“At this stage of development seedlings have to compete with other plants, mainly weedy species, for limited resources such as water, nutrients and sunlight.” —Mr Thea. Image: Elizabeth DonoghueMURDOCH University PhD student So Thea is researching a number of different techniques to find ways to improve seedling success rates that will assist in reforestation programs.
The reforestation of degraded or cleared woodlands can be a difficult and expensive process and while the use of nursery raised seedlings can provide improved success rates it also comes with substantially higher costs and labour.
Direct seeding—planting seeds directly into the soil instead of using nursery raised seedlings—may provide a viable and cheaper alternative.
Mr Thea says the survival and growth of seedlings during the first one to two years after planting is a key problem faced in many revegetation programs.
“At this stage of development seedlings have to compete with other plants, mainly weedy species, for limited resources such as water, nutrients and sunlight,” he says.
“Assisting seedlings to survive the first planting season is essential to ensure successful revegetation.”
Mr Thea’s research was based around a number of test sites in Australia, Cambodia and Thailand.
At one of the test sites south of Mandurah near the Yalgorup National Park a technique that involved priming seedlings of tuart (Eucalyptus gomphocephala) and orange wattle (Acacia saligna) were studied.
The area has been the site of massive tuart woodland losses since European settlement and these two species are important in reforestation programs on the Swan Coastal Plain.
The hope is that priming the seeds with microorganisms—mycorrhizal fungi and N2-fixing bacteria—may help to improve germination and growth and lead to improved revegetation rates.
Although the germination rates for the tuart were quite high for the first three months of the experiment, Mr Thea says he was surprised to see that most of the newly emerged seedlings had died toward the end of winter and only a few survived the first season.
Although it showed the microorganisms had no significant effect on the survival rate this technique is only one of many being looked at and Mr Thea says there are other methods which may assist in reforestation programs.
“In the future we are looking to improve soil moisture holding capacity coupled with increasing soil microorganisms by testing the effects of water retention polymers in combination with composts,” he says.
The research was part of So Thea’s PhD Thesis titled Improving reforestation success of high-value and key forest species by direct seeding and Southeast Asia and Western Australia and can be found here.
