From the outside, planting trees seems easy. Seedlings want to grow – put them in the ground, water them and walk away.
But Australia has never serious invested in recovery and barely monitored the results when it was done. Recent research in the replanting of 20 million trees across the country found little impact on the endangered species these trees were supposed to support.
This matters because Australia is a major global deforester. Efforts to conserve forests are important, but what remains are highly fragmented. Before 1788, the forest was estimated to cover 30% of the mainland. Only half of Australia’s forest cover survived colonisation.
For a little over ten years we have been experimenting with different planting methods on our own land in the wet tropics of Queensland. In our recent research, we’ve collected what works well and cheaply. Using a plant spade, make sure both the sapling and the soil are wet, gently push the seedling into the hole and spray weed killer only where necessary.
Australia is still not serious about recovery
Forests support most of life Soil. But in the last century, the world is lost as much forest as in the previous 9,000 years. Today, half of the Earth’s surface formerly covered by trees has been cleared. Of the woods that alone remain 40% have high ecosystem integrity.
Led by First Nations, about 30% of Australia was originally covered with forest.
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Australia remains one of the worlds top deforesters – the only developed nation on the list.
All climate action pathways limiting warming to 1.5℃ relies on intact forests. But we still lack basic information on how best to do the restoration. Most native species have not been tested for their survival and growth rate.
Globally, improving seedling survival has proven difficult due to lack of evidence of best practices. The evidence we have shows that seedling mortality can be as high as 30-40%.
Landscape-scale restoration is now largely dependent on private investment, often done on a small scale in forest blocks owned by individuals and small groups.
A big problem is money. Community restoration in the wet tropics is estimated to cost more than A$60,000 per hectare for densely planted native seedlings. This cannot extend to the scale of restoration much needed in Australia’s iconic landscapes.
But there is good news: since 2011 we have been experimenting with how we can restore land effectively and for much, much less money.
Restoring forests means mastering replanting
Eighteen years ago we bought Thiaki, 180 hectares of land on the Atherton Tablelands, in the wet tropics of Queensland. This biome covers just 0.3% of Australia and supports more species diversity than anywhere else, including cassowaries, tree kangaroos, striped and lemuroid possums.
A lot was made available for dairy early on. But since the 1940s, many farmers have left the industry because of new economic realities. This has opened up new opportunities for recovery.
We bought a piece of forest and set it as a research project looking at cost-effective carbon and biodiversity restoration using native species.
While the immediate challenge was cost, there were other challenges. What trees do you plant, where do you plant them and at what time of year? How do you plant them quickly and economically?
This is what works
In our latest research, we tested many combinations of technique, spacing and plant care in three landscape-scale experiments. What we found sounds simple. But recreating a forest depends on doing these things right.
Here are five tips:
Use a spade: Using a two-person auger for planting trees made no difference to survival versus a simple planter’s spade. But the simple plant spade was four times cheaper and four times faster, which significantly reduces the cost of repair.
Saturate the seedling and soil. This sounds like common sense, but it is often overlooked, especially when plantings are scheduled for drier months. When we planted seedlings in drying soil, we lost up to 40% in the first four months.
Handle saplings with care. Damaging roots by yanking or kicking a seedling instead of gently closing the soil with the toe of your boot can reduce the chance of survival by 20%.
Don’t lose sleep over the distance. We found that the distance between plants had little impact on survival. It didn’t matter if we planted six or 24 different varieties.
Do not cover the area with weed killer. In places like the wet tropics, fast-growing grasses can make it impossible for trees to become established. But it is not necessary to spray weed killer over an entire area. We found that just spraying the rows where the seedlings are planted yielded the same survival rates. This saves costs, reduces erosion and protects soil biodiversity.
What else have we learned?
It is vital to maximize survival in the early months. Increasing survival rates by 10% in the first four months of a planting program was found to be an indicator of up to a 40% better survival rate 18-20 months later.
Many restoration programs plant species that are expected to grow as they do in intact forests. However, their behavior in the wild does not necessarily translate into saplings in recovery projects. It is therefore also important to gain experience with the survival of saplings in other plantations, and experience with the nursery and origin.
We stayed close cost registration, and found that it was possible to reduce restoration costs more than sevenfold, to less than $8,000 per acre – even in areas where costs tend to be higher. Keeping costs that low will make carbon farming worthwhile in agricultural landscapes (when prices exceed $37/ton CO₂).
Some of these tips may not be that important in every ecosystem. But caring for saplings will be true everywhere.
To help Australians get to work restoring their forest blocks, it would be helpful to have regional best practices, particularly in cost-effective planting, monitoring, species selection and case studies.
While the work of individual landowners is commendable, it will not be enough – even if the markets for carbon farming and biodiversity take off.
Ideally, governments would join forces and help restore these denuded landscapes on a large scale. But if they prefer to distance themselves, the only option is to set prices for carbon and biodiversity to reflect the true value of bringing back our forests.
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