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Why I became, and remain, a clearwood advocate

Wink Sutton, New Zealand Tree Grower August 2019.

Only recently have I become aware of the concept of unique special product or proposal. However, I now realise that for most of my forestry life I have been seeking to find how New Zealand’s radiata plantations can be managed to grow our own unique special product or USP.

I have long been aware that attempting to grow a commodity is most unlikely to be our best strategy. It is far better if we are able to produce a quality product that other species or other countries are not able to produce. I now find that while my vision is generally supported by small plantation owners, especially those who are distant from log markets, my USP vision is not shared by the large plantation owners of the central North Island.

First, some history and my early involvement with radiata clearwood. The first sawing of our plantations in the first half of the 20th century produced sawn timber which was full of knots, often large dead knots. Some trees had long internode logs or were of true uninodal form from which at least four feet, 1.2 metres, of clear cuttings could be sawn for the production of factory grade sawn timber or peeled for the production of knot free surfaces on plywood.

In the mid 20th century it became obvious to New Zealand forestry planners that, although the nation’s indigenous forest had for more than a century been the source of large mature trees which produced an abundance of clear sawn timber, that supply would eventually be either exhausted or put into reserves which prevented harvesting.

We owe an enormous debt to Stan Reid and Mat Grainger for their early advocacy of pruning our plantations. Stan Reid maintained that when it was defect free or clear, our radiata was the equal of old growth ponderosa pine from the West Coast of the USA.

Pruning needed

In 1959 the NZ Forest Service economist Mat Grainger was aware that, before indigenous sawmillers were granted a licence for the current year, they had to provide a return on volumes of indigenous tree species by sawn timber grades they had sawn in the previous year. Mat asked the Forest Service Head Office Timber Sales Branch, who held those sawmill returns, if they could use them to calculate the percentage of indigenous saw timber cut that was clearwood or defect free. I was a third year Forest Service trainee in 1959, seconded to work part time in the Timber Sales Branch. I was asked to undertake the task of data extraction and collation for Mat.

From what I remember just on half of the indigenous timber cut was heart dressing A grade − in other words quality clearwood. Mat used my calculations to advocate that if New Zealand was to have an equal volume of locally produced long length clears, the state plantations must all be pruned. The private sector which controlled about half of the nation’s plantation was generally not interested in pruning. Mat assumed that because we used a large volume of indigenous clearwood our plantations had to be a replacement source of supply. Indigenous clear saw timber was supplied so cheaply that this top grade was often used wastefully – for example as minor construction jobs like chicken coups.

Pruning evaluation

Because of the sirex wood wasp epidemic from 1945 to 1955 in our maturing radiata pine, and along with our past concentration on radiata, most new state plantings in the 1940s and the 1950s were of Douglas- fir, Corsican pine and Ponderosa pine along with a few other tree species. As most of our radiata pine plantations were then too old to be pruned, pruning was generally restricted to tree species other than radiata. For most of the next three decades pruning became an act of faith in many state plantations.

In the summer of 1960/61 I was assigned to the Forest Research Institute and asked to evaluate pruning of Ponderosa pine in Karioi forest. I have no idea why I was selected to do this as I had done no real research before. The evaluation was to follow George Brown’s node study method. This used a small axe to split the biscuit-sawn timber to contain the pruning scars to determine the depth of clearwood outside the pruned stubs and occlusion.

Some Karioi Ponderosa had been first pruned in 1943 which was 17 years before my evaluation, yet on some of those trees the clearwood sheath had not yet started. I came to the conclusion that rotations of at least 70 years were needed before significant amounts of clearwood would be produced. My report almost disappeared except I had given a copy to the Director of Economics Ron Williams and he was impressed.

The sequel was that the Wellington Conservancy had asked for head office approval to spend about a million pounds pruning and thinning Karioi forest. The Director of Management, Alan Familton, was highly sceptical but did not have any convincing evidence on which to decline the request. He discussed his misgivings with the Director of Economics and my report came up.

Alan Familton used the report to decline the request and asked Wellington Conservancy to provide alternative evidence. None was ever supplied. I felt rewarded – my first research effort had saved a greater sum than all the money I would ever earn in my entire career.

