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Woody pear

Image showing the tree Xylomelum occidentale.
Image showing the wood of Xylomelum occidentale.
Xylomelum occidentale

Woody pear is generally a small tree growing to 5 to 8 m tall, with a short bole that can occasionally reach 30 cm in diameter. Individuals in open spaces can develop a broad canopy of spreading limbs. Trees often have an untidy form, bark is fibrous and flaky. The elliptical or oblong foliage is bright green and has serrate margins. The large woody fruit is pear-shape, hence the common name. Woody pear mostly occurs on sandy soils between the Darling Scarp and the ocean coast. Other populations are found on sandy gravels in the Jarrah / Marri forest east of the scarp's western edge. Although it has a wide distribution, it is a minor species in any of its habitats, large populations are rarely found.

Wood descriptionThis description can include heartwood and sapwood colour, grain, figure.

Heartwood is a dark reddish colour with a decorative figure. Sapwood is a contrasting pale cream colour. Timber treated with wax can produce a silk finish.

Wood density

Green density is the density of wood in the living tree, defined as green mass divided by green volume, and useful for estimating transport costs. It varies with season and growing conditions.

Air-dry density is the average mass divided by volume at 12 per cent moisture content (this is the average environmental condition in the coastal capital cities around Australia).

Basic density is oven-dry mass divided by green volume. This measure has the advantage that moisture content variations in the tree during the year are avoided.

Air-dry density is about 620 kg/m3.

Drying and shrinkageAs wood dries, it shrinks more in the tangential direction (i.e. parallel to the growth rings) than it does in the radial direction (i.e. at right angles to the growth rings). The figures given are shrinkage from green to 12 per cent moisture content, before steam reconditioning treatment, and with some species after stream reconditioning. Reconditioning is essential for recovering collapse which may have occurred during the drying process, and is essential for species such as the ash-type eucalypts of eastern Australia.

Tangential and radial shrinkage are estiamted as about... per cent respectively.

WorkabilityWith south-west and plantation-grown trees, comments are made on the comparative ease or difficulty of turning, nailing and bending, on susceptibility to splitting and other working properties. With semi-arid, arid and desert species, a more complex survey was made and reported in Siemon and Kealley (1999). The properties assessed were turning, machinability, boring, screwholding, stability, sanding, gluing and finishing. A semi-quantitative score was used: very poor = 1, poor = 2, average = 3, good = 4, and excellent = 5. This book uses the descriptive terms rather than numbers.

Very easy to dress, however, care must be taken when sanding as timber tends to develop high and low points similar to cedar. Quarter or back sawing will both provide an attractive grain pattern. Gluing, turning and finishing are rated as good. Drilling is rated as fair, a heavy hand is not required. Carving is rated as fair.

Strength group and properties

Minimum values (MPa) for strength groups for green and seasoned timber come from Australian Standard AS2878-1986 'Timber - Classification of strength groups'. In grading structural timber, each species is allocated a ranking for green timber of S1 (strongest) to S7, and for seasoned timber SD1 (strongest) to SD8.

MOR is modulus of rupture or bending strength, MOE is modulus of elasticity or 'stiffness', and MCS is maximum crushing strength or compression strength. Hardness refers to the Janka hardness test and is a measure of resistance to indentation.

Minimum values (Mpa) for green timber

Strength Property S1 S2 S3 S4 S5 S6 S7
MOR 103 86 73 62 52 43 36
MOE 16300 14200 12400 10700 9100 7900 6900
MCS 52 43 36 31 26 22 18

Minimum values (Mpa) for green timber

Strength Property SD1 SD2 SD3 SD4 SD5 SD6 SD7 SD8
MOR 150 130 110 94 78 65 55 45
MOE 21500 18500 16000 14000 12500 10500 9100 7900
MCS 80 70 61 54 47 41 36 30

Where test data were available, they are shown in bold print. Most values are from Bootle (1983), Wood in Australia. Types, properties and uses. (McGraw-Hill), or Julius (1906), 'Western Australian timber tests 1906: The physical characteristics of the woods of Western Australia'.

Where no strength data were available, air-dry density was used in accordance with the Australian Standard AS2878-1986 Timber - Classification of strength groups to predict the strength group. Consequently, the strength values quoted are from the above two tables.

Green and dry strength groups are (S6) and (SD6). The brackets indicate conservative provisional ratings based on the air-dry density. The more important strength properties based on strength group are given in the table below.

Property Units Green Dry
Modulus of Rupture MPa 43 65
Modulus of Elasticity MPa 7900 10500
Max Crushing Strength MPa 22 41
Hardness KN - -
AvailabilityTimber from many species is available only in limited quantities, from near the areas where the trees grow naturally (or in plantations). There are other species such as red tingle and yellow tingle whose timber is rarely commercially available because the areas of occurrence are predominantly in conservation areas. Other species such as Goldfields timbers are only available in limited quantities because of their scattered occurrence and the fact that the industry is in the early stages of development.

Limited availability from private property, because the species is not harvested from state forests.

UsesVarious past and potential uses are given as a general guide, but the list is obviously not conclusive. In particular, there is increasing interest in specialty timbers, and the semi-arid, arid and desert area species have considerable potential for this use.

Timber is recognised as a specialty timber by wood craftsmen. Small pieces of furniture and ornamental trinkets are the major product from this timber, but it is also used for decorative turnery.