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<< Dean Satchell's blog

Ringbarking as a method for thinning trees

Friday, April 13, 2018

Radiata pine, because of a long history of genetic improvement, is often planted at stockings of less then 1000 stems per hectare. Douglas fir, on the other hand, is often planted at high stockings of 1600 stems per hectare, to minimise branch size and improve selection of crop trees. Other species planted as unimproved seedlings, such as cypress and eucalypts, benefit from high initial stockings to improve selection of crop trees and to minimise branch size. This means removal of large numbers of trees is required for crop trees to put on diameter.

Traditional thinning to waste can be problematic when the tree stocking is high. Problems include "hangups" where trees being thinned hang up in crop trees, which can be dangerous to resolve. Thinned trees on the ground get in the way of access and branches sticking up are a hazard, especially for eyes. Thinned trees get in the way for years.

Thinning should be staged in multiple operations to minimise windthrow risk for residual trees. Because access is impeded from previously thinned trees, removing as many as three trees in four is often accomplished in as few operations as possible. Sometimes a single thinning operation, sometimes two, but overall costs increase with number of operations

Furthermore, thinning trees with chainsaws is inherently dangerous work. the chainsaw is dangerous and the falling tree is dangerous. Dangerous work requires skills and such skills require adequate remuneration. Workers also cannot thin trees on their own, they are required to work in pairs just in case something happens, which in itself can be dangerous and requires careful planning and good communication.

Alternatives to chainsaw thinning are rarely considered economically viable, it seems the assumption is that this model cannot be improved upon. Indeed, although methods of ringbarking and tree poisoning have received some attention at times, this has not been sustained as issues emerged. Poisoning of trees carries with it a risk that non-target crop trees will be poisoned too, because root grafting between neighbouring trees translocates the poison, with disastrous consequences. How much poison to use and how to apply it is under-researched for reliable prescriptions for thinning trees to waste. Ringbarking is very effective at killing young trees, especially conifers, and simple methods have been devised to achieve this. However, once roots start to graft, the ringbarked tree often doesn't die with less and less successful results as trees age. Ringbark thinning becomes haphazard and inconsistent.

Chemical ringbarking

By combining ringbarking with the application of chemical herbicide, consistent results are achievable. The tree dies every time and its neighbours don't. The concentration of chemical I have found to be effective is 3% glyphosate in water, with a little spray dye added to clearly see where the chemical is applied and the mosaic of trees that have been ringbarked.

The advantage with this method is that it is cost-effective. The use of a reciprocating saw means it is effortless and fast to ringbark trees, which allows progressive thinning of a forest to be staged over a time frame that minimises risk of windthrow. The drawback is that for it to be easy it must be done in spring when the sap is flowing, so the bark peels easily off the tree.

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5 posts.

Post from Gary Fleming on April 17, 2018 at 1:25pm

Why doesn't this method kill neighbouring trees? You are still spraying the phloem which transmits substances down to the roots, which could be grafted to other trees. If you only sprayed the upper bark above the removed bark then it would only be able to move up the tree to kill the above ground part of the tree, Alternatively if you only put the herbicide in the Xylem (Sapwood), where the bark has been removed, it would only kill the tree above the ringbark as the xylem only moves substances in one direction - up, and could not be moved back down to the roots in the phloem as it has been removed in the ringbark. 
Gary Fleming

Post from Dean Satchell on April 17, 2018 at 11:33pm

There isn't enough chemical applied to actually poison the tree, what the chemical is used for is just to kill the cambium below the ringbark, to enhance its effectiveness. It works and doesn't kill adjacent trees, but takes a while to take effect. A much faster way is to drill holes at regular intervals around the tree and squirt some 2% glyphosate into these. This goes up the tree in the xylem and kills the tree much more quickly, but requires sufficient chemical to poison the tree.

Post from Dave Persson on April 17, 2018 at 11:40pm

I've used ring barking without the use of herbicides successfully to thin Macrocarpa's after trying thinning to waste with a chainsaw and losing too many final crop trees to toppling caused by the weight of hangups and high winds. Aside from a few trees needing ringbarking twice all was good...and I had dry year round firewood to boot because they weren't lying dead on the ground...☺

Post from Dean Satchell on April 19, 2018 at 7:54pm

Thanks for your comments Dave. What I've found is that ringbarking tends to become less reliable as the trees get older, I assume because of root grafting. The chemical just ensures success.

Post from Laurie Bennett on May 13, 2018 at 12:31pm

Hi Dean, I didn't get a chance to talk to you last week about this in detail. I understand your ring bark and spray technique. Your second post states that drilling & spraying is faster acting- I take it that this does not result in crop trees dying due to translocation of spray through root grafts. Some people tell me that Cypresses don't root graft and some say they do. I am not keen on testing this to see who is correct!.

Disclaimer: Personal views expressed in this blog are those of the writers and do not necessarily represent those of the NZ Farm Forestry Association.

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