Here's how we can help you get the forest onto your farm.
Harvesting must be planned around:
- The need to minimise negative environmental impacts
- The need to maintain a flow of high value products over the lifetime of your planting
- The safety of those doing the harvesting
- The type of harvesting equipment available
- The terrain
- The preservation of the non-timber values of the planting
- The regeneration or rehabilitation needs of your site, and
- The legislative requirements of harvest security, environmental protection and soil conservation.
Harvesting should be seen as an overall plan of management that aims to produce a high value product of specified dimensions. Planning your pruning and thinning operations to produce well-spaced trees with an appropriate merchantable log length and diameter will help make logging easier and lessen environmental impacts. For example, with cabinet timbers, it is unlikely that you would ever need a bole length of greater than 4.5m. A bole length of 6m offers a high degree of flexibility in the length of timber produced for the market while making falling, snigging, loading and milling significantly easier.
The major negative environmental impacts of harvesting are the gross disturbance of soil involved in falling, snigging, loading and transporting of logs. Soil erosion and sedimentation of streams associated with logging operations is probably the most important area to be considered in harvest planning.
Research carried out in State Forests in NSW and Queensland shows that the main soil losses result from gross disturbance along logging roads, snig tracks and loading areas. Areas between tracks where machinery was used to extract logs suffered virtually no accelerated soil loss. All roads and tracks must be returned to a stable, vegetated condition as soon as possible after logging operations. Common strategies for restabilisation of tracks and roads include backblading with a tractor or grader to even out topsoil and fill in wheel ruts accompanied with seeding the area with shade tolerant grasses.
Attention to road design; carefully controlled outfall of drainage to stable, vegetated areas,
construction of cross drains, minimising road gradients, batter slope and length are
essential parts of erosion prevention in harvesting.
Buffer zones must be provided to prevent the pollution of waterways with sediments and harvesting operations must not be carried out within 10 metres of major drainage lines and within 20 metres of a stream.
Before commencing logging, ensure that all trees to be retained are clearly marked (or mark only those to be removed) paying particular attention to retaining any trees of high habitat value or high quality seed trees.
Much of the equipment used for the harvesting of woodlots will be available on the farm. There is no reason that experienced operators should not carry out their own harvesting, but it is important to remember the high level of risk involved in falling trees. An experienced logging contractor needs a high level of skills to survive from both a safety and a commercial perspective. If you are unsure of your skills it is much safer (and probably more cost effective) to employ a contractor who can safely harvest your trees with minimal damage to the surrounding standing timber.
Larger scale logging operations are better carried out using the sort of specialised equipment operated by logging contractors in State Forests. Excavators fitted with hydraulic chainsaw heads capable of falling, delimbing and bunching logs are able to extract large volumes of timber efficiently with a high degree of safety and with minimal soil disturbance.
Personal safety is a major concern and landholders would be well advised to undertake a chainsaw operator’s course (through TAFE) before attempting any felling of trees. A good knowledge of equipment maintenance accompanied with regular safety checks, the use of ear muffs and safety helmets with visors, appropriate clothing and footwear are all essential parts of harvesting. Trees cannot be safely fallen in gusty wind conditions or in an overgrown or slippery work area.
One of the common criticisms leveled at small scale farm forestry is that it is not economically feasible to harvest small stands of trees using the type of equipment currently employed by contractors in the harvesting of large stands of timber (eg. in State Forests). However, inexpensive, cost effective harvesting equipment is available and is well suited to use in smaller private plantings. Use of this equipment actually minimises environmental impacts. For instance, pit-prop contractors in NSW have used modified farm tractors successfully for many years to extract full-length logs which are then cut into a variety of products of varying lengths. Logs are either simply dragged behind the tractor or fitted with skids to cut down soil disturbance. Similarly, modified and purpose built tractors are widely used throughout Europe for selective harvesting of farm woodlots. For farmers with a medium sized (60 HP+) 4 WD tractor it may be economical to modify their machines for skidding of logs.
Where logs of smaller diameter are to be extracted, it is more efficient to strap or chain together a number and skid them as one unit. Where logs need to be moved over longer distances to loading areas (or even over a few kilometres to the mill) a forwarding tractor can be used to carry rather than skid or drag timber. These have a specially designed, hydraulically driven crane mounted on a bogey trailer and can sort and carry logs up to about 6 metres in length safely over any roads designed for a standard tractor.
