05. Restoration of oak habitats

When restoring oak habitats, the area’s unique characteristics must be prioritised. How overgrown the area is, landuse history, presence of species and access to grazing animals are examples of factors that affect how the restoration is implemented. In Life Bridging the Gap, the aim has always been to vary the design of the restoration work, to achieve diversity both in and between areas.
Betande kor i ekhage i Johannishus Åsar naturreservat.

In the Life Bridging the Gap project, the most extensive measures have been to restore different types of oak habitats – everything from oak dominated, overgrown oak pastures to deciduous broadleaf woodlands with a considerable oak component. At project start, several Natura 2000 areas had unfavourable conservation status. This was due to the amount of overgrowing, low or non-existent grazing pressure, too few old trees, too little dead wood or poor conditions for the species associated with the habitat types. The objective has been to reverse this trend, and to improve the status by way of restoration and other complementary measures.

Variation in aims

The aim of the restorations in the project has been to recreate mosaic, warm and diverse pasture and deciduous broadleaf woodlands – with open glades of various sizes, older oaks that have been cleared around, sunny wetlands and areas with a more dense canopy. In larger glades, the ambition was to have flowering bushes along the woodland edge, preferably to the north of the glade. Through clearing around, old open-grown oaks and their successors their crowns have been given the chance to expand, while root competition and mechanical damage from younger competing trees, in some cases also hazel, was removed. This puts the older oaks in a good position to become even older, and to keep providing habitats for cavity-nesting birds, and bats, insects and lichens. Older oaks offer more habitats because they develop cavities with wood mould, coarse bark and other structures, and therefore are conducive to greater biodiversity.

Before restoration begins

Before restoring an oak pasture or deciduous broadleaf woodland, there must be a well-considered plan. A good starting point is to evaluate the area’s composition of species that are red-listed or relevant for conservation, in a range of organism groups. Are additional species inventories required? How are red-listed and endangered species favoured?

Looking more broadly at the surrounding landscape and at any areas of particularly high ecological value can bring valuable knowledge. Also, in protected areas, it is important to be aware of the objectives in the management plan and the conservation plan. Additionally, the budget and how overgrown the area is, determine how extensive the management measures can be. When restoring heavily overgrown land – that has not been grazed for many years – restoration should be done in several phases, preferably at intervals of at least five years.

By considering these questions, a target and plan for the area can be developed. The target gives all the stakeholders involved clarity regarding what is to be achieved.

Other factors that affect the design of the restoration are:

  • How long is the delivery time for important habitats such as hollow oaks? Is there a need for temporary measures such as placing out coarse dead wood and wood mould boxes, to overcome the lack of various habitats?
  • How will the land be managed after restoration – cut for hay or grazing? Will there be access to grazing animals that can keep the land open in the long term? Is it possible to create large enclosures? What type of grazing animals are available? Assess pros and cons of various types of animals.
  • Is there fauna that is disturbed in the local area, such as breeding white-tailed eagles, that affect when the management measures can be implemented?
  • What are the ground conditions like? Do they affect the transport of cleared materials? Should cleared materials be left or burned?
  • What is the landuse history of the area?
  • Will the restoration be done in a single step or in several?
  • Are there conflicts in the aims, and how can this be solved?
  • Are there any invasive species, and how will these be handled?
  • Are there any ancient monuments or other cultural relics present, and how will these be taken into consideration when undertaking the work?
  • Landowner matters: are there livestock owners and any other important stake- holders in the area?
  • Visitor numbers of the nature reserve: Must adjustments be made for visitors to the reserve?

Planning of measures in the field

Based on the aforementioned considerations, trees that are to be removed and places where extra care is required are selected and marked using spray-paint or tape. There are different ways to select and mark an area in preparation for procurement of the management actions. It can be done on area that is typical of the whole area, and the contractor works based on this. Other options are a written instruction, or that the entire area is marked out.

Early in the process, decisions are made regarding how to achieve the target. Should the measures be done manually, with machines, or using arborists? Sometimes the manager lacks the practical knowledge of what is possible at the site in question, but has a vision of the desired appearance of the site. In this case, it is often good to, in the field, talk to people with practical experience, to identify ways to achieve the target.

Issues to discuss and take an early stance on can include: should the cleared material be completely or partially left on site, or removed? Where are suitable locations for wood, branches and tops? Time of year: is the ground firm enough year-round, or only for a short period? How are the logistics: will everything work from the start of felling until all the wood has been collected, and the branches and tops have been chipped? Wood, branches and tops should be taken care of by April 1. If it is left for longer, cleared mate- rial will become a trap for many insect species that lay their eggs in it, which is subsequently sawn up or chipped. Is there a need for road repairs and clean-up after the measures are completed?


When removing cleared material, access roads and tracks for forwarders must be planned carefully, to protect cultural-heritage values and ancient monuments, the root systems of older trees, and other red-listed species. Forwarding through wetlands should be completely avoided.