Scientific pruning

In 1963 before going overseas I was assigned to the Forest Research Institute to work with Bob Fenton. I was asked to look at the relation in pruned logs between the small end diameter, the size of the knotty core and the final log size log. (See the paper by Fenton, Sutton and Drewitt in the proceedings of the First Pruning and Thinning Symposium.)

What that research clearly showed was that the maximum volume of clearwood was obtained by keeping the knotty core as small as possible and the final log diameter as large as possible.Yes, the study was theoretical, but in 1963 there were few large pruned logs with small defect cores available for sawing. In 1965, after getting my forestry degree, I was posted to the Forest Research Institute and joined a new research group, the economics of silviculture branch, with specific responsibility for pruning and thinning.

It was not until the late 1960s that pruning became ‘scientific’, in other words based on measurement and economics. Then pruning was applied generally only to young radiata plantations. This meant pruning early, to restrict the size of the defect core, with heavy early thinning to a low final crop stocking to maximise the diameter of the butt log.

By the end of the 1960s or early 1970s two principles emerged from our plantation management research −

  • That the size and the quality of trees at harvest were determined by the decisions at the time of planting − site, species, genetics and spacing − and by stand management in the first few years such as thinning and pruning. This meant that by five or six years the quality of those trees had already been determined, even though the trees would not be harvested for another 20 to 25 years.
  • Log and tree returns at harvest time are determined not by log and tree costs at the time of early management decisions but by the price which exists on the day of harvest.

Export dependent

For radiata pruned sawlogs there are at least two decades between the time of early management decisions and that of the final harvest. In the early 1970s I was aware of these principles, and as New Zealand already had a greater area of plantations than we could expect to use locally, it was obvious that our forestry future depended on wood exports. The trees which we were tending in the early 1970s, and whose quality we could still influence, would be finally harvested around the year 2000.

I wanted to know what wood products could be in demand and at the highest prices around the year 2000. In 1972 I obtained a scholarship for a doctorate on this question. The key to my assessment of the year 2000 was the realisation that, although most overseas forest managers were largely unaware, the principles that we had found for our plantations were just as applicable to all of the world’s forests, especially plantations.

I researched all of the world’s major softwoods and came to the conclusion that our radiata clearwood was not only a substitute for old growth Ponderosa pine, which was probably the most valuable softwood in North America, but also that there were very few other tree species which could compete with our radiata. I independently confirmed what Stan Reid had been telling us decades before.

With the advantage of hindsight I should have expanded my study to cover hardwoods because these have continued to supply the global markets which I expected would have needed our clear radiata. However, there is a limit to what can be done on your own within three years and I was also limited by what information was available.

Convincing owners to prune

On my return to New Zealand in 1975 I gave hundreds of presentations summarising my supporting evidence and advocating timely pruning. My major concern was how to convince forest owners to prune when there was no established market for radiata pruned logs and none could exist until pruned logs became available for sawing or peeling in about 20 to 25 years’ time – a classic Catch 22 position.

My talks were generally well received but there were significant objections. Probably my most ardent critic was the then Director of the Commercial Division of the Forest Service, Bruce Webby. Bruce, at the conclusion of my Rotorua presentation, claimed that ‘plantation owners can prune as much as they like but sawmillers will never pay anything more for pruned logs.’ Of course, he could not have experienced or seen the sawn output of a well pruned log.

As for exports, Webby also claimed that nobody overseas will buy that ‘crap’ referring to long length radiata clears. With some notable exceptions, sawmillers seemed to have generally agreed with Webby − probably because sawmillers had sawn logs that were claimed to have been pruned but had been pruned so late that there had been little or no improvement in grade out-turn.

To enhance the quality and the volume of the butt log, timely early pruning with heavy early non- commercial thinning to a low final crop stocking has been advocated. However, this increases the management costs as well as reducing tree growth. Selective pruning, just pruning some of the final crop trees, is not practicable as experience and research has demonstrated that selected pruned trees tend to be quickly overtaken by their unpruned neighbours.

