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Like other urban green spaces, urban community gardens can act as biodiversity refugees, especially for small organisms like arthropods. In turn, arthropods can provide important ecosystem pest control services to these agroecosystems. Thus, an often‐asked question among urban gardeners is how to improve gardens and surrounding areas for natural enemies and associated pest control services. We examine how local vegetation and garden characteristics, as well as the surrounding landscape composition, affect ground‐dwelling beetles (Coleoptera: Carabidae and Staphylinidae), spiders (Araneae), opilionids (Opiliones), and ladybird beetles (Coleoptera: Coccinellidae), all of which are important predators. In the summer of 2019, we collected predators, vegetation, ground cover, and garden and landscape characteristic data from 10 community gardens in the city of Seattle, Washington. We found that different groups of natural enemies are associated with different environmental variables and at different scales; probably related to differences in their dispersal capabilities, habits, and diets. Floral variables (number of flowers and number of species in flower) had a negative effect on nonflying natural enemies (spiders, opilionids, and ground‐dwelling beetles), but not on flying ones (ladybird beetles). The only taxon that was significantly affected by a landscape‐scale variable was Opiliones, the only group examined that exclusively disperses by ground. Our results show contrasting results to similar studies in different regions and highlight the need to expand the taxa and regions of study.

It is often argued that biodiversity and ecosystem functioning are linked by both habitat and species composition, and that this relationship is particularly critical for mobile ecosystem service providers. This may be especially true for pollinators, which are essential for the reproduction of the majority of flowering plant species, are highly mobile, and can exhibit dramatically different foraging behaviors across ecosystems. Understanding how habitat and community composition impact pollination is especially relevant in urban environments where pollinators can promote food security. We examined the relationships between local resource density, landscape composition, pollinator abundance and richness, and pollination services in an urban agricultural system spanning >125 km of the California central coast. We used a replicated, experimental approach to evaluate the reproductive success of jalapeño peppers across urban gardens and conducted a greenhouse experiment to evaluate the benefits of insect-mediated pollination to pepper reproduction. In the greenhouse, we found that jalapeño fruit weight and seed number was significantly greater with insect-mediated pollination than without. In the field, we found that jalapeño seed number increased significantly with herbaceous (weed, crop, and ornamental) plant richness and the number of perennial trees and shrubs at the site level, but decreased with the amount of natural landscape cover. We also found that higher pollinator richness enhanced seed number in floral-dense gardens, likely due to the greater functional complementarity of a more diverse pollinator community. Furthermore, there was a positive relationship between pollinator abundance and seed number, but it weakened in gardens with more flowers, likely through lower per-plant pollinator visitation in the presence of competing floral resources. As in past studies, we found that mulch had a negative impact on pollinator abundance, highlighting that abiotic factors commonly managed by gardeners can directly impact ecosystem service providers. This study demonstrates that local conditions can significantly influence ecosystem service provision and that urban gardeners need to optimize for both pollinator richness and floral resource availability to achieve optimal pollination.

Agriculture is being challenged to provide food, and increasingly fuel, for an expanding global population. Producing bioenergy crops on marginal lands—farmland suboptimal for food crops—could help meet energy goals while minimizing competition with food production. However, the ecological costs and benefits of growing bioenergy feedstocks—primarily annual grain crops—on marginal lands have been questioned. Here we show that perennial bioenergy crops provide an alternative to annual grains that increases biodiversity of multiple taxa and sustain a variety of ecosystem functions, promoting the creation of multifunctional agricultural landscapes. We found that switchgrass and prairie plantings harbored significantly greater plant, methanotrophic bacteria, arthropod, and bird diversity than maize. Although biomass production was greater in maize, all other ecosystem services, including methane consumption, pest suppression, pollination, and conservation of grassland birds, were higher in perennial grasslands. Moreover, we found that the linkage between biodiversity and ecosystem services is dependent not only on the choice of bioenergy crop but also on its location relative to other habitats, with local landscape context as important as crop choice in determining provision of some services. Our study suggests that bioenergy policy that supports coordinated land use can diversify agricultural landscapes and sustain multiple critical ecosystem services.

