Urban agriculture: a global analysis of the space constraint to meet urban vegetable demand

Urban agriculture (UA) has been drawing a lot of attention recently for several reasons: the majority of the world population has shifted from living in rural to urban areas; the environmental impact of agriculture is a matter of rising concern; and food insecurity, especially the accessibility of food, remains a major challenge. UA has often been proposed as a solution to some of these issues, for example by producing food in places where population density is highest, reducing transportation costs, connecting people directly to food systems and using urban areas efficiently. However, to date no study has examined how much food could actually be produced in urban areas at the global scale. Here we use a simple approach, based on different global-scale datasets, to assess to what extent UA is constrained by the existing amount of urban space. Our results suggest that UA would require roughly one third of the total global urban area to meet the global vegetable consumption of urban dwellers. This estimate does not consider how much urban area may actually be suitable and available for UA, which likely varies substantially around the world and according to the type of UA performed. Further, this global average value masks variations of more than two orders of magnitude among individual countries. The variations in the space required across countries derive mostly from variations in urban population density, and much less from variations in yields or per capita consumption. Overall, the space required is regrettably the highest where UA is most needed, i.e., in more food insecure countries. We also show that smaller urban clusters (i.e., <100 km2 each) together represent about two thirds of the global urban extent; thus UA discourse and policies should not focus on large cities exclusively, but should also target smaller urban areas that offer the greatest potential in terms of physical space

Modelling public health benefits of various emission control options to reduce NO2 concentrations in Guangzhou

The local government of the megacity of Guangzhou, China, has established an annual average NO2 concentration target of 40 μg m−3 to achieve by 2020. However, the Guangzhou Ambient Air Quality Compliance Plan does not specify what constitutes compliance with this target. We investigated a range of ambition levels for emissions reductions required to meet different possible interpretations of compliance using a hybrid dispersion and land-use regression model approach. We found that to reduce average annual-mean NO2 concentration across all current monitoring sites to below 40 μg m−3 (i.e. a compliance assessment approach that does not use modelling) would require emissions reductions from all source sectors within Guangzhou of 60%, whilst to attain 40 μg m−3 everywhere in Guangzhou (based on model results) would require all-source emissions reduction of 90%. Reducing emissions only from the traffic sector would not achieve either interpretation of the target. We calculated the impacts of the emissions reductions on NO2-atttributable premature mortality to illustrate that policy assessment based only on assessment against a fixed concentration target does not account for the full public health improvements attained. Our approach and findings are relevant for NO2 air pollution control policy making in other megacities

Butterfly communities in miombo woodland: biodiversity declines with increaing woodland utilisation

Deforestation and degradation is threatening forests and woodlands globally. The deciduous miombo woodlands of sub-Saharan Africa are no exception, yet little is known about the flora and fauna they contain and the implications of their loss. Butterflies are recognised as indicators of environmental change; however the responses of butterflies in miombo woodlands have received little attention. This paper describes butterfly assemblages and their response to woodland utilisation in an understudied area of miombo woodland in south-west Tanzania. This is an area representative of miombo woodlands throughout sub-Saharan Africa, where woodland is utilised by local communities for a range of products, and is being rapidly converted to agriculture. Baited canopy traps and sweep nets were used to sample frugivorous and nectarivorous butterfly communities at different vertical stratifications in nine different study sites. 104 species were recorded, of which 16 are miombo specialists that have been recorded in Tanzania to the west of the country only. Indicator species were identified for three different levels of utilisation, with species from the sub-family Satyrinae indicating moderate utilisation. Generalised linear mixed effects models showed that butterfly species richness, diversity and abundance all decreased in response to increasing agriculture and anthropogenic utilisation. The loss of miombo woodlands is likely to result in declines in butterfly diversity. However, there was evidence of an intermediate disturbance effect for butterfly species richness, diversity and abundance with one utilisation variable, suggesting that a miombo woodland management plan that allows moderate sustainable utilisation in a heterogeneous landscape of mature miombo woodland and agriculture will simultaneously maintain butterfly communities and enable agricultural production