MATERIALS AND METHODS

Study area: The study was conducted in three locations in the former Sokoto state, now Sokoto, Kebbi and Zamfara states. The three locations/study sites are Gidan Kaura town (Gada Local Government area, Sokoto state) Kalgo town, (Birnin Kebbi Local Government area, Kebbi state) and Kaura Namoda town (Kaura Namoda Local Government area, Zamfara state). They are located in the north western part of Nigeria between latitude 10° 8 and 13° 55’ N and longitudes 3° 30’ and 7° 15’ E with a total land area of approximately 94,588 km² (Ojanuga, 2006).

Procedure for tree sampling: In each of the sites selected for the study, matured E. camaldulensis trees were chosen by purposive selection using a diameter of at least 20 cm to be considered as small diameter log as a basis for selection in the three study areas for the research. Adekunle (2007) only used tree with diameter at breast height of = 20 cm for timber volume estimation. A total of 5 tree samples were selected from each of the three research locations as in Mackes et al. (2005).

For density determination, specimens were cut to standard sizes in accordance with STAS 6087:72 as cited by Pescarus and Cismaru (1979).

The bending strength test was carried out after almost four months of keeping the samples in the open laboratory space and confirming the moisture content at 12%. The test was done using the procedure prescribed by ASTM (2006).

Statistical analysis: The data collected for all test parameters were analyzed using analysis of variance (ANOVA) at p<0.05 probability level and Duncan’s New Multiple range Test (DNMRT) was used as a follow up analysis to separate the means.

RESULTS

Wood density: Values of density for all the 225 specimens were computed based on masses as shown in Table 1. At 12% moisture content, results showed that density variation ranged from 920.30 kg m^-3 to 1084.25 kg m^-3 with a mean value of 1003.58 kg m^-3 in Sokoto. In Kebbi, the density variation was from 920.89 kg m^-3 to 1082.07 kg m^-3 with a mean value of 1008.77 kg m^-3 while in Zamfara state, the density variation showed lower values ranging from 857.48 kg m^-3 to 964.74 kg m^-3, with a mean value of 920.39 kg m^-3. The overall mean density value for E. camaldulensis across the three study sites was 977.58 kg m^-3. Table 1 shows the density values of E. camaldulensis.

Table 1:	Density (kg m-3) of E. camaldulensis (Denhn) from Sokoto, Kebbi and Zamfara states of north western Nigeria
*1: Bottom, *2: Middle, *3: Top, Values in column with same latter are not significantly different

Table 2:	Static bending strength parallel to grain (N mm-3)
*1: Bottom, *2: Middle, *3: Top, Values in column with same latter are not significantly different

Table 3:	Modulus of elasticity (MOE) in bending (N mm-2)
*1: Bottom, *2: Middle, *3: Top, , Values in column with same latter are not significantly different

Static bending: Static bending of E. camaldulensis was 133.33 N mm^-2 (Table 2). In Sokoto, values for static bending ranged from 88.86 to 153.84 N mm^-2 with a mean of 125.29 N mm^-2. Static bending for Kebbi and Zamfara states ranged from 98.42 to 157.66 N mm^-2 and 105.11 2 to 154.79 N mm^-2 with mean values of 133.96 and 137.27 N mm^-2, respectively. From the ANOVA, it is depicted that the locations show significant difference (p<0.05) while all other parameters were highly significant (p<0.01) in static bending stress.

Modulus of elasticity (MOE): In Sokoto, the modulus of elasticity in bending ranged from 9048.49 to 18428.92 N mm^-2, with a mean of 14668.13 N mm^-2 (Table 3). Values for Kebbi and Zamfara states ranged from 10568.52 to 18912.96 N mm^-2 and 11203.37 to 19388.71 N mm^-2, respectively. Mean values for the two states were 15276.99 and 16014.65 N mm^-2 respectively. The overall mean value across the northwest ecological zone was 15319.89 N mm^-2 (Table 3).

DISCUSSION

The density values of E. camaldulensis as revealed in this study favorably compares with timber specification as stipulated in the standards of NCP 2 (1973). With the high density of E. camaldulensis the wood would be especially attractive for general timber utilization in the north zone in particular and in the country in general. By these values, the wood is at a greater advantage over the light density species. Similarly, the wood stands another advantage of repelling insects and fungi attack for which light wood species are more susceptible (Raven et al., 1997). The value tends towards the high density category in which case the use may be restricted to structural construction. When compared with the available wood species. E. camaldulensis will thus, be a very promising timber species. Some of these local timber species and their densities include Triplochiton scleroxylon (400 kg m^-3), Pycanthus angolensis (480 kg m^-3), Khaya ivorensis (485 kg m^-3), Gosweilerodendron balsamiferum (497 kg m^-3), Terminalia ivorensis (550 kg m^-3), Mitragyna ciliata (560 kg m^-3) and Terminalia superba (580 kg m^-3) (Hall, 1998; Kwame, 2001). Others are Mansonia altissima (615 kg m^-3), Entandrophragma cylindricum (620 kg m^-3) and Nauclea diderrichii (660 kg m^-3) (Scheffer and Morrell, 1998; Ogunsanwo and Onilude, 2002; Fuwape and Fabiyi, 2003). However, the density of E. camaldulensis was lower than that of Gliricidia sepium whic was 1025 kg m^-3 (Oluwafemi and Adegbenga, 2007). The fact that the density of E. camaldulensis was higher than most commercial timber indicates that it is a heavy wood but not as heavy as G. sepium. Poku et al. (2001) stated that wood density is a good indicator for selection of wood for use. It therefore implies that E. camaldulensis could be used where most of the commercially available Nigerian timbers are being utilized like in building and construction applications. The Analysis of Variance (ANOVA) shows that there was highly significant difference between locations and trees as well as between location/tree and tree region interaction. However, no significant difference was observed between regions. The significant difference in the location may be due to the site quality.

