F. D. KAMALA ET AL.
OPEN ACCESS
The grade yield for MOE in mature wood was highest for
Grade Ten at followed by Grade Seven. Grade II was lower and
there was no grade yield for Grade Five and XXX with both
grades yielding according to MOE in mature wood (Figure 9).
The grade yield according to MOE and MOR was different
for juvenile wood and mature wood. Some grades had high
yields in juvenile wood but low yields in mature wood. In other
cases, grades with high yield in juvenile wood were non-exis-
tent in mature wood. The results show that mature wood
yielded more grades with high values of MOE and MOR. This
clearly shows that mature wood for Pinus patula is superior in
strength and grade than juvenile wood. The implication for this
is that mature wood and juvenile wood should be used for dif-
ferent purposes to avoid underutilization. Uniform use of juve-
nile wood and mature wood for structural purposes would be
potentially dangerous because juvenile wood has inferior me-
chanical performance. To improve lumber strength, one can
process logs of older trees and minimize the use of the interior
portion of the log. Correct drying of the boards will increase the
most important lumber strength traits of modulus of rupture and
modulus of elasticity. Export of dried lumber of P. patula oc-
curs and should increase if uniformity can be maintained.
The common steps in establishing grades for lumber are:
testing of small clear specimens according to guidelines, estab-
lishing strength values and allowable properties, establishing
visual grading rules and lastly verifying grades using in-grade
testing. The contribution of this research towards creating an
accept able gr ading sy ste m is that it has clarified the variation of
mechanical propertie s. More mechanical propertie s data, through
testing of small clear wood specimens, from other areas in Ma-
lawi need to be accumulated.
This research has established first steps in assigning allowa-
ble mechanical properties for Pinus patula grown in Malawi.
After accumulating more small clear wood specimen data, test-
ing using the “in grade” approach, in which large representa-
tives samples of full size lumber can be tested to destruction is
recommended to compare the results. This will help in the as-
signment of standard grades that will ensure the efficient utili-
zation of Pinus patula structural lumber in Malawi.
Conclusion
At about 12% moisture content, the tested five Pinus patula
families have average MOR and MOE of 105.17 MPa and
10.93 GPa, respectively. There were significant correlations at
1% level between air-dry density and MOE (R = 0.85) and
between air-dry density and MOR (R = 0.83). There was also a
significant correlation between MOE and MOR at 1% level (R
= 0.90). There was no significant variation in MOE and MOR
among the five families. Stem level variation in MOE and
MOR is not significant. Mature wood of Pinus patula has more
superior mechanical performance than juvenile wood. The
growth rate did not affect the mechanical properties of the spe-
cies. This study suggests that it is potential to simultaneously
improve tree growth, density, and some mechanical properties
of the wood of this species. The results of this study are a
foundation that will provide a technical basis for the machine
grading of Pinus patula structural lumber in Malawi.
REFERENCES
Anon (1947). Annual report. Pretoria: Department of Forestry.
Anon (1980). Estudio de las propiedades fisicas y mecanicas de las
maderas de cipres (Cupressus lusitanica Mill.) y pino patula (Pinus
patula) procedente de la cuenca de Piedras Blancas. Medellin: La-
boratorio de Productos Forestales, Universidad Nacional.
Bier, H. (1983). The strength properties of small clear specimens of
New Zealand grown timber. Bulletin No. 41, Rotorua: Forest Re-
search Institute.
Craib, I. J. (1939). Thinning, pruning and management studies on the
main exotic conifers g ro wn in So u th Africa. S cien ce Bulletin No. 196,
Pretoria: Department of Agriculture and Forestry.
Deresse, T. (1998). The influence of age and growth rate on selected
properties of Maine-grown red pine. Ph.D. Thesis, Oro no, ME: Uni-
versity of Maine.
Forestry and Forest Products Research Institute (FFPRI) (1975). The
properties of tropical woods, 21: Evaluation of the wood properties
and wood processing s uitabilities of ti mbers fro m Southeast As ia and
the Pacific regions. Bulletin of the Government Forest Experimental
Station, 277, 87-130.
Han, Y. (1995). The site and age effects on the selected physical and
mechanical properties of red maple in Maine. Ph.D. Thesis, Orono,
ME: University of Maine.
Kamala, F.D., Sakagami, H., Oda, K., & Matsumura, J. (2013). Wood
density and growth ring structure of Pinus patula planted in malawi,
Africa. IAWA Journal, 34, 61-70.
http://dx.doi.org/10.1163/22941932-00000006
Ordonez, V., Barcenas, G., & Quiroz, A. (1989). Caracteristicas fisico-
mecanicas de lamadera de diez esp ecies de San Pab lo Macuilitanguis ,
Oaxaca. Madera y Su Uso, 21, 30p.
Otto, K. P., & Van Vuren, W. F. J. (1976). The mechanical properties
of timber with particular refer ence to those grown in the Repub lic of
South Africa. Bulletin, Pretoria: Department of Forestry.
Paterson, D. N., & Campbell, P. A. (1970). Strength variations and
correlations in East African exotic pines and their effect on engi-
neering properties. East African Agricultural and Forestry Journal,
35, 7-19.
Perem, E. (1958). Effect of compression wood on mechanical proper-
ties of white spruce and red pine. Forest Products Journal, 8, 235-
240.
SANS 10163 (2003). South African national standard. The structural
use of timber—Part 1: Limit-states design. Edition 2.3.
https://www.sabs.co.za/
Shepard, R. K., & Shottafer, J. E. (1992). Specific gravity and mechan-
ical property—Age relationships in red pine. Forest Products Jour-
nal, 42, 60-66.
Shmulsky, R. , & Jones, P. D. (2011). Forest products and wood science,
an introduction (6th ed.). West Sussex: Wiley Blackwell.
http://dx.doi.org/10.1002/9780470960035
Shottafer, J. E., Kutscha, N. P., & Hale, R. A. (1972). Properties of
plantation grown red pine related to its utilization. Technical Bulle-
tin, Orono, ME: Life Sciences and Agriculture Experiment Station,
University of Maine at Orono.
Stanger, T. K. (200 3). Variation and genetic control of wood properties
in the juvenile core of Pinus patula grown in South Africa. Ph.D.
Thesis, Raleigh, NC: Department of forestry, Graduate Faculty of
North Carolina State University.
Wright, J. A. (1994). Utilization of Pinus patula: An annotated biblio-
graphy. O.F.I. Occasional Papers No. 45, Oxford: Oxford Forestry
Institute, Department of Plant Sciences, University of Oxford.
Wolcott, M. P. (1985). Age and growth rate relationships of selected
mechanical properties in red spruce. M.S. Thesis, Orono, ME: Uni-
versity of Maine.
Zhang, S. Y. (1995). Effect of growth rate on wood specific gravity and
selected mechanical properties in individual species from distinct
wood categories. Wood Science and Technology, 29, 451-465.
http://dx.doi.org/10.1007/BF00194204
Zhang, S. Y. (1997). Wood specific gravity-mechanical property rela-
tionship at species level. Wood Science and Technology, 31, 181-191.
http://dx.doi.org/10.1007/BF00705884