Urban farming, especially on rooftops, is a popular and growing topic in both the media and the scientific literature, providing a genuine opportunity to meet some of the challenges linked to urban development worldwide. However, relatively little attention has been paid to date to the growing medium of green roofs, i.e., Technosols. A better understanding of the influence of Technosols and the link with ecosystem services is required in order to maximize the environmental benefits of urban rooftop farming. Between March 2013 and March 2015, a pilot project called T4P (Parisian Productive rooftoP, Pilot Experiment) was conducted on the rooftop of AgroParisTech University. Urban organic waste was used, and results were compared with those obtained using a commercial potting soil, based on yield and trace metal concentrations, substrate characterization, and the amount of leaching. An assessment of the ecosystem services expected from the Technosols was undertaken in terms of the output of food (food production and quality), regulation of water runoff (quantity and quality), and the recycling of organic waste. Indicators of these ecosystem services (e.g., yield, annual loss of mass of mineral nitrogen) were identified, measured, and compared with reference cases (asphalt roof, green roof, and cropland). Measured yields were almost equivalent to those obtained from horticultural sources in the same area, and the Technosols also retained 74-84% of the incoming rainfall water. This is the first quantitative analysis of ecosystem services delivered by urban garden rooftops developed on organic wastes, and demonstrates their multifunctional character, as well as allowing the identification of trade-offs. An ecosystem services approach is proposed for the design of soilbased green infrastructure of this kind and more generally for the design of sustainable urban agriculture.

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Urban agriculture is sprouting throughout the world nowadays. New forms of urban agriculture are observed such as rooftop farming. In the case of low-tech rooftop farming projects, based on recycled urban waste, one of the key issues is the type of substrate used, as it determines the functions and ecosystem services delivered by the green roof. Using a five year experimental trial, we quantified the food production potential of Technosols created only with urban wastes (green waste compost, crushed wood, spent mushroom), as well as the soil fertility and the potential contamination of food products. Regarding food production, our cropping system showed promising results across the five years, in relation with the high fertility of the Technosols. This fertility was maintained, as well as the nutrients stocks after five cropping years. Most of the edible crops had trace metals contents below existing norms for toxic trace metals with nevertheless a concern regarding certain some trace metals such as Zn and Cu. There was no trace metal accumulation in the Technosols over time except for Zn. This study confirmed that constructing Technosols only from urban wastes is a suitable and efficient solution to design rooftops for edible production.

Rooftop gardens are a promising way to supplement the growing demand for local food production, and are especially relevant in large cities with acute space constraints. However, they face the challenge of achieving viable food productivity while minimizing their impacts on the environment, two priorities that often oppose one another. Also, the actual impacts of management practices, which are deemed environmentally friendly in principle, are rarely quantified. Therefore, evaluations that encompass all components of urban gardens and a comprehensive range of environmental issues are necessary to reveal potential trade-offs and provide guidance in the design of these systems.In this study, we evaluated the environmental and economic impacts of rooftop gardening practices, focusing on crop and substrate selection, which are key parameters in system design but whose consequences have seldom been evaluated so far. Life cycle assessment (LCA) and life cycle costing (LCC) were used to analyze a case study in the center of Paris (France). The production systems considered involved crop rotations of tomato and lettuce each grown in three different substrate types: compost and wood chips; compost, wood chips, and earthworms; and conventional potting soil.Despite the large environmental burdens of compost production, systems with compost performed better environmentally and economically than the system involving potting soil, specifically having 17-47% less greenhouse gas emissions per kg of product. Across systems, length of cultivation and yield appeared to be the most influential determinants of the environmental impacts. Within the compost systems, the most impactful component was the material used for garden infrastructure, and substrate production for the potting soil systems. This is the first study that considers compost as a substrate, weighs its benefits and impacts, incorporates it into a complete garden, and compares it to potting soil. Our results demonstrate that careful system design could significantly abate environmental impacts. They provide critically needed information to people implementing urban rooftop agriculture and considering the trade-offs involved in each decision.

