Introduction

Since the seventeenth century, camphor ,laurel has been used commercially for its timber and essential oils in China and Japan. By the late nineteenth century it was cultivated in many countries for its chemical constituents, or as a shade or ornamental tree. It is still used in Southeast Asia for its timber but has not been used for commercial production of camphor oil since the 1920s, when that substance was made artificially. Camphor is now largely replaced by eucalyptus oil on the world market.

Many other plants including crofton weed, water hyacinth, groundsel bush, lantana and privet, have been introduced as ornamentals and have become weeds. However, the history of camphor laurel is a little different. Its value as an ornamental tree was actively promoted in municipal parks and gardens and in school grounds along much of the east coast of Australia, especially in New South Wales and southern Queensland.

By 1900 it was "growing like a weed in many parts of the colony of New South Wales," although this was probably in reference to the adaptation of the species in the Sydney area rather than the extent of its naturalisation. Between 1900 and 1910 camphor laurel was widely planted as a shade and ornamental species, and also for shade and shelter on. north coast dairy farms, since wholesale clearing of the 'Big Scrub' in the late 1800s had removed most tree growth on the elevated red soils.

The density of camphor trees resulting from plantings in villages, towns, and farm shelterbelts in the Richmond-Tweed region, together with ideal climate and soils for its growth, allowed it. to naturalise and spread extensively to become serious weed there. However, it is also a weed other parts of the State, including the Orara Valley on the north coast, and in Sydney region.

Why Camphor Laurel Is a Problem

Camphor laurel has the usual attributes of a weed:

• adaptation to disturbed environments,
• effective spread,
• prolific seed production,
• rapid growth rate,
• absence of serious predators or diseases.

• Large size; mature trees are difficult to remove.
• Longevity; some trees are over 100 yeaqrs old and some up to 500 years old in their native habitat.
• Trees regenerate after lopping; control requires more than simple cutting down.
• Formation of single species communities.

Description

1. Scattered seedlings and small trees.
2. Scattered trees of various ages but canopies do not touch.
3. Closed stand with canopies touching.
4. Closed canopies with a variety of other species as a ground stratum.

Growth cycle

Flowering, fruiting and spread

Fruits mature in autumn and are small, round, green berries (drupes) about 8 mm in diameter which turn black on ripening in April-May. They contain a single seed about 5 mm in diameter. Over 100 000 fruits are produced on a mature tree, which bears good crops every year.

The ripe fruit is easily ingested and spread by birds. A number of species of birds eat them, especially pied currawongs, flock pigeons, magpies, figbirds, olivebacked orioles, blue-faced honeyeaters and blackfaced cuckoo shrikes. Fruits can also be transported a long way by water.

Germination

Soaking seeds in water for up to 40 days appears to hasten germination, possibly through removing inhibitors in the seedcoat.

Seedling growth

In closed stands of camphor laurel, seedlings grow slowly along with some native species until the stand is disturbed. This allows more light to enter, after which seedlings grow more rapidly., In old undisturbed stands, native rainforest species grow together with camphor laurel seedlings, but it is not known whether or not the native species can complete successfully in later years.

Control

Currently, there are two ways of controlling camphor laurel:

• Ecological. Management to prevent invasion by the species. This involves:
  • Intensive use of land, for example, for horticulture, and managing grazing land by intensive pasture production with appropriate grazing intensity, to exclude camphor.
  • Agroforestry, i.e., planting desirable forest species for aesthetic pleasure or as a timber resource on poorer or steeply sloping land so that potential sites for establishment of camphor are excluded.
  • Removing existing trees by:
    • Lopping. This is ineffective unless followed by chemical treatment of stumps, spraying of seedlings and planting of alternative tree or pasture species to help prevent reestablishment.
    • Bulldozing (without prior chemical treatment). While removing the entire tree and clearing the land, the disadvantage is the high cost and disturbance of soil. Soil disturbance can lead to rapid re-establishment of camphor laurel and other weeds, and possible soil erosion on slopes unless a desirable ground cover is established quickly.
• Chemical control. This is an effective but environmentally unfriendly way of controlling existing infestations. It allows control without disturbing soil or other vegetation. In areas to be cleared, prior chemical control makes rapid grubbing of dead stumps easier and hastens revegetation.