Nils Fagerberg grew up in the countryside, in a family where both parents were agronomists. From an early age, he was interested in forests and nature. In time, he trained as a forester – an expert in forestry – and worked as a consultant in the forestry sector. He also bought his own plot of woodland, which he wanted to manage without clear-cutting.
“I didn’t want a clear-cut area right outside my home. I wanted to keep the forest and preserve all its natural values, while still gaining an economic return”, says Nils.
Rotation or continuous-cover forestry?
Swedish forestry is conducted mainly through what is known as rotation forestry. This means that all trees are felled at the same time, leaving a clear-cut area, after which new seedlings are planted. This has been the standard method since the mid-20th century.
An alternative, which so far has been relatively uncommon, is to use continuous-cover methods, where the ground is always tree-covered. The advantages include increased biodiversity, sustained carbon sequestration, and a more attractive landscape for recreation.
However, he found it difficult to find research-based information on how to go about this in practice. In other words: How should one choose which trees to harvest in order to achieve the best profitability? Despite his education, he had not received much training in continuous-cover methods.
“There is a widespread misconception that continuous-cover forestry is unprofitable. But I haven’t been able to find any evidence that this is the case. That’s why I decided to dig deeper into the issue.”
Nils’ commitment resulted in a doctoral thesis that answers several of the questions he himself had struggled with as a forest owner. It is based on studies in five test plots of spruce forest in southern Sweden and shows how forest owners can harvest in a way that increases profitability in a multi-layered forest – that is, a continuous-cover forest where large and small trees grow side by side.
Nils Fagerberg
Senior lecturer in forestry and wood technology
Nils Fagerberg is a trained forester with a doctorate in forest industry production systems. Alongside his work at Linnaeus University, he manages his family’s farm outside Vetlanda, which practises continuous-cover forestry.
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SEK 11 million
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Clear deviations
He began by testing the Heureka Forest Simulator program, which is widely used in the forestry sector to simulate forest growth. However, the program is designed for rotation forestry, and Nils’ tests confirmed what he had suspected – that Heureka misjudged the trees in the multi-layered spruce forests of Småland. The analysis indicated that the small trees were growing faster and the large trees much slower than they actually were.
“This shows that the results can be distorted when simulating growth in a multi-layered forest, and that we cannot, in fact, draw any conclusions about profitability in such a forest based on Heureka simulations.”
I didn’t want a clear-cut area right outside my home.
To solve this problem, Nils decided to develop his own growth model specifically for multi-layered forests. Together with programmers, he created a digital model that takes into account an important aspect missing in Heureka: competition between trees. Trees growing close to one another compete for the same resources. When one tree is removed, the conditions for the surrounding trees generally improve, as they gain more sunlight and space. The key is to determine whether the overall economic return for a group of trees increases when one tree is removed – or whether it actually decreases.
Shows profitability per tree group
Nils’ model incorporates these aspects. It describes the size of both the central tree and the trees within its competition zone – a ten-metre radius in the case of spruce forest. The model takes into account the distance to surrounding trees and their species, since different tree species influence growth in different ways. For example, spruce is a tougher competitor than pine.
“My diagrams show when the economic return is at its highest for a particular area of forest. They show at what diameter an individual tree is ready for harvesting, depending on how dense the forest is around it. In a dense forest, profitability increases if the trees are harvested earlier than in a sparse forest”, says Nils.
The model can be used by forest owners who want to manage their forests using continuous-cover methods, as a guide to selecting trees and achieving the best profitability. The diagrams work for any spruce forest in southern Sweden.
Course in continuous-cover forestry
Nils makes use of his expertise as one of the teachers in the distance course Clearcut-free forestry at Linnaeus University. The course is aimed at those who wish to work with continuous-cover methods and covers, among other things, the advantages and disadvantages of different management approaches such as selective cutting, individual tree selection, group selection and shelterwood systems.
He believes that there is really no problem in managing a forest using continuous-cover methods – as long as one is interested and committed.
“Continuous-cover forestry suits the engaged forest owner who wants to gain more from their forest than just financial returns – for example, environmental values, carbon sinks and a pleasant forest to spend time in. If you are interested in that, you shouldn’t hesitate. Many believe they will lose money doing it this way – but that’s not true”, Nils concludes.