Progress report for GNE24-317
Project Information
Insects and other arthropods are pivotal components of agricultural landscapes. They contribute to ecosystem services such as pollination, but can also cause devastating crop damage as pests. Impacting the effect of their interactions with crops, arthropod diversity is associated with many factors, among which are the local (e.g. plant, plot, field) and landscape (garden, surrounding ecosystems) habitats described by factors including plant diversity and land uses. Though a growing literature investigates the effects of local and landscape factors on the arthropod community, limited research has focused on these dynamics in urban agriculture, a particularly complex and heterogeneous landscape.
This study aims to better understand the effects of plant diversity and site characteristics at different spatial scales on the arthropod community composition in urban community gardens, which are increasingly recognized for their social and ecological benefits. To capture the diversity of agriculturally significant arthropod groups, we designed surveys of crop pests and herbivory and flower-visiting insects in gardens with different plant management intensities across spatial scales. We collected crop pests and herbivory during the harvest season, as well as local and landscape scale site characteristics in the community gardens, such as plant diversity, through on-site observation. We plan to survey pollinators with parallel methods for site characteristics during spring. We will further collect plot and garden sizes and the amount of green space in the neighborhood using remote sensing methods. By analyzing and determining crucial factors and scales that arthropod communities respond to, we aim to inform sustainable management practices in urban community gardens to optimize beneficial insects and reduce pest impacts while conserving the overall arthropod community through collaborations with urban gardeners, garden managers, and city planners.
Objective 1: To determine the role of plant diversity and site characteristics in affecting overall arthropod diversity (pollinator and pest) in community gardens. Using targeted sampling methods, we collected pests and other arthropods on crops in individual gardeners’ plots to assess arthropod species richness and abundance. We further collected plant diversity through plant censusing and site characteristics to describe individual gardeners’ plots and the gardens. We will collect pollinator richness and abundance along with plant diversity and site characteristics in the spring and integrate the results with the pest survey. We will address the question by determining the relationships and significance of the relationships between local and landscape factors and arthropod richness and abundance.
Objective 2: To investigate the effect of spatial scales of plant diversity and site characteristics on arthropod diversity (pollinator and pest). By using plant diversity collected at the plot level scale, and the garden plant diversity estimated from the samples of plot level diversity, we will compare the effect size and significance of the effect size of plant diversity at the two levels on arthropod richness and abundance. Site characteristics describing land uses and plant communities will be collected at the individual plot level scale, garden level scale, and neighborhood scale (from a buffer distance of the garden) and we will compare the effect size on the arthropod community.
Objective 3: To assess if and how pollinators and pests respond differently to plant diversity and site characteristics across various spatial scales, as well as their impact on crop success. By examining the two groups, we will compare the responses of pollinators and pests to landscape factors. In examining pest richness and abundance, we also included herbivory as an additional measure that directly reflects crop damage and influences gardeners’ management and crop yield. By connecting herbivory and pest communities, we aim to deepen our understanding of the impact on gardeners of potential response in pest communities to landscape factors.
The purpose of this project is to better understand the plant diversity and site characteristics at different spatial scales that affect arthropod community composition in urban community gardens. This work will inform managers and gardeners of best practices to optimize the landscape for sustainable management of arthropods.
Insects and other arthropods are an important part of agricultural landscapes, serving essential roles in the success of crops, and other plants and animal communities in the agroecosystems (Pedigo et al., 2021; Weisser & Siemann, 2008). Pollination, for example, is a fundamental ecosystem service integral to the fruit set of many crops, valued at US $215 billion globally in 2005 (Gallai et al., 2009; Losey & Vaughan, 2006; Vanbergen & Initiative, 2013). Meanwhile, arthropod pests destroy an estimated 18 - 26% of annual crop production worldwide, with damages valued at US $470 billion (Culliney, 2014), making pest control an integral management aspect in crop production. Although insects and other arthropods can affect agricultural production, the reverse is also true. Agricultural intensification is a major driver that contributes to the declines in arthropod diversity and abundance worldwide, with most well-documented cases in Europe recording more than 75 percent decline over 27 years (Hallmann et al., 2017; van der Sluijs, 2020; Wagner, 2020). Land use changes associated with agricultural intensification in particular have led to drastic changes in arthropod community composition, through both direct losses of habitats and the effects of the spatial patterns in the newly created landscapes. (Crist et al., 2006; Outhwaite et al., 2022). In these landscapes, spatial heterogeneity created by different land use fragments provides suitable and unsuitable patches of habitats, and barriers and corridors that dictate insect population persistence and movement (De Carvalho Guimarães et al., 2014).