Since two decades, urban agriculture has been booming and a wide range of forms, from urban allotment gardens to rooftop farming under greenhouse, is developing. Various benefits are recognized for urban agriculture integration within the city and a specific consideration is dedicated to ecosystem services. In this article, we have focused on cultural ecosystem services provided by urban micro-farms. The state of the art reveals that urban agriculture delivers cultural ecosystem services that are well perceived and evaluated by users, but there are still few studies on this topic. Based on the analysis of specific literature on cultural ecosystems and micro-farms in parallel to a period of observation and documentary research of five urban micro-farms either on rooftop or at soil level, located in Paris and its surroundings, we proposed a specific methodology. This methodology aimed at quantitative and qualitative evaluation of the cultural ecosystem services provided by urban micro-farms and is based on a framework, which distinguishes exogenous and endogenous cultural ecosystem services.

<p><strong>Are Collembola flying onto green roofs?  </strong></p><p>With a worldwide urban population projected to reach 5 billion by 2030 (Véron, 2007), the roles and benefits of urban green spaces cannot be denied, like climate regulation by trees or water flow regulation (Gómez-Baggethun and Barton, 2013). If green spaces are among the new societal expectations of urban people, they also play a crucial role in preserving biodiversity in urban areas. Among them, green roofs are a great opportunity to create green space in cities as they represent 32% of cities’ horizontal surfaces (Frazer, 2005). Their installation is also perceived as a possible way to preserve biodiversity in cities. However, the effectiveness of green roofs in supporting biodiversity, especially soil biodiversity, has rarely been studied.</p><p>Thanks to different research programmes (TROL, SEMOIRS and T4P), we investigated the taxonomic and functional collembolan biodiversity in both extensive and productive green roofs as well as in ground-level urban microfarms in order to (i) evaluate the effectiveness of green roofs in supporting soil biodiversity, (ii) identify the mechanisms of colonisation by soil organisms and (iii) separate the effect of landscape and soil conditions on collembolan communities assemblages.</p><p>Surprisingly, green roofs are supporting high levels of soil biodiversity. Despite various soil characteristics (organic matter and water avaibility), no difference was found between extensive roofs and rooftop gardens concerning the taxonomical structures of collembolan communities (e.g. species richness, abundances). In contrast, there are differences concerning both taxonomic and functional compositions. Two ways of colonisation are suggested: a passive wind dispersal − the “flying” collembolans − and a settlement through compost inputs. We conclude that stakeholders should take into account the spatial connections of green roofs with other green spaces in order to support urban soil biodiversity.</p>

There is a lack of data on resources used and food produced at urban farms. This hampers attempts to quantify the environmental impacts of urban agriculture or craft policies for sustainable food production in cities. To address this gap, we used a citizen science approach to collect data from 72 urban agriculture sites, representing three types of spaces (urban farms, collective gardens, individual gardens), in five countries (France, Germany, Poland, United Kingdom, and United States). We answered three key questions about urban agriculture with this unprecedented dataset: (1) What are its land, water, nutrient, and energy demands? (2) How productive is it relative to conventional agriculture and across types of farms? and (3) What are its contributions to local biodiversity? We found that participant farms used dozens of inputs, most of which were organic (e.g., manure for fertilizers). Farms required on average 71.6 L of irrigation water, 5.5 L of compost, and 0.53 m2 of land per kilogram of harvested food. Irrigation was lower in individual gardens and higher in sites using drip irrigation. While extremely variable, yields at well-managed urban farms can exceed those of conventional counterparts. Although farm type did not predict yield, our cluster analysis demonstrated that individually managed leisure gardens had lower yields than other farms and gardens. Farms in our sample contributed significantly to local biodiversity, with an average of 20 different crops per farm not including ornamental plants. Aside from clarifying important trends in resource use at urban farms using a robust and open dataset, this study also raises numerous questions about how crop selection and growing practices influence the environmental impacts of growing food in cities. We conclude with a research agenda to tackle these and other pressing questions on resource use at urban farms.