The great winter rainfall across many parts of WA has meant a bumper wildflower season, with many people visiting to admire them in local areas or on wildflower tours. However, in areas impacted by disturbance and urban zones (which includes Banksia and Tuart Woodland, and coastal heath), some of the species that are flowering at the moment are actually invasive species, which often compete with native species.
Native annual species such as many of the everlastings (such as Swan River daisy or Brachyscome) that light up the understory of local woodlands in Spring are particularly susceptible to being displaced by their weedy competitors. Banksia Woodlands are renowned for the rich herb understory, making these Woodlands particularly susceptible to the competitive impacts from weeds. Many of these weedy species, such as cape weed, thrive here as they are from other countries with similar climatic conditions (i.e., South Africa). While some of these species may be attractive, they can form dense monocultures that completely replace native herbs, daisies and tree seedlings, which in turn can affect ecosystem function and biodiversity, including insects (particularly butterflies and moths), birds and mammal populations.
Weeds in Banksia and Tuart Woodlands that have a similar appearance to natives are the pretty Betsy or Spanish valerian (Centranthus macrosiphon). This is in full flower at the moment and, when prolific, typically overtakes native parsnip (Tracymene species) and native daisies.
How can we best overcome this problem? The first step is knowing what species it is. There are a great range of resources out there to help with identifying plants. Spring is the best time to do this when most species in the southwest are in flower. Books such as Perth Plants have high quality photos of common native and weed species. If you have your own patch of bushland, identifying your plants is an important first step, but understanding approaches to overcoming the problem of understory weeds can be challenging. Minimising disturbance in natural areas, priorisiting which weeds have the greatest impact and starting work in the best condition areas working toward the most degraded are key principles to apply.
This project is supported by the PHCC through funding from the Australian Government’s National Landcare Program.