Tombleson in 2018 quotes estimates that, to compensate for the cost of pruning, as well as the volume loss per hectare as a result of pruning, pruned logs at felling should have premiums of at least $100 a cubic metre greater than unpruned logs. Current premiums for pruned logs are about half this estimate. Possibly for this reason, the two largest plantation investment companies in the central North Island have generally decided not to prune.

These investment companies have no doubt carried out studies on future markets as well as assessed other possible global sources of supply and concluded that there will be a limited profitable market prospect for pruned radiata clears. As no other country or species can grow clearwood, these companies must have good and strong evidence that our radiata clearwood will not find ready and profitable export markets.

Adding value

New Zealand is concerned about exporting low value unprocessed green and wet logs so a sure way of ensuring domestic processing is to prune in a timely fashion. Domestic processing and exporting just dry finished timber virtually eliminates the risk of sap stain. By concentrating on current log sale values, New Zealand could be seriously under-estimating the long-term benefits of pruning.

The current premiums for pruned logs are lower than most growers or investors expected and are probably less than the compounded cost of pruning and volume loss. However, the downstream added-value benefits of pruning have been generally ignored.

Because of the possibility of pruned logs becoming sap stained during sea transport, it is better to process pruned logs in this country. Tombleson estimates that the 12 plants in the central North Island process 1.226 million cubic metres of pruned logs a year, employ 1,575 staff and have an annual turnover of $734 million. These returns work out at $586 a cubic metre or $466,000 per process employee.

This is an added value multiplier of more than three or four times the return that growers receive from supplying the domestic and export log market for the best quality unpruned logs. The return to a processor of pruned logs, especially the return per employee, is not as good as this analysis suggests because processors need to buy the pruned logs in the first place. Even if there is a lower current harvest price than expected, the case for timely radiata pruning appears to be overwhelming, especially as it ensures we have our own unique special product.

Unique story

While on the theme of clearwood I am reminded of an incident which occurred when I was employed by Fletcher Forests. The company was exporting clear mouldings to the USA through a north American joint venture company. That company sent a senior manager to access the sustainability of future clearwood supplies.

Just the drive down from Auckland to Rotorua was enough to satisfy him that there would be few problems obtaining future supplies. As part of his New Zealand tour I took the company representative on my plantation history tour. At the end of the tour he commented ‘you claim that in the 1970s New Zealand was tending its plantations to supply us with radiata clears in the 1990s.’ I, of course, replied that we were. Then he completely blew my confidence away by saying ‘but you never told us so’. To this day we have largely not told our unique story to the world. As a marketing tool we should because it is a good and interesting story.

Long internodal or uninodal trees

It is now almost overlooked, but in our 1968 paper advocating heavy early thinning to the final crop stocking, Fenton and I included the recommendation that pruning selection be biased towards the tendency of the second log, the one above the butt log, to have long internodes. These logs could later be sawn for clear cuttings.


The head of the Forest Research Institute’s tree improvement section, Ib Thulin, appears to have been very much against uninodal or long internode trees. He maintained that uninodals were never straight and were never dominant.

How was it that an obvious uninodal was selected as a 26-year-old representative of un-thinned and unpruned radiata pine? The photograph above, published by the government printer in 1964, clearly shows a uninodal which is both straight and dominant. Since then there has been little selection for long internodes and uninodals, and most of the tree breeding effort has been to reduce internodal length and increase the number of branches. Tree breeders often maintain that their basis of selection has the support of the captains of industry.

Although long length clear radiata is required for mouldings and plywood, most of the clearwood users, such as furniture and joinery manufacturers, do not require long length clearwood. I am aware that the recovery of radiata short clear cuttings of 1.2 metres and longer is uneconomic at present. New Zealand and Chile have largely abandoned the process.

I contend, however, that we should be taking a long-term view. If this were 1900 there would be an abundance of high quality clears form the likes of kauri and rimu available for little more than the cost of felling and sawing. An advocate for clear radiata pine would never attract support in 1900 even though it was obvious to some that one day there would be almost no New Zealand indigenous trees available for sawing and peeling.

Recovery of clear cuttings is currently uneconomic but will this always be the case? In 20 to 30 years’ time most of the world’s large high quality trees will have been felled or be unavailable for exploitation. Although most of the world’s indigenous forests are claimed to be sustainably managed, I have serious doubts that most of these forests will have large trees capable of producing clearwood.

