Tree shelters work on some species
During the 1980’s English foresters began using 4-foot-tall narrow plastic guards that became know as ‘treeshelters’. The primary purpose was to protect slow-growing seedlings from deer and other browsing animals. They soon found that deciduous trees grew a lot faster in the tubes and that they also protected the trees from herbicide spray during follow-up weed control.
The guards were made from a cylinder of corrugated plastic and held in place using a tall timber stake. Now sold as Tubex Treeshelters they come in a range of lengths and are common-place across Europe. I first saw them when I visited a research farm in Scotland where they were being used to establish trees in open paddocks with sheep.
In the late 1980’s Treeshelters were imported to Australia but never really gained favour. The cost of more than $4 each was prohibitive and our evergreen trees became wispy and unstable due to the staking. Many trees also suffered fungal infections due to the high humidity in the tubes. Another problem was that small native birds, possibly attracted by insects, would often be found dead in the tubes.
Having been given some of the tubes to test I set up a small comparative trial using long Tubex Treeshelters and a length of ‘vine tube’. I planted a small forest of English Oak (Quercus robur) using each type of guard. Vine tube is made of standard UV resistant tree guard plastic but only opens up to about 12cm in diameter. It comes in roll so it can be cut to length and is a fraction of the price of the Tubex guards. I used the same 1.2m tomato stakes to hold up both guards.
The one-year-old, open-rooted oak seedlings grew really well in both the English Treeshelter and my home-made version. I never bothered measuring the trees as there was clearly no difference in height, diameter or form.
I then began testing the vine tube guards on other species. For some time I have had trouble with wallabies that were attracted back to the farm as my trees began to offer cover. Blackwood (Acacia melanoxylon) and Shining Gum (E. nitens) seemed particularly tasty. I planted both species on my well-wooded slopes hoping the vine tube guards and various types of stakes including 6mm and 10mm steel rod would do the trick. The idea was to protect the trees from not only wallabies but also sheep.
If effective, individual tree guards would allow me to plant trees at wider initial spacing (as they would be less reliant on mutual shelter) and place the trees anywhere I wanted (targeting promising micro-sites) without the need to fence areas off from stock. Planting at 6m spacings (around 250 stems/ha) would reduce my establishment costs by as much as 75 % allowing me to invest a little more in each tree.
I learnt a lot from the experience. Timber posts were pushed over by sheep, kangaroos and wallabies and I was forever straightening them up. The steel rod was a little better but once bent was difficult to straighten. The humidity inside the tube was too much for many of the eucalypts resulting in fungal infections and poor growth. To be effective for cross-bred sheep, wallabies and kangaroos I need to have a height of about 1.5m. For less palatable species 1.2m is probably sufficient. The UV Polyethylene tube comes in a 250m roll. Laying flat the tube is 135mm across giving a tube with a diameter of 86mm.
The Blackwoods were fine and shot up through the guard. The next problem was stability, being firmly staked the trees were a little unstable and the guards had to remain on until the tree stem was about 6cm in diameter. From my old tree physiology classes I knew about the phenomenon of thigmomorphogenesis. Essentially, if you shake a plant it will respond with slower stem elongation (height) and increased stem diameter. By sheltering the trees from the wind in a firm tube they grew taller but not stable. This is less of a problem in deciduous trees as the stem hardens up in winter.
I then set about designing a better option. The stake had to be flexible returning to the upright position after being battered by wind or stock. This would encourage greater stem diameter growth. A flexible guard would also be of less value as a rubbing post for sheep. I tired a number of options and have settled on and 2m length of 20mm electrical conduit cut from 4m lengths. These are flexible and durable enough to be used a number of times. To fix the plastic tube to the pole I now use 2 or 3 cable ties.
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