Pest plant - Olives

The olive tree (Olea europaea) was introduced from the Mediterranean area as a tree crop. It is now established in many parts of South Australia, causing a major problem in native vegetation.

Description

• erect, bushy evergreen tree to 12m, with a deep, widely-branched, woody root system
• trunk branches from the base and has rough black bark
• leaves are 3-8cm x 1-4cm, narrow and tapering to a point, glossy dark green on top, silvery below
• in late spring, tiny cream flowers in large clusters with four petals and four protruding stamens
• fruit is ellipsoid, 1.5-3cm long, purple-black when fully ripe
• each fruit contains one brown oblong seed, 1.5cm long
• seedlings have smaller oblong leaves, arranged rigidly in opposite pairs.

Why is it a problem?

• invades native vegetation, especially in dry sclerophyll forest or woodland and adjoining cleared, ungrazed land
• can alter the composition of native vegetation and decrease biodiversity
• fire hazard.

Distribution

• Eyre Peninsula – isolated infestations but high risk of spread to native vegetation
• Northern pastoral – common in southern Flinders Ranges, isolated plants elsewhere
• Northern agricultural districts and Yorke Peninsula - common on roadsides and native vegetation in the higher rain fall areas
• Murray Mallee - isolated outbreaks along the Murray River and in irrigated areas
• South East - isolated plants on roadsides and some reserves
• Central region - common in the Mt Lofty Ranges.

Ecology

• grows well in most environments, particularly where winter rainfall is high and summers dry
• grows on a wide range of soil types but will not survive in waterlogged soil
• highly inflammable due to their oil content and can regenerate from stumps after fire
• seeds germinate mainly in autumn and seedlings grow during winter
• flowering does not begin for several years appearing in October and November
• fruit develops slowly over summer, the ripe fruits hanging on the tree for a long period during the following winter.

How it spreads

• birds and foxes eating the fruit and dropping the seeds elsewhere
• development of commercial olive orchards has increased spread throughout South Australia
• seed may be moved locally in soil during earthworks.