Studies on the early establishment of dipterocarp seedlings in a Malaysian logged hill forest
A 5.6 ha research plot in logged hill forest in central Peninsular Malaysia at Berkelah F. R., Pahang was set up to study the early establishment of dipterocarp species in the field. The site of the logged forest could be broadly grouped into three classes based on the degree of canopy opening and soil compaction: (1) categories B&A: open (25-55 % relative light intensity (RLI) as a high light level) and compacted or less compacted soil, respectively (2) category C: partial shade (8-9 % RLI as a medium) and less compacted soil, and (3) categories D&E: closed canopy (2-3 % RLI as a low light level) with high and low dipterocarp abundances, respectively. Planting trials in the field were conducted with two dipterocarp species, Hopea odorata and Dryobalanops oblongifolia. Application of Triple superphosphate (TSP), a fast-release fertiliser, (0.33 - 0.40 g per pot) in the nursery increased the P concentrations of the two dipterocarp species, Hopea odorata and Dryobalanops oblongifolia, and improved the performance of their seedlings when outplanted in the field plot. The growth of the species under high light level was greatly increased, but the concentration of foliar nutrients of the seedlings was correspondingly reduced. The order of performance in the field subplot categories was A&B>C>D&E and the order of foliar concentrations was D&E>C>A&B. The study of the effect of P fertiliser, light and types of soil on the growth was supplemented by nursery experiments using two dipterocarp species, Hopea odorata and Shorea acuminata. Soils from the plot and nursery soil as a control were used for potting the seedlings under two light levels, open (high) and shade (low). Adding P increased the infection of ectomycorrhizas (ECM) on the root tips and also increased the foliar P concentrations of Hopea odorata. Light appeared to reduce the infection of ECM. Experiments using sand cultures showed that P and Mg play an important role in influencing the growth of dipterocarp species. The growth of Hopea odorata significantly reduced when the concentrations of P was less than 2.07 mg 1.1 and when Mg was less than 3.63 mg 1-1 . The growth and the concentrations of foliar P and Mg of Hopea odorata were increased in response to an increase in external P and/or Mg supply. These results are interpreted as support for the hypothesis that P and maybe Mg availabilities would limit the establishment of the dipterocarp species. Based on these results, Hopea odorata is grouped as a light demanding species, Shorea acuminata is shade tolerant and Dryobalanops oblongifolia is intermediate species. Reforestation of the logged areas by means of enrichment planting with mixed species of different ecological requirements is one possible way of reclaiming the disturbed areas. Boosting P levels prior to planting may be an effective silvicultural approach in enrichment planting.