Lauren C. Ponisio

Diversification practices reduce organic to conventional yield gap

Agriculture today places great strains on biodiversity, soils, water and the atmosphere, and these strains will be exacerbated if current trends in population growth, meat and energy consumption, and food waste continue. Thus, farming systems that are both highly productive and minimize environmental harms are critically needed. How organic agriculture may contribute to world food production has been subject to vigorous debate over the past decade. Here, we revisit this topic comparing organic and conventional yields with a new meta-dataset three times larger than previously used (115 studies containing more than 1000 observations) and a new hierarchical analytical framework that can better account for the heterogeneity and structure in the data. We find organic yields are only 19.2% (±3.7%) lower than conventional yields, a smaller yield gap than previous estimates. More importantly, we find entirely different effects of crop types and management practices on the yield gap compared with previous studies. For example, we found no significant differences in yields for leguminous versus non-leguminous crops, perennials versus annuals or developed versus developing countries. Instead, we found the novel result that two agricultural diversification practices, multi-cropping and crop rotations, substantially reduce the yield gap (to 9 ± 4% and 8 ± 5%, respectively) when the methods were applied in only organic systems. These promising results, based on robust analysis of a larger meta-dataset, suggest that appropriate investment in agroecological research to improve organic management systems could greatly reduce or eliminate the yield gap for some crops or regions.

Habitat restoration promotes pollinator persistence and colonization in intensively managed agriculture.

Widespread evidence of pollinator declines has led to policies supporting habitat restoration including in agricultural landscapes. Yet, little is yet known about the effectiveness of these restoration techniques for promoting stable populations and communities of pollinators, especially in intensively managed agricultural landscapes. Introducing floral resources, such as flowering hedgerows, to enhance intensively cultivated agricultural landscapes is known to increase the abundances of native insect pollinators in and around restored areas. Whether this is a result of local short-term concentration at flowers or indicative of true increases in the persistence and species richness of these communities remains unclear. It is also unknown whether this practice supports species of conservation concern (e.g., those with more specialized dietary requirements). Analyzing occupancies of native bees and syrphid flies from 330 surveys across 15 sites over eight years, we found that hedgerow restoration promotes rates of between-season persistence and colonization as compared with unrestored field edges. Enhanced persistence and colonization, in turn, led to the formation of more species-rich communities. We also find that hedgerows benefit floral resource specialists more than generalists, emphasizing the value of this restoration technique for conservation in agricultural landscapes.

Pyrodiversity begets plant-pollinator community diversity.

Fire has a major impact on the structure and function of many ecosystems globally. Pyrodiversity, the diversity of fires within a region (where diversity is based on fire characteristics such as extent, severity, and frequency), has been hypothesized to promote biodiversity, but changing climate and land management practices have eroded pyrodiversity. To assess whether changes in pyrodiversity will have impacts on ecological communities, we must first understand the mechanisms that might enable pyrodiversity to sustain biodiversity, and how such changes might interact with other disturbances such as drought. Focusing on plant-pollinator communities in mixed-conifer forest with frequent fire in Yosemite National Park, California, we examine how pyrodiversity, combined with drought intensity, influences those communities. We find that pyrodiversity is positively related to the richness of the pollinators, flowering plants, and plant-pollinator interactions. On average, a 5% increase in pyrodiversity led to the gain of approximately one pollinator and one flowering plant species and nearly two interactions. We also find that a diversity of fire characteristics contributes to the spatial heterogeneity (β-diversity) of plant and pollinator communities. Lastly, we find evidence that fire diversity buffers pollinator communities against the effects of drought-induced floral resource scarcity. Fire diversity is thus important for the maintenance of flowering plant and pollinator diversity and predicted shifts in fire regimes to include less pyrodiversity compounded with increasing drought occurrence will negatively influence the richness of these communities in this and other forested ecosystems. In addition, lower heterogeneity of fire severity may act to reduce spatial turnover of plant-pollinator communities. The heterogeneity of community composition is a primary determinant of the total species diversity present in a landscape, and thus, lower pyrodiversity may negatively affect the richness of plant-pollinator communities across large spatial scales.

