Polyculture agroforestry is a new sustainable agriculture system modelled on the plant structural and species diversity of native oak savanna. Advocates of the system claim that it will advance conservation goals by providing ecosystem services like habitat provision and carbon sequestration, but also provide localized ecosystem services that benefit farmers. Pest control by wild predators and parasitoids could be an especially valuable service in fruits and nuts, the main cash crops in polyculture agroforestry systems. To understand how diverse agroforestry’s unique traits would affect pest control, I evaluated the response of arthropod pest and natural enemy guilds to variations in shrub layer composition and alley mowing. Shrub composition affected guilds on shrubs but had little effect on arthropods in neighboring apple trees. Pest guilds linked to apple damage were not affected by shrub composition, and pest damage rates were unchanged. Mowing did cause arthropods in groundcover to use shrubs and trees as refuge habitat. However, the shrubs and trees that offered suitable refuge were alternate hosts to pest insects. Mowing thus increased abundance of pests but not enemies, likely resulting in higher rates of pest damage rather than the opposite. I found no evidence that either strategy has potential to improve pest outcomes. Overall, I conclude that pest management in polyculture agroforestry systems is likely to be an obstacle for farmers rather than a boon. This fact should be made clear to potential adopters of the system, and future designs should choose crops that are tolerant or immune to pest damage to the extent possible.
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Conservation biological control in a multi-strata agroforestry system
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