Local and landscape drivers of arthropod diversity and decomposition processes in oil palm leaf axils

Oil palm expansion results in a loss of biodiversity and associated ecosystem services. However, there are factors that influence the severity of these impacts and enhancing biodiversity within plantations is important. In the present study, we examined the role of epiphytes for supporting arthropod communities in oil palm plantations in Sumatra, Indonesia. We considered the effects of landscape context and local characteristics (epiphyte cover, herbicide use and local microclimate) on arthropod communities and litter decomposition in oil palm leaf axils. We surveyed arthropods and measured decomposition rates at two different heights on 80 oil palms located at the centre and edge of eight plantations. We found that oil palms at the edge of plantations hosted a higher abundance and more arthropod taxa than oil palms in the centre of plantations. Moreover, organic matter mass and height of the leaf axil were important for arthropod communities, and the decomposition rate was negatively related to ant abundance. However, epiphyte cover did not influence arthropod communities. The results of the present study show that leaf axils with more organic matter and at a higher location on the oil palm promote arthropod biodiversity. Furthermore, oil palm plantations adjacent to different land-use systems have enhanced biodiversity

Biological control in Indonesian oil palm potentially enhanced by landscape context

Oil palm plantation expansion is occurring at a rapid pace. However, substantial yield losses from pest attacks are becoming major threats to the oil palm industry, while the potential role of conservation biological control, a sustainable and environmentally friendly solution for pest control, is still largely unknown. The type of vegetation surrounding oil palm plantations is likely to influence pest predation, and we tested this in Indonesia (Sumatra), the world's largest palm oil producer. We studied six different vegetation types adjacent to oil palm plantations: another oil palm plantation (control), weedy oil palm, weedy rubber, scrub, jungle rubber, and secondary forest. Each border type was replicated eight times. We quantified predation rates and predator occurrences using dummy caterpillars and mealworms 20 m inside of the adjacent vegetation (OUT 20) as well as 20 m (IN 20) and 50 (IN 50) m inside the oil palm plantation. Ants and bush crickets were the most prominent predators in the plantations, whereas birds, bats, monkeys, beetles, and molluscs played a minor role. Mean percentage of ant and cricket predation rate in control border OUT 20 were 16.39% and 7.16% respectively, IN 20 were 16.03% and 6.1%, and IN 50 were 14.47% and 7.48%, while for other borders other than control, mean percentages OUT 20 m were 28.90% and 12.26% respectively, IN 20 m were 26.61% and 12.40%, and IN 50 m were 22.93% and 10.58%. Predation rates were ∼70% higher in non-oil palm habitat, indicating the need for improved vegetation diversification inside plantations. Overall predation rates in oil palm decreased slightly but significantly with distance to the border. Our results suggest that maintaining non-oil palm vegetation in the areas adjacent to plantations and promoting weedy strips within the plantations are potentially effective management tools for conserving and developing biological control in oil palm in the future

Cultural homegarden management practices mediate arthropod communities in Indonesia

Tropical forest loss and transformation to agroecosystems have serious impacts on biodiversity, associated ecosystem services and the livelihood of local people. The high crop plant biodiversity and low intensity management in many homegardens could play an important role in the preservation of biodiversity in modified landscapes, as well as sustain food security of low income households. In this study, we focused on the role of the owner’s cultural background as migrants (from the island of Java) or non-migrants (local residents) for homegarden characteristics, such as size, management diversification, and crop species richness, and their effect on arthropod communities in Jambi province, Indonesia. Vane traps, pitfall traps and sweep netting were used to survey the arthropod communities, in particular bees and wasps, in 24 homegardens. Our results show that the native Jambi locals used a smaller number of management practices and had smaller homegardens than the Javanese transmigrants, whereas crop species richness did not differ. Management diversification and crop species richness were positively related to arthropod abundance as well as species richness of bees and wasps, presumably due to the enhanced homegarden heterogeneity. Our findings suggest that the cultural practices of migrant versus non-migrant land-use managers, which is usually neglected in agroecology, can be a major determinant of management practices shaping community structure and services of beneficial arthropods

Data from: Experimental evidence that even minor livestock trampling has severe effects on land snail communities in forest remnants

1. Land-use intensification is increasing dramatically in production systems world-wide. Livestock production is an important component of production land use, and increases in livestock densities have had a wide range of negative consequences. The off-site effects of livestock grazing and trampling on native vegetation adjacent to pastoral land have received less attention than on-farm effects. Moreover, where significant ecological effects of livestock spillover have been identified, the mechanistic determinants of these effects have not typically been investigated. 2. Here, we tested the mechanistic drivers of livestock trampling effects on land snail communities in forest remnants using simulated trampling under field conditions. We used a factorial combination of leaf-litter manipulation and trampling treatments to partition different causal drivers of livestock impacts on land snail communities and related them to five environmental variables that are altered by livestock. 3. We show that even very low frequency trampling caused severe changes to land snail communities. Land snail density, even under the lowest trampling frequency, declined by an average of 42 individuals m−2 and land snail species richness decreased by an average of 10 species per plot compared with control plots. 4. The underlying drivers of changes in land snail communities varied, but were primarily linked to leaf-litter mass, rather than soil compaction. 5. Synthesis and applications. Overall, these results suggest that even minimal disturbance by livestock has large effects on land snail communities, but the underlying drivers of these effects require further investigation in longer duration and more intensive studies. Our results provide strong support for livestock exclusion as an important management tool for native forest remnants embedded within production landscapes

