Habitat heterogeneity supports day-flying Lepidoptera in oil palm plantations

Oil palm is one of Southeast Asia's most common crops, and its expansion has caused substantial modification of natural habitats and put increasing pressure on biodiversity. Rising global demand for vegetable oil, coupled with oil palm's high yield per unit area and the versatility of the palm oil product, has driven the expansion of oil palm agriculture in the region. Therefore, it is critical to identify management practices that can support biodiversity in plantations without exacerbating negative impacts on the environment. This study focuses on day-flying Lepidoptera (butterflies and moths), which contribute to the ecosystem functioning as pollinators, prey, and herbivore species. We assessed whether density and behaviours of day-flying Lepidoptera varied between different habitats within oil palm plantations and across seasons. We surveyed the density and behaviours of Lepidoptera communities in mature industrial oil palm plantations within the Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA) Programme sites, in Riau, Indonesia. We surveyed two distinct habitats within the plantations in March and September 2013: Edge habitats, which were bordered by plantation roads on one side, and Core habitats in the centre of oil palm planting blocks. We conducted analyses on the effect of habitat type and season on both the overall density and behaviour of Lepidoptera communities and, independently, on the most common species. In our surveys, we observed 1464 individuals across 41 species, with a significantly higher density in Edge than in Core habitats. While there was no significant difference between overall density in March and September surveys, there was an interaction between season and habitat, with density increasing more markedly in Edge than Core areas in September. There was also a significant effect of habitat and season on behavioural time budget for the community as a whole, with more active behaviours, such as foraging and mating, being recorded more frequently in Edge than Core habitats, and more commonly in September than March. The effect of habitat type, season, and their interaction differed between the six most common species. Our findings indicate that Lepidoptera abundance is affected by habitat characteristics in a plantation and can therefore be influenced by plantation management practices. In particular, our study highlights the value of road edges and paths in plantations for day-flying Lepidoptera. We suggest that increased non-crop vegetation in these areas, achieved through reduced clearing practices or planting of flowering plants, could foster abundant and active butterfly communities in plantations. These practices could form part of sustainability management recommendations for oil palm, such as those of the Roundtable on Sustainable Palm Oil

Maintaining understory vegetation in oil palm plantations supports higher assassin bug numbers

1. The expansion of oil palm agriculture across Southeast Asia has caused significant biodiversity losses, with the reduction in habitat heterogeneity that accompanies the conversion of forest to oil palm being a major contributing factor. However, owing to their long commercial lifespan, oil palm plantations can support relatively high levels of vegetation complexity compared to annual crops. There is therefore potential for the implementation of management strategies to increase vegetation complexity and associated within-plantation habitat heterogeneity, enhancing species richness and associated ecosystem functioning within productive oil palm landscapes. 2. This study focusses on two species of assassin bugs Cosmolestes picticeps and Sycanus dichotomus, which are important agents of pest control within oil palm systems. Using a Before-After Control-Impact experimental manipulation in Sumatra, Indonesia, we tested the effect of three alternative herbicide spraying regimes and associated vegetation complexity treatments on assassin bug numbers. Our treatments encompass a range of current understory vegetation management practices used in oil palm plantations and include removing vegetation only in areas key to harvesting (“Normal”), removing all understory vegetation (“Reduced”), and allowing native vegetation to regrow naturally (“Enhanced”). We assessed both the long-term (18 months) and short-term (within 2 weeks) effects of our treatments following herbicide spraying. 3. Pre-treatment, we found high numbers of assassin bugs of both species in all plots. Long-term post-treatment, the abundance of both C. picticeps and S. dichotomus declined in Reduced understory plots, although this decline was only significant for C. picticeps (98%). In contrast, there were no significant differences in the post-treatment abundance of either species in the short-term. 4. These results suggest that the long-term decline in assassin bug abundance was likely to be caused by loss of vegetation, rather than any immediate effects of the herbicide spraying. Our findings have clear management implications as they demonstrate that maintaining vegetation in oil palm understories can benefit an important pest control agent

Understory vegetation supports more abundant and diverse butterfly communities in oil palm plantations

