Forest Decline Observed in the Department of Isere (France) on Silver Fir Trees (Abies alba Mill) and Norway Spruce Trees (Picea abies (L) Karsten)/ Relationships With the Physico-Chemical Characteristics of the Barks.

1993

S. 235-246

17 Lit. Ang.

Unselbständiges Werk

200041746

In recent years, the decline of the mountain forests in Europe has been given very serious consideration; this phenomenon has been partly attributed to diffuse atmospheric pollution. As it was impossible for us to study the effects of such pollution on trees directly we concentrated on the relationships that might exist between bark physico-chemical characteristics and criteria of tree decline (thickness of the 3 outermost tree rings, percentage of needle loss, percentage of abnormal colour). In 50% of the trees studied (165 silver firs and 235 Norway spruces), bark samples were taken to measure their pH and conductivity in the laboratory. Before starting this study, methods had to be defined: an experimental procedure had to be drawn up for bark analysis suited to our objectives. The processing of all data was based on statistical methods. The study of the criteria of tree decline, including that of bark hysico-chemical characteristics, highlighted the following important points: - the Belledonne massif is more affected by the decline phenomenon and in this massif, silver firs are more affected than Norway spruces; - it was noted that Norway spruce barks are on average more acid than silver fir barks, and that they are also thinner; - the correlations between bark acidity, conductivity and thickness showed that conductivity is closely related to bark thickness, whereas for acidity, there is no significant difference to be observed; - differences in acidity, conductivity and bark thickness are to be noted between the various massifs; these differences can be explained; - the study of the correlations between the criteria of decline and bark characteristics showed that the seriously damaged silver firs had more acid barks in general than healthy trees. Conversely in the Norway spruces, this aspect was not observed possibly because their barks are already naturally more acid; - as far as conductivity is concerned, this appears to be lower in the barks of damaged trees, both silver firs and Norway spruces. It is suggested that the differences observed are not directly due to the deposition of polluting agents on the barks, but that the process of 'recretion' in the leaves could provide an explanation: among damaged trees and hence the most defoliated specimens, rainwater is less charged in cations in contact with the leaves, and as the water runs down the bark there is less protoncation exchange, and the bark remains more acid than in the case of a healthy tree.