Ecological Approaches to Managing Crop Diversity for Sustainability and Resilience in the Great Lakes Region

Abstract

Mounting evidence suggests that increasing crop diversity on farms improves agroecosystem sustainability and resilience, especially when increasing functional diversity, such as with non-harvested cover crops. However, crop diversification practices remain understudied in the context of working farms, where a wide range of factors interact to influence plant growth and associated benefits. Chapter 1 introduces how this dissertation integrates principles of functional, community, and ecosystem ecology to investigate outcomes of different types and levels of crop rotation diversity across the heterogeneous environmental and management conditions present on farms in the Great Lakes region.

In the first dissertation study (Chapter 2) I explore how functionally diverse cover crop species respond to a gradient of soil health and interspecific interactions when grown together in mixture. Using a trait-based approach, this two-year experiment on eight farms with distinct management histories revealed species-specific responses to soil properties. Competitive and facilitative interactions drove trait plasticity within species, and trait variation within species was as large as that between species, highlighting the need for considering both inter- and intraspecific trait variation when selecting cover crop species. Because trait variation can scale up to influence agroecosystem function, these findings demonstrate that tailoring cover crop management based on context is important for meeting sustainability goals.

In the second study (Chapter 3) I use an observational, citizen science approach to examine patterns and drivers of cover crop performance on 253 farm fields across the Great Lakes region between 2021-2023. Cover crop performance was highly variable across fields. Compared to cereal rye, the most popular cover crop in the region, mixtures accumulated twice as much biomass and nitrogen, in part because they were grown as part of more diverse crop rotations. Mixtures with high species richness performed best, suggesting that functional redundancy offers insurance across heterogeneous growing conditions. For lower diversity mixtures, use of organic soil amendments buffered against the negative effects of low precipitation. These findings demonstrate that increasing plant diversity can optimize cover crop outcomes on working farms, and highlight synergies when using multiple ecological management practices.

In the final study (Chapter 4) I use remote sensing data to test relationships between crop diversification and agroecosystem climate resilience for the lower peninsula of Michigan from 2008-2019. Results of panel fixed effects models and linear regressions indicate that adding overwintering cover crops into rotations offers significant benefits for yields and yield stability. Although heavy spring rainfall delayed primary crop planting dates, delays were reduced with each year of prior cover crop use. Importantly, the positive effects of cover crops took several years to appear, underscoring that continued, long-term use is critical for restoring ecological processes that build climate resilience.

Chapter 5 summarizes key takeaways and implications. Taken together, the three studies highlight the importance of functional diversity for supporting beneficial outcomes in agroecosystems, and that research situated within real world farming conditions is critical for identifying context-dependent relationships. The wide variation in cover crop performance, and benefits that may not be immediately apparent, suggest a need for greater technical and financial support during early stages of transitions to more diversified systems as farmers gain experience and wait for tangible benefits to accrue. In sum, results demonstrate that integrating ecological science with agricultural research is key to advancing food system sustainability and resilience.