Eucalyptus plantations support less bird diversity than native and pine forests.
A growing body of evidence, solidified by large-scale ecological analyses, reveals that eucalyptus plantations—while economically vital for timber and pulp production—function as poor habitats for birds, supporting significantly fewer species than the native forests they often replace. The research indicates these monoculture landscapes also underperform compared to non-native pine plantations, challenging the assumption that all reforested areas offer equivalent ecological benefits and highlighting a critical conservation trade-off in landscape management.
The findings carry global significance. Eucalyptus is one of the most widely planted hardwood genera in the world, covering tens of millions of hectares across South America, Europe, Asia, and Africa. Praised for its rapid growth and commercial value, its expansion has raised persistent questions about its environmental cost. Birds are considered crucial bioindicators, meaning their presence, diversity, and abundance reflect the overall health of an ecosystem. A decline in avian communities signals deeper issues, including a lack of food resources and habitat complexity that affects insects, mammals, and overall ecosystem function.
A Stark Reduction in Avian Life
Synthesizing data from dozens of individual studies across multiple continents, researchers have painted a clear picture of the ecological consequences of converting native habitats to eucalyptus monocultures. A landmark meta-analysis examining global data found that, on average, eucalyptus plantations host 35% fewer bird species than native forests. The impact is even more severe for birds that are highly adapted to forest environments.
These forest specialists—birds that rely on the unique conditions of a mature, complex forest for food and shelter—experience a staggering drop in numbers. The analysis revealed their abundance plummets by more than 50% within eucalyptus stands. The most vulnerable groups include insectivorous birds that forage in the understory and among bark, as well as fruit-eating species, which find little sustenance in a landscape dominated by a single, non-native tree species.
The studies consistently show that while some generalist bird species can survive or even thrive at the edges of plantations, the core of these vast, uniform landscapes becomes a “green desert” for a majority of native avian fauna. The lack of diversity is not just in species count but also in functional roles, leading to simplified and less resilient ecosystems.
Unpacking the Ecological Drivers
Scientists point to a combination of factors that make eucalyptus plantations inhospitable for most native birds, primarily stemming from their structural simplicity and the scarcity of critical resources.
Structural Simplicity
Native forests are characterized by high structural complexity. They have multiple vertical layers: a dense understory of shrubs and young trees, a mid-canopy, and an upper canopy, sometimes with emergent giants. This variety creates a multitude of niches for different bird species to nest, forage, and hide from predators. In stark contrast, commercial eucalyptus plantations are typically even-aged monocultures. Trees are planted in dense, uniform rows, and the understory is often suppressed through management practices or the natural chemical properties of eucalyptus leaf litter.
This homogeneity eliminates the niches that specialized birds depend on. Without a shrub layer, ground-dwelling and understory insectivores lose their foraging grounds and cover. The absence of old, decaying trees means no cavities for birds like woodpeckers, owls, and parrots to nest in.
Resource Scarcity
Beyond physical structure, eucalyptus plantations offer a poor menu for native birds. The foliage of non-native eucalyptus trees does not support the same abundance or diversity of local insects that native trees do. This creates a critical food shortage for insectivorous birds, which constitute a large portion of avian biodiversity in many ecosystems.
Furthermore, the flowers and nectar of eucalyptus may not be accessible or suitable for native nectar-feeding birds, and the lack of diverse, native fruit-bearing trees starves frugivorous species. The leaf litter from eucalyptus trees is also problematic; it contains allelopathic chemicals that can inhibit the growth of native understory plants, further simplifying the habitat and reducing food availability at the forest floor.
The Pine Plantation Comparison
Interestingly, the research also draws a distinction between eucalyptus and pine plantations. While both are vastly inferior to native forests, some studies suggest that pine plantations can, under certain conditions, support slightly higher bird diversity than their eucalyptus counterparts. This difference is not fully understood but may relate to several factors.
Pine plantations, especially older ones, can sometimes develop a more substantial understory of native shrubs and ferns, adding a layer of structural complexity. The composition of their leaf litter creates a different soil environment that may be more permissive to native plant regeneration compared to the chemical-laden litter of eucalyptus. This allows a more diverse community of insects to establish, providing a better food base for birds. Nonetheless, researchers stress that both plantation types are poor surrogates for native forest habitat.
Balancing Forestry and Conservation
The consistent findings from this research present a major challenge for policymakers and land managers aiming to balance economic development with biodiversity conservation. The studies do not call for an end to eucalyptus farming, which is a cornerstone of many regional economies, but rather for a shift toward more ecologically sensitive management practices.
Based on the ecological principles identified, researchers propose several strategies to mitigate the negative impacts of plantations on bird diversity:
- Landscape Mosaics: Instead of vast, unbroken monocultures, a more effective approach is to embed plantations within a landscape mosaic that includes significant patches and corridors of native forest. Proximity to native habitat has been shown to increase bird diversity within the plantation itself, as birds can use the plantation for supplementary foraging while relying on the native forest for core habitat needs.
- Promote Understory Growth: Forestry management could be adjusted to allow or even encourage the development of a native understory within plantations. This could involve less intensive weeding, reduced herbicide use, and thinning of trees to allow more light to reach the forest floor.
- Mixed-Species Plantations: Incorporating native tree species alongside eucalyptus can dramatically increase habitat value, providing more diverse food sources and structural complexity.
- Protect Riparian Zones: Maintaining and restoring native vegetation along rivers and streams that run through plantations can create critical wildlife corridors and resource-rich habitats.
As the global demand for wood products continues to grow, the area covered by plantations is set to expand. The scientific consensus is clear: the design and management of these future landscapes will determine their capacity to support life. While eucalyptus plantations can provide essential economic goods, they cannot replace the ecological richness of a native forest. The path forward requires a more integrated approach that deliberately plans for biodiversity within working landscapes.