Yet rarely have investigators tied performance or mortality of individuals within a species population to subtle differences in aspect that occur within a single population . Here we found that aspect was the strongest predictor of dieback over time, with plants in SW aspects showing greater dieback than plants on more north-facing aspects. This influence of aspect may be the result of direct negative effects of sun exposure and higher temperatures ina semi-arid environment or maybe indirect whereby influences of aspect are mediated through aspect-effects on soil and microbes. For example, Gilliam et al. 2015 demonstrated greater soil organic matter accumulation and different microbial community composition in N facing compared to S facing slopes. Regardless of mechanism, the finding that SW aspect is detrimental to these plants could be important for restoration practitioners seeking to identify promising sites on the landscape where restoration of individual species may be more successful . Another source of variability both within the landscape region we studied, and across Southern California chaparral, which was not directly measured in this study, is the occurrence of fog. The Santa Barbara region experiences predictable fog in May and June, flower bucket and late summer cloud shading and fog events have been demonstrated to reduce vapor pressure deficit , slow plant seasonal water loss and provide direct foliar uptake of water .

We observed significant variation in fog intensity between sites, particularly at night during the early summer months , even between sites on a given night. Sites C and D in particular often experienced heavy fog drip, while other sites remained dry. We found plants saturated by fog to exhibit higher water potentials on such nights, similar to findings in Mahall et al. , suggesting that fog drip may be sufficient enough to percolate to shallow roots. As mentioned previously, A. glauca is considered to be a relatively shallowly rooted chaparral shrub species and has been shown to be sensitive to even small changes in rainfall . Additionally, some coastal California shrub species have been shown to exhibit foliar water uptake from fog , though this has not yet been demonstrated for A. glauca. Regardless, variations in summer fog patterns have previously been shown to influence late-season water potentials in other Arctostaphylos spp. , possibly causing populations with greater exposure to fog to have higher “safety margins” with which to avoid cavitation . Similarly, Emery et al. have shown that fog can reduce the rate of water loss in coastal shrublands in California. Mortality of A. glauca during drought documented in other studies occurred in more interior sites, with less fog influence. Thus, we believe the role of local and regional variation in fog occurrence in A. glauca drought resistance warrants further research. Urban agriculture is sprouting up in the empty spaces of post-industrial landscapes throughout the industrialized world—in vacant lots, road medians, parks—evoking the patchwork of vegetable gardens and livestock enclosures that are a part of the urban street scape in much of the global South.

The spike in oil and food prices in late 2007 and early 2008, and the shocks of the current economic meltdown has led to a tightening of belts and a growing interest in urban agriculture as a way to lower food costs. Sales of vegetable seeds since the meltdown have increased 20 percent and stories on urban agriculture crop up in the news on a daily basis. In Washington First Lady Michelle Obama and a handful of fifth-graders from a nearby elementary school plant a vegetable garden, the first of its kind at the White House in sixty years. In Vancouver the city council legalizes chicken ownership. In London “guerrilla gardeners” plant a vegetable patch on a roundabout. In Detroit goats and chickens graze some of the 60 square miles of vacant lots left fallow as capital abandoned the city. Historically, urban food production in the US and Britain has flourished in such periods of economic crisis. As we find ourselves once again in the throes of a crisis of capitalism, the popularity of urban agriculture in the Global North has surged and the discourse surrounding it has shifted from one of recreation and leisure to one of urban sustainability and economic resilience. Even the terms used to describe it have shifted in the Global North; “urban agriculture” is replacing “community gardening” in everyday parlance, placing it in the same category as urban farming in the Global South, where livestock and small plots of food crops have persisted as part of the urban landscape. While the motivations and functions of urban agriculture vary greatly across the globe, the widespread discourse surrounding urban agriculture in the North does little to differentiate it from its Southern counterpart.