One of the functions of a Farm Forestry Growers’ Cooperative will be to ensure the availability of such low impact, low cost harvesting equipment, either through joint ownership or by ensuring that contractors are aware of the commercial opportunities created by private plantings.
Recent changes have been made to legislation relating to farm forestry and private native forestry. The most up to dat information can be found on the epa website.
You must consider what is the most efficient and convenient way to mill your timber and which method will give you the most saleable product from the youngest possible tree. Different mills have varying degrees of efficiency in both time and timber recovery from your logs.
A number of different types of portable mills are available all of which have advantages and disadvantages.
Chainsaw mills or Alaskan mills have the great advantage that they can generally be set up to work anywhere where you can carry in a chainsaw and are sometimes the only option when a tree cannot be gotten out in one piece. However, they are not ideal for general use because of the large amount of wood wasted as sawdust with every cut (at least 8mm) when compared with a modern bandsaw with a 2mm blade.
Lewis mills or similar portable mills with a circular saw blade, which runs on rails over a log fixed in place, are efficient ways to cut certain sizes of timber (e.g. 3 x 2 studs). They again generate a lot of sawdust when compared with a bandsaw and are not suitable for the cutting of wide slabs.
Bandsaws are excellent for the cutting of slabs and flitches but are not an efficient way to cut timber of smaller dimensions. The best designs are capable of cutting very fine slabs accurately and with minimal wastage.
The most effective way to get maximum value from your logs, with minimum wastage is to use a combination of different machines to suit the type of timber being cut. This inevitably means transporting timber to the mill. The cost of transporting logs to and from the mill as opposed to milling on site and selling a finished product direct to the end user must also be taken into account.
Other milling options include the use of double edgers and radial sawing. Both these techniques make it possible to obtain stable, saleable product from smaller diameter logs with a higher percentage of recovery. Double edgers use two saw blades which cut side by side releasing the tension in the tree equally and eliminating many of the problems experienced when timber bends away from the heart of a log as it is being cut and has to be resawn to straighten it.
Radial sawing uses a technique where the log to be cut is rotated and the saw blade passes along a rail cutting wedges of stable timber with a round outer edge. These can then be used as is, resawn as conventional, rectangular timber or laminated to form squared sections. Because the grain is always at close to 90° to the edge of the board it is highly stable and it is possible to utilise much younger trees of smaller diameter.
General Marketing Trends
General trends in timber markets both nationally and internationally are highly encouraging for private growers. As the world population increases and more people in the developing nations become wealthier demand for timber products is growing exponentially. At the same time, supplies of timber from traditional sources are decreasing and prices are rising to better reflect the cost of production in plantations. In the twelve months to March 1997 NSW State Forests increased royalties for all species and grades of logs by an average of more than 70%. This reflects a move to pricing based on the cost of plantation production, a result of corporatisation and the introduction of the Joint Venture Scheme.
Currently there is no public advertising of log prices and royalties paid for various products sourced from State Forests in NSW but State Forests has agreed to advertise these prices in the near future. This should provide a listing of average royalties paid for a range of species and grades of timber on a regional basis. Experience in New Zealand has shown that this information is invaluable to growers and a basic requirement for the sound financial management of plantations and farm forestry.
The International Tropical Timber Organisation produces a comprehensive fortnightly bulletin listing current timber prices and market trends for a very large range of products and species in most major national markets. The contact for this information is Dr M. J. Adams who can be contacted at:
International Tropical Timber Organisation
International Organisations Centre
YOKOHAMA, 220-0012, JAPAN
Dr U.N. Bhati of the Department of Forestry, Australian National University, produces a regular market report listing stumpage returns for a limited number of species and regions. These are published in the Victorian Department of Natural Resources and Environment’s Agroforestry News. Dr Bhati can be contacted at:
The Fenner School of Environment and Society
Australian National University
CANBERRA, ACT, 2600
Phone: +61 (02) 6125 3220Fax: + 61 (02) 6125 0746E-mail: email@example.com
At present many Australian furniture manufacturers rely on imported rainforest cabinet timbers because there is insufficient local production to supply their needs. The large volumes of tropical rainforest timber now on the market cannot last. The rate of harvesting is well above sustainable levels and more often than not land is not returned to forest once it has been clearfelled. Currently, the large volumes of timber available and the low cost (below production costs for Australian growers) allow buyers a great deal of choice and some certainty in quality. If we are to capture this market, as imported timbers become increasingly unavailable, we must ensure buyers are able to be confident about the quality and quantity of timber from Australian plantations.
