Growth performance of Acacia species and Eurycoma longifolia Jack mixed planting on BRIS soils

A study was undertaken to assess i) the growth performance of four years-old Acacia mangium, A. auriculiformis and Acacia hybrid trees on two different BRIS (Beach Ridges Interspersed with Swales) soil series, ii) the growth performance of three years old Eurycoma longifolia Jack trees mixed planting with Acacia spp on BRIS soil and iii) to study the soil nutrient, light penetration (gaps) and litterfall of the mixed Acacia spp. and Eurycoma longifolia stands planted on BRIS soil. The growth performances of A. mangium, A. auriculiformis, Acacia hybrid and Eurycoma longifolia trees mixed planting on two different BRIS soil series were considered satisfactory. Generally, the average height of four-year-old A. mangium trees planted on Rhu Tapai soil series was measured 13.60 m taller than Acacia hybrid and A. auriculiformis, 12.84 m and 12.44 m respectively. On Rhu Dua soil series, the average height of A. mangium trees was also the tallest (12.83 m), followed by A. auriculiformis (11.69 m) and Acacia hybrid (11.65 m). In term of diameter growth, the average diameter of A. mangium trees on Rhu Tapai soil series was 11.10 cm, bigger than the average diameters of Acacia hybrid (10.82 cm) and A. auriculiformis (10.31 cm). Average heights of Eurycoma longifolia trees planted on Rhu Tapai and Rhu Dua soil series were 0.78 m and 0.85 m tall respectively. While the averages root collar diameters of trees were 14.76 mm and 14.80 mm. The average root lengths and root dry weights of Eurycoma longifolia trees planted on Rhu Tapai and Rhu Dua soil series were 0.30 m and 0.33 m and 11.48 gm and 11.88 gm respectively. The soil pH values for both study sites were ranged from 4.7 to 5.5. The total N, P and Ca values in Rhu Tapai plots were higher than Rhu Dua. The average values of total N from top soil and sub soil samples taken from Rhu Tapai soil series were 0.7% and 0.5% respectively and 0.4% and 0.2% for Rhu Dua soils series. The average values of total P in Rhu Tapai soil series were recorded higher, ranged from 8.6 ppm (top soil) to 11.7 ppm (subsoil) than Rhu Dua soil series ranged from 1.4 ppm (top soil) to 2.3 ppm (sub soil). The average litterfall productions in Rhu Tapai were relatively higher than Rhu Dua, measuring 23.9 metric tons / ha / year and 20.5 metric tons / ha/ year respectively. However, among the study plots in Rhu Tapai showed variation in the average annual litterfall production, with the minimum value of 18.2 metric tons and the maximum value of 30.5 metric tons / ha / year. Whereas, for Rhu Dua study plots there were a small variation in the average litterfall collection. Nevertheless, the production of litterfall of Acacia species and Eurycoma longifolia in both study sites were much higher compared than reports on Acacia plantations in India, Malaysia and Congo by O’Connell and Sankaran (1997) and litterfall production by Acacia mangium trees planted on infertile soil in Malaysia (Wan Rashidah et al., 1999). The canopy of Rhu Tapai stand was more open than Rhu Dua with average canopy openness of 4.43% and 3.10% respectively. In general, the canopy openness in both study sites is much bigger than tropical natural forest which is less than 1.0%. However, for rubber and oil palm plantations the averages canopy openness are much bigger, 15% at the tree age of six to seven years (Wilson and Ludlow, 1990). The results obtained from this study are very important for future reforestation programme on BRIS soils. The ability of A. mangium, A. auriculiformis, Acacia hybrid and Eurycoma longifolia to grow on BRIS soils will definitely help local farmers to involve in herbal industry and to produce general utility timbers and fuel wood for their own consumption.

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