Maximizing Ecosystem Services Provided To The New Oil Crop Brassica carinata Through Landscape And Arthropod Diversity

Abstract

Prairies, once spanning the Upper Midwest, have now largely been replaced by agriculture. The lack of resources available to pollinators in agricultural fields and practices commonly employed has led to a decline in insect diversity. To enhance sustainable practices, we must better understand how ecosystem services such as pest control and pollination services provided by a diverse insect and pollinator community scale to current farming practices as related to crop yield and how landscape features may positively contribute to insect and pollinator diversity. We examined how landscape heterogeneity relates to insect and pollinator diversity, as well as how insect and pollinator diversity relates to crop yield across common farming practices. We planted 35 single acre sites of Brassica carinata, a generalist flower possibly capable of supporting a diverse insect community. We randomly assigned each site with a combination of three common farming practices: tilling (yes/no), added honey bee hives (yes/no), and treatment with systemic neonicotinoids (yes/no). Insect and pollinator diversity and the surrounding landscape at multiple spatial scales were calculated. We observed a significant positive relationship between insect (and pollinator) diversity with yield in the absence of any farming practice. All farming practices will increase yield. However, farming practices alter the relationship between yield and diversity. The addition of seed treatment or tillage negates the relationship between insect (and pollinator) diversity with yield. Seed treatment alone results in a flat relationship between diversity and yield for all insects and a negative relationship for pollinators. Increased landscape heterogeneity results in a positive relationship between insect diversity at the 1000 m scale and pollinator diversity at the 3000 m scale, suggesting large-scale heterogeneity contributes to overall insect diversity. Our results show that increasing large-scale landscape heterogeneity increases diversity serving as a substitute for common farming practices such as application of pesticides, tilling, or bee hives. Increased heterogeneity could save farmers from the input cost of treatment or tillage, by way of increased insect diversity, while still providing similar yields.