Options for the sale of timber range from selling trees as standing timber and allowing the purchaser to fall, snig and load the timber and take it to a mill to retailing sawn timber milled and dried on site, either through a Cooperative or agent or privately. (Paul Snape’s paper in Section 6.3.6 addresses these issues in more detail).
Potential yields from Farm Forestry
Pulp and Woodchip
- Early thinnings
- Framing scantlings
- Flooring, cladding, lining boards
- Internal fixtures, slabs
- Poles and roundwood
- Bearers, beams
- Wild herbs/bushfoods
- Tool handles
- Essential oils
- Marine piles (Turpentine)
- Bridge decking
- Fence posts (split and strainers)
Furniture Grade Timbers
- Veneer peeler logs
- Turning wood and inlay
- Hollow logs for landscaping, planters, letterboxes, etc (objets de kitsch)
- Any unusually shaped or weathered pieces
- Turning wood and inlay
- Improved tree seed
There are opportunities for the growers to do their own value adding and marketing, however one needs to recognise this takes time and a certain level of understanding. A decision needs to be made as to what the target product will be, who are the potential buyers, what is the demand and supply situation and what are the economic factors involved, including production, transport and marketing costs, as well as current market prices.
Timber sales can be made by auction, by the calling of tenders or by direct sale to manufacture or the end user. It is important to be able to describe the product in a meaningful way in order to give buyers the correct description of the product. You should be able to describe:
- Species and trade name
- Presence and type of any defects
- How it has been milled (eg fully quarter sawn, commercial quarter sawn, etc)
- The type of finish (rough sawn, fine sawn etc)
- Whether air or kiln dried and to what percentage of moisture
- Potential uses
Unless one has expertise in these aspects careful consideration and research needs to be undertaken, otherwise it maybe prudent to employ an agent, consultant, broker or join a growers' cooperative.
Cooperatives exist solely for the purpose of trading in a particular group of commodities or services to the mutual benefit of their members. All active members of the cooperative hold an equal number of shares and have equal voting rights. To be an active member you must trade in goods, or provide a service through the cooperative to a specified minimum in any twelve-month period.
Members must support their cooperative and not trade outside it if it is to survive. The Cooperative’s main source of income is the commission it gains from sales of members’ goods. If it fails to deliver a premium price to members they will begin to take their trade elsewhere and it will eventually fail. A guide to starting a treegrowers cooperative has been published by the Australian Forest Growers (Australian Forest Growers, 1999).
Some of the many advantages of Cooperative membership are:
- Single desk marketing from a computerised database
- Ability to guarantee continuity of supply to medium to large end users
- Quality assurance controls which deliver a standardised quality product inspiring confidence in buyers
- Greatly enhanced market intelligence and the development of new markets not accessible to individual producers
- Access to equipment which no one small grower could afford to own alone
- Economies of scale, energy and materials efficiency, and resultant savings in transport and marketing costs
- The ability to lobby effectively at regional, national and international levels.
The type of single desk marketing service provided by a Cooperative relies on the ability to accurately describe a standard product. Various grades and quality of timber from diverse sources can then be offered to buyers with a guarantee that the product will meet definite criteria and suit their exact requirements. Quality assurance is critical to collective marketing.
The Pruned Stand Certification Scheme mentioned earlier (Chapter 5) is one example of the type of quality assurance practices which will ensure that cooperative members are able to obtain premium prices for premium quality timber. Without reliable records and independent auditing of timber, there is no guaranteed market premium for high quality timbers.
A major part of the difference between prices paid for standing timber and the final product as milled timber is the inability of the buyer to accurately calculate the volume of useable timber. This is because of the losses from defects that are not visible before the tree is broken up, ie the purchaser is assuming a high percentage of risk. Quality management, quality assurance and independent auditing effectively reduce that risk. Both the grower and processor stand to benefit financially from this reduction in risk and the end result should be cheaper timber.