In response to the decline in arthropod biodiversity and abundance and the complex feedback between arthropods and agriculture, the management of the heterogeneous landscape around agriculture, namely the agricultural matrix, has become a new focus (Vandermeer & Perfecto, 2007). Plant diversity, land use fragment types, sizes, landscape configurations, and spatial connectivity can all impact arthropod community composition through the provision of resources and habitats (Vandermeer & Perfecto, 2007; e.g. Diekötter et al., 2008; Lemessa et al., 2015). Pollinator diversity, for example, benefits from local diverse floral resources and the amount of high-quality habitats on the landscape scale, while being less impacted by the configuration of habitats (Kennedy et al., 2013). The diversity and abundance of natural enemies that are associated with lower pest abundance (Letourneau et al., 2009) have often been found to respond positively to complex structures of vegetation locally, but may respond negatively to land cover diversity based on the insect groups and their use of resources and habitats (Holzschuh et al., 2010; Karp et al., 2018; Martin et al., 2016). Pest diversity is often correlated with local plant diversity due to the evolutionary history, but mixed effects have been seen with respect to pest abundance and further overall crop damage (Chaplin-Kramer et al., 2011; Dangles et al., 2009). These studies have provided a basis for understanding landscape management for insects and other arthropods in agriculture.
However, studies establishing these trends have been conducted primarily in rural areas, while less is known in urban agriculture which has become increasingly important for addressing challenges in cities’ access to fresh food and nature (Kuddus et al., 2020). In urban ecosystems, insects and other arthropods face a unique landscape, often inhabiting the rare green spaces surrounded by urban environments. Urban community gardens as a major form of urban agriculture create a landscape where land use fragments of different quality and size may transition sharply at different spatial scales. From local plots that each gardener manages differently, to the gardens bordering roads and buildings, to neighborhoods where additional green spaces exist to provide additional habitats, arthropods of different groups may see and use the landscape differently, contributing to the complexity of management in urban community gardens (Barr et al., 2021; Ong et al., 2020).
In this study, we aim to understand the impacts of factors including local and landscape plant diversity, land use patches and configurations on arthropod diversity. Specifically, we focus on plant diversity and site characteristics that describe spatial patterns at different spatial scales in urban community gardens and investigate their effects on pollinators and pests, one beneficial and one detrimental group of agriculturally significant arthropods. This study will help inform sustainable management of the landscape to optimize agricultural productivity and biodiversity conservation.
References
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Chaplin-Kramer, R., M. E. O’Rourke, E. J. Blitzer, and C. Kremen. 2011. A meta-analysis of crop pest and natural enemy response to landscape complexity. Ecology Letters 14:922–932.
Crist, T. O., S. V. Pradhan-Devare, and K. S. Summerville. 2006. Spatial variation in insect community and species responses to habitat loss and plant community composition. Oecologia 147:510–521.
Culliney, T. W. 2014. Crop Losses to Arthropods. Pages 201–225 in D. Pimentel and R. Peshin, editors. Integrated Pest Management: Pesticide Problems, Vol.3. Springer Netherlands, Dordrecht.
Dangles, O., V. Mesías, V. Crespo-Perez, and J.-F. Silvain. 2009. Crop damage increases with pest species diversity: evidence from potato tuber moths in the tropical Andes. Journal of Applied Ecology 46:1115–1121.
De Carvalho Guimarães, C. D., J. P. R. Viana, and T. Cornelissen. 2014. A Meta-Analysis of the Effects of Fragmentation on Herbivorous Insects. Environmental Entomology 43:537–545.
Diekötter, T., R. Billeter, and T. O. Crist. 2008. Effects of landscape connectivity on the spatial distribution of insect diversity in agricultural mosaic landscapes. Basic and Applied Ecology 9:298–307.
Gallai, N., J.-M. Salles, J. Settele, and B. E. Vaissière. 2009. Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecological Economics 68:810–821.
Hallmann, C. A., M. Sorg, E. Jongejans, H. Siepel, N. Hofland, H. Schwan, W. Stenmans, A. Müller, H. Sumser, T. Hörren, D. Goulson, and H. de Kroon. 2017. More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLOS ONE 12:e0185809.
Holzschuh, A., I. Steffan-Dewenter, and T. Tscharntke. 2010. How do landscape composition and configuration, organic farming and fallow strips affect the diversity of bees, wasps and their parasitoids? Journal of Animal Ecology 79:491–500.
Karp, D. S., R. Chaplin-Kramer, T. D. Meehan, E. A. Martin, F. DeClerck, H. Grab, C. Gratton, L. Hunt, A. E. Larsen, and A. Martínez-Salinas. 2018. Crop pests and predators exhibit inconsistent responses to surrounding landscape composition. Proceedings of the National Academy of Sciences 115:E7863–E7870.
