Etienne Sutton's Dissertation Defense
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Dissertation Title: Ecological Approaches to Managing Crop Diversity for Sustainability and Resilience in the Great Lakes Region
Chair: Dr. Jennifer Blesh
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 real farms in the Great Lakes region.
The first dissertation study (Chapter 2) explores 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.
The second study (Chapter 3) uses 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.
The final study (Chapter 4) uses 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. Given wide variation in cover crop performance,
and that their benefits may not be immediately apparent, this suggests 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, this dissertation
demonstrates that integrating ecological science with agricultural research is key to advancing
food system sustainability and resilience.