Design of restoration
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.
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.
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.
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.