Complexity within an oil palm monoculture: the effects of habitat variability and rainfall on adult dragonfly (Odonata) communities.

Recent expansion of oil palm agriculture has resulted in loss of forest
habitat and forest-dependent species. However, large numbers of species –
particularly insects – can persist within plantations. This study focuses
on Odonata (dragonflies and damselflies): a charismatic indicator taxon,
and a potentially valuable pest control agent. We surveyed adult Odonata
populations biannually over three years within an industrial oil palm
plantation in Sumatra, Indonesia. We assessed the effects of rainfall
(including an El Niño Southern Oscillation-associated drought), the role
of roadside ditches, and the importance of understory vegetation on
Odonata populations. To assess the impacts of vegetation we took advantage
of a long-term vegetation management experiment that is part of the
Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA)
Programme. We found 41 Odonata species, and communities varied between
plantation core and roadside edge microhabitats, and between seasons.
Abundance was significantly related to rainfall levels four months before
surveys, probably indicating the importance of high water levels in
roadside ditches for successful larval development. We found no
significant effect of the BEFTA understory vegetation treatments on
Odonata abundance, and only limited effects on community composition,
suggesting that local understory vegetation structure plays a relatively
unimportant role in determining communities. Our findings highlight that
there are large numbers of Odonata species present within oil palm
plantations, and suggest that their abundance could potentially be
increased by maintaining or establishing waterbodies. As Odonata are
predators, this could bring pest control benefits, in addition to
enhancing biodiversity within intensive agricultural landscapes.