Akkerenven Kortenhoeff: how one plant helps us fight the other
The Akkerenven, located in Kortenhoeff, a subarea in Grenspark Kalmthoutse Heide was struggling with the invasive exotic water crassula.
Dredging of the Akkerenven and removal of the water crassula has now been carried out by the manager Staatsbosbeheer and the fen seems to be ready for the future. But we are not there yet! Invasive species like water crassula spread very easily through all kinds of routes and can thus reach a recently cleaned area again. This could be through birds, for instance. Staatsbosbeheer has taken all kinds of additional measures in Akkerenven to make the resettlement of water crassula as difficult as possible (e.g. disconnecting a ditch with nutrient-rich water) but preventing birds from coming here to rest and/or forage is obviously not one of them. After all, birds represent an important part of the natural values in the sites on the Brabant Ridge.
Auxiliary troops
To still be prepared to some extent for a new infestation, the Forestry Commission is calling in auxiliary troops. This does not mean an army of volunteers or foresters who will permanently guard the terrain, but help from nature itself. This is because it comes in the form of bankweed. At first glance, this plant seems to be the last candidate to counterbalance water crassula. Bank weed is small, stays low to the ground and makes a fragile impression. But in a nutrient-poor and sufficiently wet environment, shore weed turns out to have unexpected qualities. Via offshoots, this species can then form large continuous vegetations. There is plenty of opportunity for this, as few other species thrive in such a strict environment. Should water crassula then end up in the Akkerenven, much of the potential habitat has already been taken. It has also been experimentally demonstrated by the Bargerveen Foundation that water crassula loses the battle for scarce nutrients to bank weeds. So when a well-developed riparian weed vegetation is present, it will be much more difficult for water crassula to develop into mass vegetation.
Introduction
Staatsbosbeheer has therefore planted a large number of riparian plants in the Akkerenven. Introducing a species is something that is not taken lightly at Staatsbosbeheer, but the chances that bankweed would spontaneously appear in large numbers are very slim. Given its great usefulness in keeping water crassula in check, it was decided to do so anyway. In the restored nutrient-poor fen, the species will hopefully expand rapidly and serve two purposes at the same time. Firstly, a characteristic fen vegetation, which used to be much more common in the Netherlands, will form, and secondly, there will be enough gatekeepers on site who will skillfully help keep the invasive exotic under their thumb. The chances of a long-term presence of an Akkerenven with high natural values are therefore enhanced. But nature is recalcitrant and we need to keep an eye on how things will develop. Staff from Staatsbosbeheer and the Bargerveen Foundation will therefore closely monitor developments in the coming years.
