Restoring oil palm rivers: assessing the effects of riparian re-vegetation and in-channel modifications on biodiversity and functionality

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Vast areas of tropical forest, predominantly in Indonesia and Malaysia, have been replaced by monocultures of oil palm (Elaeis guineensis). Conversion of tropical forest to oil palm plantations (OPPs) reduces habitat heterogeneity, and is associated with declines in terrestrial biodiversity and ecosystem functioning. The environmental and ecological effects on freshwater habitats situated within OPPs are less well understood but include increased sedimentation, bank erosion and pollution, and altered river morphology and hydrological regimes, with negative implications for freshwater fauna and flora.Riparian buffer zones (i.e. areas of forest and/or non-production vegetation with no chemical inputs along the river) can mitigate negative impacts of OPPs on riverine biodiversity and functioning, and are now a legal requirement in Indonesia. However, many older OPPs often extend to riverbanks. In these cases, restoration of riparian areas, addition of in-channel features and/or alteration of channel morphology may provide effective mitigation strategies. Although multiple large-scale projects have focused on the restoration of temperate rivers, much less work has been done on tropical river restoration. As such, there is an urgent need to identify restoration approaches in OPP-rivers that maximise benefits to biodiversity and functioning whilst maintaining oil palm crop productivity.Making use of a large-scale, long-term riparian restoration experiment in Indonesia - the Riparian Ecosystem Restoration in Tropical Agriculture (RERTA) Project, this project aims to identify effective strategies for restoring OPP-rivers. Objectives are to:(O1) Quantify how different riparian vegetation restoration treatments affect river morphology and processes, water quality and biodiversity in the long- and short-term;(O2) Quantify how in-stream restoration combined with/without riparian restoration approaches affect river morphology and processes, water quality and biodiversity; and(O3) Quantify to what extent specific ecosystem functions and services of biodiversity are supported by the restoration treatments tested.