When clear, radiata pine is among the best softwoods in the world. In 20 to 30 years our clears from timely pruning and our clear cuttings from long internode and uninodal trees will be in great international demand, and prices for both will be higher than those today. Remember there will be almost no international competition.

Silvicultural research

I am also concerned about direction of some silvicultural research, especially the drive to increase average wood density and to advocate for higher final crop stockings. The push to increase average wood density has come from a desire to increase radiata’s structural wood properties, especially to increase the modulus of rupture or stiffness.

Compared with overseas plantations our radiata may have slightly lower average wood densities but our radiata is not as stiff as comparable plantation woods – wood such as that of the southern pines and Douglas- fir. But our radiata is not brittle when compared with comparable tree species. For its wood density radiata tends to have a higher modulus of elasticity or ease of bending compared with comparable plantation tree species.

We are constantly told that average wood density is an important measure of wood quality. If that is so we would expect that balsa wood, one of world’s lowest density woods, to be virtually unsaleable and Amazonian hardwoods, which have average dry wood densities of over 700 kilograms a cubic metre, to be in great demand.

In fact, the opposite is true. Balsa wood is in great demand and attracts high prices while dense Amazonian hardwoods are often unsaleable. Radiata wood has excellent finishing properties – the result of radiata latewood only having slightly higher wood densities than the earlywood. In addition, there is a gentle transition between the earlywood and latewood bands.

No competition

I just trust that the attempt to increase wood density is not at the expense of radiata’s excellent finishing properties. I am yet to be convinced of the need to produce a better structural timber, that is one with a greater modulus of rupture, from our radiata plantations. My analysis of the future global wood supply shows that there will probably be no shortage of structural timber unless the trend to build using wood results in a quantum increase in wood demand.

Compared to clears, structural sawn timber grades do not attract high prices. Anyway, even if a building requires mostly structural grade sawn timber, some finishing grade sawn timber will be required for interior fittings. There is no chance of New Zealand swamping the global clearwood market. We can never supply more than a few per cent of the global wood supply and our clears face almost no competition.

Chile may prune but, because of the demands of the pulp industry, it is locked into short rotations and high stocking levels. Most of major radiata growing areas of Australia generally do not prune. South Africa has a very small area of radiata plantations. Spain generally does not prune its radiata. Globally, no other plantation trees have the potential which our radiata has.

Increasing wood density or stiffness in no way qualifies our radiata as a unique special product − such a move makes us just another commodity producer. It may be to our advantage if we aimed to reduce radiata’s wood density as well as less difference between the densities of earlywood and latewood to improve radiata’s finishing properties. If wood users require a higher density wood then there are chemical and other treatments available which can achieve this. Perhaps there is a case for breeding two separate radiata types – one specialising in low density radiata clearwood to be pruned and the other in higher density and stiffer structural timber which will not be pruned.

Yield and returns

I am also not impressed with the attempt to maximise yield and returns. Harry Bunn, Bob Fenton and I attempted to do this in the late 1960s but to my knowledge, because it appeared to be so obvious, we never published our findings. With flat stumpages, that is with no price premiums for log size or log quality, it is possible to theoretically maximise yield and returns, but you introduce realistic premiums for log size and log quality and it is nearly impossible to maximise both volumes and financial returns. High stocking reduces average piece size as well as increases the yield of pulp wood which universally does not command high prices. In addition, when the stocking level is high and the average piece is small there will be a greater volume of slash left on felled areas. The day may come when the public object to minimally tended radiata stands, especially when they realise that this treatment could be depriving the nation of increased employment and overseas earnings opportunities.

Wood wasp

Most are no longer aware that the driving force behind the original John Ure radiata regime was New Zealand’s experience with the sirex wood wasp. Although up to 90 per cent of unthinned stems could be killed by the wood wasp, some trees survived. I can just remember seeing sirex affected stands – they looked terrible. They gave the appearance that every tree had been killed.

No wonder overseas visitors as well as local critics were quick to condemn the nation’s concentration on radiata.

