People have made left their mark on the Swedish forest in various ways over the centuries. Going back 500 years or more, through slash-and-burn agriculture. In the seventeenth century, the forest was consumed in charcoal stacks for the production of iron and copper. By the eighteenth century, the forests of southern Sweden were emptied and eyes turned north, where ironworks were built on the estuaries of rivers in the counties of Västerbotten and Ostrobothnia, along with the accompanying charcoal burning. In the early nineteenth century, deciduous trees were burned to produce potash – used to manufacture soap among other things – and pines to produce tar. The middle of the century was a boom time for the forest industry and sawmills sprang up along the coast for the export of timber. A few decades later came the pulp mills and by end of the nineteenth century the Swedish forest was being overexploited.
Today, however, 70 per cent of Sweden’s land area is forested, mainly with pine, spruce and some birch. Other species are rare to a greater or lesser extent. The total volume of trees in Swedish forests has doubled over the last century, despite continued harvesting for the production of sawn timber and paper products.
“The challenge now is to identify tree species that can not only grow in today’s climate, but that will also be able to cope in 70 years when conditions will be completely different,” says Isabella Hallberg-Sramek, a researcher at the Swedish University of Agricultural Sciences (SLU) in Umeå.
Each year, over 400 000 seedlings are planted in Swedish forests. Previously, most were spruce, but since 2020 pine has taken the lead. Less sensitive to storms and drought, they are now replacing spruce in dry and nutrient-poor areas that are better suited to pine forests.
The availability of pine trees that are mature enough to be harvested has also increased in relation to spruce. The encroachment of the European spruce bark beetle into southern and central Sweden over recent years has led to an increase in spruce felling.
The state of forests today is the result of what earlier generations did, and what we do today will have an impact on future generations.
“Industrial interests have been a powerful force in shaping our forests. Although their numbers are now increasing, 40 years ago deciduous trees were viewed as a problem that needed to be eradicated,” says Isabella Hallberg-Sramek.
From the mid-twentieth century onwards, former grazing land in southern Sweden was planted with spruce, while in the north deciduous trees were kept in check by all available means, including the biocide Hormoslyr until it was banned in the early 1980s. In the south, this resulted in large swaths of continuous spruce forest, while large areas of forest in the north had virtually no deciduous trees.
“One reason for the forest industry’s earlier disinterest in birch was that the logs tended to sink in water, and so couldn’t be rafted. Once timber lorries were introduced, this was no longer a problem,” explains Hallberg-Sramek.
Production goals and environmental goals are equalized
Amendments to the Swedish Forestry Act in 1993 meant considerable changes for the industry, the most significant being that the new act equated production goals with environmental goals. The act also gave greater freedom to forest owners, but with added responsibilities, whereas the original act had regulated what they could and could not do in greater detail.
“This shift was not limited to Sweden. There was a global movement to define sustainable forestry. Environmental considerations and forest production were to be given equal weight under the law.”
While the amended legislation of 1993 certainly led to an increase in the number of deciduous trees, we can also thank the pulp industry for this development. The industry realised that high-quality paper required hardwood fibres in the mix and, birch being in short supply, the price of pulpwood was high.
Sustainable forestry standards such as FSC and PEFC have also led to an increase in the number of deciduous trees, as certification requires a certain percentage of deciduous forest.
“The overall effect of these changes is that Sweden has significantly more deciduous trees in young forests than old. This is a positive development as. generally speaking, a forest with diverse tree species is more robust and richer in biodiversity. Deciduous trees are also key to increasing the forest’s climate resilience.”
For Sweden, global warming may bring longer periods of drought and longer periods of heavy rainfall, as well as milder winters. The risk of damage due to storms, insects, fungi and forest fires will increase. Unfortunately, the choices already made concerning tree species will exacerbate the impact of climate change.
The damage inflicted by the spruce bark beetle in the forests of southern Sweden is largely the result of planting spruce on land that is slightly too dry; when trees are under stress during dry periods, they are more susceptible to attack. In northern Sweden, the situation is reversed, with pines planted on land better suited to spruce. This has resulted in pines suffering from fungal infections.
Right species in the right place
“Climate change has increased the importance of site adaption by ensuring that the right species are planted, or self-seed, in the right place. Less consideration was given to this previously, when planting was mostly based on demand. This damage demonstrates just how important it is to read the site.”
Non-native species were previously introduced into Swedish forests from similar latitudes to the west. Results have been mixed.
“Introducing new species always involves the risk of new pests and a negative impact on biodiversity,” says Hallberg-Sramek.
Climate change has raised a new discussion about transplanting species from south to north. The idea is that by helping trees to establish themselves, other species may also migrate north, such as sessile oak, silver fir and Douglas fir, trees that thrive in mountainous areas of Central Europe and that may be suited to Swedish forests in future.
“But there are also many tree species in southern Sweden, and there is also a discussion about whether we can use other native species to a greater extent than we do today. Aspen, maple and wild cherry are among those considered to have potential. Even the Siberian larch, which was once a native species, has been discussed,” says Hallberg-Sramek.
Increased interest in mixed forests
Interest in mixed forests has increased as an insurance policy in areas under attack from spruce bark beetles. The preferred option is birch, as there is already a market for it.
However, there are few with the courage to invest solely in deciduous forest, or larch, which are viewed as a risk as there is no guarantee that there will be any demand when the times comes to harvest the trees. Hallberg-Sramek describes this as a vicious circle: Sweden’s 320,000 forest owners are unwilling to invest unless there is a market, while manufacturing industry refuses to invest until the raw material is available.
“In my opinion, the solution is for the various stakeholders to come together to deal jointly with issues related to new tree species.”
A further obstacle to action is the desire for certainty regarding what will happen in future.
“Conducting forestry based mainly on two species is already a risky proposition. For example, we are already seeing new pests attacking young pines.”
Climate change demands that we develop platforms to mitigate the risks associated with forestry. This is a prioritised issue within Swedish research. One issue being addressed by a project in which Hallberg-Sramek is involved is how to adapt forests to make them more resilient to climate change.
“One lesson of this is that we have short memories. Historically, our forests have suffered many major storms, fires and insect attacks. We can learn from these events and, from a historical perspective, they are to be expected. While we can’t prepare for every eventuality, being prepared that something might happen is often enough to be able to cope with momentous events,” says Hallberg-Sramek.
Text: Carl Johan Liljegren Photo: Olle Melkerhed
