Invasive Strawberry Guava Blocks Rainforest Recovery

An invasive tree introduced more than a century ago is quietly reshaping Madagascar’s rainforests — and stopping them from growing back.

A new study published in Biological Conservation, February 11, 2026 finds that strawberry guava (Psidium cattleyanum) is preventing natural forest regeneration in parts of Ranomafana National Park, one of the island’s most important biodiversity strongholds.

Researchers from Rice University and Malagasy institutions report that while native tree seedlings still emerge after forest disturbance, many fail to grow beyond early stages once strawberry guava dominates the understory.

“Following forest disturbance, we would normally expect to see a gradual process of natural regeneration,” said Amy E. Dunham, associate professor of biosciences at Rice University and the study’s corresponding author. “But when strawberry guava becomes established, that regeneration process can stall.”

A Forest Stuck in Early Recovery

Madagascar’s rainforests have long faced pressure from logging, slash-and-burn agriculture and land clearing. In many tropical systems, forests can slowly regenerate once disturbance ends. Seedlings emerge, saplings compete for light and, over time, the canopy closes again.

But in guava-invaded areas, that recovery appears frozen.

The research team compared forest plots long dominated by strawberry guava with nearby non-invaded areas inside Ranomafana National Park, a UNESCO World Heritage site known for its high levels of endemism.

They found that guava thickets create a dense understory that blocks light and restricts the vertical growth of native tree saplings. Although seedlings of native species were present in similar numbers across both invaded and intact plots, their development stalled beneath guava cover.

“This suggests a bottleneck in succession,” said Matthew A. McCary, co-author of the study. “The early stages are happening, but the forest isn’t progressing toward canopy recovery.”

Without canopy formation, long-term forest structure — and the species that depend on it — remain vulnerable.

Soil and Insect Communities Also Shift

The impact goes beyond tree growth. Soil samples from invaded plots showed significantly lower levels of carbon, nitrogen and organic matter compared with native-dominated forest areas. These nutrients are essential for sustaining forest productivity.

The researchers also recorded reduced diversity of ground-dwelling invertebrates in guava-dominated plots. Such organisms are critical to decomposition and nutrient cycling.

“When you alter plant dominance, you’re not just changing vegetation,” McCary said. “You’re influencing soil chemistry and the entire network of organisms that maintain ecosystem function.”

In other words, strawberry guava does not simply occupy space — it reshapes ecological processes.

A Complicated Conservation Dilemma

Yet the story is not entirely straightforward.

Strawberry guava produces abundant fruit that is consumed by wildlife, including Madagascar’s iconic lemurs. In some invaded areas, fruit-eating animals were observed more frequently.

“Strawberry guava is providing a food source for animals that are themselves endangered,” said Eric F. Wuesthoff, graduate student and study co-author. “At the same time, it may be undermining the long-term stability of the forest habitat they ultimately depend on.”

The plant, native to Brazil and introduced to Madagascar in the 19th century, has become deeply embedded in disturbed landscapes. Its usefulness to local communities and wildlife makes management decisions more complex.

“What this research highlights is the complexity of conservation work,” Dunham said. “Strawberry guava is extremely difficult to remove. It’s useful, it feeds wildlife. But its presence disrupts the forest at many levels and may prevent full recovery after deforestation.”

Implications Beyond Madagascar

Strawberry guava is considered one of the world’s most problematic invasive plant species and has altered ecosystems in other tropical regions, including Hawaii.

As global forest restoration efforts accelerate in response to climate change, the findings underscore a critical reality: recovery is not guaranteed simply because deforestation stops.

In ecosystems like Madagascar’s — shaped by millions of years of isolation — invasive species can redirect the future of entire landscapes.

For conservationists working to restore rainforest biodiversity, the study delivers a clear warning. Without addressing invasive plants such as strawberry guava, forest regeneration may remain incomplete — and fragile — for decades to come. (Sulung Prasetyo)