Karaktärisering av Gremmeniella-skadade bestånd inom Holmen Skog AB :

Sammanfattning: Since the end of the eighteenth century forest damage caused by the pathogen Gremmeniella abietina has been observed and documented. During the latest epidemic in Sweden more than 480 000 hectares forest land have been injured and this has lead to considerable economic losses. For the pathogen to succeed with infection, spore dispersal and colonization the right environmental conditions is required. The aim of this paper is to describe the diseased stands using site and stand characteristics and to evaluate the effect of these variables on the disease incidence. Further, the thinning performed during the time for spore dispersal and its relationship to injured stands is examined. The stand data material originates from Holmen Skog AB database for their forest land holdings. This survey was made upon 670 diseased stands and the same number of reference stands. The variable included in the database was used in a logistic regression analyze to detect their effect on the diseased stands. An analysis was also done on whether the diseased stands where over-represented on land that former hold Norway spruce (Picea abies). Two different definitions were used. The analysis revealed that some of the districts in the three analysed regions showed a larger amount of diseased stands than others. These differences may not only depend on variation in stand characteristics but also on differences in recommendations used for the inventory. The logistic regression analyze showed that the variables altitude, latitude, temperature sum, type of vegetation, site index and sites better suitable for spruce were significant. The disease shows a positive correlation with height above sea level because it increased with an increasing altitude. The regression analyze also showed a positive correlation between Gremmeniella abietina and stands on land suited for spruce according to the National Forest Inventory i.e. there is a risk to establish pine on too fertile soil. However, the analysis of the site index variable could not support this. The outcome showed that only 12 percent of the diseased stands were located on former spruce sites. In the comparison between stands thinned in the summer during spore dispersal and later Gremmeniella-injured stands the results showed that there were too few stands diseased to give any significant results. In the future research and evaluation of diseased stands distinguishing features may be used to facilitate the identification of risky objects so that sufficient treatment will be implemented in time. Subjective judgments may be prevented by the use of satellite images when making estimating inventories of Gremmeniella-diseased stands.