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Pests and pathogens cause devastation in nature reserves

Last changed: 19 November 2024

It may be tempting to perceive damaged forests as primarily a problem for the forest owner or the industry. A factor affecting price on wood, but of limited importance to society. Pests and pathogens can however cause great devastation to treasured nature reserves, and diminish their ecological, cultural, social or aesthetic values. Relatively speaking, the effects can be greater than in productive forests, since the reserves’ management guidelines can make it difficult to protect them.

Nature reserves are established by the Swedish provincial government Länsstyrelsen, at their own behest or on the land owner’s or public’s initiative. The reserve must fulfill a certain purpose: preserve biodiversity; preserve, restore or create valuable natural environments; provide outdoor activities for the public; or protect, restore or create habitats for endangered species.

If Länsstyrelsen judges that the reserve would fulfill such purposes, creating high enough environmental values, the reserve can be established. During establishment, detailed management guidelines are written that describes the purpose and the rules that must be followed for this purpose to be met.

These rules have been phrased differently during different periods of time. During the 20th century, they primarily prohibited actions. Preservation was assumed to require human passivity – so called “free development”. Today, we know that this is not always the best approach, in particular when the purpose is to protect and preserve natural environments. In modern reserves, the manager has more room for manouevre. It is however difficult to alter the guidelines or purposes of older reserves, which limits the possibility for protective actions there.

The case of Örups almskog

The elm forest, the only of its kind in Sweden, mainly consists of elm, mixed with oak, ash, hornbeam, maple, and lots of wild apple.

Valdemar Bulow, 1916

Just south of Tomelilla in Skåne in southern Sweden is Örup castle, a manor dating from the late 13^th century. In 1913, the grounds were divided and sold off, and as a result, an 8,5 hectare large area were given to the Swedish Society for Nature Conservation (SNC). The area primarily consisted of an elm forest, the largest of its kind in Sweden. Some of the trees were old, but most originated from the 19^th century. At that time, the area was used as pasture for the manors’ horses. With no grazing animals, the trees grew freely, and the elms soon dominated. The forest developed into a quite unique Swedish biotope of almost exclusively elm trees, and it was turned into a nature reserve in 1928.

“Örups almskog” (elm forest) became a concept and a cherished field trip destination for ecologists and nature loving families alike. It was even more cherished by some sixty species of mosses, lichens, insects and fungi that relied on elm trees for their existence, and by another 400 that in some way or other used the trees.

Örup 1982_2_Mårten Lind (Gunvor Lind).png

A picture from Örup nature reserve, the year is 1982. Foto: Gunvor Lind

Enter the elm disease

However, this little paradise is no more. In 1978, the dutch elm disease struck the forest. This malady is caused by a fungus called Ophiostoma. It is unknown how the fungus ended up in Sweden, but it can only travel over large distances through human dislocation of infected elm wood. By the time, the fungus had not yet been found elsewhere in Skåne, and might have arrived in a shipment of logs from Poland, Germany or the Baltic States. The Swedish Forest Agency began monitoring the development in 1980, and found that one of seven elms in Örup was dead already. In 1982, it was 4 out of 10, and two years later, 7 out of 8.

The fungus is the killer, but to spread locally it needs to hitch-hike on elm bark beetles. The beetle deposits its eggs in diseased trees, and when the next generation emerges from the bark, they are covered in Ophiostoma spores. They seek out new trees on which to feed on leaves, and thus transfer the disease over to the new host. One of the few effective ways known to limit the spread is to remove all trees showing symptoms of disease, since all that are left standing will produce hundreds of new beetle the next spring.

Much has been written about the SNC’s decisions when the disease was found in Örup in 1979. Since the forest was a nature reserve, the SNC objected to any kind of counter actions, on the argument that diseases are natural events and that in a reserve, nature shall run its course. They also expressed the hope that some resistant trees would survive, from which a new elm forest could sprout. The guidelines of the reserve did prohibit intrusive action, but also allowed thinning and other actions deemed necessary to preserve the area such as intended. In other words, the SNC were allowed to act, but chose not to.

This represents an environmentalist standpoint that had gone out of fashion already by 1980, and the SNC was heavily criticized for their decision. Critics argued that a disease introduced by man could not be seen as natural, that the disease could have been stopped or slowed and a unique ecosystem saved, and that there were no scientific reasons to believe that any trees would be resistant. Someone even filed a police report, accusing the SNC for willfully having allowed the elm disease to establish in Sweden.

