Young beech leaves accentuating the beauty of the bluebells, but also starting their doom: when they start shading too much, the flowers will disappear again.

This week brought the field course to the ‘Hallerbos’, Brussels world-famous forest with the purple bluebell carpet.

Young hazel leaves on a purple background

Of course it is mostly this endless see of purple that attracts the thousands and thousands of tourists every year (oh, dear lord, can someone please tell them to stay on the trails!), yet for me there is more that attracts me to this forest.

The wood anemone, the true star of the Hallerbos, almost as common as its purple counterpart, but harder to see as it grows less tall.

What I love the most is that this forest is a clear example of the interaction between abiotic and biotic conditions in an ecosystem. Soil nutrients and humidity from one side define the plants that can grow there (with the bluebells performing best on intermediate conditions for both), and the range of all conditions is easily to track through the forest.

Oxlips, wood anemones and cuckoo flowers in a wet and nutrient rich forest patch, the most abundant part of the forest.

The trees themselves, on the other hand, also affect the nutrient conditions ànd the understory vegetation: old beech stands tend to have acid soils and a more dense canopy, reducing the presence of bluebells and wood anemones. This is the exact reason why wood harvesting is so necessary in the Hallerbos: the forest needs to be kept young to ensure this density of bluebells.

Lonely bluebells in an old and dry patch of beech forest

Pine trees, as another example, also acidify the soil. As they are not native in the forest anyway, they are now often removed (sometimes showing impressive regrowth of the bluebells over the course of a year). Unfortunately, removing all of them might impact several bird species that started to count on these trees in particular.

For an ecologist, this forest is thus much more than only bluebells. There is a lot to learn there if you roam over these trails. But if I convinced you to go and check it out for yourself, there is one other thing I should ask: please make sure you stay on the tracks! There is another important factor defining the ecosystem here, and that is human presence.

If you walk through the fields of bluebells, you do not necessary damage the plants from this year too badly, but you do compact the soil with the weight of your feet, making it impossible for the tiny roots of new bluebells to pierce through it. The result? Empty spaces the next year, less beauty to look at…