Growth response to cuttings in Norway spruce stands under even-aged and uneven-aged management

This study evaluated the basal area growth of Norway spruce stands subjected to different management strategies; specifically, even-aged (EA) stands treated with thinning from below and uneven-aged (UEA) stands treated with selective cutting. Analysis was based on extensive empirical data obtained from permanent longterm experiments established in 23 even-aged and 26 uneven-aged Norway spruce (Picea abies (L.) Karst.) stands in Southern and Central Finland. The specific goals were to determine whether there are differences in: (a) the relationship between the stocking level and the stand basal area growth, (b) the stand basal area growth rates at a given stocking level, and (c) the stand basal area growth responses to cuttings between EA and UEA stands. A model-based approach was adopted in the analysis. Modelling was used to describe general trends and patterns in the data, emphasising the effects of overall stand density, cutting intensity, and management strategy on post-treatment stand growth. A model for a stand basal-area growth was fitted as a mixed linear model to the pooled data from EA and UEA stands. Model simulations were conducted to elucidate how the treatment of stands affects the predicted stand basal area growth. The analysis revealed a clear general effect of stocking level on stand basal area growth for all data. Growth increased with increasing stocking density. There was a significant difference in the stand basal area growth of EA stands and UEA stands. The growth of UEA stands was ca. 20% smaller than that of EA stands. There were also major differences in the timing and magnitude of the growth response to cutting between EA and UEA stands. Post treatment growth was noticeably slower in UEA stands than in EA stands, especially during the first 10 years after cutting. The results clearly show that the growth response of the trees remaining in EA stands is faster and greater than that in UEA stands, enhancing the stand basal area growth.