Effects of Habitat Heterogeneity on Crop Yield and Biodiversity

View the project final report

Commodities

• Agronomic: grass (misc. annual), grass (misc. perennial), peas (field, cowpeas), wheat
• Additional Plants: native plants
• Animals: bees

Practices

• Crop Production: application rate management, crop improvement and selection, cropping systems, crop rotation, double cropping, forest/woodlot management, intercropping, nutrient cycling, nutrient management, pollination, pollinator habitat, pollinator health, tissue analysis
• Education and Training: demonstration, extension, farmer to farmer, focus group, networking, on-farm/ranch research, participatory research, workshop
• Farm Business Management: budgets/cost and returns, feasibility study
• Natural Resources/Environment: biodiversity, drift/runoff buffers, habitat enhancement, hedgerows, hedges - grass, hedges - woody, wildlife
• Pest Management: biological control, field monitoring/scouting, integrated pest management, traps, weed ecology
• Production Systems: agroecosystems, holistic management
• Sustainable Communities: community development, partnerships, social networks, sustainability measures

Agricultural ecosystems comprise roughly half of the global land surface and are faced with competing tasks of feeding a growing population and conserving global biodiversity. While agriculture has been widely critiqued as a primary driver of habitat fragmentation and biodiversity loss, recent studies have found positive relationships between habitat heterogeneity and biodiversity in agricultural landscapes. Thus, on-farm conservation practices that enhance habitat heterogeneity have the potential to increase biodiversity while having neutral or positive effects on crop production. To test this idea, ecological refugia (defined as uncultivated patches in production fields) were identified on three farms and assessed for their capacity to support biodiversity, enhance ecosystem services, and increase crop yield and crop quality. The research approach included plant surveys, insect collection, seed predation experimentation and grain sampling on each farm. In addition, precision agriculture and remote sensing data were obtained from combine-mounted yield sensors and Google Earth Engine. For data analysis, linear and nonlinear regression were used to analyze plant diversity, insect diversity, seed predation, crop quantity and crop quality as a function of distance from the center of each ecological refuge. Results from fields with ecological refugia were compared to those without refugia to test for a significant difference between field types.  Lastly, a random forest model was built using field survey data and remote sensing variables to clarify what explanatory variables were driving responses in crop yield and crop quality.

Crop fields that had ecological refugia tended to support higher plant diversity than fields without refugia. Furthermore, crop fields with refugia hosted higher levels of native plant diversity than nonnative diversity. On Farms 1 and 2, plant diversity declined significantly with distance from naturally occurring refugia into the crop field. On Farm 3, plant diversity declined significantly with distance from a recently restored refuge by the third year of data collection. On all farms, insect diversity declined significantly with distance from refugia. A higher abundance of beneficial insects was found in crop fields with naturally occurring refugia, while a higher abundance of pest insects was found in the crop field with a newly created refuge and in control fields without refugia. Seed trap data indicated that beneficial weed seed predation services were higher on organic farms while crop seed predation disservices were higher on a conventionally managed farm. Divergent trends for crop yield indicated that yield declined significantly with distance from a naturally occurring refugia on Farm 2 while crop yield increased with distance from a created refuge on Farm 3. A variable importance plot indicated that distance from refuge was the most importance predictor of yield and raised the R-squared value of the yield model from 0.57 to 0.70. Lastly, grain protein concentration had an inverse relationship with grain moisture content and grain phenolic compounds tended to increase with distance from the refuge, suggesting that crops growing near an ecological refuge may be less stressed than plants growing far from one. 

These results highlighted potential tradeoffs of implementing ecological refugia in agroecosystems and demonstrated how habitat heterogeneity impacts crop yield and biodiversity whether heterogeneity is created intentionally or occurs naturally. Encouraging adoption of ecological refugia as an on-farm conservation practice will depend on site-specific evidence that refugia can maintain or increase crop yields, decrease farm inputs, increase beneficial biodiversity, enhance ecosystem services, and increase farm net return. To do so, future research must empirically test the relationship between on-farm biodiversity and habitat fragments at multiple scales, clarify the association between functional groups and ecosystem services, and apply on-farm technology to collect site-specific data that guides on-farm experimentation. One participating farmer planted pollinator strips in an additional field on their farm in attempt to maximize beneficial ecosystem services associated with habitat heterogeneity. Other applications of on-farm habitat conservation planning could enable farmers to identify low-producing areas in their fields and strategically remove them from production, potentially resulting in reduced input costs and enhanced conservation habitat in agricultural landscapes.

The project objectives were to quantify the biodiversity, agronomic, and economic impacts of habitat heterogeneity in dryland small grain production in the Northern Great Plains. Specifically, we quantified the effects of ecological refugia on biodiversity, ecosystem services and crop production on three farms in Montana.

1. First, we aimed to quantify the biodiversity trends associated with ecological refugia on farms. To do so, we measured and compared differences in plant diversity, insect diversity, and insect functional groups between fields with and without ecological refugia. We also quantified how biodiversity trends changed with distance from each refuge.
2. Second, we aimed to determine what ecosystem (dis)services were provided by ecologial refugia. To do so, we measured seed predation rates for crop and weed species in fields with and without ecological refugia and analyzed how seed predation changed with distance from each refuge.
3. Third, we aimed to quantify the costs and benefits that ecological refugia brought to crop production. To do so, we compared differences in crop yield and crop quality between fields with and without ecological refugia and analyzed how crop yield changed with distance from each ecological refuge. 
4. Fourth, we aimed to share findings on ecological refugia and biodiverse farming practices with farmers, undergraduate students and the general public through participation in academic conferences, farmer-led workshops, university courses, public seminars and online formats.