Can trees and their associated organisms still benefit arable crops in the presence of pesticide use?

Abstract

CONTEXT

Trees growing in and around the field (agroforestry) attract a range of organisms and empirical studies indicate that these are overall beneficial to the arable crop. A recently modelling study of English organic silvoarable using a new approach based on Boolean regulatory network modelling supported this conclusion.

OBJECTIVE

Here we develop this model further to consider the impact of pesticide use on the benefits trees can bring to crops through living interactions.

METHODS

Pests in the model agroecosystem are selectively and non-selectively removed from the agroecosystem under a range of intervention thresholds to simulate pesticide use, and the benefits of trees quantified and compared to benefits accrued under a baseline treatment of no pesticide use.

RESULTS AND CONCLUSIONS

Selective interventions for crop disease and crop insects (pests and non-target natural enemies) dramatically reduce the benefits of trees, even at relatively high intervention thresholds. Intervention for crop weeds increases the benefits of trees, as weeds are often considered a burden associated with tree understories. Less selective, double interventions (weed-disease, weed-pest-natural enemy, disease-pest-natural enemy) all reduce the benefits of trees, but the weed-pest-natural enemy intervention least so. Unsurprisingly, removing all living associates of trees renders trees of no benefit to crop yield through biotic mechanisms but, more surprisingly, this conclusion applies when intervention thresholds are high and delayed to late in the growing season.

SIGNIFICANCE

Caution is urged in the interpretation of model findings but this study provides a first guide to how pesticide use in agroforestry systems modulates the benefits of trees. These findings may be particularly useful to growers in the increasingly popular area of regenerative agriculture which permits restrained and selective use of pesticides.