In hindsight, it can be argued that the SNC’s logic was flawed, but it is still unclear whether a fight in Örup would have made a difference in the long run. The disease would never have been eradicated once it reached Sweden. The spread could have been slowed, which in and of itself would have been a good thing. The elm forest’s role as an origin, a driver for the following outbreak in Skåne, would have been less intense. But the elms of Örup would certainly have kept on dying, and sooner or later they would have been gone. Perhaps they could have remained 25 years instead of 10. What those fifteen differing years would have been worth in retrospect is a difficult question to answer.

A call for elm

The elm forest disappeared regardless. Since the disease is less aggressive on smaller trees, some elms still grow old enough to produce seeds and generate new trees. The species elm remains in Örup, but not the tree elm. It is reduced to bushes and the occasional slender stems. As soon as they reach some three or four meters of height, the disease strikes. The area is still a reserve, but today the purpose is to preserve other values altogether than in 1928. How many of the sixty elm-dependent species that remain is unknown, but most of them were epiphytes such as mosses and lichens, specialized on the unusual bark of the large trees (elm bark has a much higher pH than most other deciduous trees). Such bark is long lost in Örup.

If the elm forest is to one day come back, it will come down to finding individual trees that happen to be resistant to the disease. Such exist, but they are very rare. Skogforsk, the research institute of the Swedish forest industry, has initiated a “call for elm”, a plea to the public to report any healthy elms found in the vicinity of diseased ones. In 2023, some hundred such reports were received and are being followed up. Also, breeding aimed at producing resistant individuals are ongoing. In a report from 2024, ordered by the Swedish government, it was suggested that the government would provide funds for the continuation and development of this work. If that would come to pass, it is possible that we can plant resistant elms in Örup some day in the future, and recreate the forest. Perhaps the lost mosses and lichens would return as well. But even if such trees were available today, which they are not, it would take 150 years for Örups almskog to retrieve its lost glory.

Dead trees in Örup nature reserve. Photo: Mårten Lind

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In the nature reserve of Örup you find dead trees after elm disease. Photo: Mårten Lind

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In Fiby Nature Reserve, dead spruces stand eerily after the spruce bark beetle infestation that has affected the reserve. Photo: Mårten Lind

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In Fiby Nature Reserve, there are also several dead spruces that have fallen due to the spruce bark beetle infestation. Photo: Mårten Lind

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If you look closely at the fallen trees, you can see traces of insects where the bark has come off. Photo: Mårten Lind

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The case of Fiby urskog

Since January 2022, the visitor to the nature reserve Fiby urskog (primeval forest) is greeted by a sign:

Warning!

Due to high risk of falling trees, the pathway is closed until further notice and will not be maintained. Visitors enter at their on risk.

Fiby is an 87 hectares large natural reserve west of Uppsala. It is a typical primeval forest, mainly consisting of mixed conifer forests, mixed with large swathes of deciduous trees of various kinds. The ground is hilly, with valleys and depressions, and littered by large mossy boulders. There is a lake in the northern end. The serene ambiance under the dark trees is like something out of a fairy tale. At least, it used to be that way.

The forest was “discovered” during an excursion in plant biology in 1910, led by professor Rutger Sernander. He described a primeval forest with huge spruce trees, almost a meter in diameter, and enormous juniper bushes. It would later be revealed that the forest was basically untouched since the late 18^th century. During the coming decades, Sernander worked hard to make the forest a natural reserve to protect the unique environment. A reserve finally was established in 1966, twenty years after Sernander’s death. The only human involvement for the last 250 years has been Länsstyrelsens work to keep the pathways open by removing fallen trees. No forestry has been conducted.

Fiby urskog is probably Uppsalas most famous natural reserve. It is a spot for school trips, mycological excursions and relaxing forest strolls, and the number of visitors is large enough that the forest is suffering from significant wear and tear. Länsstyrelsen thus has the right to close certain areas from public access.

The drought and the spruce beetle

As stated by the sign, the reserve is today closed, although it is not forbidden to enter. The reason is the large spruce beetle attack that has ravaged Sweden and large parts of Europe all since the severe drought of 2018.