IntroductionThe cultivation of oil palm, from which palm oil, the world’s most widely traded vegetable oil, is processed, has had marked effects on ecosystems and native species across the tropics. While declines in biodiversity due to conversion to oil palm have been well recorded across plant and animal taxa, less work has been done to identify approaches to plantation management which will enable producers to satisfy growing global demand while limiting environmental damage.MethodsThrough a large-scale understory management experiment, we investigated the long- and short-term effects of varying vegetation management regimes on the abundance, richness, and diversity of day-flying Lepidoptera.ResultsOver the long-term, the lowest levels of vegetation complexity resulted in significantly lower Lepidoptera abundance, species richness and evenness. Less intensive understory clearing resulted in healthier communities, with limited differences between removal by herbicide application or chemical-free removal. Over the short-term, biodiversity was not directly affected by vegetation complexity, suggesting that manual removal of vegetation may be equally damaging to butterfly or moth communities as removal by intermediate levels of herbicide spraying.DiscussionThese findings substantiate calls to limit vegetation clearing and maintain habitat heterogeneity on both a local and landscape scale, while also suggesting that a hard “no-spray” guideline may not be the only option to support butterfly friendly plantations

BEFTA Lepidoptera Raw Data 2013-2015

Excel file containing supporting data for “Removing understory vegetation in oil palm plantations reduces butterfly and moth biodiversity”, collected from 2013 – 2015 in SMARTRI industrial oil palm plantations in Indonesia through the BEFTA program. Sheets are as follows: 1. Collated Count – Morphospecies. Abundance data for Lepidoptera populations in industrial oil palm plantations, grouped to morphospecies. Data is identified to species level where possible. Data was collected from February 2013 – Feb 2016 across 21 study plots with differing levels of understory management. Column C ‘Box/Road’ refers to the location of the plot (see full manuscript for further information). Column E ‘Before/After’ refers to if the sample was taken before herbicide application or before. Column K ‘Treatment’ refers to the understory treatment applied to the plot (see full manuscript for further information). 2. Collated Count – Split. Contains the same data and columns as sheet 1, but with species not grouped to morphospecies. 3. Collated Activity. Morphospecies data on the behaviour of Lepidoptera in the same surveys as sheets 1 and 2. 5 – 14: Raw data sheets which were used to produce sheets 1-3

Data supporting "Maintaining understory vegetation in oil palm plantations supports higher assassin bug numbers"

Dataset includes - site information, assassin bug counts and rainfall measurements. Research Project Data relates to a study that tested the effect of three alternative herbicide spraying regimes and associated vegetation complexity treatments on numbers of two species of assassin bugs (Cosmolestes picticeps and Sycanus dichotomus). The treatments encompassed a range of understory vegetation management practices used in oil palm plantations and include removing vegetation only in areas key to harvesting (“Normal”), removing all understory vegetation (“Reduced”), and allowing native vegetation to regrow naturally (“Enhanced”). Both the long-term (18 months) and short-term (within 2 weeks) effects of treatments were assessed following herbicide spraying. Study Site Data was collected in industrial oil palm plantations in Riau Province, Sumatra, Indonesia (N0 55.559, E101 11.619). The region has a wet tropical climate, with an average annual rainfall of 2,350 mm. Data was collected across two neighbouring plantation estates (Ujung Tanjung and Kandista). These estates were planted between 1988 and 1993, meaning oil palms were mature (aged 20 – 27 years) at the time of data collection in 2013, 2014 & 2015. Across the two estates, oil palms were planted in staggered rows at a density of 136 palms/ha, or approximately 8 m apart. Project sites consisted of eighteen plots, arranged into six triplets. Each plot measured 150 × 150 m and was made up of a central 50 × 50 m core section and an outer buffer region. The three plots within each of the six triplets were randomly allocated to one of three understory treatments. Collection Methods Adult assassin bugs (Reduviidae) of the species Cosmolestes picticeps and Sycanus dichotomus were surveyed along transects in the core of each study plot. Transect walks consisted of a recorder walking at a steady pace, counting any adult C. picticeps or S. dichotomus that were visible or flew up in front of the recorder (without deliberately disturbing vegetation) within a 5-m-sided cube of space in front of them. The transect was 200 m in length and followed the edge of the central 50 x 50 m core section within each plot. Transects were walked between 9:00 and 17:00 and were not conducted when it was raining.Long-standing partnerships between the University of Cambridge and Sinar Mas Agro Resources and Technology Research Institute are partly funded by the Isaac Newton Trust Cambridge, Natural Environment Research Council (grant number NE/P00458X/1), and Golden Agri Resources. JS received funding from the Biotechnology and Biological Sciences Research Council (BBSRC) (USN: 304338625)