All the talk in the 1940s and 1950s was the need to thin radiata to a final crop stocking below the mortality line. Experience had shown that for mature stands this was about 80 stems an acre or 200 per hectare. Because of the introduction of parasites, sirex is no longer a problem, but with high final crop stockings we run the risk of some unknown destructive insect or disease being introduced causing havoc in highly stocked, and ever-increasing stressful conditions as stands age.

A New Forest Service?

With the philosophy that plantation forestry was now a mature industry and that all decisions, especially financial, could be better done by the private sector, the Labour government of the second half of the 1980s broke up the Forest Service. State plantation forests were sold, other functions dispersed and forest research became a crown owned research institute, now called Scion. Remnants of the Forest Service were absorbed into the Department of Primary Industries. Largely lost in the breakup was the planning function of the Forest Service .This provided politicians with independent advice on the forestry sector.

However, the current Labour coalition government has re-established part of the former Forest Service – Te Uru Rakau. I trust that planning is one of the responsibilities of this new government department. There is an urgent need to address the wood supply problems that will arise from the nation’s grossly uneven past plantings. The 1990s saw a great new planting effort which was followed by almost two decades in which there was more plantation conversions, especially to dairy farming, than new plantation establishment.

New Zealand could see an export bonanza in the 2020s followed by a severe wood export shortage in the 2030s. Only an independent agency can solve this and other problems and advise the government of possible courses of action.

Final comment

New Zealand is fortunate to have introduced radiata pine in the latter half of 1800s. The plantation tree proved ideal for our climate and our soils. Experience and research over the last 150 years have given the tree species advantages that should be the envy of most other countries.

With stand management we can grow large diameter trees in 25 to 30 years. With timely pruning and thinning, combined with tree improvement concentrating on long internodes, we can produce clearwood that is the equal of best softwoods in the world. As other counties either cannot grow radiata or choose not to manage their radiata for maximum clearwood production, New Zealand is in a unique position.

Clearwood is our USP – uniquely special product.

Further reading

Brown G.S. (Comp), Bunn, E.H.(Ed) 1963: Pruning and Thinning Practice in New Zealand FRI Symposium No 3 New Zealand Forest Research Institute.

Fenton R.T. Sutton W.R.J. (1968): Silvicultural Proposals for Radiata Pine on High Quality Sites.
New Zealand Journal of Forestry 13 (2): 220-8

Sutton W.R.J. (1975): An Evaluation of New Zealand’s Forestry Export Potential. D. Phil thesis Oxford University.

Tombleson J. (2018) Pruned log supply from the Central North Island and disrupter influences on wood processing. NZ Journal of Forestry 62(4): 5-9.

Ure J. (1949) The Natural Regeneration of Pinus radiata on Kaingaroa Forrest. NZ Journal of Forestry 6 (1): 182- 192.

One post

Post from Shem & Jen Kerr on October 11, 2019 at 12:44PM

I attended a loppers ladders pruning saws Bunn-Barr clinic. There was lots of enthusiasm. More of a religious conversion event than science. Then I went to the field day at Inglewood Timber Processors. Totally unpruned trees were cut into boards cambian to cambian which were then kiln dried before being trucked to the factory where the knots were sawn out and bagged for firewood. The remaining timber was finger-jointed and exported to USA as balustrade; architrave; door blanks; etc. This is with 18 – 23% return on investment, as against 7 – 9% return for pruned trees. That was all last century,- has anything changed? Well, further disruption to the 27 year clear-pruned rotation: short rotation forestry at close spacing, - where pruning makes even less sense with radiata pine; though it might make sense with short rotation eucalypts. Is there a game changer or two that could advantage the concept of clear pruning?

Please can we have a recalculation of the costs/benefits of clear-pruning done by robots; or pruning machines. I know NZ likes to think that it's forestry is leading edge, but I can't find any evidence: maybe it's all top secret. There are some overseas examples: Pruning trees with the Clouston Tree Pruner (video); and article ; " A Pruning Robot With a Power-Saving Chainsaw Drive," by Yasuhiko Ishigure, Katsuyuki Hirai, and Haruhisa Kawasaki. 

Advaligno Patas 2018/09 - maschinelle Hochastung - mechanical delimbing - élagage – prototype

I can see some issues. What do you think?






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