Certification of ecologically sustainable production is another area that promises to generate a market premium for sound management practices. European consumers are currently paying up to 20% higher retail prices for Caribbean cabinet timbers labelled as a sustainably produced village product. Greenpeace, The World Wildlife Fund for Nature and the Forest Stewardship Council have been instrumental in the drawing up of international guidelines for the ”eco-labelling” of timber products but there remains some dispute as to their applicability in practice in Australia. Virtually all of the plantation timber produced in Australia and the bulk of that produced from native forests with current management and harvesting standards would qualify for certification. Therefore, there is no incentive for improved environmental management with the current standards and no market premium to be had within Australia unless a new and higher benchmark is set.
Standards for all products within Australia are set by the International Organisation for Standardisation (ISO). ISO standards are not sector specific and therefore there are no standards specific to the forestry sector. The ISO 14000 series is a set of environmental management systems and environmental management tools that are designed to enable companies to define and implement environmental objectives. For more information check out the ISO website.
A salvage sawmiller's perspective
The paper that follows was first presented by Paul Snape of Fox timbers at a Farm Forestry Introductory Course held at Dorroughby Field Studies Centre in 1994.
Harvesting and milling of your woodlot (by Paul Snape, Sawmiller)
The woodlot that you have planted and watched grow is starting to come to maturity and you now have to think of how to get logs and poles out of your woodlot. The simplest would be to cut down every tree, sell what you have to whoever will take it and start all over again. Rather like the slash and burn method of agriculture. Your returns for your investment would be once every so many years of maturity rate of the species of trees that you planted. Not very good, although in some cases it may be the way to go.
A much better way would be to start your harvesting to a plan by working out what you want felled to suit your woodlot and to bring in a return on your investment. For example, in a woodlot of a certain size trees on the outside would be of smaller trunk height than trees towards the centre of the woodlot. Therefore your best returns would be to fall towards the centre and leave trees on the outside, replacing the trees fallen on the inside with new plantings. This in turn would give you a continual harvest. It must be remembered that you are to harvest to suit your woodlot, offering logs as they become available. This does, by its very nature, make things hard for the very small woodlot. The economics of getting someone to return time and time again to fall and get out one or small numbers of trees at a time are prohibitive, so some sort of compromise would have to be reached.
This comes back to a few basics of woodlot design that maybe you are not thinking about at the moment but you will find that they play a huge part in how you can harvest your woodlot to its best advantage. These are the layout, the species, and the terrain.
The layout becomes very important when you come to harvesting as you can be sure that the best of your trees are going to be in the centre. Can you get to them? It is quite easy to put a big dozer in and knock down other trees to get to the ones you want? Is that what you want? You would be destroying part of your crop to get to some other part of your crop. Sure you could get a small dozer or four wheel drive tractor which might not do as much damage to the other trees, but you have to remember that logs are not light; they are heavy and you need heavy machinery to move them around. A good sized sawlog, say thirteen metres long and with a 500mm diameter, has a cubic capacity of nearly three cubic metres and with the bark on will weigh about 4 tonnes. Not at all easy to move about! So the layout of your woodlot should allow access to as many of your trees as possible, but at the same time not to have too many large gaps in the woodlot.
The terrain now comes into effect because the steeper it is the harder it is to get logs out. Instead of getting the log out in one piece you might have to cut it up into two or three pieces to get it out, creating more chances of damage to your other trees and of course adding to the cost as well. By thinking now about your design and not just planting your trees, you can save a lot of time and bother later on. A good idea would be to have a track to wander through your woodlot for access as much as possible. It would also provide access for the Bushfire Brigade in case of emergency.
Some species are best cut only when you are ready to have them milled (eg. Blue Fig, Elaeocarpus grandis - borers love it and you can’t leave it on the ground for any length of time). Some species can be fallen and left for a few years, others can be left for longer periods (e.g. Blackbutt and Teak), and some should be ring-barked and then left for up to 6 months and then fallen (e.g. White Cedar).
So, all of these things have been sorted out and you are ready to get to it. If you have got flat ground and a large plantation with fairly straight rows and they are all the same species (pines lend themselves to this very well), you could get someone with a large harvester which is like a Hy-Mac but instead of a bucket on it there is a hydraulic cut off saw. It grips the tree and then cuts it off, holds the tree and then goes up and takes the head off, and there is your log. It is then loaded straight on to a forwarder and taken out of the forest to waiting trucks to be taken the mill.