Urban gardens are vital green spaces, providing food for residents and space for engaged citizenry and community development. In California, climate change conditions (heat and drought) are becoming more extreme, threatening the resilience of urban gardens. Water use restrictions limit the timing and amount of water that gardeners can access, exacerbating these climate challenges for urban food production. Together with volunteer gardeners, we examined how ambient temperature, water use, vegetation, ground cover, and soil management affect rates of soil moisture gain and loss in urban gardens for a six-week period in the summer of 2017, during the hottest part of the growing season. We found that plot-level management of soils is essential for creating urban garden plots that maintain stable levels of water within garden soils. Although plots with better soil quality (i.e. water holding capacity) experienced slower rates of soil moisture gain after a watering event, they also experienced slower rates of soil moisture loss after the event, leading to soils with more stable, less fluctuating moisture profiles over time. This may benefit gardeners because under extreme climates (such as heat and drought) and water use restrictions, maintaining more stable soils for their plants means that the soils will retain water over a longer period after each watering event. Overall, such results highlight that better soil management that improves soil quality measures such as water holding capacity are potential solutions for maintaining soil moisture and reducing water use under changing climate conditions.

Although urban gardens are often celebrated for supporting bee abundance and diversity within cities, little is known about how garden management and urbanization levels influence bee foraging behavior and ability to utilize resources within these landscapes. Specifically, the preferences and diet breadth of bees may depend critically on local and landscape conditions in human-managed, urban environments. To understand how foraging patterns and pollen preferences are influenced by urban landscape composition, we first examined if bees visit plants grown within urban gardens and second assessed the relationships between local floral resources, urban land cover, and pollen collection patterns, focusing on 20 community gardens across 125 km of the California central coast. We targeted a well-studied, essential native pollinator in this ecoregion, Bombus vosnesenskii, and analyzed pollen on the bodies of individuals collected in our study gardens to compare their contents to local and landscape garden composition factors. We found that greater landscape-level urban cover and greater plant species richness in the garden both drove higher within-garden pollen collection. We also found that B. vosnesenskii preferred ornamental plant species over highly available crop species in the gardens. Our study indicates that landscapes that support plant diversity, including both ornamental plants and sustenance-oriented food crops, promote greater within-garden pollen collection patterns, with likely benefits for urban garden food production.

The strength and prevalence of trophic cascades, defined as positive, indirect effects of natural enemies (predatory and parasitic arthropods) on plants, is highly variable in agroecosystems. This variation may in part be due to the spatial or landscape context in which these trophic cascades occur. In 2011 and 2012, we conducted a natural enemy exclusion experiment in soybean fields along a gradient of landscape composition across southern Wisconsin and Michigan, USA. We used structural equation modeling to ask (1) whether natural enemies influence biocontrol of soybean aphids (SBA) and soybean yield and (2) whether landscape effects on natural enemies influence the strength of the trophic cascades. We found that natural enemies (NE) suppressed aphid populations in both years of our study, and, in 2011, the yield of soybean plants exposed to natural enemies was 37% higher than the yield of plants with aphid populations protected from natural enemies. The strength of the trophic cascade was also influenced by landscape context. We found that landscapes with a higher proportion of soybean and higher diversity habitats resulted in more NE, fewer aphids, and, in some cases, a trend toward greater soybean yield. These results indicate that landscape context is important for understanding spatial variability in biocontrol and yield, but other factors, such as environmental variability and compensatory growth, might overwhelm the beneficial effects of biocontrol on crop yield.

Urban community gardens are important social–ecological systems from which urban citizens receive many benefits. In this study of 18 urban community gardens in the Central Coast of California, USA, we use a combination of gardener surveys and field-based measurements to evaluate the amount of fresh fruit and vegetables produced by gardeners. We then investigate how food production differed between segments of the gardening population, specifically as a function of gardening experience, time spent in gardens, and food security status. Lastly, we ask gardeners to describe their motivations for gardening to better understand how motivations may relate to individual levels of food production. Thirty-eight percent of gardeners estimate harvesting one to five pounds of food per week, with another 26% estimating six to ten pounds. These estimates were corroborated by field measurements of tomato, squash, and pepper cultivation, where gardeners produced, at the height of the harvest season, an average of four pounds of food per week—an estimated savings of ~ $16USD per week (compared to the cost of local organic fruits and vegetables, June 2023 prices). Regarding the ability of community gardens to reduce food insecurity, gardeners who spent more time in the garden and with higher incomes reported higher food security, while those with larger families or lower incomes were more food insecure. These results show that gardeners in most need of food support were not necessarily the ones cultivating the most fruits and vegetables. While 48% of gardeners reported food cultivation as a primary motivator for gardening, many other motivations (e.g., hobby, being outdoors, relaxation, social interaction, and exercise) were identified as reasons to spend time in the garden, indicating that food production is not the only factor motivating gardeners. Overall, we document that community gardens can be highly productive and provide valuable produce that substantially offsets high fresh food costs; however, gardeners with the greatest food needs are currently not the largest producers, but could benefit from additional resources and support.

