The hidden danger inside Spain's eucalyptus forests that worries scientists

From a distance, Spain's vast eucalyptus plantations look like thriving forests. Their dense green canopies stretch across large parts of the country's northwest, giving the impression of healthy woodland. But scientists say appearances can be deceptive.

A new study has found that these commercial plantations function very differently from native forests, supporting significantly fewer birds, insects and plants. The findings have renewed debate over the ecological cost of replacing diverse natural woodlands with fast-growing eucalyptus trees, a species introduced from Australia to fuel Spain's paper and timber industries.

Why are eucalyptus plantations called 'green deserts'?

Researchers use the term "green deserts" to describe landscapes that appear lush but support relatively little native wildlife.


Unlike natural forests, which contain a rich mix of tree species, shrubs, fungi and undergrowth that have evolved together over centuries, eucalyptus plantations are typically monocultures planted for commercial harvesting.

This simpler habitat offers fewer nesting sites, less varied vegetation and limited food sources for wildlife. As a result, many native species struggle to survive despite the forests appearing green throughout the year.

Study links eucalyptus expansion to declining bird diversity

The latest research, published in Forest Ecology and Management, examined 240 sites in and around Galicia's Fragas do Eume Natural Park, one of the last remaining Atlantic coastal forests on the Iberian Peninsula.

Scientists from the University of Santiago de Compostela and Spain's National Research Council found that the proportion of eucalyptus in a landscape was the strongest predictor of declining bird diversity.

According to the study, eucalyptus plantations consistently supported fewer bird species than neighbouring native forests. Even mature eucalyptus stands failed to provide the ecological functions offered by older native woodlands.

Birds that depend on insects for food and those that nest inside tree cavities were among the most affected. Species such as the great spotted woodpecker and the coal tit struggled because eucalyptus plantations offered fewer insects and almost no natural nesting holes.

The loss of insects creates a ripple effect

Researchers say the problem extends well beyond birds.

Many native insects have difficulty feeding on eucalyptus leaves because the trees evolved alongside Australian ecosystems rather than European ones. As insect populations decline, birds lose one of their most important food sources, particularly during the breeding season when chicks require protein-rich diets.

Scientists warn that fewer insects can also affect pollination, seed dispersal and natural pest control. The decline may eventually influence reptiles, amphibians and small mammals that rely on healthy forest ecosystems.

For this reason, researchers consider bird diversity one of the clearest indicators of overall forest health.

Why native forests are difficult to replace

One factor contributing to lower biodiversity is a natural chemical process known as allelopathy.

Eucalyptus trees release compounds into the soil that inhibit the growth of many native plants beneath them. With fewer shrubs and wildflowers, insect populations also decline, reducing food availability for birds and other wildlife.

Commercial forestry practices add another challenge. Eucalyptus plantations are generally harvested every 10 to 15 years, preventing trees from growing old enough to develop the hollows that many woodland birds use for nesting.

Why Spain continues to rely on eucalyptus

Despite environmental concerns, eucalyptus remains one of Spain's most valuable commercial tree species.

In Galicia alone, the forestry and timber industry generates around €2.5 billion annually and supports more than 19,000 jobs, according to the A Cadea Forestal-Madeira de Galicia 2025 report.

The tree's rapid growth makes it highly profitable for the pulp, paper and timber sectors, creating a difficult balance between economic development and environmental protection.

In 2017, Spain's Scientific Committee under the Ministry for Ecological Transition proposed classifying eucalyptus as an invasive alien species because of its ecological impact. The recommendation was ultimately not adopted, largely due to the species' economic importance.

Scientists suggest a practical solution instead of removing plantations

Researchers are not calling for eucalyptus plantations to be eliminated.

Instead, they recommend leaving strips of unmanaged native vegetation within plantation areas. Allowing indigenous shrubs, grasses and trees to regenerate naturally could provide habitat for insects and birds while maintaining commercial forestry operations.

The team believes this relatively low-cost approach could improve biodiversity and even benefit plantation owners by encouraging insect-eating birds that naturally help control pests.

The issue extends beyond Spain

The environmental debate surrounding eucalyptus is not limited to Spain.

Portugal, where eucalyptus is now the country's most widespread forest tree, has also experienced growing concern over the species. Following the devastating Pedrógão Grande wildfire in 2017, researchers highlighted how the tree's oil-rich leaves and bark can intensify fires and spread embers over long distances.

The disaster prompted Portugal to introduce tighter restrictions on new eucalyptus plantations near roads and populated areas.

Can forestry and biodiversity coexist?

The new research suggests the answer may be yes, but only if commercial forestry incorporates ecological planning.

Scientists argue that preserving patches of native vegetation within eucalyptus landscapes could help restore wildlife without undermining the timber industry's economic value. As European countries continue balancing conservation with growing demand for forest products, the study offers a reminder that forests should be measured not only by how green they appear, but also by the life they sustain.