Measuring the effect of different silvicultural treatments on radial stiffness distribution within 15-year-old radiata pine.

Type of content
Theses / Dissertations
Publisher's DOI/URI
Thesis discipline
Forestry
Degree name
Bachelor of Forestry Science
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Journal Title
Journal ISSN
Volume Title
Language
English
Date
2021
Authors
Lilburne, Michael
Abstract

Pinus radiata (radiata pine) is a common plantation species grown extensively across New Zealand (Cown, 2005). It has good form and fast growth making it a good species for timber production (Cown, 2005). However, the timber produced from radiata pine tends to be of relatively low quality for structural purposes. It has poor strength qualities, particularly in the corewood region, due to low stiffness and high microfibril angle (MFA) within this region (Jakawickrama, 2001).

This study has investigated how different silvicultural treatments have affected the radial stiffness distribution within the stem of 15-year-old radiata pine. Silvicultural treatments observed include herbicide and fertiliser application, stocking, and clone type.

Acoustic velocity measurements were recorded using time of flight and radial disc scan tools. The time of flight measurements were taken at approximately 1.2 m and the disc scans were taken at approximately 2.2 m height. Two linear mixed-effects models were developed for each of the datasets. Modulus of elasticity and microfibril angle were inferred using formulas developed in Mason et al. (2017).

Herbicide: Herbicide had a significant effect on stiffness (P<0.01). The application of herbicide treatment reduced average stem surface MoE by 4% regardless of stocking level or clone type. Herbicide application increased DBH by 3.5%. Herbicide treatment had the greatest effect on MoE close to the pith. Effects were greatest and longest lived at 625 stems ha-1. Effects of herbicide were minimal at the stem surface.

Stocking: A planting density of 625 stems ha⁻¹ achieved the lowest surface MoE. On average, surface MoE was 10.6% lower at 625 stems ha⁻¹ than that achieved at 1250 stems ha⁻¹ and 2500 stems ha⁻¹. Stocking of 2500 stems ha⁻¹ achieved the highest MoE throughout the stem but also had the highest gradient change in MFA and MoE with distance from the pith. The high stocking also had the smallest DBH. On average, DBH was 23.2% and 41.9% lower at 2500 stems ha⁻¹ than 1250 stem ha-1 and 625 stems ha⁻¹ respectively.

Clone: Clone 3, a clone bred for low MFA and high basic density, had the highest MoE. On average Clone 3 had a MoE that was 13.0% higher than the other clone types. Clone 3 had the lowest radial gradient change of MFA and MoE. There was greatest variation in MoE between clone types at 625 stems ha⁻¹. The difference between clones was less at 2500 stems ha⁻¹. This suggests that genetics had a greater effect when environmental pressure was minimised.

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