Maintaining understory vegetation in oil palm plantations supports higher assassin bug numbers

Publication status: PublishedFunder: Biotechnology and Biological Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000268; Grant(s): USN: 304338625Funder: Gates Cambridge Trust; doi: http://dx.doi.org/10.13039/501100005370Funder: Golden Agri ResourcesFunder: International Conference of Oil Palm and Environment (ICOPE)Funder: Isaac Newton Trust; doi: http://dx.doi.org/10.13039/501100004815Funder: Marshall Aid Commemoration Commission; doi: http://dx.doi.org/10.13039/100014014Abstract The expansion of oil palm agriculture across Southeast Asia has caused significant biodiversity losses, with the reduction in habitat heterogeneity that accompanies the conversion of forest to oil palm being a major contributing factor. However, owing to their long commercial lifespan, oil palm plantations can support relatively high levels of vegetation complexity compared to annual crops. There is therefore potential for the implementation of management strategies to increase vegetation complexity and associated within‐plantation habitat heterogeneity, enhancing species richness and associated ecosystem functioning within productive oil palm landscapes. This study focusses on two species of asassin bugs Cosmolestes picticeps and Sycanus dichotomus, which are important agents of pest control within oil palm systems. Using a Before‐After Control‐Impact experimental manipulation in Sumatra, Indonesia, we tested the effect of three alternative herbicide spraying regimes and associated vegetation complexity treatments on assassin bug numbers. Our treatments encompass a range of current understory vegetation management practices used in oil palm plantations and include removing vegetation only in areas key to harvesting (“Normal”), removing all understory vegetation (“Reduced”), and allowing native vegetation to regrow naturally (“Enhanced”). We assessed both the long‐term (18 months) and short‐term (within 2 weeks) effects of our treatments following herbicide spraying. Pre‐treatment, we found high numbers of assassin bugs of both species in all plots. Long‐term post‐treatment, the abundance of both C. picticeps and S. dichotomus declined in reduced understory plots, although this decline was only significant for C. picticeps (98%). In contrast, there were no significant differences in the post‐treatment abundance of either species in the short‐term. These results suggest that the long‐term decline in assassin bug abundance was likely to be caused by loss of vegetation, rather than any immediate effects of the herbicide spraying. Our findings have clear management implications as they demonstrate that maintaining vegetation in oil palm understories can benefit an important pest control agent. </jats:p

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

Data_Sheet_1_Understory vegetation supports more abundant and diverse butterfly communities in oil palm plantations.PDF

IntroductionThe cultivation of oil palm, from which palm oil, the world’s most widely traded vegetable oil, is processed, has had marked effects on ecosystems and native species across the tropics. While declines in biodiversity due to conversion to oil palm have been well recorded across plant and animal taxa, less work has been done to identify approaches to plantation management which will enable producers to satisfy growing global demand while limiting environmental damage.MethodsThrough a large-scale understory management experiment, we investigated the long- and short-term effects of varying vegetation management regimes on the abundance, richness, and diversity of day-flying Lepidoptera.ResultsOver the long-term, the lowest levels of vegetation complexity resulted in significantly lower Lepidoptera abundance, species richness and evenness. Less intensive understory clearing resulted in healthier communities, with limited differences between removal by herbicide application or chemical-free removal. Over the short-term, biodiversity was not directly affected by vegetation complexity, suggesting that manual removal of vegetation may be equally damaging to butterfly or moth communities as removal by intermediate levels of herbicide spraying.DiscussionThese findings substantiate calls to limit vegetation clearing and maintain habitat heterogeneity on both a local and landscape scale, while also suggesting that a hard “no-spray” guideline may not be the only option to support butterfly friendly plantations.</p