To protect the ground, mats can be placed out in damp areas or by ancient monuments? Or even better, is it possible to create another route? Careful planning of when the measures are to be implemented considerably reduces the risk of ground damage. In parts of the country where the winters are usually mild and the ground may not freeze, the best time for measures that involve hauling out cleared material is August to October – before the autumn rains begin and the ground becomes sensitive. This applies mainly to clay soils and areas with a thin layer of soil. For deeper soils and exposed bedrock, well-drained soils and where the ground freezes in the winter, the time span is longer. When clearing around trees is done mainly by ring-barking, veteranisation, felling of selected trees and where the material is left on site or burned, the entire clearing season is available.

To avoid disturbing breeding birds and other animal life, management measures should generally be avoided from April to mid-July. Sometimes this period must be even longer, depending on the species found in the area.

Communication with contractors

In order for the restoration measures to be successful and be carried out according to plan and how the site has been marked up, it is important to have frequent contact with the contractors.

With regular meetings it is possible to follow the progress of the restoration, and any misunderstandings between manager and contractor can be remedied.

Information to neighbours and public

Before the measures are begun, it is important to inform neighbours and the public, For instance by way of simple notices at the entrance to the reserve. If the reserve is close to aresidential area, it is a good idea to organise a walk where neigh- bours can learn more about and offer suggestions for the planned measures.

Design of restoration

The trees

When selecting and marking up for management, the selection should create variation in the area as a whole. Here it is a good idea to first consider the older open-grown oaks and other older trees in the pasture or the deciduous broadleaf woodland. For example: Is the older open-grown oak standing alone or in a group of older oaks? Are these oaks to coexist as they have done for centuries, and be seen as a unit? Or should some be favoured by having their neighbour veteranised? Should competing trees be ring-barked, or perhaps felled? Are there plenty of fallen trees and standing dead wood, or must the proportion of dead wood be increased?

The next generation

It is important to consider the need for successors in the area. After restoration, some trees die or are blown over in storms. For instance, trees that have been cleared around can be shocked by the sudden and drastic change in light, water and nutrient conditions. This is particularly important in areas where dense spruce needs to be cleared. Trees that are intended to be successors can also be lost during restoration. For this reason, it is important to have somewhat greater density of trees than the final target.

Glades with bushes

It is important to have glades of various sizes. If it is possible, grazing animals can be released into the overgrown area, so they can show the way to the glades that should be enlarged and recreated. Often it is also a good idea to clear a glade on the south side of a large oak that you want to clear around, so the trunk receives plenty of sunlight.

Other questions to keep in mind are if there are older glades that can be extended and cleared of vegetation. And what bushes are present in the area? When restoring oak pastures, it is important to favour hawthorn bushes, but also other thorny bushes such as sloe and dog rose. Other flowering bushes and valuable pollen and nectar resources include guelder rose, bird cherry, and trees such as goat willow, rowan and whitebeam. Try to make sure that there are plenty of flowering bushes and small trees in the glades, forming “warm spaces” in the area, by providing shelter from cold winds. If possible, have the bushes form arches, similar to arbours, in the glade. Flowering bushes standing on their own are much less useful for the insects looking for pollen and nectar.

Coastal areas

In coastal areas, it is important to save a strip of trees and bushes, as protection against the cooling sea winds. This protection is needed in order to create the warm zones inside the areas. The strip can preferably have a ragged, uneven shape, like a natural woodland edge.

Dead wood

By creating standing dead trees with the assistance of an arborist or in some cases a harvester, the shade from the canopy disappears, and the supply of standing dead wood increases. Fallen dead wood is created by entire trees being felled and left, with or without a crown. To favour species that are associated with oak and deciduous broadleaf habitats, a large portion of dead broadleaf wood is left, both entire trunks and piles of smaller branches. If possible, wood that is already dead is left untouched; it is only moved in order to improve access for removal of material. For areas with grazing animals, a balance needs to be struck between the animals being able to graze and the benefit of creating and leaving large amounts of dead wood.

In older fields with islands of valuable trees, the trees which are to be removed can be felled and left on the old fields, to create woodland edges both vertically and horizontally. This will eventually create warm zones. To break up large open fields, an option is planting solitary trees or rows of bushes. In the project, both oaks and different types of bushes have been planted. Read more about dead wood.

Tree diseases

Chalara ash dieback disease has afflicted the country, and many dead ashes have fallen during the winter storms. Dutch elm disease has led to the death of large number of elms. Affected trees that are large can be left standing, or be felled with the trunk in one piece. Smaller sizes of dead elm and ash may need to be removed or collected in piles.

Older ashes that have died from Chalara ash dieback disease soon fall over because their root system is quickly consumed by fungi and insects. If a standing dead stump is made from the old tree, there will be less risk of the tree falling.