Biotic and abiotic factors at local to landscape scales influence insect pest and disease dynamics in agricultural systems. However, relative to studies focused on the importance of these drivers of crop plant damage in rural agricultural systems, few studies investigate plant damage from herbivore insects and plant diseases in urban agroecosystems, and consequently, most urban farmers lack knowledge on crop protection tactics. Here we use three common crop species within urban agroecosystems (community gardens) distributed across an urban landscape as a model system to ask how local, landscape, and microclimate factors relate to herbivore and disease plant damage. We hypothesized that plant damage would be lower in gardens with greater local vegetation complexity, landscape‐scale complexity, and less variable temperatures, but that the importance of factors is species‐ and damage‐specific. By measuring Brassica, cucurbit, and tomato insect pest and disease damage across the growing season, we confirmed that the importance of factors varies with crop species and by damage type. Both local complexity factors (e.g., number of trees and shrubs) and landscape complexity (percent natural cover in the landscape) relate to lower incidence of herbivore and disease damage on some crops, supporting our prediction that habitat heterogeneity at both local and landscape scales lowers plant damage. Greater temperature variability related to higher disease damage on tomatoes linking microclimate factors to disease prevalence. Yet, local complexity factors also related to higher incidence of plant damage for other crop species, indicating variable species‐level impacts of local management factors on plant damage. By measuring the abundance of fungus‐feeding lady beetles (Psyllobora) on cucurbits, we confirmed a strong association between natural enemies and powdery mildew. We provide a case study on how changes in local to landscape‐scale factors relate to plant damage in urban agroecosystems and suggest how urban farmers and gardeners can apply this ecological knowledge to improve sustainable urban food production.

Biological pest control relies on interactions between herbivores and their natural enemies. Maintaining this ecosystem service requires considering herbivore and natural enemy interactions and their response to anthropogenic change at multiple scales. In this study, we used ecological networks to quantify the network structure of interactions between herbivorous insects and their parasitoids. We examined how herbivore host abundance, parasitism rates, and shifts in network structure relate to changes in local habitat management and landscape context. We sampled herbivores and parasitoids in Brassica oleracea plants at 22 urban gardens in the Central Coast of California. At each site, we measured local management characteristics (e.g., vegetation, ground cover, canopy cover) and quantified surrounding landscape composition (e.g., urban, natural, open, and agricultural cover). For the eight sites with large enough networks, we calculated three network structure metrics (interaction richness, vulnerability, and functional complementarity). We then used generalized linear and mixed models to examine relationships between herbivore host abundance, parasitism rates, garden management and landscape characteristics, and network metrics. We found that both local management and landscape composition influenced parasitism, while only local factors affected host abundance and network structure. Higher network interaction richness was marginally associated with enhanced parasitism rates for two host species and lower parasitism rates for one host species. Our results suggest that local garden management decisions may shift the structure of host–parasitoid networks, which may subsequently affect host parasitism rates, but outcomes for biological pest control will likely vary across host species.

Spatial heterogeneity is essential for the persistence of many inherently unstable systems such as predator-prey and parasitoid-host interactions. Since biological interactions themselves can create heterogeneity in space, the heterogeneity necessary for the persistence of an unstable system could be the result of local interactions involving elements of the unstable system itself. Here we report on a predatory ladybird beetle whose natural history suggests that the beetle requires the patchy distribution of the mutualism between its prey, the green coffee scale, and the arboreal ant, Azteca instabilis. Based on known ecological interactions and the natural history of the system, we constructed a spatially-explicit model and showed that the clustered spatial pattern of ant nests facilitates the persistence of the beetle populations. Furthermore, we show that the dynamics of the beetle consuming the scale insects can cause the clustered distribution of the mutualistic ants in the first place. From a theoretical point of view, our model represents a novel situation in which a predator indirectly causes a spatial pattern of an organism other than its prey, and in doing so facilitates its own persistence. From a practical point of view, it is noteworthy that one of the elements in the system is a persistent pest of coffee, an important world commodity. This pest, we argue, is kept within limits of control through a complex web of ecological interactions that involves the emergent spatial pattern.