Respacing naturally regenerating Sitka spruce and other conifers
The document focuses on the management and respacing of naturally regenerating Sitka spruce and other conifers in British upland forests, emphasizing practices to optimize stand development and timber quality. Its purpose is to provide guidance for forest managers on when and how to intervene in naturally regenerating stands—through respacing, thinning, and site assessment—to enhance stability, tree quality, and long-term productivity, supported by experimental evidence and operational considerations. The intended audience includes forest managers, silviculturists, and forestry professionals involved in the regeneration, thinning, and sustainable management of upland conifer stands.
Summary
Introduction
The document discusses the increasing occurrence of dense natural regeneration of Sitka spruce and other conifers in upland Britain, emphasizing that these patterns are common in both recently clearfelled areas and continuous cover forestry stands. It explains the variability in natural regeneration densities and outlines management strategies, including natural self-thinning and intervention through respacing to improve stand quality and stability.
Natural Self-thinning in Regeneration
Dense natural regeneration often experiences high mortality due to competition, leading to self-thinning after 25–30 years. The relationship can be modeled to predict stand development. The article notes that stands generally do not stagnate but tend to decline in stocking density over time due to self-thinning, with high mortality rates on suitable sites.
Guidance on Respacing Natural Regeneration
The document reviews historical and recent experiments guiding the respacing of naturally regenerated Sitka spruce, highlighting the importance of timing and target densities. An experiment from 1973 and subsequent studies in the 1990s are summarized, illustrating how respacing impacts stand density, growth, and windthrow risk.
Experimental Evidence and Findings
The 1973 Ae experiment tested various respacing methods, showing that selective respacing increased diameter growth and reduced mortality compared to uncontrolled stands. Additional experiments in the late 1990s examined different spacing targets, confirming that respacing reduces tree density, enhances growth, and decreases windthrow risk, with less mortality and better stand stability.
Management Recommendations
Forest managers are advised to consider respacing based on site stability, wind risk, and stand development stage. It is recommended to delay respacing until trees are 3–4 m tall for better quality selection, and to choose target densities based on site conditions and the timing of intervention. The importance of removing small dead stems and creating access racks for mechanization is emphasized.
Other Conifer Species and Mixed Stands
The principles of respacing apply broadly to other conifer species and mixed stands, where self-thinning naturally occurs. In mixed forests, faster-growing conifers tend to dominate, and respacing can help maintain species diversity. Dense regeneration in continuous cover forestry also benefits from similar management approaches, with the removal of ‘wolf’ trees and overstorey management.
Summary and Practical Advice
Key recommendations include using respacing for stand stability, favoring quality stems, delaying intervention for better selection, targeting densities of 1750–2500 stems per hectare, and removing small dead stems. Managing regeneration involves strategic timing, site assessment, and consideration of wind risk.
Additional Information and References
The document provides references to related publications, experimental studies, and sources for further information on forest management, natural regeneration, and specific research on Sitka spruce, with contact details for further inquiries.
[https://cdn.forestresearch.gov.uk/2022/02/fcpn016-1.pdf Respacing naturally regenerating
Sitka spruce and other conifers] (en)
Number of pages: 6
Target countries: Britain
Key takeaways
- Respace natural regeneration to optimize stand stability and timber quality
- Managed respacing, particularly delaying until trees are 3–4 m tall, can improve diameter growth, reduce stand stagnation, and facilitate mechanized harvesting operations.
- Target stand densities of 1750–2500 stems per hectare based on site stability and management objectives
- Lower densities are recommended on less stable, high windthrow risk sites, while higher densities are suitable for productive, stable sites where subsequent thinning may occur.
- Natural self-thinning can significantly reduce stand density over time, which can be predicted using existing yield models
- High mortality in dense stands occurs mainly between 25–30 years, leading to a natural decline in stocking without intervention, but respacing can accelerate this process.
- Selective respacing favors better quality and forms of trees, enhancing future stand stability and timber value
- Decisions to remove suppressed, dead, or inferior stems improve stand quality and facilitate safer, more efficient harvesting.
- During respacing, cutting below the bottom live whorl prevents regrowth from stumps
- This practice helps control residual competition and facilitates the development of a well-structured stand.
- Use of racks and mechanical disturbance can facilitate access but should be timed with stand development
- Cutting access racks around 1–2 m height, followed by selective respacing at 3–4 m, balances operational safety with quality improvement and is supported by operational studies.
- The principles of stand management apply similarly to conifers other than Sitka spruce, with easier workability in dense regeneration
- Stand development and respacing strategies can be adapted for mixed conifer stands and species with faster growth, promoting diversity and healthier mixtures.
Sources
- Respacing naturally regenerating
Sitka spruce and other conifers - 2010-12-01 - https://cdn.forestresearch.gov.uk/2022/02/fcpn016-1.pdf