As it is most unlikely that you will have either the area or the species in sufficient numbers, it is most likely that your woodlot will be harvested by more conventional means, that is by a faller going in and falling the trees that you want and then getting them out by either pulling them out by heavy machinery or using a winch. Whatever you decide the logs will have to be brought to a central point to be able to be loaded onto trucks to be taken to the mill. As stated before, the way your woodlot is designed is going to have a major impact on harvesting.
The other aspect that will have to be taken into account when harvesting is marketing, which I will come to shortly, and milling. Milling of your logs comes into effect when you want to get a better return for your investment. Your decisions with harvesting and marketing really become important here, for you cannot market your timber if you do not have the right product and you cannot get that product unless you have the right logs.
Logs are traditionally taken to a sawmill to be cut up to timber and although there is now milling on site, all the same principles still apply. The percentage of sawn timber varies greatly with the size and quality of the logs available, as also does the rate of production. The latter is also related to the size of the product cut and quality demanded and is influenced by the type of saw, the layout of the mill and the judgment of the sawyer. The yield is generally between 40% and 50% of the theoretical log volume.
Each sawmill is designed for the cutting of certain species (eg. pine or hardwood) and/or the cutting of certain sizes (eg. banana cases). This does not mean that they cannot cut other timbers just that they were designed to do a specific job and they do that best.
Logs being large and unwieldy they must be cut into manageable sizes. They are usually cut down the centre using a large diameter circular saw. These large saws have a diameter of about 1800mm giving a cutting depth of about 825mm. However, as this is often not enough, another saw is run down it and to the back of it, thereby giving cutting depths of up to 1600 mm. The single saw is called a Single Canadian, the two saws a Double Canadian. These saws are designed to break the log down to manageable sizes; they are not designed to be really accurate. They are used to get a flat surface so the flitches can be put onto the bench and cut to size. The Canadian saw is a thick saw cutting up to 8mm so it is used only to break down otherwise too much timber is wasted.
On small logs which are fairly straight, there are two other ways to get that flat surface. One is the log edger, which is two saws mounted on the one spindle or on two spindles in line with devices for moving these saws at predetermined distances apart. The second unit is a gang saw which is a number of circular saws mounted on a common spindle. This does not cut for quality just for standard sizes that can be recut on the bench.
Another way that is being used more to get flitches from your logs is the bandsaw. This is a relatively thin blade which has a fairly fast cutting speed. The thickness of these blades is between 1.5mm and 3mm. They are a continual band of steel toothed on one or two edges passing over two wheels either mounted horizontally or vertically.
Whichever way the log is broken down it now has to be cut to the sizes required. This is mostly done with a smaller circular saw on a bench. These saws are mostly in sizes that can cut manageable timber; most cut about 300mm and have a thickness of about 5mm. Once a cut is put through the flitch at right angles to the original breaking down cut you are able to then cut to size, by putting up against a fence which is movable, and in this way all of your sizes are cut. It must be remembered that logs and flitches have got stress in them and getting the stress out of the timber is the sawer’s job. Every flitch and every log is different so the sawyer is constantly on the watch to see where the stress is. The object of all these saws is to get a product from raw material, and no matter what the saw is called it will do the job in basically the same way.
There are two main ways of sawing a flitch and sawing around a defect. These are back sawing and quarter sawing. Back sawing is the most common method used. Back sawing aims at the production of boards with faces roughly tangential to the annual growth and at right angles to the rays. Any boards with the growth rings at less than forty-five degrees to the face are considered as back sawn. Back sawing enables high-grade timber to be obtained from faulty logs. It is very flexible and generally gives a higher recovery than does quarter sawn. It is simpler milling and has greater speed of production. Usually you can get wider boards from a given size log and more of them than you can from quarter sawing. Knots if present show as a round form and not as a spike and gum veins in one board may not affect a lot of boards as in quarter sawn.
Quarter sawn is also called rift sawing. The aim of quarter sawing is to cut as many boards as possible with their faces parallel to the rays. Timber is called fully quarter sawn when the growth rings show an angle of not less than eighty degrees to the face of the board. For normal milling an angle not less than forty-five degrees is acceptable in quarter sawn material. This is called commercial quarter sawn.
