Sweet Pittosporum, Pittosporum undulatum, that beautifully perfumed tree when in flower, is the bane of my life, thanks to the ubiquitous blackbird.
A member of the Pittosporaceae, along with Billardiera, Bursaria and Sollya, its common names are numerous: native daphne, orange pittosporum, Victorian-box, mock orange, Victorian laurel, cheesewood.
Normally confined to warm temperate rainforest and lowland forests and woodlands from the Great Dividing Range seawards (Brisbane to (perhaps) Westernport Bay), it is now a weed on four continents and Australia's WORST NATIVE WEED. It invades dry coastal vegetation, heathland, dry sclerophyll forest, lowland grassland and woodland, almost unstoppable because it is adaptable and tolerates drought, frost and shade. According to the Flora of Victoria2, it is "now a more widespread environmental weed in wet forests and coastal shrubs of south-eastern Victoria, largely due to dispersal of seed from cultivated sources (chiefly by blackbirds) and altered fire regimes.
Tim Low1 claims that it has become a major invader because it likes pollution. Pittosporums cluster around the roots of eucalypts and kill them, starving the trees of water and minerals. Smaller plants such as grasses, orchids and shrubs are shaded out. With excess runoff and fertilisers, pittosporums dominate. Botanists call this “mesic shift” – a switch to a wetter community; rainforest is escaping from fertile fire-protected valleys and sprouting everywhere. 'Vegetation shift" is a change induced by people - garden plants, escapees. [Prof. Ewart even sowed seeds at Wilsons Promontory in 1912].
The pittosporum reproduces by seed and suckers, “spread by birds internally and sticking to feet and feathers, mammals, (brush tailed possums, foxes, black rats), sticks to human shoes, dumped garden waste and contaminated soil.
How does one deal with Pittosporum undulatum?
Around Sydney it is culled to prevent a monoculture of pittosporum.
In Victoria it is officially listed as a Potentially Threatening Process. Hot fires have been used to kill pittosporum at Buckley's Reserve, Mornington Peninsula where invasive pittosporum covered 66 per cent; sundews, lilies, honeypots rose from the ash.
According to Blood: “Low-intensity fires do little permanent damage and saplings under 2m tall coppice vigorously, Can reshoot after being cut. Insect pollinated. Seeds may germinate after seed fall in spring, but most germinate in autumn. Plants flower when only 4-5 years old and when 1m tall or less. Seedlings can establish beneath tree canopies because of their higher drought tolerance in shade. Very high seed production, rapid dispersal, early seed production and fast growth contribute to its weediness.”
I am now a PPP (Perpetual Pittosporum Puller-outer). Join me.
1. Tim Low, The New Nature, Viking, 2003
2. Flora of Victoria Volume 3, Inkata Press, 1996, Ed Walsh & Entwisle
3. Kate Blood, Environmental Weeds, CH Jerram Science Publishers, 2001 pp 28-29