Abstract

The effects of the intensity and timing of commercial thinning and fertilisation on tracheid properties and lignin content of Norway spruce [Picea abies (L.) Karst] were studied in two long-term fertilisation-thinning experiments in central and eastern Finland. The experiments consisted of three thinning and three fertilisation treatments in a randomised block design. Fertilisation levels were: unfertilised (F ₀), 150 kg N ha^-1 (F ₁), and 300 kg N ha^-1 (F ₂). Thinning treatments were: delayed first thinning (T ₀), normal thinning (T ₁), and intensive first thinning (T ₂). A total of 85 trees were sampled 26 years after treatment onset. Tracheid length was measured for 24 trees and cell wall thickness and lumen diameter for 16 trees grown under treatments F ₀ T ₀, F ₀ T ₂, F ₁ T ₀, and F ₁ T ₂. Lignin content was determined for all trees sampled (n=85) grown in all the different treatment combinations. We found only small differences in tracheid length (0–6%), cell wall thickness (1–17%) and lumen diameter (0–9%), depending on the different fertilisation and thinning conditions. We also found only slightly (1–2%) higher lignin content for fertilised (F ₁ and F ₂) than for unfertilised (F ₀) trees (25.8% and 26.0% vs. 25.4%). Trees yielded 26.0% lignin content after intensive first thinning (T ₂), 25.9% following normal thinning (T ₁), and 25.4% after delayed first thinning (T ₀). Thus, the prevailing fertilisation and thinning practice for Norway spruce stands in Finland may not cause essential changes in tracheid properties and lignin content.