In the restoration work, living ash tree have generally been favoured, because the species is red listed. It is vital to save live ash trees because although many are attacked by Chalara ash dieback disease, they may not die from it.

Veteranisation, pollarding and top-cutting

Veteranisation is a good measure for retaining trees, while also creating more habitats that there is a shortage of. When veteranised, a tree is weakened, while decay is accelerated and consequently also the formation of cavities in the tree. Additionally, younger deciduous trees can be pollarded when they have a trunk dia- meter of about ten centimetres, instead of being removed. In the long term, the pollarded tree will grow old and develop many cavities. Even at larger dimensions, lime and other tree spe- cies can be topped instead of felled. These tend to develop many shoots, but the shoots grow only on the surface and not well attached to the tree. Nor is it historically “correct” to top a tree in this way, but the method is a good alternative to felling. if the topped tree dies, it will become standing dead wood.

By pollarding and the creation of standing dead stumps, open sections can be protected from the wind, and stratification can be created in the woodland or pasture. Shading or competing crowns disappear or become much smaller. Read more in the chapter about veteranisation.

Hazel-rich oak woodland

Oak and hazel have a very rich flora of mycorrhiza-forming fungi. In elevated, drier locations with oak, hazel bushes and exposed bedrock, the ground becomes warmer. Here one often finds hotspots for red-listed fungi species, that is, places with a large number of red-listed species. This applies particularly to chalky soils. At these “heights”, one must take care when removing trees and bushes so as to minimise negative impacts on the mycelium.

Generally, older hazel bushes with large trunks or large stools should be saved when felling.

Hazel bushes grow radially outwards. Most of the hazel bushes that are cut down are left as brushwood in the area, because many red-listed species are associated with hazel. An alternative to removing the entire hazel bush is to cut it to half its height. This way, large branches with lichen and fungi are left. Also, the shading effect of the bushes is reduced and mechanical damage to adjacent trees is reduced.

Wetlands are good for oaks

Oaks often establish themselves close to wetlands because they can grow in moist conditions. Also, wetlands have a more open canopy, enabling the oak seedling to establish in woodland. When restoring, the bushes around the wetlands should be opened towards the south. To the north and west, bushes should be retained as wind protection. Goat willow should be favoured, for the sake of the early bees.

In wetter habitats, there is often dense overgrowth. Consequently, a dense area with plenty of dead trees and thick undergrowth can be left without any measures.

As part of the project, older ditches have been blocked or filled, so that the water can return to the original route through the landscape. When several small, temporary pools of water are formed, oaks benefit because they can withstand wetter conditions better than other tree species. This type of action requires that one has authority over the area and that other landowners must not be affected. This must be evaluated using elevation models in GIS prior to restoration. Permits or consultation with relevant agencies may be required.

Ivy: to be or not to be?

In the project, many large ivy bushes growing on older oaks have been cut. On oaks which assessed as having nature conservation values, a 10-20 centimetre piece of the ivy’s lower stem is cut, if possible. When choosing whether to cut or not, one must consider that ivy eventually dominates many oak tree crowns, such that the oak’s leaves have difficulty photosynthesising, and the tree dies. Together with all the ivy, the tree crown catches a lot of wind, and consequently many of these oaks are blown over in storms. Also, a balance must be found between aesthetic values for the visitor to the reserve and the needs of the area’s bat population – trees with lots of ivy can provide important homes for bats.

Positive effects, challenges and important lessons from the project

Life Bridging the Gap has been a conservation project with high ambitions when it comes to restoring grazing and opening up oak pastures and deciduous broadleaf woodlands. Large areas have been restored. The project has run for several years, which has been an advantage because this enables a long-term approach and the opportunity to restore heavily overgrown areas in several stages. Moreover, the project has resulted in a lot of new knowledge about how oak pastures can be restored and managed. In the short term, the project has had positive effects on the conservation status of the land. Many oaks that have been cleared around have regained their vitality and are producing new shoots. Successors have more space and the opportunity to develop extensive crowns. Formerly absent species have returned to the land. And the response from visitors has been positive, when the areas are perceived as more attractive.

One lesson from the project is that when planning future restoration measures, climate change should be given more consideration. Milder and wetter winters are expected to become more common in the future. This could mean that the ground will freeze less frequently. As a result, there is a greater risk of storm damage, regardless of changes in the wind climate. Even in areas that have been restored with care, trees have been blown over in storms.

The dry summers of 2018 and 2019 took a great toll on trees and bushes in some areas, and many trees died. The past three years have been unusually dry in many parts of the country, and there is concern that climate change can make this type of situation more common in the future, at least in southeastern Sweden. This is another factor to consider ahead of future restorations.

The Life Bridging the Gap project has faced many challenges in terms of the scope of the measures. Strengths include clear targets for what was to be done, and within which time period. The project placed strict demands on planning and structure, but ultimately it has delivered huge advances in the work to restore these species-rich habitats.