Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The influence of spruce budworrn (Choristoneurafumiferana (Clem.)) defoliation was analysed at different stem heights by counting the number of latewood tracheids and measuring tree-ring width. The total height of the tree was divided into three different equal parts: the lower, the middle, and the upper sections of the total stem length. However, only the results of the lower and the upper sections will be presented in this paper. The reduction of ring widths started in the upper part for the living crown and continued downwards to the stem base (0 m) with a delay of 1–2 years. The number of latewood tracheids generally showed a reduction 1 year earlier than the ring widths, particularly in the crown, but also in the other parts of the stem. Considering this, we think that the reduction of the number of latewood tracheids may date the beginning of spruce budworm defoliation more accurately and present a better characterization of the first impact of spruce budworm than the measuring of the ring widths. This parameter will be particularly helpful (when expensive equipment, such as a densitometer or an image analysis system cannot be used) in detecting past outbreaks in the tree-ring records, especially when defoliation records are missing and when the reduction of the ring widths is not very pronounced.