Removing the invasive Brazilian pepper tree is no easy task. Its deep-rooted presence in Southern California’s ecosystems outcompetes native plants and poses a serious threat to the biodiversity of riparian woodlands. The intensive process required to eliminate this tree has raised ecological concerns. However, a recent study from the University of California, Irvine, has discovered that the complete removal of Brazilian pepper trees can lead to an increase in beneficial soil fungi.
The issue with Brazilian pepper trees
The Brazilian pepper tree was initially introduced to North America as an ornamental plant, but as time went on, it eventually began to invade forests and take over. Its rapid growth outcompetes native plants for resources, which ultimately reduces plant diversity and impacts the animals and insects reliant on native plants for food and habitat. Additionally, the tree produces chemicals that limit the growth of surrounding plants and make it more challenging for native plants to establish themselves in the area.
Unfortunately, the Brazilian pepper tree is difficult to remove because it has an extensive root system and can resprout from cut stumps. Although several methods have been attempted to eradicate this invasive species, none have proven to be entirely effective or without significant damage to the surrounding environment.
Surprising results
Despite the damage the tree causes to native species, scientists initially feared that completely removing it could cause more harm than good and disturb the ecosystem. Compared to native species, the Brazilian pepper tree has associations with a higher diversity of beneficial fungi, like ectomycorrhizal fungi (EM fungi), which form symbiotic relationships with plant roots, helping them absorb more water and nutrients.
Researchers worried that removing the tree might negatively impact the soil and the broader ecosystem by disrupting this balance. Yet, on the contrary, the study revealed that removing the tree led to an unexpected increase in the diversity of EM fungi in the soil.
The findings suggest that the invasive tree may have been suppressing the presence of these fungi, which, in turn, hindered the growth of surrounding native plants. Once these trees were removed, the soil environment actually became more favorable for these beneficial fungi, leading to an overall healthier, more resilient ecosystem.
In contrast, the selective removal of the Brazilian pepper tree, where only some were removed to protect native plants, led to a decrease in EM fungi. Although this approach is considerably less disruptive in the short term, it did not support the fungal communities as effectively as hoped, demonstrating the complex nature of managing invasive species and the importance of considering soil health in restoration efforts (1).
The future of invasive plant removal
As efforts to control Brazilian pepper trees continue, the findings from this study provide valuable insights into how to deal with this species while keeping all ecological factors in mind. Understanding both above and below-ground ecological processes is crucial for maintaining a more supportive environment for native plants to reestablish and thrive.
References
- Bañuelas, David C, Neil C Shah, Jennifer E Perez, Samantha A Bellier‐Igasaki, Emily McGauley, Amanda C Swanson, Alys Arenas, and Kathleen K Treseder. 2024. “Response of Ectomycorrhizal Fungi to Full and Selective Removal of an Invasive Tree in Riparian Woodland.” Restoration Ecology, June. https://doi.org/10.1111/rec.14204.