Socioecological data from smallholder oil palm plantations in Riau, Sumatra, Indonesia, 2021-2022

Biodiversity, environmental and social data were collected in a series of field campaigns, led by researchers from Institut Pertanian Bogor (IPB) University, supported by researchers and staff from Sinar Mas Agro Resources and Technology Research Institute.

Biodiversity data collection included standard transect walks of 100m to record abundance and activity of butterflies, as well as numbers of Assassin bugs and Nephila spiders within a 5m x 5m box in front of the recorder. At four points along the transect, separated by 20m, we also recorded ground invertebrate abundance, understory flying invertebrate abundance, and predation. Plastic cups, filled with 70% alcohol and a few drops of detergent, covered with a plate to protect from rain, were used as pitfall traps to sample ground invertebrates. Samples were stored in 70% alcohol. Clear plastic sheets smeared with glue were used as sticky traps, suspended 40cm above the ground and facing south, to collect understory invertebrates. Both traps were collected after 24hours. Sticky traps were photographed to allow later recording of invertebrate abundance. Cards with 6 dead meal worms attached and hung on palm trunks next to sample points were used to assess predation, by recording removal over 24 hours. Finally, the plots were thoroughly searched for any open male or female oil palm inflorescences. These were scored for % openness and observed for 10 minutes, during which time the highest number of insects in major groups were recorded. This survey was repeated 24 hours later.

Environmental data collection methods included visual inspection of plots to record cover of different crop types, and using handheld GPS units to record plantation boundaries and size of plantations. At the same four sample points used to set pitfalls and sticky traps, we also made direct measurements of vegetation, palm and soil characteristics. These included field readings of canopy openness using a convex spherical densiometer, direct measures of vegetation height and cover (into categories by eye within a 3m x3m area), and field measures of soil pH and moisture using a Suplong probe. We also scored height, health, % epiphyte cover on the trunk, and level of herbivory by eye on the closest palm to each point. We also dug small soil pits to assess leaf litter depth and then used a standard 10cm deep and 5cm diameter tube to collect soil samples. We also conducted a Visual Evaluation of Soil Structure (VESS) survey to measure depth of soil horizons and associated characteristics, following standard methods.

Social data were collected through a mixture of telephone and face to face interviews with smallholders, at a time convenient to the smallholders. Some telephone interviews were necessary owing to the impacts of COVID. Ethical permission for interviews were gained from the University of Cambridge Department of Psychology ethics board before work took place, no information was withheld from participants and full written consent was obtained in advance.

On return to the lab, collected pitfall trap insects were stored in fresh alcohol and identified to order-level. Soil samples were weighed wet and then dried to a constant weight, allowing water content and soil compaction to be calculated. Sticky trap photos had insects counted and identified to order-level.

Data were entered digitally by field teams and returned to the University of Cambridge for quality and error checking, and to ensure a standard format.

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