I am a fan of the black wattle (acacia mearnsii) tree and have been propagating and growing them for many years. This species is a fast growing acacia and has many advantages. In the right conditions it can grow quite large very quickly. On my 20 acres at Ensay I have planted them for more than 30 years and in some places third generation trees were growing quite strongly when the property was sold.
They are leguminous (fixing nitrogen in the soil), provide a small amount of shade and shelter and attracted a number of species of birds. When flowering they add colour to paddocks and attracted honey eaters. They generally produce abundant crops of seed and I have sometimes harvested small amounts for propagation. As long as the area around the trees is not grazed they will self-sow in abundance. Where areas in the bush have been burnt the germination of black wattles is sometimes very thick. After the 2007 fires in the Tambo valley the wattles regenerated at Wattle Circle were so close together – a matter of 10cm or so – as to make these parts of the country impenetrable.
The dried timber is a hot, but relatively fast, burning fuel and was the fuel of choice when the Swifts Creek bakery used their wood fired oven. After harvesting a large amount of windfall timber in the 1990s this dried wood became the main (carbon neutral) fuel in our heater and was occasionally used in our slow combustion stove. Dry and dead limbs off living trees were handy to the house providing an inexhaustible supply of kindling. When harvesting the dead and fallen timber for firewood I made sure that the stump remained and was left to rot – hopefully leaving a substantial amount of the carbon in the root system to remain in the soil. (It has been estimated that up to half the carbon of some trees is in their root system.) I have even experimented with making charcoal, or agrichar as I prefer to call it, but that is another story.
Counting the carbon in the root systems mature black wattles generally store about half a ton of carbon each. I have had trees growing fast and large where the household waste water was fed into the paddock. These I estimated stored about one ton of carbon each. Farmers generally consider them a weed. Perhaps if they could crop them, and be paid for the carbon that is stored in the trees and soil and removed from the atmosphere this could change. For the tree is the only CCS system we have at the moment that actually works.