Temporal dynamics influenced by global change: bee community phenology in urban, agricultural, and natural landscapes.

Urbanization and agricultural intensification of landscapes are important drivers of global change, which in turn have direct impacts on local ecological communities leading to shifts in species distributions and interactions. Here, we illustrate how human-altered landscapes, with novel ornamental and crop plant communities, result not only in changes to local community diversity of floral-dependent species, but also in shifts in seasonal abundance of bee pollinators. Three years of data on the spatio-temporal distributions of 91 bee species show that seasonal patterns of abundance and species richness in human-altered landscapes varied significantly less compared to natural habitats in which floral resources are relatively scarce in the dry summer months. These findings demonstrate that anthropogenic environmental changes in urban and agricultural systems, here mediated through changes in plant resources and water inputs, can alter the temporal dynamics of pollinators that depend on them. Changes in phenology of interactions can be an important, though frequently overlooked, mechanism of global change.

System-level approach needed to evaluate the transition to more sustainable agriculture.

We disagree with Leifeld fundamentally on the purpose of our agricultural system—our goal should be to produce nutritious, affordable and accessible food in a socially and environmentally sustainable manner and not just ‘keeping prices low’. So-called low-cost food produced by industrialized,

Hedgerow presence does not enhance indicators of nest‐site habitat quality or nesting rates of ground‐nesting bees

RESEARCH ARTICLE Hedgerow presence does not enhance indicators of nest-site habitat quality or nesting rates of ground-nesting bees Hillary S. Sardinas 1,2 , Lauren C. Ponisio 1 , Claire Kremen 1 A major challenge in habitat restoration is targeting the key aspects of a species’ niche for enhancement, particularly for species that use a diverse set of habitat features. However, restoration that focuses on limited aspects of a species’ niche may neglect other resources that are critical to population persistence. We evaluated the ability of native plant hedgerows, planted to increase pollen and nectar resources for wild bees in agricultural landscapes, to provide suitable nesting habitat and enhance nesting rates of ground-nesting bees. We found that, when compared to unmanaged field edges (controls), hedgerows did not augment most indicators of nest habitat quality (bare ground, soil surface irregularity, and soil hardness), although coarser soils were associated with higher incidence and richness of nesting bees. Hedgerows did not augment nesting rates when compared to control edges. Although all the bee species we detected nesting were also found foraging on floral resources, the foraging versus nesting assemblages found within a site were highly dissimilar. These results may reflect sampling error; or, species found foraging but not nesting in hedgerows could be utilizing hedgerows as “partial habitats,” nesting outside hedgerow plantings but foraging on the floral resources they provide. We conclude that although hedgerows are known to provide critical floral resources to wild bees especially in resource-poor intensive agricultural landscapes, simply increasing vegetative diversity and structure may not be simultaneously enhancing nesting habitat for ground-nesting bees. Key words: agriculture, conservation, emergence traps, field edges, nesting resources, pollination services, restoration Implications for Practice • Increasing flowering vegetation does not necessar- ily translate into increases in nesting habitat for ground-nesting bees. • Using indicators of nest-site quality may not correlate with ground-nesting bee abundance and richness. • Bee species found foraging in hedgerows will not always be indicative of the bee species nesting within hedgerows. • Some bees foraging in hedgerows use hedgerows as a partial habitat that provides critical flowering resources. • Limited nesting habitat will limit the ability of nesting bees to establish in restored habitats. Introduction For restoration projects aimed at promoting specific species or guilds, it is important to enhance habitat characteristics on which target taxa rely (Miller & Hobbs 2007). Yet the autecol- ogy of many species, particularly invertebrates, is complex and often poorly understood (Murray et al. 2009). Thus, a restora- tion project may elect to focus on readily managed factors known to affect a species’ life-history. However, if only one dimension of a species’ niche is restored, other factors critical to their establishment may be inadvertently neglected. For species reliant on restored fragments, an absence or lack of specific fea- tures could cause an area either to be unoccupied or to function Restoration Ecology as a sink (Pulliam 1988). Determining whether restoration of some habitat elements can enhance other key habitat features may be important for sustaining local populations of the species of interest. Wild bees (Hymenoptera: Apoidea) are critically important species in natural and agricultural areas (Memmott et al. 2004; Garibaldi et al. 2013), and as such, have been the focus of habi- tat enhancement projects (Dixon 2009; Winfree 2010; Menz et al. 2011; Garibaldi et al. 2014). Pollen and nectar are the sole food supply for bee larvae, therefore floral blooms are essential for bee reproduction. In addition, bees require nest- ing substrates (e.g. appropriate soil conditions for belowground nesters; pithy stems or cavities in wood for aboveground nesters) and nesting materials (e.g. mud or leaves to construct partitions between brood cells). Bees are central place foragers; thus flo- ral and nesting resources must be within flight range of their Author contributions: HSS, CK designed the research; HSS carried out the research; HSS, LCP conducted the analyses; HSS, LCP, CK coauthored and edited the manuscript. 1 Department of Environmental Science, Policy, and Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720, U.S.A. 2 Address correspondence to H. S. Sardinas, email hsardinas@berkeley.edu

