The conversion of natural forest to oil palm plantation is a well-documented threat to the biodiversity conservation in South East Asia. This study examines how oil palm and land conversion affect avian diversity and tree structures in oil palm concession under the RSPO scheme in Semitau West Kalimantan. Birds and trees were sampled in three remnants corresponding to different forest types inside the oil palm concession: a Peat Swamp forest patch, a Mixed Dipterocarp Forest (MDF) patch, and a Kerangas forest. We laid plots for tree measurements and herbarium collection and recorded bird species using point-count and mist nets, exploring potential indicator species for future monitoring. The non-metric multidimensional scaling ordination of birds and trees showed well-separated clusters, confirming sites difference in species composition. In the MDF remnant (84 ha), 56 tree species were recorded, while it was 66 for the Kerangas forest (778 ha), and 51 for the Peat swamp forest patch (280 ha). Robust tree indicator species for the Kerangas forest patch was Calophyllum sp., for the MDF remnant Gymnacranthera farquahariana, and for the Peat swamp forest Cephalomappa malloticarpa. The high number of lesser-known timber species in the three remnant forest patches was striking, confirming their high conservation value. For birds, 45 species were recorded in Peat swamp forest, 23 species in MDF remnant, and 36 species in Kerangas forest remnant. Strikingly, only 22 species (24%) of the 91 recorded species were common between the three sites. Bird indicator species in MDF remnant were Harpactes kasumba and Pycnonotus eutilotus that are also near threatened species. Number of frugivorous birds in the Peat swamp forest was noteworthy, linked also to the low tree disturbance and higher food availability (fruit trees) compared to the other forest remnants. The simplification of the habitat had a strong impact on bird and tree diversity. Oil palm plantation forest patches are poor habitats compared to the natural forest but, in this particular concession, forest patches still harbor high diversity and high conservation value species. The forest patches for this company are not the usual one ha blocks preconized for RSPO scheme but are much bigger to compel with local community wishes. The question remains if these patches will remain resilient in the long run.

Trifosa Iin Simamora