Abstract
13C data on two sets of Eifel (Germany) trees are presented, which demonstrate severe non-temperature environmental influences disturbing the normal trend of data in this century. For five isolated trees exposed during the last 25 years to higher than normal CO2 content and other pollution gases, an unexpected increase in 13C values has been found, which is explained as pollution effect altering the photosynthetic CO2 fixation. For five other formerly forest trees of the same location, increasing 13C values during the youth stage have been observed, which later became adapted to the normal trend with clearing of their habitat. The 13C record for both sets of trees is similar at time periods of similar atmospheric environment. Ring width data of the trees and pollution experiments on barley confirm the observed effects. DOI: 10.1111/j.2153-3490.1979.tb00909.x