Saturday, December 8, 2007

Land clearing makes droughts hotter - let's plant trees!

A large scale research project undertaken by the University of Queensland shows how the clearing of native vegetation in Australia in the last 150 years has made droughts hotter in Australia. According to University of Queensland News Online, the researchers found that "mean summer rainfall decreased by between four percent and 12 percent in eastern Australia, and by four percent and eight percent in southwest Western Australia. These were the regions of most extensive historical clearing."

Equally significantly, "Australian native vegetation holds more moisture that subsequently evaporates and recycles back as rainfall. It also reflects into space less shortwave solar radiation than broadacre crops and improved pastures, and this process keeps the surface temperature cooler and aids cloud formation."

The research makes it clear that we not only have to protect our existing native forests but we also need to increase our efforts to restore previously cleared areas. Unfortunately, it is always much easier to chop down trees than to replant agricultural wastelands where the topsoil has blown away, the rains are failing and ground water levels are dropping away. Anybody who has tried to plant lots of trees in this dry part of the world will have had the heart-breaking experience that many seedlings do not survive, particularly in drought years - and we certainly had plenty of those recently!

So what is the secret to keeping trees alive? At a recent field day I attended at Mulloon Creek Natural Farms, Matt Kilby from Trees for Earth (pictured on the left above) outlined a number of principles that will significantly improve the survival chances of young trees. Matt said that his aim was to "plant as many trees as possible" and that he plants on average 500 trees a day on his own. He claimed that his system achieves 97 per cent survival rates in commercial timber plantations and regeneration projects. Here are the main steps for a successful planting regime:

- Let the grass grow around your planting site and when you mow it, leave the clippings so that they can turn into mulch.

- Deep rid the ground 6 months prior to planting to aerate the ground and overcome compaction. It is a good idea to rip the whole area along the contours to catch all possible rain. It is also important to allow the soil to settle as airspace in the ground will dry out the seedlings.

- Remove all grass around the tree planting site. Matt explained that trees need fungi to thrive, whereas grasses are driven by bacteria, making it harder for trees to get established. While this is often done with herbicides, it is also possible (and in my view by far preferable) to do this through heavy mulching.

- Digg a big hole, twice the depth of the roots. In degraded and marginal sites, add a cup of tree starter which needs to incorporate a range of minerals and structures that "open" the soil and maximise water and nutrient holding capacity.

- Dip the roots of the tree into some tree tonic, then plant.

- Use a weed mat made from waste paper to retain moisture and keep weeds down around the tree.

- Water each tree with 3-10 litres of root tonic.

- Add a good quality tree guard which needs to stay around the tree for 12 months or longer. Tree guards protect young seedlings from wind stress. Matt suggested using pink tree guards. Apparently, the colour pink increases the CO2 uptake of the tree and thus improves the trees growth and survival rates.

- Mulch, mulch, mulch. Mulching is critically important, and you cannot have enough. Mulch at least 1 metre around the tree and at least 15 cm high.

- At the 12 months stage add half a cup of complete carbon fertilizer about half a metre around the tree.


  1. Interesting. I have grown native trees from seeds for planting in the local area. You present the next stage. Many chances for trees to die, especially with the very arid conditions.

  2. hi, just letting you know I dropped by your blog, fabulous as always. Jxx