Raw material requirements
Resin tapping operation
Labour and organization
The fundamental requirement is an adequate number of suitable, mature pine trees available for exploitation over the lifetime of a processing plant. Both natural forests and plantations may be used, although the high tree density and easier terrain which enables the tapper to visit a greater number of trees per day, makes resin collection cheaper and easier to manage in plantations. If the annual yield of resin is 3 kg/tree, at least 330000 mature pine trees would be necessary to provide resin feedstock to a small processing plant with an annual throughput of 1000 tonnes.
Many countries have substantial resources of pine trees of one or more species, either as natural forests of indigenous species or as plantations of introduced exotics. Although all pines are capable of yielding resin, both the obtainable yield and the intrinsic quality of the rosin and turpentine can vary considerably according to the species. The way in which these genetic factors can influence resin characteristics at the species, provenance and individual tree level are discussed in more detail in Appendix 3. Species selection is therefore crucial to the marketability of the products and the profitability of the overall operation. The principal pine species tapped in various parts of the world have already been noted in Chapter 1. It should be appreciated, however, that those which are tapped are invariably chosen from the standing resource already existing within the country either as natural stands or plantations. Pines are usually planted for timber or pulp rather than resin, and whether the species originally selected for wood or fibre quality are also suitable for resin production is a matter of chance. P. patula, for example, which is one of the most widely planted pines in Africa, produces a very poor quality resin in low yields and cannot be tapped economically.
As well as being dependent on the species of pine tapped, the quantity of resin that may be obtained from a particular group of trees depends on a number of other factors. The most important of these include ambient temperature (and altitude insofar as it affects temperature), rainfall, diameter and crown size of the tree, method of tapping and length of tapping season.
High temperatures are conducive to good resin flow, while prolonged periods of high rainfall are not, and the extent of seasonal changes in climate will largely determine the period during the year when it is profitable to tap the trees. In temperate countries such as Portugal, tapping takes place for eight to nine months of the year. The time between the end of one tapping season and the beginning of the next is used for cleaning or replacing tools and accessories and installing or raising gutter systems and cups on the trees. In more tropical countries, where there are no prolonged cold periods, tapping may proceed all year round, although seasonal heavy rains may interrupt it.
In general, the greater the diameter of the tree tapped and the bigger the proportion of live crown, the greater the resin yields. Selection of groups of trees for tapping will therefore be made on the basis of utilizing the oldest or largest trees available of the preferred species. Plantation pines are usually at least 15-20 years old before tapping commences; some countries have regulations which limit tapping to those trees with diameters greater than about 20-25 cm. Comprehensive data are available, from many sources, relating diameter and crown size to expected resin yields However, although such data may serve to illustrate the general dependence of yields on tree size, they apply only to a particular species; they might also be misleading if used directly to estimate yields outside the country from which they were derived. Furthermore, as resin yields are known to be genetically determined, considerable provenance and tree-to-tree variations may exist. As a guide, suitable species grown under favourable conditions can yield 3-4 kg/tree annually. Minimum acceptable yields are around 2 kg/tree; it is unlikely that yields much below 2 kg could support a viable resin tapping operation.
Tapping trials to assess yields
should there fore complement any feasibility study which examines the prospects for
establishing a gum naval stores industry. At the same time, samples of the resin obtained
should be analysed to determine quality. Regardless of the quantity produced, if the
quality of the rosin and turpentine derived from the resin is so poor that the products
are unacceptable to the market, the trees will not be worth tapping. Quality assessment
criteria for gum rosin and gum turpentine are described in Appendix 2. In general, as far
as international markets are concerned, the products from Portugal and the People's
Republic of China will set the standards against which gum naval stores from new sources
will be judged.
System of tapping using a wide face
System of tapping using a narrow face
Resin is obtained from the tree in a manner analogous to rubber tapping except that the exudate is more viscous and slow-running than rubber latex. Tapping generally involves the following basic steps:
preparation of the face of the tree
installation of the resin c collection system
wounding of the tree to induce resin flow
application of a chemical formulation to stimulate and maintain resin flow
collection of the resin, re-wounding of the tree, and application of the stimulant at suitable intervals.
In some countries, traditional methods of tapping are used which do not entail application of a chemical stimulant and which are generally less efficient.
The precise manner in which the above steps are carried out in the various producer countries has developed in different ways over the course of many years. Nevertheless, it is generally recognized that tapping should be carried out carefully and in such a way as to avoid permanent damage to the tree. Older methods in which cuts were made deep into the wood have mostly been replaced by more modern practices involving removal of bark alone. Some producing countries have spent much time and effort developing and refining procedures and investigating the use of different materials and accessories such as cups and gutters. Others still adhere to traditional methods and materials. In Indonesia, trees are tapped by the frequent removal of slivers of wood from the stem without the application of stimulant (although steps are being taken to introduce alternative methods which do not involve the removal of so much wood). In India, although tapping is still carried out which entails removal of wood from the tree in the form of 'blazes', the 'rill' method, in which an acid-based stimulant is applied to small channels cut in the xylem in a 'herring bone' fashion, is advocated. The method of tapping usually followed in the People's Republic of China is unusual because it involves moving down the tree during the course of the season rather than starting at the base and moving up; although the benefits of using stimulants to enhance resin yields have been demonstrated, the practice has not been widely adopted.
