The effects of thinning and fertilisation on wood and tracheid properties of Norway spruce (Picea abies) – the results of long-term experiments

Abstract

The aim of this thesis was to study the basic relationships between thinning and fertilisation, tree growth rate and wood properties of Norway spruce (Picea abies (L.) Karst.) throughout a stand rotation. The material consisted of a total of 109 trees from both long-term thinning (Heinola, 61°10’N, 26°01’E; Punkaharju, 61°49’N, 29°19’E) and fertilisation-thinning experiments (Parikkala, 61°36’N, 29°22’E; Suonenjoki, 62°45’N, 27°00’E) in Finland. Wood properties, i.e., radial increment, wood density, latewood proportion, tracheid length, cell wall thickness and lumen diameter, as well as relative lignin content, were measured in detail from the pith to the bark, as well as from the stem base towards the stem apex. Intensive thinning and fertilisation treatments of Norway spruce stands increased (8%–64%) the radial increment of studied trees at breast height (1.3 m). At the same time, a faster growth rate slightly decreased average wood density (2%–7%), tracheid length (0%–9%) and cell wall thickness (1%–17%). The faster growth resulted in only small changes (0%–9%) in lumen diameter and relative lignin content (1%–2%; lignin content was 25.4%–26%). However, the random variation in wood properties was large both between and within trees and annual rings. The results of this thesis indicate that the prevailing thinning and fertilisation treatments of Norway spruce stands in Fennoscandia may significantly enhance the radial increment of individual trees, and cause only small or no detrimental changes in wood and tracheid properties.