A comparison of the soil water, nutrient status, and litterfall characteristics of tropical heath and mixed-dipterocarp forest sites in Brunei

Two of the main hypotheses to explain the distribution and special characte ristics of tropical heath forest are nutrient and water limitation. A study was undertaken to investigate both factors on two sires under tropical hea th forest (Badas Forest Reserve) and mixed-dipterocarp forest (Andulau Fore st Reserve) in Brunei. Soil water potentials wore monitored at depths of 20 , 50, and 90 cm over wet and dry periods for five months at each site. The results showed the mixed-dipterocarp forest sire to be drier at 50 cm depth compared to the tropical heath forest sire. There was no significant diffe rence in water potentials between sites at 20 or 90 cm. Nutrient concentrat ions in the soil solution were monitored at the same depths over a seven-mo nth period at the same sites. A 12-month litterfall study was also undertak en to monitor nutrient returns from the canopy at each site, The results of both studies suggest that the tropical heath forest sire is poorer in nitr ogen, bur richer in calcium, than the mixed-dipterocarp forest site. The re sults for phosphorus are less clear, but do not suggest that its limitation is a significant factor at the tropical heath forest site compared to the mixed-dipterocarp forest site. Phosphorus and magnesium concentrations in t he soil solution showed a strong positive correlation with sliding 30-day r ainfall totals at both sites.