Effects of potting mixtures, potting sizes and ground aspects on growth of seven indigenous tree species in Forest Management Unit 11, Sabah

The main objectives of this study were to investigate the effects of potting mixtures, potting sizes and ground aspects on growth of seven indigenous tree species in a degraded forest located in FMU 11. The first two experiments were conducted at the tree nursery while the effects of ground aspects was done in the field. Seven indigenous tree species were chosen for this study; Parashorea malaanonan, Parashorea tomentella, Shorea symingtonii, Diospyros discocalyx, Shorea faguetoides, Aquilaria malaccensis and Hopea ferruginea. One of the reasons for choosing these species was to widen the species choices for reforestation purpose. The potting mixture experiment consisted of two treatments - T1 (3 parts forest topsoil, 2 parts rice husk and 1 part sand) and T2 (3 parts forest topsoil, 2 parts sawdust and 1 part sand), and Control (3 parts forest topsoil, 2 parts peat and 1 part sand). Two potting sizes were investigated in the potting size experiment – P1 (15.2 x 22.9 cm) and P2 (17.8 x 30.5 cm) and Control (7.6 x 22.9 cm). Both experiments consisted 30 seedlings per species per treatment. In the field trial, the planting site was divided into five aspects - north, south, east, west and zero. Seedlings were planted in an east-west direction in rows. Height (cm) and diameter (mm) increments in the three experiments were measured and the relative growth rates (RGR) were calculated for three months. Potting mixture T1 and potting size P2 resulted in best seedling growth. Potting mixture T1 and potting size P2 achieved highest growth rates at 0.1376±0.0801 cm (SD) and at 0.1235±0.0766 cm. In the field trial, growth rates of seedlings were found highest in east-facing at 0.1390±0.0606 cm. All three null hypotheses were rejected. Relative growth rates in potting mixture, potting size and ground aspects were significantly different [Potting mixture: ANOVA, RGRH: N=210, F=4.807, p=0.008; RGRD: ANOVA, N=210, F=20.256, p<0.001); potting size: (ANOVA, RGRH: N=210, F=8.000, p<0.001; ANOVA, RGRD: N=210, F=5.041, p=0.007); ground aspects: (ANOVA, RGRH: N=140, F=34.812, p<0.001; RGRD: N=140, F=16.817, p<0.001)]. In potting mixtures, there were interactions in terms of height and diameter between two factors [UNIANOVA, RGRH: F=2.388, R2=0.745, p=0.005; RGRD: F=3.088, R2=0.804, p<0.001]. There was no interaction in potting size experiment (UNIANOVA, F=1.500, R2=0.728, p=0.119). For ground aspects, there was interaction between the factors (UNIANOVA, F=27.795, R2=0.904, p