Buggenhoutbos climate

The influence of climate change on our Buggenhout forest.

The beech is an important deciduous tree species in Flanders. And not least for Buggenhout, our municipality name is derived from it!

However, beech is also a drought-prone tree species. Drought is increasingly a problem. The past decade has been the warmest since the sightings. In addition, extreme summer droughts as observed in the years 2003, 2010, 2018, 2019 and 2020 are expected to occur even more frequently in the future. It is therefore important to increase our knowledge about the effect of drought on the growth of beech and to have the ANB (Agency for Nature and Forest) look for management measures that can reduce the effects of drought on beech.

Beech mortality, such as now in the Buggenhout forest, and the occurrence of heat waves and drought appear to be strongly related. It is not for nothing that in the Mediterranean climate there is no place for beech. They simply do not occur in those countries. Furthermore, it is often too cold in Scandinavia in winter. But you do see the beech trees advancing steadily to the north. There was a great wave of beech mortality in 1977, after the heat and drought of the summer of 1976. Even then, tens of thousands of beech trees died and the survival of the tree was briefly feared. In the years that followed, things did not go so smoothly and the worries disappeared again.

1. Sensitive to drought and heat

Because beech trees have flat roots, they are very sensitive to periods of drought and heat. When faced with water shortages, they respond by producing smaller leaves. The sun then gets freer play, through the otherwise closed canopy. If the drought hits harder, the leaves first evaporate extra water, then they wilt and eventually the first branches of the crown die. This allows the sun to reach directly to the trunk and causes sunburn. The trunk allows moisture to pass through and the first bark plates release. Bark beetles, wood beetles and fungi then enter and it is they who finish the job. Many factors at the same time then become fatal to the tree.

Weakened beech trees discolor, also on the trunk. Branches break off or trees fall over spontaneously. That's why there's so much wood on the ground. Once holes form in the canopy above a beech forest and trees are released into the sun, they burn, as it were.

But it is only the beech trees that are struggling, also the conifers (just think of the plague of the typesetters that affects the weakened trees) and the willows are struggling due to the too low water levels.

2021 is a year in which it rains a lot and hard and yet the groundwater level is still extremely low: too much pavement in Flanders, pumping up groundwater, drainage via the sewer system instead of infiltration,... are guilty of this.

2. What's next?

Possible measures :

By accompanying beech trees that root deeper (sessile oak, for example) we get a 'Hydraulic lifting'. The 'hydraulic lifting' effect is already known for tree species such as oak and maple. Both tree species have a deep root system that allows them to absorb water from deeper layers of the subsoil. This effect is also more pronounced during a drought period. The deep-rooted tree absorbs water during the day. At night, when perspiration decreases, the water potential rises in the xylem of the tree. As soon as the potential of the xylem is greater than that of the soil, water is released back into the soil, which then also becomes available to neighboring trees. In periods of drought, this effect is more pronounced because of the greater difference in soil water potential in the deep and shallow soil layers .

3. The surface water in the forest

The water supply in Buggenhoutbos via the Hollebeek has been disastrous for several years, large parts of the stream have been dry for years, not only detrimental to our trees but also to the amphibians. They are highly dependent on water and pools, depositing eggs and larvae and allowing them to develop into adult animals is no longer possible, pools and streams dry up very early, causing the larvae to dry up and die.

Blue-green algae that develop in the much too warm and stagnant bit of water that remains causes botulism in ducks and birds and other animals (condition that mainly kills waterfowl and fish, but people can also fall victim to this).

In addition, we are faced with the introduction of exotic species, which are alien plants and animals that show an invasive character and threaten our own native species. Especially the too warm winters contribute to this invasive character.

Measure:

• the Hollebeek has not been cleared for a while, leaving branches in the water gives a curdling effect on the stream so that water can be held up longer. Children playing already do this on the rabbit mountain.
• Making existing pools larger and deeper to still retain some residual water until after the summer... A good pool only dries once every 3 years, then invasive plants and fish that eat the amphibians disappear automatically.

4. Forest expansion 2023 - 2024

At the Agency for Nature and Forest, preparations are in full swing, not only trees but also pools, clearings, butterfly hems, insect meadows, wet zones,...

A lot of measures to absorb the climate influences as well as possible and to better protect our forest with all its life.

In the years after 1976 it was still fairly good as far as the beech trees are concerned, the question is how that will go now. Climate change has increased the frequency with which periods of heat and drought occur. The big uncertainty is whether the beech trees can keep up with that pace, or whether they will go the way of the Elms, the Horse Chestnuts, the Ash trees and the conifers that are now also sick.

Explanation and follow-up: Reinhart Cromphout, Forest ranger Agency Nature and Forest

Jurgen Vermeulen