The net return from animal activity in agro-ecosystems: trading off benefits from ecosystem services against costs from crop damage.

Abstract

Animals provide benefits to agriculture through the provision of ecosystem services, but also inflict costs such as damaging crops. These benefits and costs are mostly examined independently, rather than comparing the trade-offs of animal activity in the same system and quantifying the net return from beneficial minus detrimental activities. Here, I examine the net return associated with the activity of seed-eating birds in almond orchards by quantifying the economic costs and benefits of bird consumption of almonds. Pre-harvest, the consumption of harvestable almonds by birds cost growers AUD$57.50 ha (-1) when averaged across the entire plantation. Post-harvest, the same bird species provide an ecosystem service by removing mummified nuts from trees that growers otherwise need to remove to reduce threats from fungal infection or insect pest infestations. The value of this ecosystem service ranged from AUD$82.50 ha (-1)-$332.50 ha (-1) based on the replacement costs of mechanical or manual removal of mummified nuts, respectively. Hence, bird consumption of almonds yielded a positive net return of AUD$25-$275 ha (-1) averaged across the entire plantation. However, bird activity varied spatially resulting in positive net returns occurring primarily at the edges of crops where activity was higher, compared to negative net returns in crop interiors. Moreover, partial mummy nut removal by birds meant that bird activity may only reduce costs to growers rather than replace these costs completely. Similar cost-benefit trade-offs exist across nature, and quantifying net returns can better inform land management decisions such as when to control pests or promote ecosystem service provision.