Temperature variability influences urban garden plant richness and gardener water use behavior, but not planting decisions

Urban environments are being subject to increasing temperatures due to the combined effects of global climate change and urban heat. These increased temperatures, coupled with human planting preferences and green space management practices, influence how urban plants grow and survive. Urban community gardens are an increasingly popular land use, and a green space type that is influenced by unique climate-human behavior interactions. Despite ongoing rapid temperature changes in cities, it is unknown how gardeners are adapting to these changes, and to what extent changes influence planting decisions and patterns of urban plant diversity. In this study, we monitored the variation in daily air temperatures and measured plant species richness at the garden and garden plot scale in 11 community gardens in Melbourne, Australia. We surveyed > 180 gardeners to better understand the relationships between temperature variation, garden plant species diversity, and gardener management practices. We found that garden scale temperature variability is driven by regional context, and temperatures are more stable in landscapes with higher impervious surface cover. Gardeners agreed that climatic/temperature changes are influencing their watering behavior, but not their plant selection. Instead plant selection is being driven by desired food production. Yet, when comparing two bioregions, temperature did have a measurable relationship with garden plant composition in the region with more temperature variation. Temperature variability negatively related to plant species richness within garden plots, providing evidence that plant survival is related to climate at this scale in such regions. Although gardeners may be able to water more in response to regional climate changes, gardeners are unlikely to be able to completely control the effects of temperature on plant survival in more variable conditions. This suggests the inner city with more stable temperatures (albeit potentially hotter for longer due to heat island) may accommodate more species diverse gardens.