Species abundance

Total number of each land snail species identified in each leaf-litter sample collected from the experimental plots pre- and post treatment

Predictor variables

Values of habitat structure and microclimatic variables (‘endogenous’ predictors in SEM models) measured in each experimental plo

The role of ants, birds and bats for ecosystem functions and yield in oil palm plantations

One of the world's most important and rapidly expanding crops, oil palm, is associated with low levels of biodiversity. Changes in predator communities might alter ecosystem services and subsequently sustainable management but these links have received little attention to date. Here, for the first time, we manipulated ant and flying vertebrate (birds and bats) access to oil palms in six smallholder plantations in Sumatra (Indonesia) and measured effects on arthropod communities, related ecosystem functions (herbivory, predation, decomposition and pollination) and crop yield. Arthropod predators increased in response to reductions in ant and bird access, but the overall effect of experimental manipulations on ecosystem functions was minimal. Similarly, effects on yield were not significant. We conclude that ecosystem functions and productivity in oil palm are, under current levels of low pest pressure and large pollinator populations, robust to large reductions of major predators

Agricultural Intensification Exacerbates Spillover Effects on Soil Biogeochemistry in Adjacent Forest Remnants

<div><p>Land-use intensification is a central element in proposed strategies to address global food security. One rationale for accepting the negative consequences of land-use intensification for farmland biodiversity is that it could ‘spare’ further expansion of agriculture into remaining natural habitats. However, in many regions of the world the only natural habitats that can be spared are fragments within landscapes dominated by agriculture. Therefore, land-sparing arguments hinge on land-use intensification having low spillover effects into adjacent protected areas, otherwise net conservation gains will diminish with increasing intensification. We test, for the first time, whether the degree of spillover from farmland into adjacent natural habitats scales in magnitude with increasing land-use intensity. We identified a continuous land-use intensity gradient across pastoral farming systems in New Zealand (based on 13 components of farmer input and soil biogeochemistry variables), and measured cumulative off-site spillover effects of fertilisers and livestock on soil biogeochemistry in 21 adjacent forest remnants. Ten of 11 measured soil properties differed significantly between remnants and intact-forest reference sites, for both fenced and unfenced remnants, at both edge and interior. For seven variables, the magnitude of effects scaled significantly with magnitude of surrounding land-use intensity, through complex interactions with fencing and edge effects. In particular, total C, total N, δ¹⁵N, total P and heavy-metal contaminants of phosphate fertilizers (Cd and U) increased significantly within remnants in response to increasing land-use intensity, and these effects were exacerbated in unfenced relative to fenced remnants. This suggests movement of livestock into surrounding natural habitats is a significant component of agricultural spillover, but pervasive changes in soil biogeochemistry still occur through nutrient spillover channels alone, even in fenced remnants set aside for conservation. These results have important implications for the viability of land-sparing as a strategy for balancing landscape-level conservation and production goals in agricultural landscapes.</p></div

Components of variation in agricultural land-use intensity on farms surrounding the 21 forest remnants.

<p>‘F’ and ‘U’ site codes indicate whether the adjacent forest remnants were fenced or unfenced, respectively, but this information had no bearing on the calculation of land-use intensity. Values for ‘farm area’ that share a common superscript denote paddocks that were located on the same farm, but were at least 420 m apart. All soil measures are the average of three recorded values taken at each site.</p><p>Components of variation in agricultural land-use intensity on farms surrounding the 21 forest remnants.</p

Predicted relationships between surrounding agricultural land-use intensity and soil biogeochemistry within fenced and unfenced forest remnants.

<p>The mean (± 1 S.E.) fitted relationships were derived from the final model-averaged solution (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0116474#pone.0116474.t002" target="_blank">Table 2</a>) using the ‘lmePredict’ function, while holding other fixed effects constant at their mean values. Symbols represent the raw means (± 1 S.E.), corrected for soil moisture factor and bulk density where appropriate. For clarity, raw data and predicted relationships are only shown for the extreme edge (0 m) and interior (46.5 m) distances within forest remnants, but models were tested across all edge distances. Grey shaded intervals represent the raw mean (± 1 S.E.) reference forest interior conditions (at 243–420 m from edge). Note that the predicted relationships are conditional on the random effects specified in the model.</p