To explore whether land-use types have an effect on the within-year phenology of the bee community, we asked whether aggregate bee abundance, richness , and evenness varied differently through time based on land-use types. To test this, we used generalized linear mixed models with the community level metrics as response variables, and land-use type, day of the year, and their interaction as explanatory variables. We did not expect the relationship between day of the year and the community-level metrics to necessarily be linear so we also included day of the year as a quadratic term. A significant interaction between the day of the year terms and land-use type would indicate the bee community phenology differed between the different land-use types. To account for inter annual variability and differences in collecting methods between years, we included year as a random effect. To account for sampling the same sites multiple times, we also included site as a random effect. Day of year was normalized on a scale of 0 to 1 from the first collecting date to the last across the entire dataset and then scaled. We assumed Gaussian error for the model with community evenness as a response variable, Poisson error for bee richness, and negative binomial error for aggregate abundance. All analyses were performed in R 3.1.2 . Mixed effects models were analyzed using the R package lme4 .We found that the bee communities in human-altered landscapes experienced different phenological patterns than the neighboring less modified areas. Natural areas had the largest pulse of overall abundance and species richness in the bee community in the springtime,blackberry cultivation dropping off significantly by the end of the season when bee abundance and species richness in agricultural areas were peaking.

Conversely, peak bee abundance in urban areas was directly in the middle of the season and species richness of urban areas remained relatively constant throughout the year. Despite these seasonal differences of abundance and richness, the patterns of evenness of the bee communities across sites were similar between land-use types, indicating that the evenness of a community is robust to land-use change. We found bee community composition to vary between land-use types, but whether these differences drive the phenological patterns of abundance and richness, or the community composition is influenced by the phenological differences of the landscape remains unclear. While ecologists have used time as an important variable in many different systems, only recently have the effects of temporal variation been considered within urban contexts .We propose the timing of floral resource availability as a driver of local phenological shifts in different landscape types. Green vegetation in California grasslands is largely driven by temperature and rainfall, resulting in a large burst of blooms in the spring and very few floral resources at the end of the summer . In urban areas, the flowering season can be extended through water inputs and landscaping choices in residential, public, and commercial zones , leading to the relative stability of the bee community. In contrast, irrigation of late blooming mass-flowering crops in agricultural fields explains the shifted peak in phenology of bees in the agricultural areas. While vegetation is not a perfect surrogate for floral availability, remote sensing of the region captured similar temporal patterns of the vegetation in human-altered landscapes being out of synchronization with the phenology in the neighboring natural landscapes . Such findings offer further supporting evidence that different land-use types offer the floral resource-dependent community unique temporal opportunities.

The extended flowering season in urban areas could explain why the species richness of the bee community remains relatively consistent from the middle to the extreme ends of the season in urban sites. Urban areas offer resources at the earliest and latest portions of the season when there is little floral availability in the other land-use types.Because resources are available earlier in the season, bees could be breaking diapause early to take advantage of these resources. Bees may also be able to have an additional generation due to resources available later in the season. Other consequences include the phenologies of species in these landscapes spreading out over the season, or bees flying further distances than assumed to track resources between land use types . The phenologies of two frequently collected species further support the important role of changing floral resources, by peaking in abundance in urban landscapes at the extreme ends of the season: Eucera actuosa, a ubiquitous spring bee, was collected most frequently in urban sites in the early spring, whereas in natural sites, its abundance peaked in late spring. Conversely, Melissodes lupina, a summer bee, was collected most frequently in the early summer for natural areas, but was collected more often in the late summer in urban landscapes. Urban areas adjacent to natural areas therefore may actually help support bees to experience longer flight seasons when resources are most limited. In our study, collecting periods occurred every two months – it is likely that finer-scale temporal collecting would have captured this pattern for more species. Understanding how the dynamics of bee populations are altered by land-use change is critical because bees provide essential pollination services to managed and wild plant populations . The value of pollination in agriculture is estimated at $200 billion worldwide , largely due to many foods that are essential for food security and a healthy human diet, including numerous fruits, vegetables, and nuts that require bee pollination . In urban areas specifically, there has been growing interest in urban agriculture to ensure food security and access to healthy food. For example, the estimated economic value of urban fruit trees in the one city of San Jose, California, is worth $10 million annually .

