OOS 54-5 - 50 years in the US Southwest: changing landscapes and changing climate

The idea of islands has been explored in conservation biology, landscape ecology, and more since islands were first used to test theories about ecology and evolution. In the arid US Southwest, mountain islands and desert seas at broad scales and islands of fertility at fine scales evoke ideas of relatively productive patches separated by seemingly inhospitable (desert) land. In contrast, cities as islands in this landscape were not formed through tectonic processes or the gradual hydro-biogeochemical accumulation of resources below plants, but rather through colonization by settlers and their subsequent construction of urban habitat, which entailed manipulation of natural structures and processes and construction of new artifacts of “civilization.” The astonishing expansion of urban land in the US Southwest over the past century, particularly the last 50-70 years, has indeed yielded islands that share distinctive edges and strong contrasts with their surroundings. How does human agency in this shaping of the environment lead to different island characteristics in this region?

This talk will examine the shifts that have occurred since the beginning of Phoenix’s explosive growth post World War II in land cover, biodiversity, biogeochemical cycling, and hydrological processes in the context of climate variability and change. Rapid urban expansion replaced native floras with almost entirely introduced ones and saw declines in bird diversity but increases in abundance. Human behaviors, particularly the capture of water resources for irrigation of incongruous green lawns, shifted phenology and the rhythm of desert productivity’s response to variable rainfall. And biogeochemical processes became dominated by massive importation of materials and large throughput terms, particularly for carbon. Internal processes significantly altered atmospheric chemistry but limited effects were observed in the surrounding desert, and deposition of nitrogen as well as fertilizer applications are transported in stormwater but retained by abundant green infrastructure in the city. The metro area relies for its water supply on the Salt and Verde Rivers, the Colorado River, and groundwater, and that supply is threatened due to climate change. This urban island is highly dependent on its connections with these watersheds, food imports from Mexico, California, and elsewhere, and imported fossil fuels to support its fossil fuel-based economy. Co-produced visions for the future of the region include more self-sustaining practices, such as stormwater capture for irrigation, local food hubs, and expanded public transit, and offer some hope for a more sustainable future for this desert metropolis.