Due to many implications of urbanization, biological communities in urban ecosystems look drastically different than nearby rural ecosystems. Urban ecosystems are more strongly affected by habitat fragmentation, urban heat island effects, disturbance, and nitrogen deposition than their rural counterparts. These changes can drive declines in species diversity in most taxa, resulting in low levels of biodiversity in urban cores. However, in many locations moderate urbanization has shown to increase species diversity. Here we explore how urbanization in Los Angeles county affects biodiversity and species composition in grasslands along an urban to rural gradient. Secondly, this work explores urban heat islands in more detail. Past research has shown how urban heat islands affect plant communities, but there has been little work examining how urban heat islands affect plant-plant interactions. This study identifies and quantifies microclimate amelioration (facilitation) and resource availability (competition) in urban grasslands by sampling vegetation and collecting environmental data across Los Angeles County. We measure soil moisture, vapor pressure deficit at ground level, and light availability to address how microclimate amelioration is stronger in cities, where macroclimate conditions are hotter on average, than in rural environments where macroclimate conditions are cooler on average.
Results/Conclusions
We found significant differences in temperature across an urban gradient in Los Angeles County. Nighttime temperatures in urban locations were 2°C warmer on average than rural locations. These higher temperatures were correlated with increased temperature amelioration effects caused by vegetation in urban areas compared with cities. At the hottest points during our sampling period, microclimate amelioration from vegetation was over 5°C cooler than ambient site temperatures. These results show that the interactions between plants function differently across urban gradients. Understanding these community-scale processes is essential for predicting how natural systems will respond to global climate change. Without a complete understanding of how these processes work, increases in temperature could drive more rapid changes in composition and diversity than currently predicted.