Transitioning to agricultural systems that are both productive and sustainable is a grand challenge currently facing humanity. If food production continues to incur the environmental and social costs of the industrialized agricultural systems that dominate much of the world’s agriculture, then humanity will fail to conserve biodiversity, meet climate change goals, or create landscapes healthy for people. This project investigated to what extent diversifying farming systems could address these challenges, and what factors help or hinder transitions toward more diversified farming systems. Such systems increase above- and below-ground biological diversity directly through crop and non-crop plantings, and indirectly by nurturing beneficial organisms and soil and water conservation practices. Mounting evidence shows that increasing biodiversity supports joint environmental and social outcomes. Our coupled natural-human systems approach provided a vantage point on both how farmers navigate conflicting incentives and regulations that affect their management decisions, and the consequences of their decisions for food production and environment.

On-farm ecological research studied how diversification practices within and around farmers’ crop fields, as well as the composition of land surrounding farms, influenced the diversity and composition of birds and soil microbes, and the ecosystem services provided by each group. The project focused on organic farms growing lettuce in the Central Coast of California, a major US agricultural region where soil health, drinking water quality, and wildlife habitat have deteriorated.

For birds, ungrazed semi-natural areas surrounding farms were associated with higher bird diversity, more species of conservation concern, and fewer flocks that potentially pose foodborne pathogen risks. In contrast, on-farm diversification practices  offered weaker bird conservation benefits. Surrounding grazed lands were associated with more bird diversity but also more potentially pathogenic bird feces in crop fields, a concern for food safety. 

For soil microbes, few field practices and surrounding land use types affected microbial community diversity. Only crop diversity at the field scale positively correlated with increased soil bacterial diversity and fungal ecological guild diversity. By contrast, field practices and surrounding land use types significantly influenced soil microbial community composition to similar degrees. Thus, as for aboveground ecological communities, scales beyond the farm must be considered to steward soil microbiomes that underpin soil-based ecosystem services.

We found that within-field diversification practices were critical for soil-based ecosystem services, including soil carbon sequestration, protection of groundwater quality, soil fertility, microbial activity, and crop productivity. We observed that diversification practices (including continuous crop cover, reduced disturbance, increased crop diversity, and organic amendments) enhanced individual services, except for higher crop diversification which may have decreased lettuce yields. Tradeoffs between ecosystem services tended to be driven by fields with lower use of diversification practices. Continuous living cover (e.g., cover cropping) was most associated with agroecosystem multifunctionality, even when ecosystem services were differentially weighted according to different stakeholders’ priorities.

Despite the promise of these field practices and landscape features for supporting above and below-ground biodiversity and associated ecosystem services, these practices are not widely used across Central Coast farms. Our remote sensing studies showed that only ~6% of farmland had winter cover crops while 22% of farm fields had any amount of hedgerows or windbreaks. In-depth qualitative research revealed persistent barriers that growers face in adopting diversification practices. High land rents, the predominance of short-term leases, stringent food safety standards (especially from private markets), and other supply chain pressures significantly hamper adoption of diversification practices. Yet these barriers were not felt evenly across different types of farms. Limited resource and wholesale growers both experience distinct barriers that constrain adoption of diversification practices, while some mid-scale diversified growers can succeed in both economic and ecological terms. The key enabling factors that allow these farmers to choose diversification, however, are not directly related to their farm size, but have more to do with secure land tenure, adequate access to capital and resources, and buyers who share their values and are willing to pay a premium. Further, using a Markov decision process model based on our field research, we found that transitioning to diversified farming systems requires policies that enable decision making over long time horizons to accommodate often slow-to-appear benefits from diversification practices.

Our broader impacts include evidence to support policies that protect biodiversity, enhance ecosystem services, and allow for thriving farms. For example, habitat conservation around produce farms could support bird conservation without increasing foodborne pathogens, especially on farms further from grazing lands. Local water quality regulations that incentivize continuous living cover could in turn support multiple ecosystem services. By targeting policies at key enabling factors, it is possible to encourage diversification practices at multiple scales in California’s Central Coast. Broader impacts also included direct engagement with growers (e.g. dozens of face-to-face meetings), extension personnel, and policymakers regarding research results, as well as training from undergraduate to faculty levels in interdisciplinary science. 

Last Modified: 06/12/2024
Modified by: Timothy Bowles