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1 The resource

1.1 The coconut palm

Cocos nucifera L, the coconut palm, is an agricultural crop widely spread throughout the tropics. It has been cultivated by man for 4000 years. The main produce is copra, the dried kernel of the nut. Converted into oil, it becomes the base for a wide range of products, from cooking oil to soap and shoe polish.

Traditionally, coconut palms were found around hamlets in the tropics, in rather small stands to provide the villagers with basics such as:

-   vegetable fat (from copra)

-   roofing material (leaves)

-   ropes and strings (coir from the husks)

-   beverage (coconut juice)

-   alcoholic drink (from the inflorescence - tuba or toddy)

-   fuel (from the husks and nuts)

-   timber (from the stem).

At the end of the last century, coconut palms were planted in larger plantations, especially in the Pacific and on the Philippines, Ceylon, East Africa and the Caribbean, for large-scale copra production. Presently, more than 10 million ha are worldwide under coconut palms. According to stem height, tall and dwarf varieties are distinguished. 45 tall and 18 dwarf varieties are known. All older plantations are planted with tall varieties. Once these palms are 50 – 60 years old the copra yield declines rapidly. When the plantation-grown palms reached this age in the 1960s, replanting programmes were developed and the question of economic removal and disposal of old palms arose.

Removal was necessary in order to make space for new plantations. If the material was left to rot, the rhinoceros beetle (Oryctes rhinoceros) would start to breed in the decaying material and attack the young seedlings. Subsequently, various coconut-growing countries started to investigate the economic disposal or use of the stem. The research activities started were partly funded and backed by the governments of New Zealand and the Philippines, as well as by the FAO (Food and Agriculture Organization of the United Nations). In Zamboanga, Philip-pines, a research station was established and the utilization of the coconut palm stem as a timber resource was assessed and proven.

Table 1: Palm stem data (at 60 years of age)

Diameter max.(butt)30 cm
Diameter(top)15 cm
Heightabout20 m
Gross volume per stem0.9 m3
with ca. 100 palms/ha90 m3/ha

(Average values, dependent on age, site and variety.)

1.2 Properties of the palm stem

Although inappropriate, the term “coconut wood” has been established for the material of the coconut palm stem, and will therefore be used in this handbook as well. Unlike “conventional” trees, palms, like many other monocotyledons, have vascular fibre bundles (red-brown spots on a cross-section) scattered in a yellowish parenchymatic ground tissue. These bundles contain the water and nutrient transport system (xylem vessels and phloem) as well as thick-walled fibres giving the stem its strength, and paratracheal parenchymatic cells. The ground parenchyma has mainly a storage function and contains starch among other things. The anatomical features result in a rather non-homogenous distribution of physical properties both over cross-section and height, and thus in a very non-homogenous raw material. Principally, the density decreases towards the centre of the stem, and over stem height. Figure 1 gives a qualitative impression of the density distribution over the stem from five 80-year-old Philippine palms, Photo 1 shows its distribution (dark = high density) over a cross section.

Fig. 1: Schematic density distribution in mature coconut palm stem

Fig. 1

Source: Killmann, 1983

Photo 1: Cross section of coconut palm stem at breast height

Photo 1

The actual distribution may differ in each palm according to variety, site, and age. However, due to the absence of rays, differences of properties in tangential and radial direction, as they exist in conventional timbers, are negligible. Oven-dry density ranges from 0.85 g/cm3 at the lower periphery to 0.11 g/cm3 in the pith at the top end. Initial moisture content, on the other hand, increases in the same directions, with lowest values at the bottom periphery (50 %) and highest (up to 400 %) in the stem centre at the top (Killmann, 1983).

Figure 2 shows the potential uses of different stem parts.

Fig. 2: Use of the coconut palm stem

Fig. 2

Source: Jensen and Killmann, 1981

Depending on its oven-dry density, coconut wood can be segregated into three different groups (Figure 3):

High density timber (HD)

(> 0.6 g/cm3)

Timber from lower periphery of stem. Can be used for load-bearing structural purposes, framing, flooring, staircases, tool handles, furniture.

Medium density timber (MD)

(0.4 – 0.59 g/cm3)

Timber from upper stem periphery and lower middle section. Used for limited load-bearing structural purposes, furniture, wall-panelling, curios.

Low density timber (LD)

(< 0.4 g/cm3 )

Timber from core sections. Indoor use only, where no load is applied, e.g. wall-panelling.

Fig. 3: Cross section of coconut palm stem with density zones

Fig. 3

Source:Sulc, 1984, 1

Only when palms are over 60 years of age (that is, when the copra yield declines, and they are of less interest to the farmer), is enough “wood” built up and therefore of use to the sawmiller. This implies that there is no conflict between the use of the palm for its primary production (oil and fat) and the later stem use for timber. On the contrary: the use of the timber generates a windfall profit to the farmer.

It also implies that only stems of tall varieties can be used for timber, not those of dwarf varieties.

The percentage of the various density groups per stem depends on variety, site, age, sweep of palm, human impact (harvesting step, Figure 4), and the extent of fungus and insect damage.

Fig. 4: Harvesting steps in coconut palm stem

Fig. 4

With 80-year-old palms of the San Ramon Tall variety in Zamboanga a distribution of

High density40 – 50 %
Medium density20 – 30 %
Low density20 – 30 %

was observed.

All mechanical properties which define the use of a timber are closely related to its density (weight/volume at given moisture content). This inhomogeneity influences the methods of processing as well as the uses for the coconut palm stem. Sulc (1983, 3) has assessed the mechanical properties for the different density groups (Table 2) of 80-year-old coconut palm stems from Mindanao, Philippines.

Table 2: Mechanical properties of coconut wood, 12 % mc

Basic density(g/cm3)0.25 – 0.390.4 – 0.59>0.6
Modulus of elasticity3633711611414
Modulus of rupture3363104
Compression parallel to grain193857

Source: Sulc, 1983, 3

1.3 Defects in palm stems

Coconut palms are attacked by insects (rhinoceros beetle, palm weevil), mycoplasma-like organisms, and fungi.

Insects usually attack the growing point of the palm, reduce its vitality and finally lead to its death. Rhinoceros beetle attack can easily be detected visually. It results in palm fronds being cut in a diamond-shape.

Mycoplasma-like organisms attack the phloem and clog it. They result in the final death of palms. The diseases are known as Lethal Yellowing and Cadang-Cadang.

Fungi usually attack the palm stem, when its vitality is diminshed due to insects or mycoplasma-like organisms, or after physical damage, be it through hurricanes, or due to human impact. While the other two agents have no direct impact on the timber quality, fungal attack does. Most commonly fungi find entrance into the stem through harvesting steps cut into the outer, hard portion of the stem in some countries in order to facilitate harvesting of the nuts (Figure 4). Rainwater and dirt collects in the wounds, and fungi (and later also insects like termites) find their way into the stem and feed on the parenchymatic tissue. The attack appears as brown spots on a cross cut or as a string spot on a longitudinal cut, where the parenchyma is gone and only the bundles remain intact. This attack reduces both the properties as well as the appearance of the timber.

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