The Influence of Landscape Position on Soil Respiration and Urban Microclimate

Linking variation in ecosystem functioning to landscape drivers has become an important research need for understanding ecosystem responses to global change. Due to extensive land use and land cover changes many regions have variable distributions of landscape drivers and ecosystem processes. Furthermore, changes in local- to regional-scale climate may impact ecosystem variation and sensitivity to physiological drivers. This dissertation investigates how contrasting scale-dependent drivers of soil temperature, moisture and substrate levels influence soil respiration (Rs), a key ecosystem process, using in-situ landscape surveys and experimental subsidies of water and labile carbon. Furthermore, to improve understanding of scale-dependent sources of variation of urban microclimate this dissertation investigates how land cover and vegetation influences local distributions of air temperature (Ta), land surface temperature (LST), and relative humidity (RH), using intensive and widely distributed networks of microclimate sensors. Finally, vital in estimates of urban warming, this dissertation examines the relationships between Ta and LST among common urban land covers. I found Rs in intensively managed urban land uses has increased rates, decreased spatial variation, and decreased sensitivity to environmental conditions. Furthermore, among common urban land uses spatial variation in Rs was positively correlated with soil temperature, and negatively correlated with soil moisture and substrate. Landscape position, or land use and climate distributions, influenced Rs by altering both levels and Rs sensitivity of physiological drivers. Next, in my first microclimate study I found negative Ta and positive RH correlations with vegetation intensity. Vegetation cooling effects were greater in more arid climates and in the evening hours. Furthermore, increasing city-scale mean Ta was associated with higher spatial variation of Ta in coastal cities, and lower variation in more arid cities. In my final study I observed vertical height-dependent Ta-LST relationships associated with land cover composition. Furthermore, I observed decreased nighttime Ta-LST differences among land covers. These findings can help city planners identify potential heat risk reductions strategies associated with urban vegetation and land cover composition. Together, these systematic evaluations of landscape effects on Rs and microclimate provide a framework of understanding the effects of interactive global change drivers on urban ecosystem processes