A fallen, dead beech tree lies in forestry De Vuursche in Baarn. “Dead wood becomes very spongy,” says Mart-Jan Schelhaas, forestry expert at Wageningen University & Research, while pressing his finger into the bark. A few woodlice crawl out. “Dead trees are just as important to biodiversity as living trees.”
There is and is more and more dead wood in the Dutch forests. It is one of the trends described in the Seventh Forest Inventory, which appeared Monday. The state of the Dutch forest is inventoried every five years, on behalf of the Ministry of Agriculture, Nature and Food Quality (LNV). This is done on the basis of aerial photographs and satellite images. “And we have carried out more than three thousand measurements in forests,” says Schelhaas, lead author of the report.
The forest also appears to have become more mixed and open. There is more shrub growth. And the surface area of deciduous trees has increased and is now slightly higher than that of coniferous wood. “All that variation is intended to reduce the risk of damage,” says Bas Lerink, Schelhaas’ colleague and co-author of the report. “And a more diverse forest is more resilient to climate change.” By the way, the most common species is still a conifer: the Scots pine. It covers 28 percent of the forest area.
Less surface area
It is striking that the area of forest in the Netherlands has decreased for the second consecutive period. In 2013, there was about 376,000 hectares of forest, in 2017 that had decreased to 366,000 hectares. It has since fallen further to 364,000 hectares. While the Ministry of LNV in November 2020 the forest strategy announced that the Dutch forest must be expanded by 37,000 hectares by 2030, partly to increase the amount of the greenhouse gas CO in the fight against climate change.2 to include. “That will be quite a task,” says Lerink.
Eighty to a hundred years ago, mainly monotonous coniferous forests were planted, says Lerink. For the supply of production wood. But ideas about what a forest is, and what a forest should be, are changing. “Forests had to be tidy. There was not a dead piece of wood left.” Dead trunks and branches are now everywhere at De Vuursche forestry.
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There is also an increasing eye for variation. The summer droughts of recent years have shown how vulnerable monotonous forests are to disease. The figures show this most clearly in the case of ash and Norway spruce. In ash forests, the researchers saw trees with reduced vitality at 70 percent of the measuring points, an indicator that has now been included in the inventory for the first time. The species suffers severely from ash branch dieback, a disease caused by a fungus.
They have no definition for vitality, explains Schelhaas. “The assessment is on the trained eye.” He points to a Norway spruce further up. “It has relatively few needles. You see? And to the left of that is a Norway spruce with many brown needles.” He turns around. “Compare that with that Norway spruce over there, it has very dense vegetation.” In Norway spruce, vitality was reduced at 20 percent of the measuring points. In the dry summers in recent years, this species suffered a lot from the typesetter, a type of weevil.
‘Sweden or the tropics?’
A part of an impressive beech avenue was cleared a few years ago, says a spokesperson for Staatsbosbeheer, owner of the site. “You want to keep such a beautiful avenue, so we give the beeches space.” Young beech and larch are now sprouting up.
“Here you have a Douglas,” says Schelhaas. He counts the shoots, the pieces between the successive side branches. They indicate the annual growth. “This one is twelve years old. See how big that last shoot is? He really made a sprint.”
The spokesperson for Staatsbosbeheer emphasizes that variation in the forest is now the new aim. “Mixing, mixing, mixing, that’s what it’s all about.” The organization has started planting additional forest. “We need to reverse the downward trend.”
Changing trends can cause tensions, says Lerink. The European Commission wants more biodiversity. Hence the emphasis on more variety. But the European Commission also foresees that more wood is needed, for example in construction, as a replacement for concrete and steel. “Timber companies prefer to work with monocultures of coniferous wood. They are designed for that.”
Lerink wonders how these two futures should be united. “Will we all be getting our wood from Sweden or the tropics in the Netherlands?”
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The researchers have a strict definition for what counts as forest: an area with woody vegetation of at least half a hectare, at least thirty meters wide. The crown of the trees must cover the sky for at least 20 percent, trees must be able to reach a minimum height of five meters.
But Belgian research from a few years ago has shown that smaller forests have a relatively large amount of CO .2 record. And that the biodiversity there is relatively high. “In the eighth inventory, we will also include those smaller forests,” says Schelhaas. In the coming years, more attention will be paid to the damage caused by nitrogen precipitation on forests. “In some places in the Netherlands it causes oak deaths.” Nitrogen precipitation is a problem that has existed for some time, says Schelhaas. “But it has become more urgent now.”
A version of this article also appeared in the newspaper of 12 July 2022
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