04. Threats and opportunities

The oak is a fantastic tree species which can reach a very old age, and can function as a home for many species. The massive harvesting of oak during the nineteenth century resulted in a drastic reduction in the number of old oaks, and worsened living conditions for species associated with the oak. But there is still a chance to save these species-rich habitats, if we use the knowledge and tools we have today. Text: Jonas Hedin

Threats

Oaks begin to develop habitats for threatened species when they are 200 years old, but it can take another 100-300 years before the most demanding species find their preferred habitats. The trees in the “second oldest” category must reach about 50-250 years before they can host a rich biodiversity. For the oaks to be numerous enough to conserve endangered species, younger and middle-aged oaks must have the chance to grow biologically old.

Today there is a large extinction debt in the oak habitats. That is, the landscapes we are studying today have a larger diversity of species than what the landscapes can host in the long term. This applies particularly to species with poor dispersal ability and long generation time.

A great many oaks are needed

It’s difficult to say how many oaks are needed in one area to ensure the long-term survival of the most endangered species. The answer depends on several factors. Firstly, it’s important to remember that most endangered species only live in some of the trees that are suitable for that species. Additionally, the species might only live in one of the old oak’s successional stages, which means that for a few old oaks to be at the right stage of succession, there must be many of them.

Of the oaks that are older than 200 years, about one percent die each year. This means that older oaks will continually become fewer for many years to come. In order to reduce this death rate, the old oaks and their successors must be given the best possible conditions for growth. Gener- ally, the more old oaks there are, the better, and for there to be old oaks in various successional stages in the future, it is good to plan for the management of about one thousand oaks. A good distribution could be as follows: 100 oaks aged over 400 years, 200 oaks aged 200–400 years, 300 oaks aged 100–200 years, and 400 oaks aged 50-100 years.

Fragmentation

Fragmentation, i.e. when the landscape is divided up, is another major threat. With an increased distance between areas with really old oaks, individuals of the species that are associated with these habitats have more difficulty dispersing. This means that when local populations die out, this will not be compensated by recolonisation from other areas.

Overgrowing

In the short term, the greatest threat to oak landscapes is not the felling of the remaining old oaks, but when they become overgrown. In certain regions of southeastern Sweden, there are still relatively large numbers of old oaks. These trees often stand in former hay meadows and pastures that are no longer used. After an inventory of trees with high nature conservation values in the counties of Östergötland and Kalmar 10–20 years ago, it was concluded that more than half of the oaks urgently required clearing around them. And in the long term, the regeneration of oaks in the landscape must increase.

Development

Development can also be a big problem, as valuable oak habitats are sacrificed to make room for major infrastructure or housing projects.

Opportunities

Restoration and management

Restoration is the best option to save overgrown oak habitats. Large restoration projects can be co-funded by the EU’s LIFE Programme, although it can also be done on a smaller scale. It is also important that funding for the restoration of pastures is constructed so that different types of grasslands can also get support, e.g. wooded mosaic pastures.

There must be a major investment in the management of oak habitats. To conserve and develop oak habitats, the best and most cost-effective management method is to make them semi-open and mosaic, and to reintroduce grazing. To protect endangered species, in particular wood-living insects, there must be a major effort to increase the number of cavities and other habitats in the next generation of oaks.

Here, habitats must be created through active measures such as wood mould boxes and veteranisation (see chapters on wood mould boxes). These measures have the greatest impact in locations and landscapes where many species remain, including the endangered and red-listed species. This is because many endangered species, both insects and lichens that live near old oaks, have difficulty dispersing.

It is also important to conserve and manage other types of trees, such as ash, aspen, horn- beam, birch, beech, alder, lime and maple, because these share many cavity-dwelling species with oaks. These trees can develop holes much quicker than oaks, and the bark of ashes and maples has a high pH level, which is advantageous for many lichens.

Green infrastructure

The investment in green infrastructure is an opportunity for the oak habitats. For instance, the county administrative boards in Kalmar, Blekinge and Östergötland have developed valuable networks and deciduous broadleaf tree core areas. These help with determining which areas to prioritise in the work to connect these habitats. When this work develops into concrete implementation projects, the benefits are many.

The action programme for endangered species

Outside the protected areas, the county administrative boards can use other means to benefit the oak habitats and link together the landscape. One important tool is the action programme for trees in the cultural landscape that have high nature conservation values, and the action programme for the hermit beetle.

Municipal landscape planning

Many municipalities are large landowners. By developing ecological landscape plans, municipalities can benefit oak values, in both the long and short term. See the chapter on Linköping Municipality.

Climate change

For much of the biodiversity, climate change is a threat. However, oaks can withstand higher temperatures and wetter winters better than most tree species. For oaks, the challenge will be to survive long periods of summer drought.

Proud landowners

Many parts of the landscape in southeastern Sweden still have quite a few oak trees. And many landowners are very proud of their old oaks. This engagement should be supported and enhanced. With appropriate conservation and care, after a century or so, these habitats can once again be species-rich, and house large populations of currently endangered species.

Collaboration

To succeed in the conservation of oak habitats and all of these species, the dialogue between landowners and state and municipal agencies must function well. Also, managing this land must bring financial benefits. There must also be collaboration with the part of the woodlandry industry that uses oak to make wood products. A national plan should be devised, where industry, landowners and state agencies agree on how to manage the conservation of biodiversity in the oak habitats and the development of oak as a raw material.

04. Threats and opportunities