Pruning reduces the time it takes to grow
large logs and increases the quality of logs. Experience suggests
that pruned eucalypt plantations might be able to reach an average
diameter of 50 centimetres in half the time of conventional
plantations. This is because pruning allows farmers to space
their trees wider apart therefore allowing for faster diameter
growth. Unpruned plantations need to be held at higher stocking
rates to control branch development.
Because they are under less stress, the trees in these plantations
may also be less susceptible to drought or disease. It is common
in plantation forestry to plant more trees than are expected
to be harvested. This provides mutual shelter for the young
trees and helps control tree form and branch growth. It also
allows selection so that all the final crop trees are of high
quality. For example, if the aim is to grow a plantation of
at least 100 perfectly straight high pruned eucalypts per hectare,
the farmer might establish more than 600 stems per hectare.
As the plantation grows, the better performing trees are selected
for the first pruningfor example 400 stems per hectare
of the most vigorous straight treesand the remainder are
culled. The following season, the best 200 stems per hectare
might be selected for a second prune and the others culled.
Finally the best 150 stems per hectare might be high pruned
to the final height and the others culled. The trees are then
left to grow on with 50 trees in reserve in case of disease
or wind damage.
Farmers growing a more tolerant species, such as exotic or native
pines, might choose to aim for around 200 stems per hectare.
To achieve this, they would establish 8001000 stems per
hectare. If they were confident that the trees would not require
early shelter and growth, and would be very uniform, they might
be able to plant fewer trees initially.
Publicly available data for eucalypt
plantations up to age 40 years from Australia and New Zealand.
The data shows that pruning might allow growers to reduce the
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