The particular style of tapping employed may also be influenced by the extent to which the trees are used for purposes other than naval stores production. If tapping is conducted on plantation pines, for which the principal interest is the final sale of the logs for saw timber or pulpwood, the common practice is to tap fairly intensively, using a wide face, for four years (perhaps extending to six or eight years) prior to felling. If there are no pressing demands for felling, or if there is a large enough number of trees available to allow the use of a narrow face and still maintain the required production overall, tapping may be carried out for up to 20 years or more on the same group of trees.
Systems of tapping developed in the United States and Portugal are now described. Both entail the removal of bark and the application of sulphuric acid as a stimulant, but whereas the former uses a wide face for intensive tapping, the latter uses a narrow face with a simpler system of guttering. The two methods are illustrated in Figure 1.
Either method, adapted to meet local circumstances where necessary, could be adopted by intending new producers. Both systems are well documented and the intention here is only to give an outline of the methods and materials used, highlighting the differences between the two systems, rather than to offer a complete guide to tapping with detailed descriptions of tools and accessories.
Variations of the US system have
been used in many parts of the world including Brazil, other countries in Central and
South America, and Zimbabwe. Countries using the Portuguese narrow face method include
Mediterranean producers, South Africa and Kenya. Alternative tapping procedures which may
be used in other countries are not described here either because their use is limited to a
particular country, or because they are generally considered to be less efficient.
In order to facilitate installation of the collection system on trees which are to be worked for the first time, the rough outer bark is first removed from the area at the base of the tree where it is to be fixed. This rough shaving is usually extended for part of the way up the tree to make the subsequent tapping easier. Although a two-piece apron and gutter system made of galvanized iron is illustrated in Figure 1, this has been dispensed with in Brazil and a specially designed plastic bag is used instead; this fits across the width of the face and is held flush to the tree by wire which goes round it This system is simpler, cheaper and quicker to install than the cup and gutter system, and does not risk contaminating the resin with dissolved iron (which may result from the corrosive action of the acid stimulant on the galvanized iron gutter if its application is over-zealous). The risk of leaving the nails used to fix the apron/gutter system in the tree after tapping has finished, and of damaging saw blades if the trees are destined for sawtimber, is also removed. However, it is rather more difficult to remove the resin from the bags without wastage than from the rigid system, and the bags have a shorter life. The apron/gutter system can be nailed in position using five double-headed nails which are easy to remove and facilitate later removal of the guttering. Immediately below the guttering, a cup made of galvanized iron, aluminium or durable plastic is fixed; it is supported on a large nail and held in place by the bottom edge of the apron. In Zimbabwe, galvanized iron gutters and a small spout are used to direct the resin into glass jars.
A horizontal strip of bark 2-2.5 cm high is removed across the width of the tree, just above the gutter, to cause the resin to flow and the chemical stimulant, usually acid- is applied along the top edge of the exposed tissue ('streak'). The combination of bark removal and acid treatment makes it unnecessary to cut into the wood to open the resin ducts, which was characteristic of older methods of tapping. Wounding to the tree is therefore only superficial and loss in growth during tapping is minimal. The acid also maintains resin flow for a longer period of time and the tapper, instead of having to return to the face within two to four days, as is the case when traditional methods of tapping are used, need not repeat the task until some weeks later, at which time the bark is removed above and adjacent to the first streak. In this manner, a two-week tapping interval using a streak height of 2 cm would necessitate about 16 visits to the tree in the course of an eight month tapping season, and would result in a vertical face about 32 cm high, down which the resin would flow to the cup. It shorter tapping interval, say 10 days, would use a streak height proportionately less than 2 cm.
The first type of stimulant to be used commercially was a 50% solution of sulphuric acid, applied as a fine spray from a plastic bottle. Later developments led to the production of a specially formulated sulphuric acid paste. This is applied as a thin bead from a plastic bottle and is now quite widely used, although the precise formulation varies somewhat according to the availability of local materials*. As well as being less wasteful and less hazardous to the person using it, the paste has the advantage of requiring slightly less frequent applications than the spray. The greater penetration of the paste requires the removal of a bigger strip of bark than normal; so in spite of fewer visits to the tree, the total height of the face worked is about the same as for the spray. Whichever type of stimulant is used, its strength, frequency of application, and the height of bark removed should be optimized so that at each removal of bark there is some live xylem tissue showing. This is indicated by the paler colour of the wood above the line which shows the extent of penetration of the acid from the previous streak; the wood below the line is darker and redder in colour. More recent research has shown that inclusion in the formulation of 2-acid (e.g. EthrelTM) a chemical used to enhance yields of latex in rubber tapping, also has beneficial effects on resin production. However, further research is needed to demonstrate the long-term benefits and it is not thought to be used commercially in tapping pine trees at present.