The spruce beetle is just few millimeters large. As the name suggests, it digs tunnels into the bark of spruce trees, and deposits its eggs within. When they hatch, the larvae eat the bark, and once the beetle is developed it keeps on eating for a few weeks before digging itself to freedom and flying off. The spruce puts up a good fight, however. During normal conditions, the beetles are no match for a healthy tree, and they go primarily for stressed or diseased ones. But every such tree will give rise to a large number of new beetles in the next generation, and if many trees in a small area are stressed simultaneously, by drought, for example, the amount of beetles can grow large enough to kill neighboring healthy trees as well. This tends to happen after around 4 000 attacks on a single tree. Just as for the elm disease, it is therefore important to remove dead trees well before the beetles emerge. That happens approximately 8-10 weeks after the eggs were laid, but the trees should preferrably by cut earlier, because fully developed beetles can survive in the large chunks of bark that fall off during harvest.

The ongoing outbreak is still driven by the momentum it received during the drought of 2018, but has since lost a lot of its ferocity. Removing the attacked trees has not had much effect on this decrease – there has just been too many of them. Seven out of ten trees that should have been removed have been left standing. In nature reserves, however, dead trees are a problem even during smaller outbreaks. The guidelines may prohibit human interference, and even when they do not, the search for attacked trees is very resource-demanding. This means that bark beetles may cause greater damage in nature reserves than in production forests (indeed, in many cases one reason the reserve was established in the first place). This is further enhanced by the fact that the beetles prefer large, older trees, of which there are many in the reserves. This sometimes cause tension between government and forest owners, since the production forests close to the reserves of course also can be attacked. Or the other way around – since a large outbreak in a production forest may spread into a reserve where counter actions are prohibited or hard to administer.

Closed reserves

The outbreak in Fiby urskog is over. Almost every large spruce has been killed, and there are no more around for the beetles to live in. The dead trees rot quickly and can break or fall even in weak wind gusts, which is why it is considered dangerous to visit the forest. This is the reason that Länsstyrelsen advises against visits. But another reason is that it is pretty much impossible to move about in the reserve without having to constantly climb over large tree trunks. It looks as if it was hit by a hurricane that took everything with it. Or perhaps rather a tornado, because the trees lie in all kinds of directions.

This is not likely to change any time soon. As long as the outbreak continues, it is dangerous as well as meaningless to clean up the pathways, and it might not happen before every single spruce tree has fallen. Also, Länsstyrelsen lacks funding to deal with this very demanding workload. Fiby urskog will not greet visitors in a long time yet.

Fiby is not the only reserve in Uppland suffering this fate. To date, six other reserves are closed. The reserves will remain reserves also after the beetles are gone, but the forests that was to be protected will look very much different, and no 200-year-old spruce trees are likely to survive. Such trees are very rare outside the reserves, and for every attacked reserve they grow fewer still, for visitors to experience and for the species dependent on them to live on. The ravages of the spruce beetle affect us in many ways – not just through the losses of the forest industry, but also limiting ours and other species access to old spruce forests.

Formal obstacles to action

Fiby urskog is, like many older reserves, an example of how guidelines written with the best of intentions may lead to a valuable environment’s destruction rather than it’s salvation. The purpose in Fiby is phrased as to “preserve biodiversity and natural areas by allowing the area to develop freely without any human interference”. The guidelines are focused on what may not be done, and one of thirteen specifically formulated prohibitions cover “harvesting, clearing, cultivating, or conducting any other action of forestry or in any other way harm living or dead trees and bushes or other vegetation.” It is easy enough to understand the thought process: here is something worth protecting, and to do so we prohibit any kind of action. If there are 200-year-old spruce trees, we must protect them by making sure they are not cut down.

But because of the spruce beetles, the result is the very opposite. In Fiby as well as Örups almskog, each dying tree contributed to a higher infection pressure on the trees that remained. If the goal was to protect what existed, the primeval forest or the unique elm forest, then the laissez-faire-approach of the guidelines was counter-productive.

Länsstyrelsen has the option to seek dispensation for circumventing the guidelines of a reserve, but never from its overall purpose. Since “develop freely without any human interference” is written into the purpose of the reserve, no dispensations could be granted, and it was thus formally impossible to protect the reserve from the beetle. However, in the case of Fiby 2018, protecting the forest never was a possibility. The outbreak was by far the most intense on record, and developed very rapidly. Länsstyrelsen would have had to identify a very large number of attacked trees already during the fall of 2018, and then harvest them all in early 2019, which would have been difficult for several reasons. For one, the same drought affected not just Fiby, but every reserve in the county. And even if such considerable resources could have been mustered, the harvest in itself would have brought new risks since many healthy spruce trees would have ended up in the edges of the clearings, and such exposed trees are much more susceptible to beetle attacks than trees in the shadow of the forest. On top of that, Länsstyrelsen would have had to publicly defend the decision to clear-cut a large area within a popular natural reserve – a pedagogic challenge to say the least.

