The Age of Pittosporum undulatum [WEED]
(c) Saahmadbulbul (Wikipedia)
An Australian native plant that is considered a weed even in places that its endemic. It truly is the age of Pittosporum undulatum. but how can it be that a native plant becomes a weed in the minds of garderners?
The term "weed" traditionally evokes images of invasive non-native species disrupting fragile ecosystems. However, the concept of native plants behaving as weeds is a complex and increasingly relevant issue. Pittosporum undulatum exemplifies this, as it has transitioned from a favoured native species with specific habitat requirements to a weed-like presence in altered landscapes out competing other natives for space and light.
I’m sure you have heard that a ‘Weed is a wild plant growing where it is not wanted and in competition with cultivated plants.’ or ‘A weed is a plant growing where a human doesn’t want it to grow.’
If these definitions are correct then undulatum sits at the top of the native weed list. As a landscape gardener, almost every garden I work in has undulatum present and an eager home-owner ready to rip it out.
The reality of the matter is, we humans are the real problem, it is our human altered landscapes that have created the perfect conditions for ‘Age of Pittosporum undulatum’ to unfold.
(c) Luca Boscain
Know the Enemy
Enemy is a dramatic word for this species, but one that is apt when it comes to talking about Pittosporum undulatum in our native bush. A Tree from 4 -15 m tall with lush evergreen domed growth, heavenly scented white/cream flowers and striking orange fruits and woody seeds that are favored by native animals as a valuable food source.
Known by its common names sweet pittosporum, native daphne, Australian cheesewood, Victorian box or mock orange, these names evoke the charm and affection we once had for this plant, even idolising it, harking back to european sensibilities.
The Perfect Storm
Pittosporum undulatum's ability to adapt to altered environmental conditions is a testament to its ecological flexibility. Originally confined to cool, damp forest areas, undulatum has successfully colonised a range of habitats, thriving in environments enriched by human activities such as nutrient runoff due to chemical fertilisers used in farming and gardening practices. Many other native species can’t handle the high levels of phosphorus leached into soils and river systems through such practices.
Pre-colonisation, Fire was a welcome and common occurrence in the Australian landscape. Our native flora harnessed the fires power, evolving with it. Many Native species need fire for seed germination, using it as an essential and irreplaceable element in their reproductive process.
The decline in fire frequency since colonisation has disrupted the natural checks on undulatum's spread, allowing it to outcompete native species that rely on fire for seed germination. This highlights the unintended consequences of human interventions in natural processes and the need for holistic ecosystem management approaches. This is something First Nations people keenly understood.
Undulatum is a plant that enjoys cool, damp forest areas what were mostly fire free which allowed them to grow, confined to wet, damp nutrient rich gullies from South East Queensland down to Victoria. Growing well in these conditions has meant they have not evolved to use fire or smoke for germination nor are they adapted to survive fire.
Understanding the mechanisms driving seed dispersal is crucial for predicting and managing the spread of invasive or weed-like species. Undulatum's prolific spread across vast distances is facilitated by birds that disperse its seeds through fecal matter. This makes management incredibly hard.
Management
Pittosporum undulatum needs a tailored management approach based on the species' status as endemic or non-endemic in specific areas. In native habitats, controlling undulatum populations is essential to prevent them from overwhelming other native species. This may involve methods such as habitat restoration, controlled burns, or targeted removal of undulatum individuals with chemicals. In areas where undulatum is non-endemic and poses a threat to local biodiversity, complete eradication is recommended to prevent further ecological harm. When it comes to keeping them as ornamental species in gardens, unless you live in a cool damp gully it is best to replace with another native species that attracts and feeds wildlife like cultivars of banksia, gravillia, or Callistemon.
Pittosporum undulatum illustrates how human actions, natural processes, and native plant behavior interact in complex ways. Dealing with native plants that act like weeds, needs an understanding of ecology, prioritising conservation and finding the missing links in our ecological ecosystems. Australia's reluctance to use fire in landscapes is starting to have consequences. Constantly suppressing fires could harm native landscapes and wildlife in the long run in ways we can’t yet imagine.