|Mora excelsa and
Other Common Names: Nato, Nato rojo (Colombia), Mora de Guayana (Venezuela), Morabukea, Mora (Guyana), Mora, Moraboekea (Surinam), Pracuuba (Brazil).
Distribution: M. excelsa: Widely distributed in the Guianas and less so in the Orinoco Delta of Venezuela; dominant on river levees and flood plains forming dense stands. M. gonggrijpii Restricted to Guyana and Surinam, a dominant species best adapted to hillsides on heavy clay soils.
The Tree: Usually 100 to 120 ft high and 2 to 3 ft in diameter with clear boles 60 ft and more above very large buttresses that may extend 15 ft up the trunk. Trees of M. excelsa 160 to 200 ft high and 4 ft in diameter are reported.
General characteristics: Heartwood yellowish red brown, reddish brown or dark red with paler streaks; sapwood 2 to 6 in. wide, distinct, yellowish to pale brown. Texture moderately fine to rather coarse, rather harsh to the feel; luster medium to high; grain is straight to commonly interlocked, very variable; astringent taste and a slightly sour odor.
Weight: Basic specific gravity (ovendry weight/green volume) 0.76 to 0.84; air- dry density 59 to 65 pcf.
Mechanical Properties: (First set of data based on the 2-in. standard, the second the 2-cm standard.)
Moisture content Bending strength Modulus of elasticity Maximum crushing strength
(%) (Psi) (1,000 psi) (Psi)
Green (75) 12,630 2,330 6,400
12% 22,100 2,960 11,840
Green (42) 13,600 2,150 7,150
12% 24,400 2,790 12,700
Janka side hardness 1,450 lb for green material and 2,300 lb at 12% moisture content. Forest Products Laboratory toughness average for green and dry material is 228 in.-lb. (5/8-in. specimen).
Drying and Shrinkage: Drying reports are variable, generally rated moderately difficult to season; a slow rate of drying and careful stacking are suggested to keep warp and other degrade to a minimum. Boxed heart pieces tend to split. Kiln schedule T2-C2 is suggested for 4/4 stock and T2-C1 for 8/4. Shrinkage from green ovendry radial 6.9%; tangential 9.8%; volumetric 18.8%.
Working Properties: The wood is moderately difficult to work but yields smooth surfaces in sawing, planing, turning, or boring unless interlocked grain is present then there may be considerable "pick up" and chipped grain.
Durability: Results are variable; material from Surinam and Guyana is rated durable to very durable in resistance to brown-rot and white-rot fungi. Service life of 15 to 20 years in ground contact is reported. M. gonggrijpii is rated very resistant to dry-wood termites; M. excelsa considerably less so, not resistant to marine borers.
Preservation: Sapwood responds readily to preservative treatments; heartwood resist to impregnation, penetration is very shallow, and absorptions are low.
Uses: Industrial flooring, railroad crossties, shipbuilding, heavy construction, high quality charcoal wood.
Additional Reading: (34), (42), (46), (75)
34. Japing, H. W. 1957. Tests of the most important mechanical and physical properties of 41 Surinam wood species. Meded. Inst. Trop. Amst. No. 122 (Afd. trop. Prod. No. 46).
42. Lavers, G. M. 1969. The strength properties of timbers. For. Prod. Res. Bull. No. 50. H. M. Stationery Office. London.
46. Longwood, F. R. 1962. Present and potential commercial timbers of the Caribbean. Agriculture Handbook No. 207. U.S. Department of Agriculture.
75. Wangaard, F. F., W. L. Stern, and S. L. Goodrich. 1955. Properties and uses tropical woods, V. Tropical Woods No. 103:1-139.
From: Chudnoff, Martin. 1984. Tropical Timbers of the World. USDA Forest Service. Ag. Handbook No. 607.