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 &ndash; particularly insects &ndash; 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 Ni&ntilde;o 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., Site.&mdash;Fieldwork was conducted within oil palm plantations in Riau Province, central Sumatra, Indonesia. The plantations are owned and managed by PT Ivo Mas Tunggal (a subsidiary company of Golden Agri Resources, GAR), with technical input from Sinar Mas Agro Resources and Technology Research Institute (SMARTRI) (the research and development centre of GAR) (Fig. S1, full manuscript). The area is naturally mixed lowland dipterocarp forest, but was deforested ~30 years ago, and is currently heavily dominated by oil palm agriculture, with very little non-converted habitat remaining. The region has a tropical climate, with mean annual rainfall of 2350 mm, spread unevenly across the year, and is based on mineral soil (Tao et al. 2016). We surveyed sites that formed part of the Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA) Programme (Foster et al. 2014; Luke et al. 2020). As part of this, the BEFTA Understory Vegetation Project tests the effects of understory vegetation complexity on the oil palm ecosystem, through varying levels of herbicide use and manual cutting of vegetation. BEFTA has established three understory vegetation treatments (see Luke et al. (2020) for full details): Reduced complexity: this involves spraying all understory vegetation with herbicides. Hereafter referred to as &lsquo;Reduced&rsquo;. Normal complexity: this is the standard practice used within the SMARTRI estates and involves an intermediate level of herbicide spraying, with harvest paths and 1.5 m circles around palms being sprayed and woody vegetation being manually removed, but other vegetation being allowed to regrow. Hereafter referred to as &lsquo;Normal&rsquo;. Enhanced complexity: this involves no spraying of herbicides and only limited hand-cutting of woody vegetation, and along harvesting paths and in palm circles. Hereafter referred to as &lsquo;Enhanced&rsquo;. The three treatments represent the range of different management strategies that occur within oil palm plantations. There are eighteen BEFTA Understory Vegetation Project plots, split across two estates (Ujung Tanjung and Kandista), and organized into six triplets, each at least 800m from the next (Fig. S1; Fig. S2; Table S1, full manuscript). Each triplet contains one 150 x 150 m plot of each treatment, with the order allocated randomly. The middle plot in each triplet is 155 m from each of the outer plots within the triplet. Each plot is located at the end of a plantation block of 900 x 300 m, so that it is adjacent to an access road, and therefore includes both core and edge plantation microhabitat (hereafter referred to as &lsquo;Core&rsquo; and &lsquo;Edge&rsquo;). Edge sites were located alongside both a dirt road and a drainage ditch filled with standing water (Fig. S2, full manuscript). These Edge sites occur around each of the 900 x 300m planting blocks. Core sites were within the interior of oil palm planting blocks, at least 50m from the edge. This led to differences in shading, exposure, and water occurrence in the two microhabitats, with consequent impacts on vegetation structure and diversity. Specifically, Edge areas had significantly higher plant biomass and cover, plant species richness, and higher occurrence of Turnera ulmifolia (planted along roadsides to promote populations of beneficial insects) than Core areas, whilst Core areas had significantly higher percentage cover of frond heaps (stacks of chopped palm fronds) (Luke et al. 2019, 2020) (and also see assessments of habitat structure presented in the full manuscript). All plots are in flat areas of the plantation, 10-30 m asl, and are in areas that were mature palm (palms planted between 1988 and 1993) at the time of survey. The SMARTRI estates are criss-crossed by a network of small streams (Fig. S1, full manuscript), and two plots had small streams running through them. There were no natural ponds or lakes nearby. Plots were marked out in October 2012 and were all managed using the standard SMARTRI vegetation practices (Normal complexity) until treatments began in February 2014, after which plots were managed according to their allocated understory vegetation treatment. Refer to Luke et al. (2020), for more details. Odonata surveying.