Urbanization affects plant flowering phenology and pollinator community: effects of water availability and land cover

Introduction: Climate change and urbanization have been shown to alter plant phenology. However, a mechanistic understanding of these changes in flowering phenology and associated pollinator communities is lacking. Thus, this study was designed to examine finer scale flowering phenological patterns and driving processes in an arid urban ecosystem. Specifically, we tested the effect of water availability and land cover type on the flowering phenology of brittlebush (Encelia farinosa) and investigated the arthropod pollinator community associated with brittlebush. Methods: The fieldwork was carried out as part of a larger community ecology experiment following a factorial nested design. We chose three land cover types, each of which had three replicates, resulting in a total of nine sites. For water availability manipulations, 60 genetically different 5-gallon potted plants were placed on the ground within each site. Pan-trapping was used to collect potential pollinators. Results: Our results showed that water availability did not produce significant differences in flowering phenology. However, brittlebush planted in mesiscaped urban sites bloomed later, longer, and at a higher percentage than those planted in desert remnant sites and desert fringe sites. Furthermore, desert remnant sites were significantly lower in pollinator abundance than desert fringe sites. Pollinator richness varied over time in all land cover types. Conclusions: This study provides empirical evidence that land cover type, which is strongly correlated to temperature, is the primary cause for altered flowering phenology of brittlebush in the Phoenix area, although water availability may also be important. Moreover, land cover affects total abundance of bee pollinators.