Tree and stand growth of mature Norway spruce and European beech under long-term ozone fumigation.

Abstract In a 50- to 70-year-old mixed stand of Norway spruce ( Picea abies (L.) Karst.) and European beech ( Fagus sylvatica L.) in Germany, tree cohorts have been exposed to double ambient ozone (2×O 3 ) from 2000 through 2007 and can be compared with trees in the same stand under the ambient ozone regime (1×O 3 ). Annual diameter growth, allocation pattern, stem form, and stem volume were quantified at the individual tree and stand level. Ozone fumigation induced a shift in the resource allocation into height growth at the expense of diameter growth. This change in allometry leads to rather cone-shaped stem forms and reduced stem stability in the case of spruce, and even neiloidal stem shapes in the case of beech. Neglect of such ozone-induced changes in stem shape may lead to a flawed estimation of volume growth. On the stand level, 2×O 3 caused, on average, a decrease of 10.2 m 3 ha −1 yr −1 in European beech.