Print PageCities occupy just 2% of terrestrial land cover, but over 50% of the world’s population lives in urban areas. Ecosystems downwind of cities are exposed to numerous compounds in the urban atmosphere that affect ecosystem properties and processes. We measured nitrogen (N) deposition, plant growth and composition, herbivory, and soil nutrient cycling in native desert ecosystems within and surrounding Phoenix, AZ as a part of the Central Arizona-Phoenix Long Term Ecological Research (CAP LTER) project. We also explored the impacts of nutrient enrichment through a factorial fertilization experiment composed of plots amended with high doses of N, phosphorus, and both in combination.
Results/Conclusions
N deposition to protected desert lands near Phoenix is lower than expected (~5-7 kg N/ha/yr) and higher in the urban core compared to outlying lands. Growth of the dominant perennial plant, L. tridentata (creosote bush), is driven by spatially patchy, summer monsoon rainfall and is insensitive to the urban atmosphere or experimental nutrient enrichment. Aboveground growth of winter herbaceous plants and rates of herbivory were also less affected by urbanization than by seasonal precipitation. In contrast, communities of winter annual plants were significantly less diverse in urban desert remnants compared to outlying desert preserves. Together, these data suggest that the urban atmosphere has larger effect on community level processes compared to ecosystem processes in the Sonoran Desert. The pulsed, patchy nature of ephemeral precipitation events in arid ecosystems may favor N losses and redistribution and limit N accumulation within biota.
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