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.
Since clearing the pine plantation and establishing the first area of biodiverse woodlot (over-wood predominantly spotted gum), I have been unable to establish additional areas of woodlot due to intense wallaby grazing pressure. The first successful year I used wallaby repellent sprayed onto the
seedlings prior to planting. In the absence of other vegetative cover this proved to be satisfactory. However, after 12 months growth of these planted trees and the regenerating native understory, there was sufficient vegetative cover to embolden the enlarged wallaby population to browse anything in the adjoining areas, especially seedlings. On the area planted 12 mont
hs after the first planting of the 1,000 trees planted only 10 survived despite further application of repellent. One area regenerated with natural seed fall (messmate) given the high density of seedlings established.
A local Landcare grant enabled me to attempt to replant two unsuccessful areas testing different tree guarding options together with removing the grassy swarth to encourage understory species to recolonise. One was to erect a “chook-wire” fence 1.5m high to exclude all browsing animals (some rabbits had been seen). This is effective after 24 months (photo 1). The other was to use wallaby repellent and guard with individual guards. A range of
guards was used; green fishnet stockings (photo2) and waterproof cor-fluting (photo 3) were tried (photos after 24 months since planting). The rabbits disappeared after 12 months but the wallabies ate anything that protruded from the guards. I then tried some larger guards after 12 months (photo 4) with the same result although the seedlings are larger and may win in the long term.
The result of not doing anything is again nothing (photo 5).
A second area was fenced off 12 months ago (photo 6) using leftover fencing material and leftover spotted gum. Additional white stringybark and sugar gum were also planted.
Unfortunately we have had an extremely cold winter with over 20 frosts (normally 1 or 2 light ones), many severe. Time will tell what survives and what doesn’t. The plan was to leave the fences up for three seasons but we will review that at the time. In the meantime the original successful plant goes from strength to strength (photo 7).