The advantages of quarter sawn material are that it may give a better appearance to hardwood by showing prominent ray figure, or the stripe or ribbon effect of interlocking grain. They tend to wear better than back sawn boards. They are less prone to cupping, warping and checking. And as they do not shrink as much as back sawn in width they are used in places where this is important, like in the decking of boats. In some species it is very important that those species be cut on the quarter for it brings out the rays to their best advantage. Most oaks are best cut this way, Silky Oak being one of the best examples.
Because of the demand more logs are now being cut by the slab method, either by bandsaw or chainsaw mill. The difference between these two ways of getting slabs out of logs is economy. They both use blades up to 1200mm in length, but where the chain saw mill puts a cut of at least 12mm in the timber with no way of getting a really smooth parallel cut, the bandsaw has a cut of only 2mm and is able to get each cut parallel making for a much better product. The main advantage of the chainsaw is being able to carry it into places from which you cannot get a log out and cut slabs and get them out. The demand for slabs of timber is preferably for slabs with one or two natural edges in thicknesses of 30mm to 100mm.
There is another aspect that comes under this part and that is hewn timber. Hewn timber is timber shaped with axe cuts. The broad axe and the adze were the two ways of getting the timber to size and although it is not used as much these days there is still some timber cut this way, and as it is popular to keep up historical ways there will always be a small demand for this.
Milling should also include logs in the round as poles and piles. The specifications that say whether they are a pole or a pile is beyond this paper, but it is important to say that they are usually logs of a certain diameter and a certain length of selected species for different uses.
How will I get a return for my trees? I have put in all this work and a lot of years now I want to sell them. Who do I approach? What is the best way to sell them?
You can get in touch with any sawmiller and they will buy trees from you. This they will do on a royalty basis. That is they will give you so many dollars per cubic metre of log. The rate depends on the species and size of the trees, and at times on the location and the terrain. You do not have to do anything else. They fall the trees and take them away; you get paid.
You can get them fallen and pulled out to a central place and then sell the logs. You would get royalty plus falling and snigging, but you would have to pay for the falling and snigging and you might pull out logs that are not wanted, so it is best to know right from the start what sort of market you are going to aim at. This comes down to the selection of your initial species for if you plant the wrong species for the market for which you are aiming you will not get your best returns.
In general it can be said that the more you go into adding value to your logs or timber the greater your percentage of return. For example, we will pick a common tree, Blackbutt, of millable size (400mm girth, 15 metres long, 1.885 cubic metres volume).
We are of course talking about a good log and the last figure is for good wide timber to be used in furniture. The point I am trying to make is that although there are pitfalls in going to the extra trouble the rewards become much greater. If we took the same chart but made it a good red cedar (which would not be very good at this size) the royalty would be $350 per m3, milling, falling, snigging all the same, which would be $1083.39, sell for $3140, a much greater return.
But these prices do not happen overnight. The Blackbutt has to grow 18-20 years; then to fall, mill, dry and get someone to buy may take up to one more year. To get a good red cedar with good colour and grain a lot more years than that.
There is perhaps a better return from the Blackbutt because you can replant and maybe get three trees in the same time as you get one cedar. The other main thing you have to look at is that some species have a limited market potential. Blue fig, for example, is an excellent fast growing tree and looks good but you have to get very large trees to get good timber. A tree with a girth of 500mm on a length of fifteen metres would most likely not be a good enough tree, the reason being that the Blue fig has a lot of sapwood and a lot of heartwood and this is no good for the market, as the market for this strong light timber is in masts for yachts and in oars for rowing. It has got to be all true wood. Even in the same species of timber you might be aiming at two different markets. The large part to milling and the top part to poles. Tallowwood is a prime example of this sort of diversity.
Marketing Plan Development
Before attempting to market your timber or timber products it is worthwhile considering the development of a marketing plan.
Many of the marketing options available to farm foresters have been addressed in other sections of this manual. One of the important preliminary considerations any tree grower should make is what market are you growing your trees for?
The essential elements of any marketing plan are summarised succinctly by the Four P’s of Marketing.
Place – Know the market, its products and requirements
Product – Know your capacity and advantages and strive to produce good quality
Promotion – Look for market niches, look for attributes, which will distinguish your product from others in the market, consider group promotion through a co-operative or growers group.
