Air pollution and climate change effects on forest ecosystems: new evidence

Abstract

The following articles of this issue report on the outcome from an international conference entitled Air Pollution and Climate Change at Contrasting Altitude and Latitude held during September 7–12, 2008, in Murten/Switzerland under the auspices of the International Union of Forest Research Organisations (IUFRO). Key factors in air pollution and climate change, and in particular, the role of pollution in a changing environment were highlighted in numerous presentations. High anthropogenic nitrogen deposition was corroborated as a main driver both of effects mediated through elevated CO2 and enhanced ground-level ozone (O3) exposure on forest trees and ecosystems. Awareness was directed to interacting effects of elevated CO2 and O3 levels (cf. Matyssek et al. 2010), as high CO2 has the capacity of ameliorating adverse O3 impact, whereas ozone may reduce the carbon sink strength, and hence, the buffering capacity of forest trees and ecosystems in relation to the increasing atmospheric CO2 level (cf. Sitch et al. 2007; Pretzsch et al. 2009). On such grounds, O3 has widely been recognized and emphasized during the conference as a major component of climate change at the global scale (cf. Fowler et al. 2008). Being another outcome of progressive climatic change, drought requires continued research efforts, as it controls— via stomatal regulation—the amounts of O3 and CO2 taken up by plants (cf. Paoletti and Grulke 2005; Kostner et al. 2008). Drought was recognized to bear the potential of protecting the vegetation from versus sensitizing it to O3 impact (cf. Matyssek et al. 2006). Recent evidence indicates aboveground O3 impact on forest trees to indirectly promote mitigation of the belowground carbon storage capacity of ecosystems (cf. Nikolova et al. 2009)—being crucial for the further progression of climate change. There was consensus that, in particular, belowground effects of air pollution and climate change must attract further attention, as associated multi-factorial interactions have hardly been covered satisfactorily toward ascertaining process-based evidence. The risk of overlooking ‘‘the unknown unknown’’ remains a challenge in research and in prognosticating future tree and ecosystem performance. In particular, such a risk applies when considering biotic agents such as mycorrhizae and soil micro-organisms, as well as of competitors and host–parasite relationships. The plants’ genotype per se was recognized as a fundamental determinant of tree and ecosystem responsiveness. Apart from the need for clarifying mechanistic grounds as pointed out above, concepts must be fostered toward concerted approaches in empirical research, long-term monitoring and modelling. Apparent trends in the research conducted and evidence acquired during the past 20 years (Paoletti et al. 2010) reflect a shift in focus from