Oostvaardersplassen: Rewilding's Cautionary Tale

The Netherlands' famed 'Serengeti behind the dikes' saw nearly 60% of its grazers die in 2018, forcing a hands-on reversal of its rewilding model.

When the Netherlands drained an inland sea in 1968 to build two new cities, the strip between them — the Oostvaardersplassen — was slated for an industrial park. Graylag geese arrived first, feeding and molting on the marshland's reedbeds and grasslands, and acting as ecosystem engineers that kept habitat open for other birds. According to Diario AS, the area became one of Europe's most important molting sites for graylag geese, with an estimated 60,000 visiting between May and June each year by the early 1990s. Protected in 1983, the roughly Manhattan-sized reserve joined the EU's Natura 2000 network, and German magazine Der Spiegel dubbed it 'The Serengeti behind the dikes.'

Biologist Frans Vera pushed further, arguing large herbivores could maintain the landscape as a Palaeolithic wood-pasture without human intervention. Heck cattle, semi-feral Konik horses and red deer were released. But with no natural predators and intervention only when animals could not survive winter, grazer numbers swelled and decimated the vegetation. Diario AS reports that nearly two dozen rare bird species disappeared between 1997 and 2016, and more than 1,600 grazers died in the winter of 2016. Then came the winter of 2018: per Diario AS, a 'mass mortality event' killed nearly 60% of the roughly 5,200 grazers, most shot because they were starving, and images of emaciated animals went viral, triggering a public outcry.

Vera defended the deaths to the BBC as 'part of nature' and 'a kind of natural correction,' citing a study that found most wildebeest mortality in the Serengeti comes from undernutrition. Critics counter that captive grazers in the Oostvaardersplassen cannot roam to new terrain the way truly wild herds can, arguing wildlife corridors should provide connectivity to other landscapes. Danish ecologist Jens-Christian Svenning of Aarhus University told the BBC the herd cap now in place is 'super unnatural,' and argues managers could monitor the system and act proactively before mass-death years arrive — a missed scientific opportunity, in his view.

The reserve has since reversed course: animals are fed when they fall below a certain body condition score, the herd is limited to 1,500 through culling or relocation, and rangers now manage water levels, plant trees and dig ponds. Newer projects are designing with such risks in mind. The Argus reports that Herstmonceux Castle Estate in East Sussex is partnering with Nattergal to rewild 240 acres of degraded farmland into wood pasture, grassland and scrub, funded by Biodiversity Net Gain credits and protected by a conservation covenant for at least 30 years. Free-roaming cattle and pigs will shape the habitat — with buffer zones and fencing developed in consultation with local farmers.