The effect of continuous-cover forest management on Norway spruce stem taper revealed by terrestrial laser scanning

In the Nordic countries, rotational forestry (RF) is the dominant silvicultural practice. RF is associated with biodiversity and ecosystem losses and may compromise wood quality. Continuous cover forestry (CCF) has been proposed as an alternative or complementary practice to RF. In CCF, the stand succession cycle differs from RF, which influences the rate and rhythm of tree growth, including the allocation of growth resources along the length of the stem. We studied whether the stem forms in mature Norway spruces ( Picea abies (L.) H. Karst.) differed between RF and CCF and how the generic Finnish stem taper model developed by Laasasenaho (1982) performed with these data. We used detailed stem data generated from terrestrially laser-scanned point clouds and calibrated the parameter coefficients of the stem taper model for each treatment. We found that the CCF trees had allocated more volume into the lower halves of their stems than the RF trees had and were more cylindrical in shape near the stem base. Model calibration improved prediction accuracy in both treatments, but more in RF than in CCF. The differences were likely due to the more open canopy space and lower stocking density, leading to longer crowns in mature trees in CCF that maintained more rapid growth in the stem basis. In conclusion, subtle, but statistically significant differences were observed between CCF and RF stem forms, and there is need to re-calibrate the stem taper model according to both management types.