Building the case for passive rewilding

It should have been prime boar territory, but after centuries of farming and human influence, large mammals had all but disappeared from the area. It was social and economic upheaval in the 20th century that accidentally transformed the area into a cradle of what is known as passive rewilding — and ecologists have been watching. These days it is almost impossible to avoid seeing wild boar in the region, and even the ibex, which had been regionally extinct for 90 years, has returned.

Passive rewilding is an approach to restoration that allows natural processes to restore themselves. It accepts a certain level of chaos as forests reclaim territory, species return, and natural disturbances such as fires, pests and floods kick in. With global biodiversity being discussed at the United Nations COP15 this week, passive rewilding is one approach that could help reverse catastrophic species loss.

There are three key components to passive rewilding, according to Pereira, a professor of biodiversity conservation at the German Center for Integrative Biodiversity Research at the University of Leipzig. The first is restoring trophic complexity by allowing wildlife to return. This usually means restricting hunting, but in rare cases it does involve some relocation.

The second component is allowing landscapes to reconnect so that plants and animals can move around. The third — and most crucial step — is allowing for unpredictable disturbances such as fires, pests and floods. But letting things run wild is anathema to the traditional approaches to restoration and can be very difficult to accept for Europeans.

His thinking is, “if you love it, set it free.” One of the strongest arguments in favour of passive rewilding is the low cost compared to more hands-on approaches, especially on a large scale. But widespread forest expansion can turn into a homogeneous landscape. And biodiversity tends to hate homogeneity. Scientists like Pereira, however, maintain that if nature is left to take its course for long enough, unpredictable natural processes will lead to the diversity needed. Large grazers such as bison can clear areas of land and create open patches where biodiversity can thrive, while wild boar disturb soil as they root around for food.

Though much harder to promote, particularly in the era of climate change, another natural disturbance that can lead to transformation and greater species diversity, is wildfires. “We have to embrace the unpredictable. We don’t even know how these landscapes may end up. We want to have these ecosystem functions restored and let nature play its role. But this is hard for many people,” Pereira said. The patterns seen in the area around Castro Laboreiro aren’t unique, with European farmland being abandoned at a rapid pace. In the first half of the 20th century, Europe was gripped by rapid urbanisation, as shifts in agriculture and globalisation made many rural lifestyles unsustainable. Remote, mountainous areas were particularly hard-hit, but it affected any areas with natural and physical limits to agricultural production. Some estimates say farmland totalling twice the size of Hungary will have been abandoned by 2030, and studies show that 30% of all agricultural land in the EU is at least at risk of abandonment. Climate change and globalisation will increase this.