Kennedy, C. M., E. Lonsdorf, M. C. Neel, N. M. Williams, T. H. Ricketts, R. Winfree, R. Bommarco, C. Brittain, A. L. Burley, D. Cariveau, L. G. Carvalheiro, N. P. Chacoff, S. A. Cunningham, B. N. Danforth, J.-H. Dudenhöffer, E. Elle, H. R. Gaines, L. A. Garibaldi, C. Gratton, A. Holzschuh, R. Isaacs, S. K. Javorek, S. Jha, A. M. Klein, K. Krewenka, Y. Mandelik, M. M. Mayfield, L. Morandin, L. A. Neame, M. Otieno, M. Park, S. G. Potts, M. Rundlöf, A. Saez, I. Steffan-Dewenter, H. Taki, B. F. Viana, C. Westphal, J. K. Wilson, S. S. Greenleaf, and C. Kremen. 2013. A global quantitative synthesis of local and landscape effects on wild bee pollinators in agroecosystems. Ecology Letters 16:584–599.
Kuddus, M. A., E. Tynan, and E. McBryde. 2020. Urbanization: a problem for the rich and the poor? Public Health Reviews 41:1.
Lemessa, D., P. A. Hambäck, and K. Hylander. 2015. The effect of local and landscape level land-use composition on predatory arthropods in a tropical agricultural landscape. Landscape Ecology 30:167–180.
Letourneau, D. K., J. A. Jedlicka, S. G. Bothwell, and C. R. Moreno. 2009. Effects of natural enemy biodiversity on the suppression of arthropod herbivores in terrestrial ecosystems. Annual Review of Ecology, Evolution and Systematics 40:573.
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Martin, E. A., B. Seo, C.-R. Park, B. Reineking, and I. Steffan-Dewenter. 2016. Scale-dependent effects of landscape composition and configuration on natural enemy diversity, crop herbivory, and yields. Ecological Applications 26:448–462.
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Research
Study site
The study is conducted in urban community gardens in Boston managed by the Trustees of Reservation. Boston is a cultural and financial center in the Northeast, playing key roles historically and continuing to evolve as a modern metropolitan. The metropolitan area has varying levels of urban density. The Inner Core consists of high-density commercial districts with little vacant developable land, and a high density of multifamily housing in dense, walkable areas (Boston Region MPO, 2019). Some regional urban centers outside of the Inner Core feature multi-story buildings at each center, and moderately dense to lower-density, single-family residential development in the neighborhoods (Boston Region MPO, 2019). Boston is located on the coast of the North Atlantic, with a climate described either as a humid subtropical climate or a humid continental climate (Beck et al., 2018). Hot and humid summers are typical in these climates (Beck et al., 2018), supporting a productive growing season for various crops and flowers and the productivity of community gardens in the heart of the urban landscape.
The Trustees of Reservations is a non-profit organization managing 56 urban community gardens in Boston, across eight neighborhoods (The Trustees, 2023). The gardens are located in neighborhoods with varying landscapes from different urban densities and unique population demographics (Boston Planning and Development Agency, 2021). Gardeners are free to decide the crops or ornamental plants in the garden, resulting in a high variation in the plant community. All gardeners are asked to follow garden rules set by the Trustees (The Trustees, 2023) with possible additional agreements within each garden. In the community gardens, pesticide and chemical fertilizer use is prohibited, while natural fertilizer and pest controls are allowed.
Sample sizes and design
Twenty-two gardens in eight neighborhoods were selected as candidates for this project based on a pilot study of plant diversity in the Boston community gardens and the interests of The Trustees, including gardens with observed different management practices, such as crop selection and diversity, ornamental plant percentage, and levels of weeds. In each garden, five plots were randomly selected for arthropod sampling of flower-visiting insects and crop pests, prioritizing plots with vegetation data from prior years. In total, we aimed to sample 100 individual gardeners’ plots for arthropods. The sample size and design are adjusted in the field for meaningful collection and by the availability of appropriate sites. We initially proposed to sample pests and pollinators concurrently but prioritized pest sampling in fall 2024 harvest season to ensure high data quality in the limited time frame and ecological relevance based on the phenology of the different groups of arthropods. Flower-visiting insect collection will be conducted in spring 2025, following parallel designs. Additional information on the method change can be found in the “Explanation and justification of methods change” section.