Results for static bending showed that E. camaldulensis with mean value of 133.33 N mm^-2 has a very high static bending stress. This places the wood at an advantage as it compares favorably with some commercially important wood species in Nigeria. For instance, Abura (Mitragyna ciliata) = 79 N mm^-2, Afara (Terminalia superba) = 106 N mm^-2, Afromosia (Pericopsis elata) = 128 N mm^-2, Ebony (Diospyros\crassiflora) = 190 N mm^-2, Ekki (Lophira alata) = 207 N mm^-2, Iroko (Chlorophora exelsa) = 130 N mm^-2, Mahogany (Khaya ivorensis) = 110 N mm^-2, Obeche (Triplochiton scleroxylon, from natural forest) = 77 N mm^-2 and Teak (Tectona grandis) = 107 N mm^-2) and Nauclea diderrichii (209 N mm^-2) (Fuwape and Fabiyi, 2003). Static bending strength of E. camaldulensis is higher than those of G. sepium = 120 N mm^-2 and plantation grown T. scleroxylon = 62 N mm^-2 (Ogunsanwo and Onilude, 2002; Oluwafemi and Adegbenga, 2007). However, it has similar bending strength with that of teak = 136 N mm^-2 (from a slow growing provenance in India) reported by Bhat and Priya (2004). The significant difference in the location may be due to the site quality.

From the findings, it is clear that E. camaldulensis with a modulus of elasticity value of 15319.39 N mm^-2 falls within the range of other eucalyptus species as well as with some timber species commonly used for structural purposes in Nigeria. Some of the eucalyptus species and their MOE values include E. paniculata (12100 N mm^-2), E. pilularis (16800 N mm^-2), E. diversicolor (17900 N mm^-2), E. cloeziana (19521 N mm^-2), E. microcorys (20500 N mm^-2), E. grandis and E. terreticornis (20869 N mm^-2) and E. paniculata (22700 N mm^-2).

E. camaldulensis satisfies the requirements of NCP 2 (1973) in respect of the standard’s stipulation for timbers for structural applications in the country. Values of modulus of elasticity of some of the commonly used timbers in Nigeria include Ceiba pentandra (4280 N mm^-2), Triplochiton scleroxylon (5500 N mm^-2), Antiaris africana (5800 N mm^-2), Alstonia boonei (6700 N mm^-2), Gossweiloredendron balsamiferum (7600 N mm^-2), Daniellia klainei (8100 N mm^-2), Pycanthus angolensis (8445 N mm^-2), Khaya ivorensis (10000 N mm^-2), Eribroma oblonga (10070 N mm^-2), Chlorophora exelsa (11000 N mm^-2) and Mansonia altissima (11175 N mm^-2) ALS (2000). The modulus of elasticity of E. camaldulensis is higher than 6239 N mm^-2 obtained for plantation grown T. scleroxylon (Ogunsanwo and Onilude, 2002). Since most Nigerian timbers are fast declining in the timber market due to over-exploitation to meet exportation demand, there is the need to find good source of substitute for them (Ogunsanwo, 2000; Oluwafemi and Adegbenga, 2007). Therefore, with the density and mechanical properties of E. camaldulensis obtained in this study, its wood could be used various applications like building, construction, flooring, cabinetry, furniture and other uses where high mechanical properties are required. Results show that there is no correlation between modulus of elasticity and density as increase in MOE does not translate to increase in density and this is different to findings by Desch (1992). The ANOVA revealed highly significant difference (p<0.05) among trees, locations regions as well as all levels of interactions. The follow up analysis further confirms this by showing significant differences between the means of Sokoto, Kebbi and Zamfara states as well as the regions. The significant difference in the location may be due to the site quality.

CONCLUSION

The large density values recorded places the wood at an elevated position of suitability in this respect enabling the wood to compete favorably with some commercially available timber species in Nigeria. The bending strength and modulus of elasticity values compare favorably and even superior to some of the species presently used in Nigeria. It can be concluded from the present study that E. camaldulensis is a promising species for timber industry in the north western part of Nigeria and in the nation in general.