Management to Promote Flowering Understoreys Benefits Natural Enemy Diversity, Aphid Suppression and Income in an Agroforestry System

Robbie Girling,Tom Staton,Richard Walters,Tom Breeze,Jo Smith

doi:10.3390/agronomy11040651

Robbie Girling, Tom Staton + Show 3 more

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https://doi.org/10.3390/agronomy11040651

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Abstract

Agroforestry systems, where productive trees are integrated into agricultural land, can deliver benefits to biodiversity, natural pest control, and pollination, but the effects are highly variable. Recent advances in our understanding of flower strips in agricultural systems suggest that the management of the tree row understorey could be an important contributor to this variation. Here, we compare two cutting regimes for an understorey, originally seeded with the same flower mix, in the tree rows of an apple-arable agroforestry system: (i) uncut vegetation to promote a flowering understorey, and (ii) regularly mown vegetation. We recorded the effects of management on invertebrate pests, natural enemies, and pollinators, in both the apple and arable components. Apple trees above flowering understoreys supported significantly: (i) more natural enemies early in the season, (ii) fewer aphid colonies, (iii) fewer aphid-damaged fruits, and (iv) higher pollinator visitation, compared with those above mown understoreys. In the arable crop alleys, both the taxonomic richness and Shannon diversity of ground-based natural enemies were significantly higher adjacent to flowering understoreys, compared with those adjacent to mown understoreys, early in the season. Financial modelling based on aphid damage to apples, mowing costs, and income from Countryside Stewardship grants, indicated that flowering understoreys increased farm income by GBP 231.02 per ha of agroforestry compared with mown understoreys. Our results provide the first empirical evidence that management to promote flowering understoreys in agroforestry systems can be a win-win option to improve invertebrate diversity, associated ecosystem services, and farm income.

Highlights

The intensification of agricultural production, including habitat loss and the increased use of inputs such as pesticides, has been identified as a major cause of the global decline in invertebrate diversity [1,2]. This loss of diversity can lead to a reduction in associated regulating ecosystem services, such as the natural regulation of agricultural pests through natural enemy activity, and insect pollination of agricultural crops [3,4,5]
Our results show that the flowering understoreys delivered multiple benefits for invertebrate diversity and associated ecosystem services, compared with mown understoreys which comprised the same plant community but were subject to frequent cutting
We found that flowering understoreys increased natural enemy abundance in apple trees early in the season, reduced aphid colony density, and reduced the number of apples lost to aphid damage, which is supported by previous research of flower strips in insecticidefree apple orchards [53,54]

Summary

Introduction

The intensification of agricultural production, including habitat loss and the increased use of inputs such as pesticides, has been identified as a major cause of the global decline in invertebrate diversity [1,2] This loss of diversity can lead to a reduction in associated regulating ecosystem services, such as the natural regulation of agricultural pests through natural enemy (predator and parasitoid) activity, and insect pollination of agricultural crops [3,4,5]. Sustainable intensification aims to reduce agriculture’s dependence on external inputs by restoring natural processes and ecosystem services in tandem with improving agricultural productivity, for example, by integrating habitats for naturally occurring pollinators and natural enemies within agricultural fields or landscapes [8,9] One such form of sustainable intensification is agroforestry, which is loosely defined as the deliberate incorporation of productive trees into livestock or arable farming systems [10]. The integration of trees into arable fields can increase biodiversity and regulating ecosystem services, relative to monocultures [11,12,13]

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