Abstract:
Hevea brasiliensis, a major source of natural rubber is an important source of timber in Nigeria as senescence occurs. However, duration of latex collection is known to affect Hevea brasiliensis wood formation and consequently, the wood properties. Knowledge on wood properties of tapped rubber tree in Nigeria which would enhance its sustainable exploitation as timber is limited. Therefore, the physical, anatomical, mechanical and chemical properties of tapped Hevea brasiliensis were investigated.
A rubber plantationwith information on years of tapping (YoT)was purposively selected from Agbarha, South-South, Nigeria. Five trees fromeach of 5, 10, 15 and 20 YoT were harvested. One billet each (60 cm long) was taken from the base and top of the bole of each tree and partitioned into innerwood, middlewood and outerwood. These were further processed into standard dimensions for determination of wood properties. Using a 4 x 2 x 3 factorial arrangement in a completely randomised design, experiments were carried out to determine physical [Specific Gravity (SG),Volumetric Shrinkage (VS, %)]; anatomical [Fibre Length (mm),Cell Wall Thickness (CWT,µm)]; mechanical [Maximum Compressive Strength parallel to grain (MCS//,Nmm-2), Modulus of Elasticity (MoE,Nmm-2), Modulus of Rupture (MoR,Nmm-2)] and chemical [Lignin Content (%), Ash Content (AC, %)] properties using standard procedures. Data obtained were analysed using descriptive statistics and ANOVA at α0.05.
Physical and mechanical properties were not significantly different. Mean SG was 0.6±0.01 across tapping age while VS was highest (11.4±0.7,YoT10) and least (9.5±0.5,YoT15). Fibre length increased from 1.4±0.02 (YoT5) to 1.5±0.02 (YoT20) while, CWT increased from 4.3±0.1(YoT5) to 4.7±0.1 (YoT20). The MCS// ranged from 69.4±2.8 (YoT5) to 77.9±1.7 (YoT15) while,MoE varied from 12459.7±789.8 (YoT10) to 14155.3±657.9 (YoT20).The MoR was highest (438.8±2.9,YoT10) and least(422.2±2.9,YoT5).Lignin Content varied from 21.4 (YoT10) to 23.8 (YoT15)while, AC ranged from0.28 (YoT5) to 0.36 (YoT10). The SG was higher at the top (0.6±0.04) than the base (0.5±0.05), but VS decreased from base (10.9±0.4) to top (9.5±0.3). Fibre Length and CWT at the base and top were 1.43±0.01;4.23±0.1 and 1.50±0.02;4.78±0.1, respectively. The MCS// increased from the base (67.4±1.0) to the top (82.4±0.9). The MoE and MoR increased from the base (10897±345.8;421.2±1.8) to the top (15540±419.8; 438.6±2.1). Lignin content varied from the base (22.3±0.5) to the top (22.8±0.5) while, AC was 0.3±0.01 at the base and top. The SG was 0.6±0.01 from innerwood to outerwood while, VS decreased from 10.3±0.6 (innerwood) to 10.2±0.3 (outerwood). Fibre length did not differ (1.5±0.01) for innerwood, middlewood and outerwood. The CWT increased from innerwood (4.4±0.1) to outerwood (4.6±0.1). The MCS// and MoE were highest at innerwood (75.3±1.7; 13738.0±676.4) and least at outerwood (74.2±1.6; 12841.6±514.9) while, MoR varied from innerwood (428.9±2.9) to outerwood (430.6±2.8). Lignin content increased from innerwood (20.4±0.4) to outerwood (24.8±0.5) while, AC ranged from 0.3±0.01 in the innerwood to 0.4±0.01 in the middlewood.
Tapping duration had no negative impact on physical, anatomical, mechanical and chemical properties of tappedHevea brasiliensis. Senescent Hevea brasiliensis may be used as timber.