Price – Be realistic in your assessment of what prices you need to achieve to be profitable, consider marketing through a co-operative or agent to allow you to negotiate from a strong position.
Mensuration - measuring trees and logs
Why measure trees?
Being able to measure trees accurately is an essential starting point in good economic forest management. By measuring trees regularly we can: identify the best performing species for our site ensure thinning, pruning and harvesting operations are carried out efficiently and at the most appropriate time assess the effects of spacing, pruning and thinning on growth rates check that contractors have carried out work as directed estimate growth rates and yields of particular wood products over time work out and adjust the dollar value of the trees.
Measuring standing trees is both an art and a challenge. It does require some experience to accurately measure the volume of timber in a stand, but there are some simple techniques and tools available which can give a grower a good estimate of the growth rates, timber volumes and potential returns from their woodlots and regrowth stands.
The most commonly used measurements in farm forestry are the diameter and length of useable timber in the bole of a tree, the basal area of a stand of trees and the total volume of a particular grade of log in a stand. Using these measures we can then estimate the volume and value of merchantable timber in the stand.
Because of the time and effort required, trees are measured in sample plots and the findings multiplied out to give an average for the whole stand. The accuracy of the measurements is very important, as any errors will be magnified in the process of averaging out the results. In order to get an accurate measure of growth we must be sure that we are measuring the same trees and /or the same sample of the trees. Permanent plots with a known area are chosen at random on a site and marked out to give a good sample of overall growth. If there are variations over the site that can affect tree growth (eg soil type) sample plots need to cover this variation.
The size and shape of the plots, their location and the number of samples needed, varies according to the stocking rate - the number of trees per hectare, size of the planting and the amount of variation in growing conditions over the site. It is usually sufficient to measure 20 trees in any sample (the minimum number being 12) so plot size will vary with the stocking rate. Plots are commonly rectangular where trees are planted at regular spacings in rows, or circular when trees are evenly spaced, eg. in native regrowth stands.
The diameter of circular plots is calculated so as to give an exact fraction of a hectare. For example, a commonly used plot size in larger stands is 17.84 metres, which gives an area of exactly 0.1 hectares. This is a good plot size for most tree measurements needed in the establishment and early management phases of farm forestry but larger plot sizes are generally used for larger diameter trees.
These plot diameters assume that the ground is flat, or virtually so, but most sites are not flat and adjustments in diameter must be made to allow for the variations in slope.
To lay out a circular plot you will need a flexible 30-metre tape measure, a diameter tape, painted wooden peg, paint and paint brush or spray can, a brush hook and an assistant. Accuracy is important and all measurements must be accurate to within 10 cm.
Measuring Stem Diameter
Stem diameter in a standing tree is always measured at 1.3 metres above ground level (this measurement is known as Diameter at Breast Height Over Bark or DBHOB). Where the tree is growing on a slope the measurement is made at 1.3 metres height on the uphill side (see Figure 5.4). A quick way to find the correct height at which to measure DBHOB is to cut a stick to 1.3 metres in length and use that to find the correct measurement point.
There are two main ways to measure DBHOB using either a set of callipers or a flexible tape measure. Foresters use a tape that shows conventional measurements on one side (circumference) and pi (ð) units on the other giving a measure of tree diameter. Trees are rarely round and it is necessary to take two measurements at right angles to each other to obtain an accurate diameter when using callipers. Where there is a bulge or deformity in the stem at 1.3 metres above ground level two measurements are taken, one above the bulge and one the same distance below. The average of these measurements is then used as the DBHOB.
Using a calculator you can convert the diameter of a stem into a cross-sectional area in
m2 by applying the formula:
Area = ð D2 / 4 or
Area = D2 x 0.0000785398
For example a tree with a 30cm diameter:
Area = ð x 302 / 4 = ð x 900 = 706.5cm2 or 0.07065m2 or,
Area = 900 x 0.0000785398 = 0.07065 m2
The sectional area of a tree at 1.3 metres above ground level, so calculated, is known as the tree Basal Area. The Australian Master Tree Grower program run by the University of Melbourne produces a diameter tape, which can be used to measure the basal area of a stand.
Figure 01 Techniques of measuring Diameter at Breast Height (DBH)
Measuring tree heights
The other measure needed to estimate the volume of timber in a tree is its height. This can be either the overall height from the ground to the top of the growing tip, or the height of the merchantable stem: the useable timber in the bole.
