One of the main reasons for the successful establishment of Hevea brasiliensis on a plantation scale was the discovery of the excision method of tapping for harvesting rubber: the same cut is regularly reopened by the removal at each tapping of a thin shaving of bark from the sloping cut. This principle is in general use today: Ridley was the pioneer of this method. Each time a tree is tapped (with a suitable knife) a channel is prepared along which the latex flows. This method avoids wounding trees.

The cut penetrates to within 1 mm of the cambium; the precise depth varying with the skill of the tapper. The same cut is regularly reopened by the removal at each tapping of a thin shaving of bark. The object of tapping should be to get as much latex as possible from the trees with the smallest excision of bark convenient, and minimize damage to the health of the trees and their capacity for continuing to yield latex.

The cut is made either with a notched knife which is drawn down the incision, or with a chisel which is pushed along it. In both cases thin slivers of bark are excised, and latex flows immediately along the cut and into a cup attached to the trunk. The flow progressively diminishes, and stops in 1 to 3 hours as severed vessel ends become plugged by caps of coagulum. Once begun, tapping is normally continued for 10-20 years, depending on how quickly the accessible bark is consumed. Consumption is determined by the degree to which new or 'virgin' bark is cut away, and to which cut bark is renewed after tapping. In conventional approaches tapping moves along successive panels, first traversing easily accessible virgin bark and then returning to cover renewed bark 6-7 years later. It may also utilize virgin bark at higher levels of the tree, and even extend to bark of third renewal.

Much depends on the standard of tapping, however. Bark consumption is higher, yield per cm of cut is less, and renewal is poor if there is a lack of skill, but under skilled operations tapping may continue for 25 or more years. Some unskilled smallholders use 2-3 times as much bark per cm as skilled tappers, and the damage may reduce the total period to 15 years or less.

The commonest tapping system with budgrafts involves a 'half spiral' cut half way around the tree. This is executed on alternate days, provided there is no substantial rain which prevents tapping by diluting latex flows and washing them down the trunk. Rainguards greatly reduce the effects of rainfall. Tapping with selected seedlings is only done every third day, since more intensive systems usually lead to a permanent drying up of latex or tapping panel dryness.

It is advantageous to begin tapping early in the day, when the turgor pressure of the latex and its consequent rate of flow is higher. Thus it is usual for the tapper to carry a light source (often a torch like a miner's lamp) to help in seeing before dawn-breaks.

The usual procedure in tapping is for one person to first tap as much as can be managed; depending on conditions, this is normally a 'task' of 500-600 trees which takes 3-4 hours. Younger trees are simpler to tap. The same person then returns to collect the still-liquid latex from the cups, emptying it into a bigger container. There is then a residual flow of latex which coagulates on the cut and in the cup; this is secured at the next tapping as 'scrap' and 'cup lump'.

A major tapping advance was the introduction, in Malaysia, in the early 1970s, of the 'stimulant' ethephon or 2-chloroethyl phosphonic acid. This is applied at intervals to bark of first, or later renewal, either close to or in the tapping cut. It dissolves slowly in the presence of water, releasing the gas ethylene in the bark and delaying plugging with consequently greater latex flow. While ethephon increases yield in the short term, however, that effect is not maintained, and the stimulant is most usefully employed in 'substituting' for labour and getting similar yields with less frequent tapping. Subsequently, the Rubber Research Institute of Malaysia has applied ethylene directly to rubber trees to stimulate latex flow using systems known as RRIMFLOW and REACTORRIM.

Stimulation introduces flexibility into tapping as labour use in this labour-intensive activity may thereby be reduced. Thus, although most tapping is still done on alternate or third- daily systems, it is possible through skilful stimulant application combined with once-a-week excision to secure perhaps 80 per cent of the yield on alternate daily; this produces crops at lower cost. It is hoped that weekly tapping may eventually be achieved.

A further significant advance has been the introduction, again in Malaysia, and following three decades of research including that on stimulation, of the puncture system of tapping. This as currently applied involves making one puncture each week on a scraped area of bark treated with stimulant. Latex flows directly into a closed receptacle, which protects it from natural coagulants. It is then collected 2-3 days later while still in liquid form, after a prolonged period of flow. Puncture tapping again saves much labour compared to conventional methods, but is capital-intensive in equipment and chemicals and requires good management. It seems more promising than the previous avenue in this research of battery-driven mechanical tapping machines; these worked well, but were far too expensive for normal use.

Better conventional tapping systems have also been initiated, and includes the 'upward' tapping of virgin bark high up on the tree, using a knife attached to a long stick. This system, which may be accompanied by stimulation, is based on earlier Indonesian methods and enables yields to be maintained once lower virgin bark has been tapped away and poor renewal threatens a drop in output. It is thus especially pertinent to smallholding conditions.

Rainguards assist in increasing both tapper and tree productivity during periods of heavy rainfall.

Tapping cups are essential implements of the industry. Earthenware cups are widely used. They are cheap, but heavy. Glass cups are used in a few plantations. Plastic cups have been introduced to the industry. Glass cups are lighter and easy to clean but are more expensive and easily broken. Further, they are easily stolen from the field. Plastic cups are lighter and easy to transport. However, rubber tends to stick to the cups permanently making cleaning difficult. The cup is placed in a wire hanger attached to two pieces of wire and an extensible spring attached to the rubber trees. A spout is fixed to the rubber trees to enable the latex to flow from the tapping cut into the cup.

In areas where cuts are opened higher than the tapper can reach, one-step or two-step ladders are used to enable the tappers to tap comfort ably. Such ladders are specially made with a platform so that when it is placed against the rubber trees, the tapper can stand on the platform to tap the tree with a good degree of stability. The ladder should be light to make carrying it from tree to tree feasible.

Slaughter Tapping

For two or three years before replanting, tapping intensity may be considerably increased, with little consideration of bark consumption and no attention to wounding of the cambium, in order to extract as much latex as possible before the trees are felled. High and low cuts may be tapped on each tapping occasion, and as replanting becomes imminent more than one cut, each with its own collecting cup, may be opened at each level and tapping frequency increased. Yield stimulants may also be used.