LONG-TERM REDUCTION IN THE DIAMETER GROWTH OF BUTT ROT AFFECTED NORWAY SPRUCE, PICEA-ABIES

The long-term effect of butt rot on the diameter increment of Norway s pruce, Picea abies Karst., was studied by analysing data collected by the Swedish National Forest Inventory. The 15698 Norway spruce trees w ere classified as healthy or infected based on bore cores taken at bre ast height. Healthy and infected trees, similar in terms of age, diame ter at breast height in 1954, increment from 1954 to 1963, and from si tes of the same productivity class in the same region were paired. Owi ng to restrictive criteria used, only 329 pairs were chosen for furthe r analysis. These trees were analysed groupwise as well as pairwise. I n the period 1954-1958, trees classified as infected grew faster than the healthy controls; however, within 5 years the relationship had rev ersed. The degree to which the growth of infected trees was suppressed increased with time, and was 8.9% and 8.2% respectively during the la st two 5 year periods. Differences in growth between healthy and infec ted trees within pairs were highly significant. The diameter growth of the infected trees was reduced by an average of 1.4 mm, or 9.4%, duri ng the last 5 years, corresponding to a 9.6% reduction in the basal ar ea growth.