Problems in the determination and interpretation of needle and leaf loss : Air Pollution and Forest Decline. 14th International Meeting for Specialists in Air Pollution Effects on Forest Ecosystems

1989

S. 229-231

4 Abb., En, Zfsg. En

Unselbständiges Werk

200034680

In 1985 the first forest damage inventory on the entire forest of Switzerland was carried out and since then it has been repared every year. The representative sample survey is based on a subsmple grid of the National Forest Inventory. The most important criterion for estimating the vitality of the some 8'000 trees is crown foliage. Foliage loss is only a very generell aspect of the tree vitality and the possivilities of an interpretation are very limited. The most important assessment problems is the reliability of the estmation of the foliage loss in 5 %-intervals. An annual independent control survey of some 15 % of the trees shows that the mean systematic deviation over alle field crews came to 0.4 % foliage loss in 1988. This systematic deviation exerts a strong influence on the inventory results as expressed in percentage of damaged trees. This fact leads to grat uncertainty in rating the changes in foliae loss within one year. One of the most important problems of interpretation is the level of foliage los at which a tree should be sonsidered as damaged. The assumed damage limit between 10 % and 15 % foliage loss seems quite reasonable as long as the diameter increment is taken into account. Even the lowest damage class, i.e; betwen 15 % and 25 % foliage loss, shows a significant decrease of diameter increment compared with trees of less than 15 % foliage loss.