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

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 (2xO(3)) from 2000 through 2007 and can be compared with trees in the same stand under the ambient ozone regime (1xO(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, 2xO(3) caused, on average, a decrease of 10.2 m(3) ha(-1) yr(-1) in European beech.