Arthropod sampling methods
Crop pest collection
We initially proposed to randomly select leaves in any plants to inspect for potential crop pests for three minutes in each plot and collect any observed pests. To standardize the arthropod collection in the field by different field researchers and minimize variability introduced by random plant sampling, we adapted the methods to observe and collect arthropods from two focal crop types, tomato plants (Solanum lycopersicum) and pepper plants (Capsicum annuum and Capsicum chinense), which are common and important crops in the community gardens.
Focusing on the effects of plant diversity and site characteristics on pest communities in the focal crop types, we selected five individual gardeners’ plots per garden, prioritizing plots containing at least three plants of each focal crop. When fewer than five plots met the criteria, we selected from the remaining plots with the highest number of focal plants. In total, we sampled pests in 109 plots across the 22 gardens across eight neighborhoods (Figure 1) and on a total of 242 tomato plants and 225 pepper plants.
At each plot, we selected three tomato plants and three pepper plants, prioritizing non-adjacent individuals. Field researchers then observed and collected all arthropods from individual focal plants within a three-minute time frame, which was sufficient for examining the entire plant. Three field researchers concurrently manually collected all arthropods from the three selected plants of each focal crop type, using forceps, insect aspirators, nets, and by hand. The samples from each plant were preserved in individually labeled centrifuge tubes containing 70% ethanol for further processing. Larger arthropods were preserved in additional labeled vials. The arthropods collected from the plots are being processed in the lab, classified by order, and identified to morphospecies.
We selected tomato and pepper plants as focal crops due to their popularity and value to the gardeners, and we additionally included herbivory levels on the plants as a response variable to better inform management implications of the pest community results. We estimated the percent herbivory damage on the plants by examining all leaves on each plant and recording the percent area lost to herbivory (e.g. Figure 2). To reduce observational bias and assess the extent of damage to the plants, the herbivory estimates were categorized into predefined damage classes to standardize observations (Table 1).
Table 1. Crop damage in percentage and the corresponding damage classes.
|
Percent damage (%) |
Damage class |
|
< 5 |
1 |
|
6 – 15 |
2 |
|
16 – 50 |
3 |
|
> 50 |
4 |
Flower-visiting insects (pollinators)
We will visually sample flower-visiting insects by adapting existing methods for pollinator sampling, by quantifying insect visitation in the plot and on specific floral resources (O’Connor et al., 2019). At each plot, one researcher will stand in front of the plot and observe a 1m*1m area for flower-visiting insects for five minutes. The researcher will assign each insect to the following taxonomic groups: bumblebees, honeybees, solitary bees (including primitively eusocial species), hoverflies, and others. The researcher will take a photo of each observed insect morphospecies and record the number for each morphospecies observed. In addition, we will bring a potted flowering plant to each plot, and place the plant in the middle of the plot. A pepper plant will be used since it is easy to acquire and is commonly found in all gardens. One researcher will observe and record the insects visiting the potted flowering plant and count the number of flower visitors during the five-minute interval. We will use the photos of the flowering visiting insects to cross-check the results if necessary after data collection and to confirm morphospecies richness. The number of unique species from the two collection methods in a plot will be recorded to construct the community composition of the groups of interest, and Shannon’s diversity index for arthropods will be calculated for each plot.
Plant diversity
Plant richness and abundance were collected at the plot level to construct measures of plant diversity. At each plot, we sampled all plants present, including crops, herbs, ornamental plants, and weeds. We determined the unique species of plants and estimated the abundance of each species and its ground cover. We recorded the varieties of common crops when known to capture finer-scale plant diversity. We further estimated the total ground cover and weed cover at each plot.
At the plot scale, the number of unique species, plant abundance, and Shannon’s diversity index were calculated to quantify plant diversity. At the garden scale, we summed the number of unique plant species in the five plots and calculated the Shannon’s diversity index by pooling the data in the five plots. The plots in the gardens all have the same garden-level diversity measures.
Parallel collection methods and measures of plant diversity will be used for flower-visiting insect sampling.
Site characteristics
Site characteristics describing the land use types and configurations were designed to be collected at the plot level, the garden level, and the neighborhood level. At the individual gardener’s plot level, we collected weed cover in percentage of the plot area, ground cover in percentage of the plot area, and use of mulch. We obtained a bird’s eye view picture of each plot. At the garden and neighborhood level, site characteristics will be constructed with a combination of on-site observation and remote sensing satellite images. At the garden level, we will use previous records for the number of trees in the garden and the presence of communal pollinator plots or pollinator strips in the garden for pollinator habitats. We will obtain both remote sensing satellite imagery and existing land use land cover GIS layers from Massachusetts and Boston government data sites, which are derived from a combination of USDA National Agricultural Imagery Program and WorldView satellite images (MassGIS Data, n.d.). With land use data combined with NDVI calculated from satellite imagery or drone images, we will measure garden green cover in percentage of the garden area, impervious surface cover in percentage of the garden area, amount of canopy cover/shade in the garden, and the garden size. At the neighborhood level, a 250 m buffer will be established from the center of the garden to capture the neighborhood landscape for each garden without overlap. Within the buffer, greenery coverage, impervious surface coverage, and road sizes of the surrounding roads will be collected from a combination of land use layers and satellite image classifications.
