Restoring European woodland means looking far into the future

The woods near Venlo are gradually getting a makeover. They have long been monocultures of pine trees intended for timber production and you can still see in some places that the trees were planted in rows. The substrate is acidic and low in nutrients. ‘These trees are also susceptible to extreme weather events such  drought, which become a bigger and bigger issue.’ explains Sara Filipek of Wageningen Environmental Research. ‘Nitrogen deposition is making the soil even more acidic. And minerals are leaching out as a result, which is having a dramatic impact on soil life. The soil is the cornerstone of the ecosystem.’

In collaboration with the Bosgroep Zuid Nederland, Filipek is planting various species of deciduous trees in the forest. Such measures go further than merely restoring the woodland to its former state. Planting deciduous trees enriches the soil because the leaves that fall produce better plant litter and humus. Filipek: ‘That is good for the biodiversity and for the wood’s resilience. Healthy woods also sequester more CO₂. ‘We call our approach “prestoration”: preparing the wood for the future.’ 

The woods near Venlo is one of the demonstration sites of SUPERB, a European research project that is co-ordinated in part by Wageningen scientists. The aim is to restore thousands of hectares of forest across Europe by linking science and practice. The project received funding of 20 million euros from the Horizon 2020 programme plus contributions from dozens of partner organizations.

The twelve SUPERB demonstration sites are located in different European countries. Filipek: ‘Every wood is different and yet they all face the similar challenges due to climate change. Bark beetles are having a devastating effect on spruces at a demonstration site in Germany and Czechia, while forest fires are increasingly common at a site in the south of France. Both woods used to be monocultures of conifers grown for timber. The lack of structural diversity makes these woods particularly vulnerable when there is a storm. In addition, extreme conditions such as droughts and floods are becoming ever more frequent. The problems are accumulating, so we need to act now.’

To obtain a picture of the future for Europe’s forests, assuming various management strategies and climate scenarios, Filipek and her colleagues have been working for the past 15 years on a model of how forests develop over time. This European Forest Resource Model (EFISCEN-Space) mainly uses data from national forest surveys, such as the size of the trees, the rate of growth of each tree species, when trees are felled and how many trees are planted. The model simulates how woodlands will develop over the coming decades under different conditions. ‘We also assess doomsday scenarios, for example where all the fir trees die off within a year due to extreme drought. That helps us figure out which measures we are best off choosing.’

For the model to work well, it is important to have data on a variety of European forests. That is easier said than done, admits Filipek. ‘Some countries treat their datasets as confidential information and are afraid of external interference. But that is precisely why closer cooperation is needed between the countries. A joint research project like this helps achieve that.’

The collaboration in Europe has another advantage, adds Filipek. ‘Other countries facing similar challenges can see how the Netherlands carries out restoration processes. For example the stakeholder engagement processes. The trick is to get everyone on board with the plans for forest restoration.’ In that respect, she sees the Venlo woods as a successful example. ‘There is often resistance to the idea of cutting the existing trees. It helped to talk in person with the individual owners of the forests. In addition, local residents could read an explanation of what was going on in the newspaper and they were invited to meetings. In the end, most of them acknowledged the benefits of the restoration measures.’ Filipek will be sharing the lessons learned from this with the European partners.

Restoring woods requires long-term monitoring. Filipek: ‘You should really monitor woods like the one near Venlo for decades to see how the newly planted trees grow to maturity and how that changes the wood. That isn’t possible within SUPERB, which is a four-year project, but we also have data on similar woods where deciduous trees were planted previously. That data covers not only the trees but also other aspects such as the minerals, soil life, microbes and the fauna aboveground. That gives us an idea of what will happen to a wood when you start to make it more diverse.’