Researching the complexities of invasive species at the Maplewood Flats Conservation Area is a priority for the Wild Bird Trust of BC (WBT).
WBT strives to better understand the complex interactions between invasive plant species, native plants, and wildlife to inform and enhance management practices at Maplewood Flats.
In 2018, Chloe Hartley, co-chair of WBT’s Habitat Committee, completed her Master’s thesis in ecological restoration, which examined the effects of two invasive species at Maplewood Flats. Hartley researched how Himalayan blackberry (Rubus armeniacus) and English Ivy (Hedera helix) influence the plant and bird community at Maplewood Flats.
Hartley surveyed the plant community on site and identified Himalayan blackberry in 95% of the survey plots with a mean coverage of 51%. Most frequently, the only other plant growing within dense blackberry patches was moss. English Ivy was found in 38% of survey plots with a mean cover of 23%. Both plants were found at higher density under the forest canopy and blackberry was associated with the lowest plant diversity. In essence, Hartley’s research indicates that as the cover of Himalayan blackberry and English ivy increases, the diversity and cover of other plants decreases. When either Himalayan blackberry or English ivy is dominant, overall plant species richness is lower.
Hartley also identified lower bird presence where Himalayan blackberry and English ivy make up the predominant cover.
Invasive species are often recognized as a significant factor in the loss of biodiversity in ecosystems. Scientists have identified that invasive species can degrade the ecological value of landscapes by displacing native species which reduces the quantity and diversity of food, shelter and space available to native species. When the establishment of invasive species reduces overall ecosystem species diversity, ecosystems may lose resilience to disturbances.
There is a robust collection of research that establishes the link between high bird species diversity and high plant community complexity and diversity. Given that large portions of the landscape at Maplewood Flats are dominated by Himalayan blackberry and English ivy, management strategies that increase native plant species cover and richness may enhance the suitability of habitat for birds and wildlife.
Himalayan blackberry originates from the Caucasus region of Asia and is labelled as an invasive species in BC. The species demonstrates a rapid growth capacity and has a high drought tolerance—it is one of the most invasive angiosperms worldwide. The plant crowds out low-growing vegetation and heavy shade likely limits seed germination of other species. Blackberry forms dense thickets that limit the mobility of large animals.
English ivy, a fast-growing species, originates from Europe and is considered an invasive species in BC. The lower mainland presents an ideal climate for the plant due to its mild winters. The plant requires little light and water. It forms a thick layer of growth along the forest floor that limits native plant growth and suppresses seed germination.
While Hartley’s research suggests that Himalayan blackberry and English ivy are associated with reduced native plant species diversity and reduced bird use, the mechanism behind this correlation is not known.
The management of invasive species can be controversial. The direct removal of invasive species in particular has raised concerns about the lack of definitive evidence of harm for specific species, and the effects of chemical control methods, disturbance of landscape from the removal process, and the impact on organisms using the invasive species as a resource must be considered.
At the Maplewood Flats, site managers have observed birds nesting and feeding in Himalayan blackberry, thus creating reservations about removing the species. Researchers have documented how Himalayan blackberry is utilized by wild creatures, but those studies also confirm that birds and small mammals prefer diverse native plant community landscapes.
Still, the removal of invasive species without replacement with a comparable structure could have an effect on bird use at the Maplewood Flats. There is a layered complexity in managing invasive species, which is taken into profound consideration as the WBT further develops the Habitat and Cultural Use Management Plan.