Counterintuitive Rewilding: Killing Trees to Revive a River in Spain's Muga Valley

This seemingly beautiful forest is actually dead inside. Scientists are calling it a **'green desert.'** However, a surprising new method of restoration is being employed: selectively removing thousands of trees to revive the flow of the Muga River. This unexpected approach is at the heart of Europe's wildest rewilding project, located in the Muga Valley in the Spanish Pyrenees—a 100,000 hectares laboratory that is reshaping the rules of nature conservation.

I. The Muga Valley: A 'Green Desert' in the Pyrenees

The Muga Valley, high up in the Spanish Pyrenees, appears to be an untouched piece of wilderness. Yet, ecological silence and a lack of undergrowth characterize the landscape, which is often dry and brittle. Generations of charcoal production have left behind a dysfunctional oak tree forest that is effectively suffocating the ecosystem.

As Stef van Dongen, co-founder of the organization Pioneers of our Time, explains: "If you look at it, it looks healthy, but in fact it's not. It's under a big stress." Van Dongen and his team have been working to restore the valley, leading what many experts believe is the most exciting rewilding project in Europe right now. To understand their work, one must first understand the Muga Valley's ecological crisis.

The Problem: Blocked Water and Suffocated Life

A healthy valley ecosystem requires flowing water, sufficient sunlight, and biodiversity, none of which were present in abundance. Up until the 1970s, the forest had been repeatedly clear-cut for charcoal production. Each time the forest regrew, the oak trees outperformed other plant species, resulting in an unusually dense and uniform woodland. This unnatural forest not only blocks out the light and suffocates the undergrowth but also efficiently sucks up all the water from the ground before it can recharge the springs and streams that feed the Muga River. During a recent drought, the basin was pushed into emergency status, forcing 22 towns to ration water and causing the nearby reservoir levels to drop low enough to reveal an ancient cannonball factory from the 1700s. The river became too weak to sustain local farming and coastal wetlands, proving that the wellbeing of the whole valley depends on the health of this forest ecosystem.

II. The Counterintuitive Solution: Selective Cutting

Pioneers of our Time found one counterintuitive action that could address all these issues: selective tree cutting.

This habitat restoration method involves strategically removing certain trees. By selectively cutting down trees, the ecosystem is given room to breathe, allowing more light to finally reach the forest floor. More importantly, it revives the Muga River by dramatically reducing water loss. The work here has already resulted in a 66% decrease in water loss.** With the new light and moisture, an undergrowth can start to form, which improves soil health and creates micro-habitats for countless creatures. For much of the area, this is the first time the forest floor has seen direct sun in 50 years. The project aims to completely transform over 10 additional hectares into a future-proof habitat and conduct a scientific study over the next five years, measuring everything from carbon capture to water flow and new habitats for wildlife.

III. The Return of Wildlife and the Missing Link

As the valley habitat improves, the iconic animals of the Pyrenees are slowly making a comeback. Otters and crayfish are returning to the river, and even wolves, which had been absent for more than 100 years, have now returned. The returning wildlife aids in retaining this natural ecosystem: deers and other grazers consume the young tree saplings, ensuring that the forest does not grow back as thick as before. However, a crucial link was still missing: scavengers.

Vultures are often misunderstood, but they are nature's essential cleanup crew. They have evolved ultra-strong stomach acids (up to 100 times more acidic than humans) which can kill dangerous diseases like rabies, botulism, and tuberculosis, preventing their spread and protecting other animal populations—including humans. According to a new peer-reviewed study, the unintentional decimation of vultures in India led to the death of about half a million people over five years, underscoring their ecological importance. The Pyrenees historically supported four species of vultures: the Eurasian black vulture, the Griffon vulture, the bearded vulture, and the now endangered Egyptian vulture. When Stef arrived in the valley in 2018, none were left. "We have to add the missing link back into the lifecycle of the valley, which means bringing back the scavengers."

IV. Vultures: Passive Lures and Restoration Support

To encourage the return of the vultures, the team employed an unusual strategy: using **vulture puppets**. Vultures are social creatures, and if a passing bird observes other vultures—even artificial ones—they are more likely to stop and settle down to nest, a phenomenon known as passive colonization. Five of these puppets were installed into new artificial nests to mimic a popular nesting colony.

Of course, a puppet colony alone won't sustain the birds. The valley is still recovering, and the natural food chain is not yet fully restored. Vultures primarily consume dead animals, so the team established a temporary feeding point using leftover meat. This provides just enough sustenance to give the birds a head start while the natural food chain recovers. This effort has already seen a community of **Gryphon vultures** return to the valley—a huge milestone for Stef and his team. They are now hoping for other vulture species to make a comeback, and a remote-controlled live camera system has been funded to keep track of all the birds arriving at the feeding site.

V. The Ultimate Success: Tagging the Egyptian Vulture

The project’s success was dramatically confirmed with the capture and tagging of an Egyptian vulture. This species is extremely rare, not only in this area. Seeing them return to the Muga Valley provides strong evidence of the project's success. To track their movements and aid recovery, two of the new vultures were fitted with lightweight **GPS tags** for three years of monitoring. If all goes well, these birds will be the final puzzle piece to complete the picture of a thriving ecosystem here in the Muga Valley.

VI. Conclusion: A Holistic Approach to Ecosystem Health

An unhealthy ecosystem can be difficult to diagnose, which is why this project takes a comprehensive, holistic approach. It involves a wide range of experts and researchers focusing on the soils, chemistry, geology, geography, and climate of the area. This collaboration is essential to developing the best strategy for the ecosystem. The Muga Valley project demonstrates that sometimes the best ecological solution is the most **counterintuitive**. In areas where the forest has been managed and the river is flowing again, the landscape feels truly revitalized, proving that these deliberate, scientifically-backed interventions are highly effective in bringing life back to a green desert.