Australian wattle poised to make hostile takeover in southern China

Yes another Acacia species called Black Wattle. Acacia mangium is a tropical species, growing naturally in northern Queensland, Papua-New Guinea through to the eastern islands of Indonesia.

As a fast growing tree with decent timber, it is also a popular species to plant in reforested areas of southern China. I saw it near Guangzhou, not far from Hong Kong, and I have some shit pictures to prove it!

The flat green flappy things (you can see a dried one above) are large, up to 25 centimetres long and 10 centimetres wide (a fat foot print). Botanists call them phyllodes (flattened leaf stalks) but they look like what most poeople would call leaves.

More uniquely - if you'll allow me to abuse the word 'unique' through inppropriate qualification - another common name is Brown Salwood. Although Salwood and Brown Salwood are names applied to other wattle species, and the Sal is an entirely unrelated rainforest tree (Shorea robusta).

The botanical species name is apparently a reference to the similarity between this species and some mangroves in Indonesia, which are called Mangge. It was first used as a genus name on a pressed specimen identified in 1750, but 'Mangium montanum' became Acacia mangium in 1806. So another common name, Mangrove Wattle, might sound odd but is perhaps more informative.

The flowers, which I didn't see, are lemon-yellow coloured and arranged like a narrow bottle-cleaner. The pods, also not seen, are tightly coiled and packed full of fertile seed.

As I say, this is a popular species in southern China, where it has been planted since 1979. Where I saw it, the wattle was used to stop erosion and increase soil fertility, but also as 'nurse trees' to allow the establishment of other understorey plants. Like many legumes, the roots of Acacia mangium form a symbiosis with the bacterium Rhizobium which converts nitrogen into forms usable by the wattle and other plants.

I note the seeds can be cooked, and eaten, and the shoots and phyllodes provide poor quality food for livestock. The wood can be used directly as firewood, or converted to charcoal and briquettes. It can be turned into pulp for paper and particleboard, or as planks for construction and furniture making.

As highlighted in a recent review of Acacia mangium, most wattles when planted outside their natural range can spread into nearby forest and displace native species. In fact it has been shown that all Australian Acacia species used for forestry or widely planted for other uses have become invasive.

In recent years, Acacia mangium has become a problematic weed in Brazil, Malaysia and Vietnam, where it has the potential to degrade soil microrganism diversity, reduce water availability (as a fast growing species, it can consume water needed for other forest or nearby crop species) and alter the diversity of plants.

For Australia, and its premier applied research outfit CSIRO, the obligation should be to not only select material of Acacia mangium for rapid growth and high wood quality, but also for reduced invasiveness. From an environmental perspective our track record in exporting and encouraging wattles, and other fast-growing Australian trees, is not good.