Wild growth in North Holland: a burden for people or a blessing for nature?

Anyone who once decided to empty his fishbowl in the Loosdrechtse Puddles would probably not have been able to foresee what the Brazilian aquarium plant ‘cabomba caroliniana’ that came with it would do. For years ‘rakes’ the Loosdrechtse Kees Blase from his boat the rampant plant from the bottom to prevent the entire lake from closing up.

“You can no longer sail in it and you can no longer even swim in it: your legs can get entangled in it,” Blase told NH Nieuws two years ago. He also says that the cabomba suppresses other plants, such as the swan flower and the water trefoil, which he says were still there eight years ago.

Thanks to Blase, his neighbors and the ports, large parts of the lake have already been stripped of the exotic plant. “But the area of ​​the Vuntus and the Raaisloot are still code red,” he says at the start of this sailing season.

Infesting pondweed

Larger guns are being worked in the Gooimeer and the Markermeer. There, the rampant pondweed infests many water sports enthusiasts, which can lead to dangerous situations. Boats – sometimes even lifeboats that need to be somewhere quickly – get the water plants in the propellers and get stuck.

Stichting Maaien Waterplanten Randmeren removes the plants from the water in large nets, which then have to be emptied. In order to work more efficiently, they are working on a machine that can raise the clippings via an automatic belt.

No chance

Is mowing also the best way to handle the aquatic plants? Ecologist Harm van der Geest thinks not. “For control purposes, mowing is a hopeless exercise. It only ensures that your plants spread more if they start floating.”

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According to him, it is better to think of solutions such as a deepened fairway in which no plants grow, and good ‘signposting’ so that boats know where they should and should not go. “You can’t sail everywhere in the Wadden Sea,” says Van der Geest.

Clean water

According to him, the fact that so many pondweeds are growing is only a sign that we have cleaner water. The waters are no longer a turbid, nitrogen- and phosphate-rich tank with water, which algae can feast on. This better water quality has been pursued for about thirty years, says Van der Geest.

Unlike the exotic cabomba, which makes other species disappear, pondweed is a food source for lots of other plants and small fish. According to Van der Geest, the large-scale presence of pondweed is only an intermediate phase on the way to better biodiversity.

He sees no problem with wild growth. “It’s part of the area. I can imagine that it causes nuisance for water sports enthusiasts, but I don’t think you should immediately declare the plants as an enemy.”

Blisters

His fellow ecologist Lonneke Klein-Aarts, advisor on nature development and invasive species, is also oDespite being concerned with combating and controlling usury, not ‘antiplant’. For every nuisance plant that is removed, another piece of greenery comes back, she says. And she never uses toxins.

That’s how she likes her business too the giant hogweed in bridle, a plant that is very common in Amsterdam South-East on the Buitensingel, for example. “It is very harmful to your skin, if you touch it and then come into the sunlight, you can get huge blisters. That is dangerous for children who play there.”

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Spring balsam can also cause damage: if this plant grows in large numbers along the water’s edge and dies in winter, this bank can become ‘weak’. Because plants no longer hold onto the soil, everything can wash away or floods can occur.

Pigs and dogs

But the most famous culprit is surely de rampant Japanese knotweednotorious for its strong roots knocking over quay walls, sewers, foundations and streets.

All kinds of creative ways have been devised for controlling this plant, such as: heat off the ground or deploying aphid† Larger animals can also be used, such as the pigs of Anoek Ursem from Anna Pavlovna. They are the terror of all usurers: even the indestructible knotweed doesn’t stand a chance with these wolverines. Reporter Mathijs Gemmink went on a treasure hunt with Anoek and her pigs. The report can be viewed this afternoon on NH Nieuws.

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But dogs also do their part: ecologist Klein-Aarts trained two of them, who can smell where the plant is in the ground, which prevents it from growing larger and making seeds.

The dog search tactic is useful to check whether the ground is ‘clean’ and can be built safely. It is one of Klein-Aarts’ spearheads: according to her, much more attention should be paid to where soil is moved when we laying roads, cables and pipelines. †We call it polluted soil. You can’t just put soil with asbestos anywhere.”