A PhD study at the University of Queensland could help open up the lucrative business of growing hardwood trees for top quality cabinet timber.
Amanda Snell completed her thesis in the Botany Department by examining various aspects of growing hoop pine and Queensland maple in plantations.
Dr Snell said Queensland maple might be good for farm forestry plantations because of the relatively high value of the wood. While prices fluctuated, such hardwoods, used for the likes of furniture and boats, generally fetched many times more than ordinary timber.
Private landowners were increasingly turning to agroforestry woodlots as an attractive long-term 'nest-egg'. The trees took around 50 years to mature and during that time offered ongoing benefits such as shade and shelter for livestock and a refuge for wildlife.
Dr Snell, who works as a research scientist for the Queensland Forest Research Institute in Atherton, said demand for forest products in Australia far outstripped local supply.
'One solution to this dilemma involves the incorporation of cabinet timber trees into farming systems,' she said.
Dr Snell examined various permutations of sites, species and planting densities for the pine and maple in an effort to find out the optimum growing conditions.
'Planting density can adversely affect competition for available resources (light, water and nutrients) between neighbouring trees if they are planted too close together,' she said.
'But poor growth form, that is too many or large branches and therefore unsaleable timber, can result if plants are grown too far apart.'
To establish the best planting densities for pine and maple, Dr Snell studied results over more than two years from eight trial plots at Mt Mee, just north of Brisbane.
'Hoop pine appeared to tolerate high planting density better than Queensland maple even though the latter is a rainforest species commonly found in dense forest,' Dr Snell said.
'It would seem that the ability of Queensland maple to compete for water, either between individuals of the same species or deeper rooted species such as hoop pine, is diminished when planted at high density at sites where seasonal droughts may occur.'
However, Dr Snell also found that maple planted at low density had more branches but similar or smaller trunk volumes than those planted at higher densities. In other words, the extra growth was being channelled into the branches.
Dr Snell concluded the optimal density for maple could change over time. High density planting might be needed initially to suppress branch growth, followed by selective thinning a few years later to allow remaining trees access to adequate light, water and nutrients.
Finding the right combination of species could be critical. A plantation of the same species meant all the trees were competing at the same time for the same light, water and nutrients, and could also be more vulnerable to insect attack.
A mixture of trees - up to 16 species are being trialled at Mt Mee - would be much less competitive though generating more work in the maintenance of the plantation.
'Any plan towards intensive management of Queensland maple in plantations should incorporate a selection of sites, species mixture and silvicultural practices,' Dr Snell said.
'Manipulating these variables could lead to an increase of sustainable timber yield beyond that previously attainable with natural forests.'
For further information, contact Dr Amanda Snell (telephone 07 4030 5269).
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