But during normal-sized outbreaks, a purpose phrased less stringently can make it easier to protect the forest. The reserve Granliden in north-eastern Uppland was established in 2017. Its purpose is “to preserve the calciferous conifer forest and marshland forests with ecosystems and biodiversity”, which is to be done by “conducting actions beneficial to prioritized species”. Such phrasing does not require dispensation for the feeling of, for example, spruce trees attacked by spruce beetles.

But even when such dispensations could theoretically be granted, they are practically difficult to use against spruce beetles. 150 of the reserves of Uppland is manged by Länsstyrelsen. The government searches for attacked trees in the spring to be able to fell them before the hatching of the beetles in the early summer, but dispensation requests takes months to administer. More than one generation of bark beetles can hatch in the reserve before the bureaucratic process has run its course. An exception is when spruce trees are felled in winter storms, and a dispensation can allow for removing the bark of the trees, or the trees themselves, before the beetles hatch in the spring.

Limited resources

This is why Länsstyrelsen focuses mainly on such reserves where actions are allowed without dispensations, and where the spruce forest is instrumental to the purpose of the reserve, such as in Granliden, mentioned above. The work is conducted by helicopter, dogs trained to discover attacked trees, and by manual search efforts on ground.

Länsstyrelsens beetle-fighting unit basically consists of two people. They describe it as impossible to address more than a fraction of the 150 reserves. Also, summer is the most important time for this endeavor, which collides with vacation. Demands for time-consuming procurement for tasks such as the felling of trees and flying a helicopter also affects the possibility to fulfill the task in time.

Such limitations also affects the establishment of new reserves. It is expensive to conduct the seek- and cleanse-efforts that is required to actively try to protect forests against spruce beetles, but it is very cheap to leave the reserves to their own devices. Sometimes, a free development type of purpose is chosen, even though a greater freedom of action would better serve to protect the environmental values at hand.

In conclusion, two types of deficiencies are aggravating damage in forest reserves. One is purely financial. The spruce beetle outbreak is too vast for more than a handful of the reserves to be protected by the financial resources available to Länsstyrelsen today. Nature preservation costs money, and how to prioritize natural reserves is ultimately a political question.

The other is a historical lack of knowledge of the devastating potential of forest pests and pathogens. That has lead to purposes and guidelines that prohibits counter actions that would have been necessary to limit the damage to the reserves. The understanding of forest pathology today makes it possible to avoid such mistakes. But the future will present new challenges after the spruce beetles are gone, which also must be met by new knowledge. In the work to develop this knowledge, SLU Forest Damage Center plays a crucial role.

Written by: Mårten Lind for SLU Forest Damage Centre

Facts:

Sources:

Örups almskog – Naturskyddsföreningen i Skåne (naturskyddsforeningen.se)

Microsoft Word - Almsjukan i Malmö - en tillbakablick.docx (slu.se)

När almen tystnar - Natur & Kultur (nok.se)

Örups almskog - ett område i förändring | LUP Student Papers

Fiby urskog | Länsstyrelsen Uppsala (lansstyrelsen.se)

Länsstyrelsen i Uppsala läns beslut, 2000-04-28, dnr 231-6952-99, ”Bildande av naturreservatet Fiby urskog”.

Länsstyrelsen i Uppsala läns beslut, 2017-12-04, dnr 511-4419-12, ”Bildande av naturreservatet Granliden i Östhammar kommun”

Länsstyrelsen i Skåne läns beslut. 2022-11-17 dnr 511-15270-2021, ”Beslut om utvidgning, ändrade föreskrifter och ny skötselplan för naturreservatet Örups almskog, kärr och ängar i Tomelilla kommun”

FULLTEXT01.pdf (diva-portal.org)

Naturreservat i Sverige ISBN 91-620-8233-7 (naturvardsverket.se)

ohrn-p-20240314.pdf (slu.se)

Granbarkborre i och kring skyddad natur (naturvardsverket.se)

Process bilda naturreservat - Dispenser och tillstånd (naturvardsverket.se)