How sensitive are forest trees to ozone? - New research on an old issue

Abstract

Studies on juvenile individuals under artificial environments dominate knowledge about the sensitivity of trees to O-3. Field approaches based on free-air O-3 fumigations of adult forest trees are a novel choice. Such a case study on beech and spruce (at the Kranzberg Forest near Munich, Germany) is used to address four long-standing issues in O-3 research: (1) Can a "unifying theory" of O-3 sensitivity be verified? (2) Are responses to O-3 consistent at different scaling levels in trees? (3) Are branch-bag experiments relevant for O-3 risk assessment of crowns? (4) Are saplings surrogates of adult trees when both are assessed under the same field conditions? Preliminary evidence from the ongoing long-term study confirms (1) and (3) but negates (2) and (4). In the absence of acute risks for adult trees, responsiveness of leaves cannot rule out long-term constraints by chronic O-3 stress.