However, honey bee populations and many bumble bee species are declining worldwide , while many other bee species have not been closely documented sufficiently to determine their status . Resource availability is different in urban and agricultural areas than in less modified areas, and these human-dominated landscapes are supporting bee communities with novel patterns of activity. Although not explored here, resource quality will also strongly vary due to differences in plant species composition between land-use types. Management of pollinator communities requires an understanding of the dynamics of these systems and how to best target restoration and conservation work to meet the unique needs of each landscape . For example, knowing that the peaks in bee community activity occur during different times of the year in different land-use types can help prioritize efforts. It is important to recognize that restoration goals may have different desired outcomes, for example, to support the largest pollinator community, or, alternately, to replicate the dynamics of the natural environment within the human-altered landscapes. Knowledge of when resources are most limiting is necessary in planning for either outcome. In agricultural areas, restoration techniques such as enhancing floral resources may benefit from a focus on providing flowers that bloom early in the season. In contrast, the floral and subsequently the bee community in urban areas are relatively stable through time, so efforts can focus on enhancing bloom availability year round. Supporting other animal populations in the different land-use types will likely involve similar considerations if the temporal dynamics of these populations are also shifted. As shifts of land use to agricultural and urban purposes continue to be the largest and fastest growing forms of land-use conversion ,plastic plant pot sizes it is critical to understand the impacts of these landscape scale changes on species’ temporal and spatial distributions in order to predict and plan for ecological impacts. While the implications of the shifts in the phenology of bee communities in human modified areas on the resilience and productivity of these populations need further exploration, the temporal dynamics of communities in anthropogenic landscapes must be considered.San Diego is a region characterized by many unique attributes, including diverse urban development, conserved lands, coastal and terrestrial ecosystems, and agricultural lands. The region is known for its Mediterranean climate of seasonality and high temporal variability of rainfall. From coastal cliffs into expansive valleys and inland mountain regions, San Diego also encompasses a high degree of spatial variation of diverse micro-climates.

These distinct and diverse features present both challenges and opportunities in light of an increasingly changing climate. San Diego is already experiencing the many impacts of climate change. Projected increases in variability and intensity of temperature and precipitation extremes are exacerbating the region’s water resource challenges. While San Diego faces vulnerability to these climatic stressors, recognition of these vulnerabilities have propelled the region forward to become a leader in innovative climate adaptation and resilience planning. Agriculture plays a prominent role in San Diego, with many small farms, preserved lands, and valuable crops that hold economic, cultural, and historic value. The agricultural sector provides many ecosystem services that benefit the region’s economy, ecosystems, watersheds, and communities. Agricultural lands have the ability to store carbon, reduce atmospheric greenhouse gases , and sustain essential hydrologic benefits, making them an important part of the climate adaptation and resilience strategy. Recent studies have highlighted the potential of agricultural working lands to increase climate resilience through increasing carbon sequestration within soils. This suite of soil management practices, known as Carbon farming, can serve as an effective climate mitigation and adaptation strategy. This study helps illustrate the role that these active soil management strategies can have for buffering the impacts related to climate change. Specifically, these practices can alleviate the water-related challenges that San Diego farmers are especially vulnerable to. As a region invested in both agriculture and sustainability, San Diego has the opportunity to further its role in climate resilience by expanding implementation of soil management practices throughout the county. While there are barriers that remain for on-the-ground implementation of carbon farming, recent advancements in climate modeling keep supportive economic policy make this an opportune time to make strides towards larger-scale implementation. With the growth of economic incentive programs, local, regional, and state agencies, and engaged citizen groups with the political will to take action, recently improved climate models need to be leveraged to inform more direct and effective efforts. San Diego can capitalize on these science-based decision support tools to understand the impacts of soil management for regional water resources and the opportunities to protect land for conservation of these agricultural opportunities. In doing so, the region can begin to scale out its carbon farming efforts, paving the way forward towards transforming the role of the agricultural sector as a major strategy in addressing the impacts of climate change. This report integrates regional climate modeling with agricultural and land use application to assess the water resource benefits that strategic soil management practices can have for San Diego’s landscapes, the existing opportunities for implementation of practices, and the importance of preserving agricultural lands given future urban development plans. Analyses aim to address the barriers to implementation of climate-smart agriculture in San Diego, including a lack of a comprehensive understanding of the region’s agricultural landscape and the areas where carbon farming practices can generate the greatest impacts for natural resources. Additionally, this report aims to quantify the potential benefits of soil management and the current opportunities for these practices. Analyses are designed to promote expanded implementation of carbon farming practices and to ultimately show the value of these lands and their ability to buffer climate change impacts, in light of warming temperatures and increased urbanization. Results highlight current opportunities for further implementation of sustainable agricultural practices and the potential benefits for water resources throughout San Diego. Additionally, analyses utilize planned land use projections to showcase the vulnerability of agricultural lands to urban development and the lost hydrologic benefit with the conversion of these lands. San Diego’s 4,530 square miles encompass a range of diverse human and natural landscapes, from iconic beaches, urban and suburban development, conserved lands, and major international seaports and airports . With 70 miles of exceptional coastline, culturally unique urban neighborhoods, and flourishing natural areas, it is no wonder that San Diego is home to a population of 3.3 million people and an abundance of natural resources. The region has 1.3 million acres of protected natural lands that buffer its growing population and conserve various ecosystems . These lands are home to some of the most ecologically and biologically diverse ecosystems in the world and support various habitats, plants, animals, and vegetation types .