Restoring forests on poor sandy soils

Restoration Story by Silke Jacobs & Lisa Raats

When visiting the Dutch SUPERB demo area at the end of January, one could see a grayish dust cloud coming from a helicopter that was flying over the forests. The helicopter was covering the forest soil with rock dust: a much-needed measure in forests growing on dry sandy soils.

The forests in the Dutch demo area depend on very degraded sandy soils which are poor in nutrients, dry and have a low pH, meaning stronger acidity. This is not what the trees are hoping for in terms of environmental conditions. While walking around, one can notice that the trees, mostly Scots pine, are quite small both in height and diameter. They are longing for a healthy forest soil.

Within SUPERB, Bosgroep Zuid Nederland will implement measures to make the forests more vital and healthier. The aim is to treat approximately 60 hectares of forests owned by 16 private forest owners. It was a huge task to track these people and involve all of them in the project.

But after this hard work and conducting research, one of the restoration measures has finally started. The helicopter is thus spreading the rock dust in the area. Rock dust contains nutrients that the forest soil could use and gradually releases calcium, magnesium and potassium.

We had a great viewpoint to see the actual restoration activities being carried out by the helicopter. It was impressive to watch! The route flown by the helicopter can be visualized after the flight and we have been told that it is very accurate thanks to a skilled pilot.

The helicopter stayed in the air the whole time we watched it, except during a short break to refuel. It has also lowered so that a shovel could add the rock dust again to its basket for another flight spreading dust over the forest.

In the picture above you can see the big pile of rock dust that still needed to be spread. After flying a couple of hours, everything was gone and it’s time for the rock dust to do its work within the soil.

Alongside the use of rock dust, another implemented measure includes planting rich litter tree species in this area. The intention is for species such as hazel, lime and maple to gradually become more prominent contributors to the leaf composition in the litter layer. As these leaves decompose, they release nutrients into the soil, replenishing the system with essential elements over time. Additionally, this results in a more diverse forest in terms of species composition.

The experiences gained from both restoration actions and involving forest owners and other stakeholders can be valuable for future forest restoration projects, especially considering the prevalence of other degraded sandy forest soils in the Netherlands.

Forests: why “doing nothing” can’t be the cure

#RestorationStory by Maaike de Graaf

A few weeks ago, I visited my son who is studying in Scotland. He took me for a walk in the Cairngorns, the UK’s largest National Park, which is a fantastic area. Only afterwards, I realised what we have lost in our densely populated Netherlands: the decreased diversity in landscapes, gradients and biodiversity became painfully apparent. For instance, in Scotland, I have seen lichens with the size of a fist, at the end of the branches of oaks. I have never seen that in my home country. Most likely this is due to air pollution as lichens are very sensitive to this. I suppose I do not have to remind you of the atmospheric nitrogen concentrations in the Netherlands, nor of the acidic rain in the past. 

Oak moss (photo: Rudolphous – Wikimedia Commons)

But why am I telling you this? I have been working in several ecosystems as a restoration ecologist but have not seen such a large public dispute on the need of rehabilitation as in the field of forests. It seems that we have 17 million forest managers in Holland, all having a strong opinion on forest management. It must be our country spirit, having strong opinions, as we also have 17 million soccer coaches. Most of these millions of forest managers are convinced that our forests are natural by origin (which they are not). As a consequence, they consider ‘doing nothing’ to be the best way to improve the quality and health of our forests. They completely ignore human impact on forest, which we apply not only by planting, management, and recreation, but also by invisible processes such as impacts of climate change and hydrological changes. Acidic and nitrogen deposition have significantly accelerated the weathering of sandy soils: in the last decades, the same amount of calcium and magnesium have leached from the top of the soil as in the 17.000 years before. And is still continuing. In Brabant, we often measure pH-values below 3. To better understand this: pH-value 3 is compared to vinegar. Imagine being a tree in such conditions: your roots develop poorly, and your capacity to take up nutrients and water is seriously hampered. Your vitality sucks, and you will feel a little unstable. On top of this, you would have to deal with lowered ground water tables, imbalanced nutrient availability (due to nitrogen deposition) and climatic changes. You are stressed by multiple factors. And in addition, you struggle with the loss of connectivity to other forests and pollution by light and sound, all factors that diminish the size of suitable habitat for forest plants and animals.  

Diversifying Pine forest in the Dutch demo: Maaike and her team cut some trees, planted others (e.g. Tilia cordata, Quercus robur; with bamboo as wild life protection bamboo)
Diversifying Pine forest in the Dutch demo: Maaike and her team cut some trees, planted others (e.g. Tilia cordata, Quercus robur; with bamboo as wild life protection bamboo)

Personally, I do not believe that ‘doing nothing’ will be the cure for large scale forest recovery. Even if we were to stop forest management, we humans still affect the forests through the processes I have explained above. This is precisely why I believe in using all knowledge, tools and means we have to help our forest to survive. This entails reinstalling higher ground water tables, cutting, planting, leaving dead wood. Introducing missing species, adding rock dust to complement leaching. We have to do it! And I am happy to see it is being done in the Netherlands and beyond, with a great variation in management being applied. Because I also believe that when the future is uncertain, we need to diversify risks, and try different approaches to find out what works and learn from practice. 

So why are many people in resistance to forest management, even in forests that should serve multiple purposes? One of my Belgian colleagues recently said that urban societies are alienated from forest practice:  Her words were: “They think the forest is their pet”, which I can truly relate to. I can understand that you don’t want to cut your pet, but why don’t you want to pamper it either? Why not revitalizing the forest, supporting it to be healthier?

Demo in Groote Heide

  

Here we forest practitioners should dare to look at our own acting. We send different messages, and we are thereby confusing our audience. We tell them about small-scale forest management in the Netherlands, reducing clearcut areas to less than 2 times the tree height. Meanwhile we proudly present pictures of helicopters spreading rock dust, in order to reduce acidification impact. Small-scale management? Such images convey the implicit message of large-scale actions, in a way that many associate with noise, air pollution and nitrogen emissions. Is this how we understand forest restoration? Let us be aware of the messages we send in our enthusiasm on forest management and put them in perspective. Let us work against the Zeitgeist pushing us to convey simple stories, and instead tell of the complex reality of gradients, nuances, and diversity, that needs a variety of solutions. 

So, to conclude, we have work to do. Both in restoration and in communication.  


On April 14th 2023 Maaike presented this column in Dutch language to the KNBV, the Netherlands organisation of Forest Managers. The column is also published at their website.  

All photos except oak moss by Maaike de Graaf