Agricultural practices for food safety threaten pest control services for fresh produce

Summary Over the past decade, several foodborne disease outbreaks provoked widespread reforms to the fresh produce industry. Subsequent concerns about wildlife vectors and contaminated manures created pressure on growers to discontinue use of manure-based composts and remove nearby semi-natural vegetation. Despite widespread adoption, impacts of these practices on ecosystem services such as pest control have not been assessed. We used a landscape-scale field experiment to quantify associations between compost applications, semi-natural vegetation, pest control services and lettuce yields on organic farms throughout Californias Central Coast, a region experiencing food safety reforms. We found that farms with surrounding semi-natural vegetation supported a diverse arthropod assemblage, whereas a herbivore-dominated assemblage occupied farms in simplified landscapes. Moreover, predatory arthropods consumed more herbivores at sites with more surrounding non-crop vegetation and reduced aphid pest infestations in lettuce. Compost improved lettuce yields by increasing soil nutrients and organic matter, but affected neither pest control nor Escherichia coli prevalence. Synthesis and applications. Food safety concerns are prompting practices that simplify farms and landscapes. Our results demonstrate that two practices – elimination of manure-based composts and removal of non-crop vegetation – are likely having negative impacts on arthropod biodiversity, pest control and soil quality. Critically, our findings and previous research suggest that compost can be applied safely and that habitat removal is likely ineffective at mitigating food safety risk. There is thus scope for co-managing fresh produce fields for food safety, ecosystem services, and biodiversity through applying appropriately treated composts and stopping habitat removal.

Pollinator Community Assembly Tracks Changes in Floral Resources as Restored Hedgerows Mature in Agricultural Landscapes

Intensive agriculture reduces wild pollinator abundance, diversity and pollination services, while depending critically on wild pollinators for crop pollination. Floral enhancements such as hedgerows (native, perennial flowering trees and shrubs) can enhance pollinator colonization, persistence, occupancy, and species richness within intensive agricultural landscapes. However, little is known about the specific features of hedgerows that promote pollinator communities in such landscapes. Understanding how pollinator communities respond to local changes in site conditions as hedgerows mature, such as the availability of floral or nesting resources, can help guide the design of more effective hedgerows that promote pollinators and/or pollination services. In an intensively-managed agricultural region of California, we found that pollinator community attributes responded principally to the enhancement of floral diversity as hedgerows mature, as well as to surrounding natural habitat. Once hedgerows matured, this relationship leveled off, suggesting either saturation of community assembly processes, or greater importance of floral density/display relative to diversity. Although we did not find any relationships between measures of pollinator community diversity and nesting resources, such resources are notably difficult to measure. Surrounding natural habitat also affected species and functional richness at hedgerows, particularly for solitary bees that nest above ground. Such species are known to be particularly sensitive to the negative effects of agriculture. Thus, hedgerows in combination with natural habitat may reverse some of the community disassembly provoked by intensive agriculture.