Contrasting assemblages of <i>Pinanga</i> palms in lowland tropical forests of Brunei Darussalam, Borneo

Abstract Pinanga represents one of the largest genera of palms and has been extensively collected by botanists, though ecological studies on Pinanga remain limited. We evaluated species diversity and assemblages of Pinanga palms in two contrasting forest types, heath forest (HF) and mixed Dipterocarp forest (MDF) in Brunei Darussalam located in the Borneo biodiversity hotspot. At three HF and three MDF sites, all Pinanga palms greater than 5 cm height within a 3-ha sampling area per site were recorded and taxonomically identified. Selected soil properties (total N and P concentrations, pH, gravimetric water content [GWC] and OM) and environmental variables (litter depth [LD], humidity, canopy openness [CO] and elevation) were determined for each study site. Our survey recorded a total of ten Pinanga species, comprising 981 individuals. Pinanga abundance was significantly higher in HF sites than in MDF sites, while Pinanga abundance and species richness significantly varied between sites. Patterns in Pinanga species assemblages were significantly influenced by soil properties and elevation in the MDF sites but were only influenced by CO and LD in the HF sites. We identified three Pinanga species found in both forest types: Pinanga lepidota, Pinanga salicifolia and Pinanga mirabilis , while seven Pinanga species were exclusive to MDF sites and none were exclusive to HF sites. Two Pinanga species ( Pinanga chaiana and Pinanga veitchii ) were recorded as singletons and thus are in urgent need of protection. The restricted distributions of these Pinanga species within Borneo signifies a need to tailor specific conservation strategies in their native habitats to avoid their local extinction.