&mdash;Within each plot, adult Odonata were surveyed along transects in the Core and Edge of the plot. Core transects followed the edge of a central 50 x 50 m sampling area within each plot and so were 200 m long, whilst Edge transects followed the roadside edge of the plot and so were 150 m long (Fig. S2, full manuscript). Recorders walked at a steady pace along each transect and identified and counted the dragonflies seen within a 5 m sided cube of space in front of them. Survey duration was not fixed because the time required to complete a survey depended on the number of dragonflies present. When a species was not immediately identifiable by sight, they were caught using a hand-net and photographed, allowing later identification by an experienced taxonomist (Rory A. Dow) and using identification guides (Orr 2003; Tang et al. 2010). Surveys were conducted at each plot during two &lsquo;Seasons&rsquo;: February-April, and September, hereafter referred to as &lsquo;March&rsquo; and &lsquo;September&rsquo;. Both seasons were surveyed in 2013, 2014, and 2015. Two repeat surveys of each plot were conducted within each season. Surveys conducted in March 2014 fell partly during the BEFTA Understory Vegetation Project pre-treatment (hereafter referred to as &lsquo;pre-treatment&rsquo;), and partly during the BEFTA Understory Vegetation Project post-treatment (hereafter referred to as &lsquo;post-treatment&rsquo;) time period, and were categorised accordingly in analyses. Surveys were conducted between 9am and 5pm. Vegetation measurements.&mdash;Vegetation measurements were taken every 10 m along each of the transects, once in March-April 2013 (pre-treatment), and again in September 2014 (post-treatment). Vegetation percentage cover (of ferns, palm fronds, bare ground, empty fruit bunch (EFB &ndash; used husks of harvested palm fruits, applied by industry as a mulch), and the non-native shrub Turnera ulmifolia (planted by industry along roadways to promote pest control)) was assessed by eye within a 5 x 5 m area at each point. Vegetation height was measured with a metre rule. At each measurement point, the metre rule was held in a vertical position, with its base resting on the ground, and an A4 clipboard lightly rested on the vegetation (to push down any single tall stems) and the height measured accordingly. Canopy openness was measured using a densiometer (Lemmon 1956), averaging four measurements taken North, South, East and West at each point. Rainfall measurements.&mdash;We recorded daily rainfall (mm) using rain gauges that each had a 100 cm2 collecting area. Rainfall values from all rain gauges within each estate (three in Ujung Tanjung, and two in Kandista) were averaged to calculate a monthly rainfall value for each estate. In analyses, we used the estate rainfall value that was applicable to each plot. We used rainfall measures from March of the relevant year as the &lsquo;monthly rainfall&rsquo; value for surveys conducted during February to April, and rainfall measures from September for September surveys. In addition to &lsquo;monthly rainfall&rsquo;, we also used the value of rainfall for the calendar month that was four months before (&lsquo;rainfall four months before&rsquo;) the March and September dragonfly surveys in analyses. This is because dragonflies have an aquatic larval stage, and therefore presence of adults at a site is dependent on sufficient water for larval development before the survey date. Although different dragonfly species exhibit a range of reproductive strategies, the majority of tropical species are multivoltine (Corbet 1980). The development time for many tropical dragonfly larvae is between 60 and 200 days (Corbet 1980), the mean of which is 130 days (4.3 months). Using this lagged rainfall value in analyses allowed us to consider the influence of rainfall on egg laying, egg survival, and larval development stages of the dragonfly lifecycle, in addition to assessing impacts of rainfall on adult presence. Statistical analyses.&mdash;We conducted analyses using R statistical program version 3.5.1 (R Core Team 2018), and the program R Studio (R Studio Team 2016). To compare 200 m-long Core transects and 150 m-long Edge transects, we standardised all abundance data to predicted values for 150 m-long transects by multiplying Core abundance values by 0.75. We included data for an unidentified teneral individual (&lsquo;Unknown teneral&rsquo;) within overall abundance models, but excluded this data point from species richness curves and family level analyses, as its species and family were unknown.</span