Tree mortality in the dynamics and management of uneven-aged Norway spruce stands in southern Finland
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ORIGINAL PAPER
Tree mortality in the dynamics and management of uneven‑aged Norway spruce stands in southern Finland Sauli Valkonen1 · Lucie Aulus Giacosa2 · Juha Heikkinen1 Received: 19 March 2020 / Revised: 2 June 2020 / Accepted: 17 June 2020 © The Author(s) 2020
Abstract This study focused on tree mortality in spruce-dominated stands managed using the single-tree selection method in southern Finland. Together with regeneration and tree growth, mortality is one of the basic elements of the stand structure and dynamics in selection stands. The study was based on data acquired from a set of 20 permanent experimental plots monitored with repeated measurements for 20 years. The average mortality in the number of stems (N) was 4.45 trees ha−1a−1, in basal area (G) 0.07 m2 ha−1a−1, and in stemwood volume (V) 0.56 m3 ha−1a−1. In relative terms it was 0.50% of N, 0.30% of G and 0.27% of V, respectively. Wind and snow were the most common causes of mortality, while deaths by biotic causes (mammals, insects, pathogens) were extremely rare. Some 6–10% of the total loss in the number of stems and volume was attributable to the loss or removal of trees that sustained serious damage in harvesting. Most of the mortality occurred in the smallest diameter classes of up to 20 cm. Such a high mortality among small trees can have an adverse influence on the sustainability of selection structures if not successfully checked in harvesting and management. Keywords Stand dynamics · Picea abies · Mortality · Silviculture · Stand structure · Uneven-aged management
Introduction Tree mortality is one of the main dynamic components controlling the development and productivity of tree stands managed with the single-tree selection system, along with tree growth, regeneration, and harvesting. The relationships between the basic elements of growth and yield with special emphasis on selection management are presented in Lundqvist (2004). Mortality is important in making the gross yield into net yield in terms of merchantable timber since dead trees are not suitable for industrial purposes. Mortality among seedlings and saplings has been addressed in many studies in the Nordic area (see review by Lundqvist 2017) Communicated by Thomas Knoke. * Sauli Valkonen [email protected] 1
Natural Resources Institute Finland (Luke), P. O. Box 2, 00791 Helsinki, Finland
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but mortality of the larger trees constituting the main crop is less studied. Experimental results on growth and structural dynamics in uneven-aged stands have mostly been presented in net values, assuming that the role of mortality is generally small. Lundqvist (1993) presented stand-level mortality rates in a set of permanent field trials managed using single-tree selection and carried out observations for many decades with repeated measurements in Sweden. Lundqvist et al. (2007)
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