q2.4) Within each species, is there a difference in the recovery capacity along the gradient?
Obj3. To evaluate the role of nitrogen deposition in driving tree and ecosystem responses to climate extremes.
Key questions: (Q3.1) Can we detect different differences in N dynamics at the contrasting levels of Ndep (i.e., sites above and below the critical loads for N) during an extreme event? (Q3.2) To what extent is atmospheric deposition mediating sensitivity to drought events and which are the underpinning mechanisms?