Tree Cover Increase Threatens Grassland Bird Populations

August 1, 2024

Increasing tree cover is usually seen as good for protecting nature and fighting climate change. But new research shows that trees spreading into places that have always been open, like savannahs and grasslands, can harm native animals, especially birds that live in grasslands. A major study in Global Change Biology found that grassland bird numbers in the African savannah have dropped by more than 20%.

Understanding Open Ecosystems

Grasslands and savannahs are very important for biodiversity. They make up almost 40% of the Earth’s land and support many different species, from large plant-eaters to unique birds. However, these ecosystems face threats from being turned into farmland, being built on, and being overgrazed. Another threat is woody encroachment.

Woody Encroachment Defined

Woody encroachment happens when open areas, like grasslands and savannahs, start to have more trees and shrubs. This change makes the ecosystem more uniform, with fewer different types of plants and animals. As a result, the overall biodiversity decreases.

Factors Driving Woody Encroachment

Several things cause woody encroachment:

Disruption of Disturbance Regimes: Natural and human activities, like stopping fires and changing grazing habits, allow trees to grow more.
Climate Change: Higher CO2 levels help trees grow more than grasses, which leads to fewer grasslands.

Consequences for Biodiversity

The change from open areas to ones with more trees has big effects on biodiversity:

Declining Bird Populations: Bird species that live in grasslands are decreasing because trees are taking over their habitats.
Altered Ecosystem Dynamics: Changes in the soil and higher risk of predation threaten animals like grassland rodents.

Invasive Species and Plantation Effects

Invasive tree species make woody encroachment worse. For example, in India, species like Prosopis juliflora have turned grasslands into dense woodlands, harming the habitat even more. To fight the negative effects of woody encroachment, more research is needed to understand its impact and to monitor open ecosystems over time. It’s also important to stop misclassifying these habitats as “wastelands” to protect them effectively.

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