On the ¹³C record in tree rings. Part II. Registration of microenvironmental CO₂ and anomalous pollution effect

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.