Data analyses and statistical test
To explore the data, I visually examined the trend in arthropod diversity and abundance across plots and gardens for potential variations. To compare arthropod communities, I will use non-metric multidimensional scaling to visually compare species similarity among plots and gardens, and I will test the differences in the arthropod community in gardens with a one-way analysis of similarities (ANOSIM).
Objective 1: With high numbers of variables in the data collection, I created a correlation matrix of all variables, and selected factors that are biologically relevant and not correlated with each other. With the selected set of factors, I will run generalized linear mixed-effect models to determine the relationship between the plant diversity and site characteristics and the arthropod abundance and diversity. Through a model selection process, I will identify significant factors impacting the overall arthropod community.
Objective 2: I will construct generalized linear mixed-effect models using factors at each spatial scale. I will determine the significance and the effect sizes for each factor at different spatial scales and run ANOVA among the models to statistically determine the differences in the models. In addition, I will analyze the data using a model selection process with all the factors collected. Through analyzing the results from the model selection process, I will identify the factors that contribute to the best-predicting models and the spatial scales of these factors.
Objective 3: I will run similar analyses as above within different groups of arthropods, to identify groups that might have a stronger relationship with specific spatial scale site characteristics.
Arthropod collection and processing materials
Camera, Ziploc bags, glass vials, 70% ethanol, insect aspirator, paper bags, centrifuge tubes, forceps, microscopes, arthropod guides, notebooks, and pencils.
Explanation and justification of method change
Due to the time constraints in the past field season and our aim for better data quality in the field collection, after careful consideration, we made adjustments to our methods while maintaining the integrity of our questions and objectives. We decided to separate the examination of the pest and pollinator communities before integrating the findings, and we adjusted the field methods for crop pest collection. This allows us to better control confounding variables and enhance data quality and ecological relevance.
During the summer of 2024 sampling, we focused on the effects of plant diversity and site characteristics on pest communities and adjusted the arthropod collection method to improve standardization and reduce confounding variables and sampling error. Initially, we proposed to randomly select leaves in any plants as researchers walk through the plot to inspect for crop pests for three minutes in each plot and collect any observed pests. Rather than a random inspection, we adjusted the methods to observe and collect arthropods from two focal crop types, standardizing the arthropod collection and minimizing variability introduced by random plant sampling. The plant community varies among plots, and a random selection of leaves from different plants introduces a significant confounding variable for the arthropod community, namely plant species identity. One group of pests, the specialist herbivores, often co-evolve with the plant species on which they feed, leading to a close association of these herbivores and specific plant identities (Leimu et al. 2012). When examining arthropod community composition, the strong relationship between specialist herbivores and specific plant identities can manifest as differences in arthropod community that are associated with species identity rather than the factors of primary interest, including surrounding plant community diversity (Dassou and Tixier 2016). By targeting a few focal plants, we eliminate the effect of variation in plant identity, thereby allowing for a more confident examination of how plant diversity and site characteristics affect arthropod communities.
Using focal plants also enabled us to enhance the data quality and data quantity of arthropod samples. Instead of randomly selecting leaves from different plants, we observed and collected all arthropods from individual focal plants within a three-minute time frame. The time frame was validated in the field as adequate for whole plant examination, leading to thorough sampling and reduced variation that would be introduced by different individuals using a random leaf sampling method. We managed to concurrently collect arthropods from three plants with three people in the field, resulting in a larger sample size of arthropods for each plot. Based on field validation, manual sampling on individual plants is effective for pest collection. In addition, we collected all arthropods observed on the focal plants during the time frame in the field and did not exclude non-pest arthropods, offering a comprehensive representation of the arthropod community that may utilize or land on the focal plants in the plot, providing supporting data to address our first two objectives.
We selected tomato plants (Solanum lycopersicum) and pepper plants (Capsicum annuum and Capsicum chinense) as focal plants. Both belong to the family Solanaceae. Tomato and pepper plants are the most common crops by the number of gardeners that have them in their plots in the Boston community gardens, based on previous crop surveys. They are not only prevalent but are also found in plots with varying crop diversity and management, making them appropriate choices for the study. Using focal plants tomatoes and peppers enables us to maintain control over plant identity where the arthropods were collected while capturing high variation in plant diversity and site characteristics at both the plot and garden levels.
