On Sunday afternoon, 22nd April, a workshop was held at Bob and Robyn Grays property at Torwood. The aim was to look at the options of managing a Blackwood plantation and put some theory into practice.
In 2011, Bob and Robyn planted about a hectare of Blackwoods on an alluvial creek flat as part of a stream front revegetation project. The Blackwoods were planted as tubes at a spacing of 2m x 2m. The intention was to encourage straight vertical growth of the young trees and to restrict their propensity to fork and branch.The trees are now in the order of 6m tall and ranging from 8 to 15 cm dia at breast height.
The field day discussed the New Zealand view that the only way to control the Blackwoods enthusiasm to fork and branch was to continually form prune and to remove any side branches from the central stem if they were more than 2cm in diameter. Viewing the trees, it was considered that this was probably the best option as despite being form pruned in 2014 (as 3yo stems) and lift pruned to 2m in 2015, there was considerable forking and co-dominant stems that had emerged since. The conclusion was that form pruning should have been carried out as an annual activity (at least) over the past 3 years.
The need to thin the plantation was also discussed. Clearly, the trees were competing given the close planting and a number had died. Small lower branches above the 2m lift prune were largely dead, significant leaf fall had occurred and the ground beneath the trees was totally bare. Misshapen trees were identified for culling and there was debate as to the best way to remove them. Stem injection was considered but rejected due to the risk of flashback. It was decided that cutting at ground level was the best option with the wallaby population taking care of the regrowth. There was also discussion as to the extent of the thinning. Removing all the identified trees (about 60%) would remove much of the vertical stimulus and probably encourage further forking . As a result, it was agreed that about half the identified trees would be removed this winter and the rest in 12 months. It was noted that this would also reduce the amount of debris on the ground at the one time. The proposed thinning would reduce the density from the current 2000 stems / ha to about 1400 with the second half of the thinning reducing this to about 800.
Lift pruning was then carried out on the selected trees to about 4m and further form pruning was undertaken.
Bob Gray GAN member