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Description

Acacia mearnsii is a fast-growing leguminous large tree native to Australia growing naturally in brown sandy clay soils and black peaty soils along swampy flats and riverbanks. Over 1000 Acacia species occur in Australia and there are over 1350 species identified so far. Typically Acacia mearnsii reaches 10m tall but can grow to 20m in the right conditions. It has a rounded crown often branching low to the ground and rough brown bark. Dark green leaves are feathery. Flowers are pale yellow. Flowering time is from early spring to late summer. Globular flower heads occur in large, fragrant sprays. Fruits dark brown pods, finely hairy This species is the world's premier source of tannins and it is widely cultivated in warm temperate to tropical areas for its wood and tannins . In areas where it has been introduced, it is often considered a weed, and is seen as threatening native habitats by competing with indigenous vegetation, replacing grass communities, reducing native biodiversity and increasing water loss from riparian zones.

Acacia mearnsii is an evergreen Tree growing to 10 m by 8 m at a fast rate.
It is hardy to zone 9 and is frost tender. The flowers are pollinated by Bees, insects. The plant is self-fertile.
It can fix Nitrogen.
It is noted for attracting wildlife.
Suitable for: light and medium soils, prefers well-drained soil and can grow in nutritionally poor soil. Suitable pH: acid and neutral soils and can grow in very acid soils.
It cannot grow in the shade. It prefers moist soil. The plant is not wind tolerant.

Cultivation

A plant of warm temperate to subtropical areas, it can also be grown at moderate to high elevations in the tropics. It is found at elevations from 300 - 2,440 metres in areas where the mean annual temperature is in the range 9 - 20c and the mean annual rainfall is 500 - 2,050 mm. It prefers a moderate climate, exhibiting great intolerance to extreme heat or cold. Its lower altitudinal range is decided by the fact that trees cannot stand high summer temperatures, and the upper altitudinal limit is based on the fact that the tree does not tolerate temperatures below 0c. Winter frosts and cold winds during the early part of the rainy season affect growth and survival rate, but older trees can withstand mild frost. Localities experiencing severe hailstorms and snowfall are unsuitable. Flourishes in deep, well drained, light textured and moist soils. It thrives in well-aerated, neutral to acid soils, loamy soils, soils derived from shale or slate and is highly intolerant of alkaline and calcareous soils. Soils with lateritic pan close to the surface are most unsuitable. Adequate soil moisture is a prerequisite for satisfactory growth. Trees cannot withstand drought because of their superficial root system and high rate of transpiration. In Hawaii, A. Mearnsii is a noxious weed and spreads prolifically at elevations between 600 - 1,200 metres in the 1,000 - 1,200 mm rainfall zones. The plant is also showing signs of being invasive in other areas, helped particularly by its prolific seed production and the long viability of the seeds in the soil. Trees begin to yield fertile seed from the age of 5 years, giving good annual crops. The tree regenerates naturally from seed after burning in clear-felled plantations. Seed may lie dormant in the soil for up to 6 years without loss of viability. The trees have strong light requirements and respond to thinning in the early years. Growth rate is comparatively slow for the first 1 or 2 years. Thereafter, both height and diameter increments are rapid up to the age of 6 - 7 years, after which they fall off gradually. The tree has low coppicing power. Taproot development largely depends upon the depth of the soil, but the tree has the general tendency to develop a superficial lateral root system. Because of this, trees are liable to being uprooted by strong gales during the monsoon season. This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby.

HabitatsAn understorey tree of tall open forests
Habitatsin fringes of closed forests or in dense thickets on recolonized lands.
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