Given the prevalence of the focal crops (tomatoes and peppers), and the high value of their fruits to gardeners, we also decided to include herbivory as an additional response variable. If plant diversity and site characteristics impact pest richness and abundance, it is crucial to determine whether these changes lead to differences in crop damage and yield. This is particularly relevant because we do not know if pest richness and abundance correlate linearly with herbivory in urban gardens due to complex herbivore-natural predator interactions (Dassou and Tixier 2016). By examining herbivory, we can provide actionable recommendations for optimizing plant diversity while balancing pest suppression, and shed light on the effects of the pertinent factors at specific spatial scales.
Pest data were collected at the plot level, while plant diversity and site characteristics were collected at both plot and garden levels, to investigate the effects of spatial scales of plant diversity and site characteristics on arthropod diversity. Plot- and garden-level plant diversities (richness, abundance, and ground cover) were collected in the field, while additional site characteristics at the garden level (e.g., ground cover and neighborhood greenness covers) are being quantified using remote sensing and existing land-use data as originally proposed. This allows us to construct statistical analyses to examine the local (plot-level) and landscape (garden-level) effects of plant diversity and site characteristics on the arthropod community in each plot, offering insights into management at the gardener, garden manager, and city scale.
The second part of the field study now examines the effect of plant diversity and site characteristics on pollinator diversity. The field study will take place from late May to June 2025, focusing on pollinators during peak pollination season. Due to time constraints during the harvest season in the past summer, we prioritized pest sampling because of its ecological relevance in the season. For the pollinator sampling, we will observe and collect data on pollinator diversity at the plot level as proposed, selecting plots and gardens matching previous pest collection. Originally, a simultaneous sample of pests and pollinators was proposed, which would have allowed for direct comparisons of the impacts of plant and site factors on these two groups. Although we would not be able to directly compare the impacts with the separation of sampling, we will still be able to integrate the data to assess the effects. Pests and pollinators are functionally distinct arthropod groups, each with unique ecological roles, phenological differences in active periods, and different mechanisms by which plants may drive their community composition. For instance, pests are primarily influenced by host plant availability, while pollinator activity is often driven by floral resources, plant structural complexity, and seasonality (Ratnadass et al. 2012, Bennett and Lovell 2019, Pardee et al. 2023). By separating their sampling periods, we can gather more targeted and ecologically relevant data, ensuring data quality while more effectively addressing each group’s unique responses to plant diversity and site characteristics.
After completing pollinator sampling, we will integrate the responses of pollinators and pests to gain a comprehensive understanding of the effects of plant diversity and site characteristics on the arthropod community. Since pests and pollinators do not directly interact, the effects of plant and site factors are likely to be additive. For example, one possible outcome could be that increased plant diversity at the garden level leads to higher pollinator diversity while having no effect on pest diversity or levels of herbivory. This will lead to the recommendation for increasing garden-level plant diversity. We will analyze both datasets within the same spatial framework to ensure a holistic understanding of how arthropods respond to plant diversity and site characteristics.
Although separating pest and pollinator sampling and focusing on specific plants required method adjustments, these refinements reduce confounding variables, improve data quality, and enhance ecological relevance while still aligning with the original research objectives. The trade-offs have been carefully considered, ensuring that the study remains robust and relevant in terms of its scientific and management implications.
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Ratnadass, A., P. Fernandes, J. Avelino, and R. Habib. 2012. Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review. Agronomy for Sustainable Development 32:273–303.
The Trustees. (2023). Boston Community Gardens. The Trustees of Reservations. https://thetrustees.org/place/boston-community-gardens/
We started preliminary data exploration focusing on plant community composition and herbivory in tomato and pepper plants. We are currently in progress with the arthropod sample processing, and once completed, we will begin data analysis to examine the relationship between plant community characteristics and arthropod communities.
In our summer 2024 sample, we surveyed plant community composition across 109 plots in 22 gardens, observing a high overall plant richness (Table 2). We observed high and variable plant richness and diversity levels at the garden scale, with crops, ornamentals, and weeds all contributing to the plant diversity (Figure 3). At the plot level, plant species richness showed a median of 18 species per plot, ranging from 5 to 43 species. This variability reflects different crop selection preferences and management styles of individual gardeners. However, we also observed more similar crop choices in plots containing tomatoes and peppers compared to those without these crops (not included in the study).