Over the last decade or so, as concern over the ecological impacts of urbanization adopts an increasingly Malthusian timbre, government agencies, NGOs, and farmers groups have touted the potential for urban agriculture to help buffer incomes and food security in the rapidly urbanizing South . They extol the virtues of urban agriculture’s multi-functionality: it improves food security and creates jobs, serves as a sink for urban waste, and cools cities. The distance between production and consumption—so-called “food miles”—decreases, lowering fossil fuel use and transportation costs. In the North, advocates echo this discourse, also adding urban agriculture’s ability to strengthen a sense of community, reconnect consumers with farmers, raise awareness of environmental and human health, and keeps money circulating locally. Ecological farming practices reduce the amount of agri-chemicals used, curbing environmental pollution and threats to public health. In short, advocates argue that urban agriculture creates a more ecologically-sound, resilient, and productive landscape . An undifferentiated view of urban agriculture and its possibilities, however, may result in its prescription as a panacea for urban ills without consideration of the geographic particularities of a city. Can we generalize about why people farm in the city? And more importantly, can we make broad claims about why people should farm urban spaces? To better understand the dynamics giving rise to urban agriculture in various settings in both the North and South and the ways in which urban agriculture has developed as a multi-functional response to these dynamics, a theoretical framework bridging political economy, urban geography, agroecology, and public health would be helpful not only for agri-food scholars, but also for practitioners wishing to engage with urban agriculture. The theory of metabolic rift offers one such lens. Over the last decade, environmental sociologists and geographers have elaborated Marx’s argument that the development of capitalism alienated humans from the natural environment and disrupted our traditional forms of “social metabolism”, the material transformation of the biophysical environment for the purpose of social reproduction . 21 Understanding metabolic rift first requires briefly addressing metabolism, a concept that has been used since the early nineteenth century to describe the material and energetic exchanges both within an organism and between the organism and its environment. To understand metabolism as a socio-ecological process, we must return to the rise of soil chemistry in the late 1830s, when Justus von Liebig, the father of modern soil science, plastic flower bucket employed metabolism to explain the cycling of nutrients between soil, crops, animals, and humans, essentially expanding the scope of metabolism from the organismal scale to the ecosystem. Following the work of Scottish political economist/scientist/gentleman farmer James Anderson, who linked the decline of soil fertility to the expansion of large-scale farming, Liebig helped reveal how the rapid urbanization that accompanied the Industrial Revolution disrupted nutrient cycling in agriculture and depleted soil fertility. As food production intensified and agricultural products were transported increasingly longer distances from rural farms to a growing population of urban consumers, soil nutrients utilized by food and fiber crops were flowing from rural soils into cities and foreign ports. There they ultimately ended up in the form of excrement polluting urban streets, sewers, and rivers, rather than cycled back into the fields from which they were extracted. As Marx noted in Volume 3 of Capital, “they can do nothing better with the excrement of 4 ” million people than pollute the Thames, at monstrous expense” . Liebig’s discovery of soil nutrients provided a scientific rationale to Marx’s attempts to understand the ways in which capitalist modes of production alienated humans from nature and from one another.

Drawing heavily on Liebig’s insights into declining soil fertility, Marx sought to explain in more detail how human action stewards, transforms, or disrupts natural processes. Labor, for him, was the key to understanding this relationship: “Labour is, first of all, a process between man and nature, a process by which man, through his own actions, mediates, regulates and controls the metabolism between himself and nature” . Many environmental sociologists have used the theory of metabolic rift to explain shifts in nutrient cycling under capitalist agriculture as Marx did , as well as the ways that sustainable agriculture might help to overcome this rift . Others have expanded the scope of analysis to include broader ecological crises: global warming , fisheries depletion , and the ways in which the development of global capitalism has driven ecological succession . Despite Marx’s conception of social metabolism as a fundamentally socio-ecological process, however, most scholarship on metabolic rift has emphasized the ecological dimensions of crises of capitalist accumulation. If, as Marxian geographers and political ecologists have argued, understanding “socionatures” demands that we uncover the ways in which social and natural processes are co-produced through social metabolism , it is first necessary to situate urban agriculture’s emergence at a particular location within the specific historical and geographical context. The purpose of this paper is therefore twofold. First, I contribute to the existing conceptualization of metabolic rift by more explicitly emphasizing its social dimensions. I discuss three interdependent yet distinct forms or dimensions of metabolic rift: 1) ecological rift, which includes both the rift in a particular biophysical metabolic relationship and the spatio-temporal rescaling of production that follows in its wake; 2) social rift, arising from the commodification of land, labor, and food at various scales; and 3) individual rift, the alienation of humans from nature and from the products of our labor. Rather than a triad of separate processes, these three unified dimensions of metabolic rift are co-produced, but can be differentiated as a function of both the scale at which metabolic rift occurs, and by the grain and extent of observation. I should stress here that my intention is not to lay claim to Marxian neologisms. Rather, I hope to bridge and clarify existing concepts and incorporate them into a single framework that accords equal weight to ecological and social aspects. As such, a theory ofmetabolic rift emphasizing its multiple dimensions may be used more precisely to analyze and explain historical and contemporary transformation of the agri-food system. My second goal in this chapter is to use this expanded view of metabolic rift both to shed light on the different dynamics driving the emergence of urban agriculture in various parts of the world, and to show how urban agriculture, in turn, attempts to overcome these three forms of metabolic rift. With added emphasis on social rifts in metabolism operating at multiple scales, this expanded framework can help us understand both social and ecological dimensions of urban agriculture’s multi-functionality, from its attempts to overcome disruptions in ecological cycles to its ability to reclaim public space, re-embed food production and consumption with sociocultural significance, and reconnect consumers with their food and the environment. Understanding urban agriculture in this way may be of service not only to academics, but also to policy makers, planners, non-profit workers, and urban agriculture advocates as they frame discussions of urban agriculture and develop future policy and programs in Oakland and elsewhere. The form of metabolic rift most discussed by scholars is what I refer to more specifically as ecological rift. According to their arguments, the imperative of spatial expansion inherent to capitalism has cleaved a rift between city and country, humans and nature. In search of new spaces for ongoing accumulation, capital has also disrupted sustainable biophysical relationships such as nutrient cycles. As Moore argues, “systemic cycles of agroecological transformation” triggered by new modes of capitalist production “usher in a new more intrusive and more globalized exploitation of nature by capital.” Capital’s ongoing expansion therefore creates a cycle of “rifts and shifts” whereby attempts to address a metabolic rift in one place simply lead to “geographic displacement” of ecological crisis .