Thinning and growth response
KEY POINTS- Evaluate thinning strategies for growth, stand structure, and economics.
- Models for competition, growth, allocation, and treatment response.
- Climate-adapted thinning
Project overview
Participants
More related research
Global goals
- 8. Decent work and economic growth
- 13. Climate action
- 15. Life on land
Short summary
The project includes the establishment and evaluation of thinning trials in spruce, pine, lodgepole pine (contorta), hybrid larch, birch, and oak across Sweden.
For decades, SLU has established thinning experiments with the aim of evaluating different strategies and how they shape individual trees and forest stands, as well as how economics and production are affected over a full rotation period. One of the larger experimental series is known as the GG trials, which were established at a large number of sites from the mid-1960s to the early 1980s. The experimental series includes both thinning and fertilization of pine and spruce as treatments.
The thinning strategies tested in the GG trials include intensity (how much is removed), thinning form (removal of smaller or larger trees), frequency (the number of thinnings and the interval between them), and the timing of the first thinning. One factor not included in the GG trials, but tested in other experimental series, is how trees are selected for thinning—i.e., whether thinning is selective or schematic (for example, corridor thinning).
Research on thinning in spruce and pine is essentially a continuous field of research that does not really have a beginning and will not have an end. During the period 2026–2028, a major synthesis of the GG series will be conducted.
Since 2020, a new series of thinning experiments has been established in pine at sites in southern and central Sweden. These trials evaluate early thinning responses together with studies of the ecophysiological reactions to heavy thinning in a stand.
The first series of thinning experiments in lodgepole pine (contorta) was established from the late 1980s to the early 1990s. A second experimental series in contorta was established in the late 2010s, and a third series is currently being established. Results from the older contorta thinning trials will be analyzed and reported in the coming years.
Thinning experiments in birch have been established during the past five years, and the establishment of additional trials is ongoing. Early results from these trials will be presented in a doctoral dissertation in 2027. There are also three thinning experiments in birch established by Skogforsk, which have been reported in a doctoral dissertation (Zvirgzdins 2025).
Two thinning experiments in oak were established during the period 2020–2024, and an additional trial will be established in 2026. There is also an older thinning experiment in oak that was established in the early 1990s.