Table 2. Total plant richness in the gardens at different phylogenetic levels. Common types refer to common names of crops and plants.
|
|
Common types |
Varieties |
Family |
Genus |
Species |
|
Crops |
127 |
327 |
32 |
87 |
140 |
|
Ornamentals |
92 |
104 |
43 |
79 |
98 |
|
Weeds |
147 |
157 |
49 |
118 |
142 |
|
Total |
320 |
540 |
79 |
229 |
334 |
Across our survey of 242 tomatoes and 225 peppers, we found a relatively low number of pests on the plants. More arthropods were observed during the sampling period on tomato plants, including aphids. Overall, fewer pests were found on pepper plants, but the average percentage of herbivory was higher in peppers than in tomatoes (Figure 4).
From the preliminary data exploration, we did not find a statistically significant relationship between plot level plant species richness and herbivory, suggesting no impact of plant richness on the amount of herbivory damage in the focal crops. We plan to further analyze our data to explore potential relationships between additional site characteristics, such as plant community composition and ground cover, and herbivory patterns at both plot and garden levels.
Education & Outreach Activities and Participation Summary
Participation Summary:
We collaborate closely with The Trustees to enhance the understanding of arthropod communities and landscape characteristics in their managed gardens. Sharing the observations and findings periodically with The Trustees is crucial to inform future management strategies effectively. Specifically, we have employed both formal and informal channels of communication, informally through direct communications in writing and in meetings biannually or when significant findings arise, and formally through reports of the results. In the past fall, we shared preliminary results from the summer sampling and a comprehensive summary of past findings from our lab. These were presented to The Trustees Boston Community Garden Team through a Zoom meeting and a visual report. The report focuses on key topics, including plant community composition, gardeners’ planting preferences, and previous findings on arthropod communities. We also created a simple infographic on plants and arthropods in the gardens and are editing the infographic for distribution through social media. We will update the findings in the spring. Furthermore, based on the study outcomes, we will work closely with The Trustees to identify potential areas of improvement to promote sustainable insect management practices, such as incorporating flower strips or promoting or reducing plant growth in peripheral lands in the gardens directly managed by The Trustees’ staff. Through The Trustees, we hope to also reach city planners to identify context-specific measures that can create a supportive landscape for both gardeners and residents, such as the improvement of urban green space and tree planting in city planning. Through the process, we hope to strengthen collaboration, build trust, and enhance our collective understanding of urban community gardens and their roles in the city landscapes.
We aim to engage gardeners within the community gardens that we sample. We aim to raise awareness among gardeners about the insects and other arthropods in their plots and the potential impact of their management choices. This year, we actively engaged with gardeners during the sampling period and through an in-person presentation on arthropods in the gardens at the garden coordinator’s meeting. During the past field season, we proactively communicated sampling plans with The Trustees and created a short project introduction that was shared with the garden coordinators. During fieldwork, we engaged in informal conversations with the gardeners, learning about their experiences with gardening and arthropods while sharing information about our research. In October, we attended the gardener coordinators’ meeting with over 25 garden coordinators and 6 Trustee's team members, and presented preliminary results from this year’s sampling and past findings on plant and arthropod communities in the gardens. Gardeners expressed interest in our research findings and shared personal anecdotes about encounters with common insects highlighted in the presentation. These exchanges helped connect our research to gardeners’ experiences and inspired more questions and discussions.
We will present arthropod groups identified during the study as well as other garden characteristics in Fall 2025 to gardeners. Taking into consideration the multi-lingual nature of the gardeners, we will translate the infographics into other commonly used languages, including Chinese, Spanish, and Portuguese. These infographics will be distributed in print to post in gardens, and digitally through gardener newsletters, fostering a greater understanding of the garden ecosystem and sparking curiosity among gardeners. In addition, we plan to create short reports annually to send to garden coordinators. We will continue to actively participate in gardeners’ meetings to present the preliminary findings of the work and will suggest strategies for sustainable management of insects and other arthropods within the gardens if appropriate, including the annual gardeners’ gathering in March. Through ongoing collaboration and community engagement, we hope to continue connecting our work with gardeners and garden managers.
We plan to extend the impact of the research by reaching a broader audience including urban gardeners and the academic community. We will leverage online social media platforms (Instagram) to share the findings of our work with the general public, with an emphasis on urban gardeners, in the hope of raising awareness about the often-overlooked or misunderstood arthropod communities within urban landscapes. By stressing the impact of personally managed land in urban areas compared to the surrounding city landscapes, we aim to inspire a greater appreciation for the unique biodiversity in urban gardens and the importance of city landscape management. We will create an iNaturalist project to share our observations of pollinators and encourage gardeners in Boston and beyond to contribute to everyone’s understanding of the garden arthropod community. In addition, we plan to publish our findings in a scientific journal to engage other academic researchers in the field. We hope to draw attention to Boston’s community gardens and urban community gardens as valuable subjects for further studies. Ultimately, we aspire to motivate more research on the topic, which will not only support urban gardeners but also inform city planning for the establishment of new urban community gardens.
