Der Zustand des österreichischen Waldes : Waldzustandsmonitoring, Ergebnisse Zukunftsperspektiven

Wien

1988

4 Lit. Ang.

SonderdruckUnselbständiges Werk

15199; 8825S

200083810

Forest condition (as far as it can be determined by crown assessment) has further improved on the whole, following a trend which could already be noticed last year. 72.2% of all sample trees did not show any crown defoliation, that is by 4.7% points more than last year. 25.2% show slight defoliation, that is by 4.7 points less than last year. The proportion of moderate or severe defoliation remain the same with 3.3%. The mortality rate of 0.11% (in the last three years 0.08% respectively) of the sample trees under observation to the amount of about 74.000 is, on the average, still within the range of the natural mortality rate of dominant trees, from the age of 60 and more. If the mean defolation degree (MDD) of each sample plot of the basic grid are considered for a forested area related evaluation instead of individual sample trees, the frequency proportion in the defoliation classes can be transposed to the forested area allowing an area related interpretation: - No defoliation at all or slight defoliation not exceeding the natural extend (MDD less than 1.50) of tree crowns could be identified in forest stands on a surface of 3,023.500ha (= 80.5% of the total forest area of 3,754.000ha ), which is an increase by 5.5 points. - There was, on the average, a slight defoliation (MDD: 1.51-2.00) of tree crowns in forest stands on 606.500ha (=16%), which is a decrease by 5.5 points. - Moderate and severe defoliation (MDD more than 2.00), on the average, could be registered in the forest area on 123.500ha (=3.5%), this area has remained the same since last year. The positive reaction to the favorable and abundant - both in this year and last year - precipitation destribution show clearly that crown defoliation is not always due to the impact of air pollution. Partly, it is to be considered as a response to less abundant precipiation activity (especially in 1983). After 5 years, those trees which then responded with slight defoliation could fully recover due to favorable weather conditions. Based on results of investigations carried out within the bio indicator grid during the years 1983 to 1986, first of all those economic losses are estimated, in which air pollutants represent the main cause of forest damage. In a second step, those forest damages are assessed, which during the inventories of the years 1984 to 1987 have manifested themselves in slight to serious degrees of defoliation. They are attributed to various abiotic damaging factors such as air pollutants, drought, hail etc. as well as biotic causes of damage such as blight fungi, hart rot - bud rot and insects. An estimated value for latent damages, i.e. damages without visible symptoms is added to the observed visible damages. Losses resulting from air pollutants each year in Austria were roughly estimated to amount up to 4.500 million AS. Losses resulting from biotic and abiotic ....