Assessing the spatiotemporal patterns of primary production in the Central Arizona-Phoenix region using remotely sensed data

The prevalence of impervious surfaces and the destruction of native vegetation in urban environments can have profound effects on native biodiversity and ecosystem functioning. Urbanization generally has been thought of as a process that decreases primary production, but for desert cities this may not be the case because of highly productive green spaces. While the growth of native desert communities depends strongly on the amount and timing of precipitation, the growth of urban vegetation is decoupled with precipitation due to human ameliorations. To better understand this issue, we quantified overall losses and gains of primary productivity due to urbanization in the Phoenix metropolitan region. We used satellite data (250m MODIS NDVI) to assess the spatiotemporal patterns of primary production (defined as the annually integrated NDVI) and vegetation responses to interpolated climate variables that were correlated with NDVI on different time scales. Our results show that native desert at lower elevations is less productive than upland communities, and that riparian ecosystems encompassing perennial streams are the most productive. Cultivated grass that occupies less than 0.5 percent of the area has a productivity level comparable to that of riparian vegetation. Urban vegetation and agricultural lands have intermediate levels of primary production. Unlike desert communities, urban vegetation and croplands are least affected by climatic fluctuations. As expected, the primary production of native desert vegetation is tightly coupled with precipitation, but with a time delay of a few months. Our work provides insights into the interactions among vegetation growth, climate variability, and urbanization.