Project Outcomes
This study examines plant-arthropod diversity and interactions within the urban landscape using Boston as a case study. The project’s findings will establish a foundational knowledge of the frequently overlooked and underappreciated diverse plant and arthropod communities in urban landscapes for Boston and cities beyond in the Northeast. Furthermore, the outcome of the project will provide opportunities for developing management recommendations that can better support urban agriculture while maintaining its critical ecological roles in contributing to biodiversity in urban landscapes.
By deepening our understanding of how plant community composition affects pest communities, we aim to provide insights that support more diverse and resilient plant and arthropod communities that also reduce management efforts. In Boston community gardens, a variety of natural pest control methods are employed, while pesticide use is prohibited. Our research may provide input into cultural management of pests. From our study, we may find that high plant diversity supports a diverse arthropod community without increasing pest diversity or herbivory. This would allow us to further promote the planting of diverse crops, contributing to positive ecosystem services and biodiversity conservation in the urban landscape. If high plant diversity reduces pests and herbivory, this would suggest that plant diversity during crop selection could serve as an additional cultural control for pests, reducing labor and costs in pest control during the growing season. Alternatively, if high plant diversity increases pest numbers and damage, we could explore strategies of pest control while maintaining plant diversity, such as using different spatial arrangements of diverse crops or limiting crop diversity at the plot scale while increasing diversity in peripheral land. The results from the study could guide planting decisions and pest control practices for gardeners and garden managers.
The flower-visiting insect study aims to provide management recommendations while raising awareness of beneficial arthropods in the garden landscape. From the study, we will identify site characteristics and practices that promote pollinator abundance and diversity, which enhance ecosystem services for gardeners, including increased plant pollination and yield. Integrating with results from the pest work, we will provide specific recommendations that maximize pollinators and minimize pests at the plot scale. We also hope to engage gardeners by highlighting pollinators as beneficial arthropods and fostering curiosity about diverse arthropods in urban gardens through presentations, workshops, and citizen science projects.
The summer 2024 sampling was both engaging and rewarding. We built upon our understanding of cultivated crops in community gardens and gained new insights into the significant role of ornamental plants and weeds in contributing to plant richness and diversity. In the completed field sampling last summer, we learned about pests and herbivory patterns in tomatoes and peppers, whose findings may be generalizable to other crops in the Solanaceae family. It was surprising but positive that herbivory levels were relatively low in both common crops across all gardens sampled, and we are excited to further analyze the relationships between different site characteristics and pests and herbivory before delving into pollinator responses.
Through informal conversations with gardeners, we also became aware of their concerns regarding different crop diseases, which could be unfamiliar to gardeners and often lack clear and accessible treatment options. These discussions presented the potential for future research and collaboration with gardeners and crop scientists, to develop practical and applicable research that benefits the gardening community in urban community gardens.
For our project, we separated pest and pollinator sampling to obtain more ecologically and socially relevant results based on the phenology of organisms and planting seasonality. This gives us more directly actionable results for the management of respective arthropod groups in the gardens while allowing for integration by using parallel methods. However, a further study using a simultaneous collection could provide more direct information on the responses of different arthropod groups to plant diversity and site characteristics, that can complement the results from this study.
In 2024, we focused on pest sampling in tomato and pepper plants by assessing leaf herbivory and manually capturing arthropods on the plants. This method allowed us to collect a relatively large sample of arthropods and herbivory on these common crops, providing a robust foundation for our analyses. By examining both the pest community composition and the herbivory levels, we aim to make meaningful conclusions about the potential influence of a diverse plant community on the arthropod community and its direct impact on crop health, which is particularly important to gardeners.
The focal plants selected, tomato plants and pepper plants, were common crops in community gardens, and we found these crops in all of the gardens we sampled. Using focal crops allowed us to make comparisons across plots and gardens, providing insights into potential trends driven by characteristics at these two scales. We observed more consistent planting choices in plots with these crops than in plots without, suggesting that gardens may exhibit more variations in planting choices than seen in our samples. Further studies may benefit from using control plants by bringing potted crops into the plots. This would enable researchers to non-randomly select highly variable plots and gardens and capture a wider range of differences in plant selection and management choices.
During fieldwork in summer 2024, we also observed that some tomatoes sampled showed signs of diseases, including signs of leaf spot and wilt. Future research that simultaneously assesses herbivory and disease will offer a more comprehensive understanding of garden pest communities and their impact on plant health.