REDUCING THE EFFECTS OF DISTURBANCE ON TREE-RING DATA USING INTERVENTION DETECTION

In order to analyse the radial growth reactions of trees caused by a s pecific forcing factor, the effects of other disturbing signals have t o be eliminated from the tree-ring chronology. The possibility of usin g detrending methods and time series analysis to determine and elimina te growth reactions caused by thinnings was studied on material obtain ed from a long-term growth experiment on Norway spruce (Picea abies (L .) Karst.) in southern Finland. Special attention was paid to interven tion analysis. The low-pass filter used eliminated long-term growth ch anges but it did not filter out rapid growth reactions caused by thinn ings. Short-term changes were modelled and eliminated from tree-ring c hronology by means of intervention analysis combined with time series analysis. Significant autocorrelation and interventions were found at lower stem heights but not in tile upper part of the stem. The pulse i ntervention whose effect died out within 3 yrs after thinning had the best fit to the mean chronology. Tree-ring series from long-term growt h experiments were shown to be well suited to intervention analysis be cause the time and intensity of disturbing silvicultural events are kn own.