Differences in tree growth of Norway spruce under rotation forestry and continuous cover forestry

Abstract

In Fennoscandia there is still lack of information for comparing the traditional even-aged management approach, or Rotation Forestry (RF), with the alternative uneven-aged management, or Continuous Cover Forestry (CCF), especially at tree level. We compared the basal area growth of more than 9000 individual Norway spruces (Picea abies (L.) Karst.), repeatedly measured in long-term permanent sample plots in both RF and CCF stands (the latter managed with single tree selection). We fitted a descriptive model considering characteristics related to tree growth potential (tree size and crown ratio), stand characteristics, site fertility, and management activities (namely forest management type, intensity and timing of last cutting before growth). Variables related to the individual tree characteristics were the most important predictors for growth. The model included two competition indexes, asymmetric (based on total basal area) and symmetric (based on on the amount of overtopping), which had both a stronger negative effect in CCF than in RF. Stand development stage (expressed by the mean height) had a slightly negative effect only in RF. Variables directly describing the intensity and timing of the cuttings had such a negligible effect in both management systems that they were discarded, likely due to their already indirect effects on modifying the stand-level structure (i.e. in reducing the competition effect). Concluding, we successfully fitted a biologically sound and accurate descriptive model that can be used in the ongoing comparison of the two management approaches. CCF trees had a consistently lower growth due to a stronger effect of the competition variables in the model. Our methods show that there is need to account for the differences in the forest structure when building a model aimed at different management systems.