What is Woody Encroachment ?

Increasing tree cover is often seen as a positive outcome of biodiversity conservation and a much-needed effort to combat climate change. What happens, then, if tree cover increases in areas that historically hosted a different habitat?

In a study published on June 5 in the journal Global Change Biology, scientists from the Universities of Witwatersrand, Cape Town, and Oxford reported that more trees in open ecosystems like savannahs and grasslands have substantially reduced the number of native grassland birds. In the African Savannah in particular, the population of grassland birds has declined by more than 20%.

Woody encroachment refers to the increasing density of woody plants, like shrubs and trees, in areas that were previously dominated by grasses or herbaceous vegetation. This phenomenon is occurring globally, particularly in grasslands and savannas.

Impacts on Habitat and Biodiversity

Woody encroachment has significant negative impacts on habitat and biodiversity:

• Habitat Loss: As woody plants replace grasses, the structure and composition of the ecosystem change dramatically. This loss of grassland habitat can lead to declines in species adapted to open environments, such as certain birds, reptiles, and insects.
• Altered Fire Regimes: Woody plants can alter fire regimes by increasing fuel loads and changing fire behavior. This can have cascading effects on the ecosystem, impacting plant communities and animal populations that depend on fire for habitat maintenance.
• Reduced Grazing Capacity: Woody encroachment reduces the availability of forage for livestock, impacting the livelihoods of pastoral communities.
• Soil Erosion: Reduced ground cover due to woody encroachment can lead to increased soil erosion, particularly in arid and semi-arid regions.
• Hydrological Changes: Woody plants have different water use patterns compared to grasses, affecting water availability for other plants and organisms.
• Carbon Sequestration: While woody plants can sequester carbon, the overall impact on carbon storage depends on the specific ecosystem and the balance between carbon uptake by woody plants and carbon losses from other ecosystem components.

Recent Examples

Woody encroachment is a global issue, with numerous recent examples:

• African Savannas: Savannas in Africa are experiencing rapid woody encroachment, driven by factors such as climate change, overgrazing, and fire suppression. This has led to declines in large herbivores, such as elephants and giraffes, and altered ecosystem processes.
• North American Great Plains: The Great Plains in North America have seen significant encroachment by woody species like eastern redcedar and mesquite, reducing grassland habitat for species like the Greater Prairie-Chicken.
• Australian Rangelands: Woody encroachment by species like acacia and eucalyptus is a major challenge in Australian rangelands, affecting livestock production and biodiversity.

Addressing woody encroachment requires a multifaceted approach, including:

• Early detection and monitoring: Identifying areas prone to woody encroachment and tracking its progression.
• Integrated management strategies: Combining various methods such as mechanical removal, controlled burning, and grazing management.
• Restoration efforts: Reintroducing native grasses and other plant species to restore ecosystem function.
• Policy and economic incentives: Supporting sustainable land management practices and providing incentives for landowners to address woody encroachment.

By understanding the causes and impacts of woody encroachment, we can develop effective strategies to mitigate its negative effects on habitat and biodiversity.