Evaluation of generic stem taper function in continuous-cover Norway spruce forests

In the Nordic countries, rotation forest management (RF) is the dominant silvicultural practice. RF is associated with biodiversity and ecosystem losses and may compromise wood quality. Due to these recognized problems 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 how the generic Finnish stem taper model developed by Laasasenaho (1982) for RF performs in CCF stands, and whether the stem forms differ between RF and CCF. We analyzed the stem form and volume of mature Norway spruces (Picea Abies (L.) H. Karst.) from both RF and CCF using detailed stem data generated from terrestrially laser-scanned point clouds. The analysis entailed re-parametrizing the stem taper model by management, canopy class and stand strata. Re-parametrizing the original stem taper model according to the strata improved the model prediction accuracy slightly, both in CCF and RF. The stem volume allocation didn’t significantly vary between the RF and CCF, although we noted slight stem form differences between the treatments. Trees were less slender and had more buttressed stems in CCF, based on smaller form height values, and higher relative volumes in stems below 50-% height than in RF. These differences were likely due to the more open canopy space and lower stocking density and therefore longer crowns in mature trees in CCF that maintained more rapid growth in the stem basis.