There are a number of methods available to measure trees depending on their height class:
- For trees less than 2 metres tall, use your own height as a reference or cut a stick to 2 metres in length and mark with whatever degree of accuracy you need
- For trees from 2-10 metres tall, segmented or telescopic height sticks are used
- For trees more than 10 metres tall, measure trigonometrically using a clinometer or altimeter.
Another quick (and rough) method to estimate the height of trees over 10 metres tall is to place a measured stick against the trunk, stand back at about the estimated tree height and estimate how many times taller the tree is than the length of the stick. This method is fine (if applied consistently) for rough estimates and comparisons of growth rates in different parts of the stand.
Where more accurate measurements are needed there are several compact and easily used instruments available which measure angles of elevation and hence height. The most popular of these are the Abney eye level, the Blume Leiss height meter, the Haga altimeter and the Suunto clinometer. The Abney eye level and the Suunto Clinometer both have degree scales and can also be used to check levels when laying out contour lines, building earthworks, etc.
Figure 02 Measuring tree height with a degree scale instrument To measure tree height with a degree scale instrument, stand at a point where your eye is above the base of the tree and you can see the whole of the tree to be measured. Using a tape, the horizontal distance from the middle of the tree trunk to the observer’s eye is measured (see Figure 5-5 below) along the line OC. Next the angle of elevation to the top of the tree is measured by sighting to A and reading off the degree scale, this gives you a measure of the angle AOC, then the angle of depression to the base of the tree at B is measured (angle BOC). Then the lengths AC and CB are calculated by multiplying OC by the Tangents of the angles AOC and BOC. The total tree height can be found by adding AC to CB. Table 5-4 gives the tangents of elevation and depression likely to be needed for calculating tree heights.
To calculate tree height with either a Blume Leiss height meter or a Haga altimeter one must stand a given horizontal distance from the tree. This distance is specified in one of four direct reading tables shown on the instrument and should be approximately the height of the tree. Sight to the tip A and base B of the tree, which will then give you two readings. These readings can be added to give a total tree height.
Whatever instrument you are using, always ensure you are standing far enough back (about tree height) from the target tree to get a good overall view of the whole of the tree, or the entire length of the bole, being measured.
Another of the most common causes of inaccurate measurements is the failure to sight accurately through the crown to the actual top of the tree. Sighting to the outer edge of a trees crown rather than the growing tip will produce a serious overestimate of height (see Figure 5-6). When measuring height it is useful to keep in mind the likely height of a typical tree of the species you are measuring, (eg. a Flooded gum at maturity is likely to be about 50m tall). If your measurement does not fit the likely range of sizes for that forest type try it again from a different viewing position.
Figure 03 Correct sighting in tree height measurements Because of the time involved in measuring tree heights, it is not feasible or necessary to measure every tree and it is usual to use some form of sampling. Where a stand is to be thinned, the height of the dominant trees to be retained is measured. Mean Dominant Height is the term used to describe the average height of the tallest trees in a stand.
Table 02 Tangents of elevation and depression for measurement of tree height
5.4.6 Measuring Tree Volume
The volume of useable timber in a tree is measured in cubic metres (m3) or fractions of a cubic metre. The most convenient and common way to calculate tree volumes is the use of specially prepared tree volume tables. These are drawn up by Forest Services and cover a single species or a group of species that have a similar degree of stem taper with height.
To calculate the volume of timber in a standing tree you must first measure height (minus any stump to be left behind) and DBHOB then apply the formula:
Stem volume (m3) = D2 x H x factor given in tree volume tables.
Where D is the DBHOB in centimetres and H is the total height in metres, eg. (for a radiata pine) if diameter is 51.5 and the height is 36m, then:
Stem Volume = D2 x H x 0.000026
Stem Volume = 51.52 x 36 x 0.000026 = 2.5m3
Philip, M.S. , 1994. Measuring trees and forests. Wallingford, Oxon : CAB International.
State Forests NSW, 1995. Field Methods Manual. Technical Paper No. 59.
Extract from SFFA farm forestry manual 2002
FARM FORESTRY MANUAL AND PLANNER for Subtropical Eastern Australia: Planning and implementing a farm forestry project