Pittosporum undulatum Vent. (Pittosporaceae)

Large ornamental temperate/sub-tropical forest tree, native of south-east Australia. Introduced to various temperate and tropical regions including Jamaica, where it invades natural forest.


Species characteristics

Life form, size, lifespan

Large evergreen tree growing to 30 m, lifespan unknown.

Taxonomy, variation and plasticity

P. undulatum is well defined taxonomically, though it hybridises with P. bicolor and perhaps P. revolutum in Australia.

Reproductive biology

Sex expression of flowers is somewhat variable but flowers are usually unisexual. Inflorescences (cymose) bear between 1 and 4 insect-pollinated flowers. Flowering starts at around 5 years of age and is enhanced by higher light levels. Fruits (capsules, ca. 12 mm across) take about 6 months to mature. Fruiting is highly synchronised in Jamaica. The capsules usually contain 20-40 sticky orange seeds, which are bird-dispersed.

Resilience and resistance

Seedlings coppice if the shoot is removed and blown-down trees sprout vigorously along the trunk. Cut stems resprout if replanted. The species is moderately susceptible to fire. VA mycorrhizae have been observed on P. undulatum in Jamaica.

Environmental requirements and successional status

Seedling recruitment occurs below the forest canopy but increases in higher light intensities (i.e. in gaps) with seedling densities up to 5000 m-2. Few seeds germinate under P. undulatum canopies. It can become dominant in Australia and elsewhere.

Products and uses

P. undulatum makes very good firewood, produces excellent charcoal and is a useful all purpose timber. It is an ornamental tree with attractive fragrant flowers. Abundant nectar production makes it good for honey bees.


Status in native range

Range and abundance

P. undulatum is native to the coastal belt and mountains of south-eastern Australia from Biggenden in Queensland to the south of Victoria. It is a common sub-canopy tree and shrub in several forest types and is also widespread in more open habitats.

Climate

The climatic conditions of its native range vary from moist sub-tropical to dry temperate (without a pronounced dry season).

Site requirements

P. undulatum is found in a variety of habitats, such as rain forest, scrub, gullies and grassland (if fire is suppressed). In the drier parts of the range it is restricted to moister sites. Fire limits its range and as the fire regime in the 20th century has decreased as a result of human management, P. undulatum has been able to spread to areas where previously it would have been killed.

Weediness

It is spreading outside its pre-European settlement range in several parts of Australia, a result of widespread planting in gardens, the fire suppression policies in many areas close to habitation and the introduction of the European blackbird, Turdus merula.

Pests and diseases

About 10 insect species in Australia feed on P. undulatum but none are believed to cause serious damage or death or significantly reduce population levels.


Status in invaded regions

History of introductions and intensity of invasions

Introduced to Jamaica in 1883 and planted in the Cinchona Botanic Gardens situated at 1450 m in the Blue Mountains. Found throughout a large part of the western end of the Blue Mountains and dominant in many areas of secondary forest close to Cinchona, locally common in more primary forest.

P. undulatum invades the Eucalyptus forests of central Victoria (Australia) where it is considered a threat to the survival of the native forests. It is invading a number of Pacific and Atlantic ocean islands. P. undulatum is spreading into scrub and riverine forest in Cape Province, South African fynbos but it has recently been affected by severe die-back.

Patterns of invasion and time-lag

P. undulatum seedlings emerge after periods of wet weather, but not beneath dense canopy cover. However the rate of spread of P. undulatum increases with large-scale disturbance such as that caused by hurricanes. Isolated P. undulatum trees occur several hundred metres from other trees of the same species.

There is no evidence for any appreciable time lag in the invasion, though the rate of invasion certainly appears to have accelerated since Hurricane Gilbert in 1988.

Site and climate

The Blue Mountains are very steep and rise to 2265 m. Mean annual rainfall is 2700 mm or more with two rainy seasons, though considerable variability in rainfall. Mean monthly maximum temperatures range from 18.5 to 20.5C. Night-time temperatures in winter can fall below 10C. Hurricanes are quite frequent.

Floristic region and vegetation types

The Blue Mountains are covered with montane rain forests containing about 550 flowering plant species, of which about 85 are thought to be endemic to the range. Canopy height ranges from 5 m or less at high altitude to 25 m plus lower down.

Pests and diseases

In South Africa die-back has occurred as a result of a recent spread of an unidentified disease.

Impact on ecosystem

P. undulatum becomes dominant in secondary forests and natural forest subjected to hurricane damage. In areas invaded by P. undulatum a sharp decrease in native species richness has been recorded, probably because of the dense shade it casts.

Impact on humans and related activities

P. undulatum wood is preferred by locals for firewood and may have potential as a source of timber.

Control

Control has not been attempted but would be desirable. However due to the steep slopes and inaccessibility of the Blue Mountains traditional methods of control would be difficult. Furthermore, gap formation following cutting promotes the regeneration of P. undulatum and other alien weeds, notably Polygonum chinense and Hedychium gardnerianum. Biological control is being considered.


Ecological differences

Existence of ecological equivalent species and competitive interactions in invaded regions

P. undulatum, when compared with native species, differs in its response to hurricane by lower mortality, less crown damage and higher rate of treefalls (trunks readily sprout after being blown down). Its crown is noticeably denser and extends further downwards than that of native species. The extensive superficial rooting system of P. undulatum is not observed in native species.

Differences in status and ecology between invaded and native ranges

The range in climates between its invaded and native ranges is considerable


Selected references

Gleadow, R.M. (1982) Invasion by Pittosporum undulatum of the forests of central Victoria. 2. Dispersal, germination and establishment. Aust. J. Bot. 30, 185-198.
Gleadow, R.M. & Ashton, D.H. (1981) Invasion by Pittosporum undulatum of the forests of central Victoria. 1. Invasion patterns and plant morphology. Aust. J. Bot. 29, 705-720.
** Goodland, T. & Healey, J.R. (1996) The invasion of Jamaican rainforests by the Australian tree Pittosporum undulatum. University of Wales, Bangor.
** Goodland, T. & Healey, J.R. (1997) The effect of Pittosporum undulatum on the native vegetation of the Blue Mountains of Jamaica. University of Wales, Bangor.
** Goodland, T. & Healey, J.R. (1996) The control of the Australian tree Pittosporum undulatum in the Blue Mountains of Jamaica. University of Wales, Bangor.
* Pickard, J. (1984) Exotic plants on Lord Howe Island: distribution in space and time, 1853-1981. J. Biogeogr. 11, 181-208.
* Richardson, D.M. & Brink, M.P. (1985) Notes on Pittosporum undulatum in the south western Cape. Veld and Flora 71, 75-77.
** Rose, S. (1997) Integrating management of Pittosporum undulatum with other environmental weeds in Sydney's urban bushland. Pac. Conserv. Biol. 3, 350-365.

Pierre Binggeli & Tom Goodland

May 1997