Above Ground Processes - Anticipating Climate Change Influences.

Increasing [CO2] along with associated changes in temperature will most likely alter the structure and function of forest ecosystems and thus will affect their Productivity and their role as stable sinks to CO2 sequestration and as regulators of the global hydrologic cycle. However, models predict that Earth's surface temperatures will increase along with shifts in precipitation that result in greater drought severity and frequency. As an example, maximum summer temperatures are likely to increase more than the average in southern and central Europe, whereas increasing water stress will dramatically affect mainly south-eastern Europe. Thus, forest ecosystems will experience a combination of numerous environmental stresses, which may significantly alter their physiological feedback on regional and continental climate. However, there is a great deal of uncertainty with regard to tree responses to interactive effects of global change scenarios. Models focusing on the interactions between climate change factors might help the scientific community to fill in the gaps in knowledge of how forest trees will respond to interacting effects. However, model accuracy depends to a large extent on our understanding of forest responses to climate changes. We conclude that there is an urgent need for multifactor climate change experimental studies examining the kinetic sensitivity of photosynthesis, stomatal conductance-transpiration, and respiration to the interactive effects of rising temperature, elevated [CO2], and environmental stress, in order to improve our ability to predict the physiological forcing of forest ecosystems on climate change.