* In addition to the sulphuric acid solution itself, a typical paste contains small amounts of a lubricant-cum (to reduce drying out and prevent sticking of the paste to the sides of the container), an acid- emulsifier (to prevent separation of the oil and aqueous phases), a pyrogenic silica (to act as a thickener) and a carrier such as finely graded pecan shell or rice bran flour (to impart adhesive qualities to the paste and provide texture). The concentration of the acid used to make the paste may be between 40% and 60% (w/w) depending on the tapping method used and the climatic conditions under which the paste is applied. Note: appropriate safety precautions should be taken when preparing, handling and using strongly acidic materials and their formulations.
During the course of its flow some resin solidifies on the face of the tree before reaching the receiver. The extent to which this happens depends on the species of pine being tapped. The solid may be scraped off periodically during the season, or it may be left to the end and collected and processed separately from the bulk of the resin as it will yield a slightly lower grade of rosin.
At about six monthly intervals, or
at the end of the season, the cup and gutter system is removed and re-installed where the
last removal of bark was made; a second season's tapping can then be carried out. This is
repeated for a third, fourth and, perhaps, fifth season (3-4 years in total), when the
height finally attained is likely to be too great for a person to reach and it becomes
uneconomic to proceed any higher. Depending on the intended use for the trees, it may be
possible to initiate a second face for tapping on the opposite side of the trunk.
Procedures using a narrow face are also based on the removal of bark with acid treatment. However, the use of a narrower face, usually 10 cm wide, brings with it several advantages, the most important being the simpler system of guttering that can be used. A small, flat, arc-shaped piece of galvanized iron is inserted edgewise into the shaved part of the tree with a special tool; it requires no nails to hold it in place. A clay or plastic pot is supported under it by a single nail or wooden splint; in appropriate circumstances, a bamboo cup or coconut shell can be used as the resin receiver. The height of bark removed at each visit to the tree is similar to that for a wide face, about 2-2.5 cm; the tapping schedule (using spray or paste-based stimulant) is also similar. After working on one vertical face for four years, another may be started about 10 cm to one side of the first. In this way, four or five faces, each lasting for four years, may be worked on large trees. If the trees are large enough, two or more faces may be worked simultaneously; however, although they will be higher, resin yields for two faces are not twice that for a single face.
Tapping remains essentially a manual operation whatever system is used, and although attempts have been made, notably in the United States, to introduce mechanization for some of the tasks, particularly those which are physically demanding such as the initial shaving of the tree and the removal of bark, they have met with little success. The tools and accessories required for tapping are relatively few and simple and include the following:
bark shaving tool
cup or other form of receiver
nail(s) (to support cup and/or to fix guttering)
file or whetting stone (for sharpening bark hack)
sulphuric acid-based stimulant (liquid or paste)
bottle (plastic, for application of acid)
bucket (into which resin from cup is emptied)
funnel (for transfer of resin from bucket to drum)
drum or barrel
protective clothing and accessories (for tapper, including visor or goggles, acid-proof gloves, plastic apron or other garment, and rubber boots).
Labour requirements and organization during the tapping season vary from producer to producer. Methods of tapping which involve the removal of bark and application of a chemical stimulant usually mean that the tapper only needs to visit the tree every 7-14 days; the interval may be even longer under favourable conditions and using acid paste. Methods which involve the removal of wood without applying stimulant require more frequent visits, every one to three days, and are therefore more demanding in terms of labour. Resin is emptied from the receiver every second, third or fourth visit depending on the system of tapping used and the size of the receiver. It is emptied into buckets and the full buckets are emptied into drums or barrels strategically located amongst the trees. When full, the drums are transported directly to the processing plant or to a central storage depot.
Productivity is dependent on the system of tapping used and the efficiency of the tapper; it is also influenced by tree density and the terrain over which the tapper has to move when going from tree to tree. Between 200 and 800 faces may be attended in one day, so in a two-week cycle of 10 working days, 2000-8000 trees (or less if more than one face is being worked per tree) can be tapped by one person. Although a different individual usually collects the accumulated resin from the trees, there may also be a division of labour amongst the tappers themselves. For example, one person in a team may be responsible for applying the stimulant and/or replacing the cup on the tree (which is either covered or removed during streaking to avoid pieces of bark falling into it) while the others carry out the streaking.
In addition to the tappers, small teams of people are required during the establishment and maintenance phases: to shave the trees and install the cups and gutters prior to tapping new groups of trees (establishment), and to remove the cups and gutters and repeat the process at the end of one season in preparation for the next (maintenance).
Several systems of remuneration exist. The hourly wage system, which requires constant supervision, increases production costs and gives the labourers no incentive to work efficiently. A system in which contractors or pieceworkers undertake the tapping has the advantage of relieving management of some of the problems associated with having a large labour force under its direct control, and payment on the basis of the quantity of resin produced encourages higher levels of production. Some supervision or checking is still required to ensure that tapping is being carried out correctly, and a system of bonuses or penalties may be adopted to reward productivity and penalize poor workmanship. In some countries a plot-holder is allocated a specific number of trees, perhaps 5000; he can then employ extra tapping labour at his own expense if he needs it, or involve other members of his family.