North American cities are currently expanding at an unprecedented rate. Rapid growth in urban development has sparked debate about how to grow cities in a way that minimizes environmental impact and provides ecological benefits to people. Part of this conversation has involved the idea that urban areas should be densely built, so as to minimize their environmental impact, and promote sustainable development goals. However, there is minimal research available on whether there may be a point at which urban areas become too dense for ecosystem service provision (the provision of benefits to humans by nature). Our research explores the relationship between urban density and ecosystem service provision by measuring indicators of health related ecosystem services (temperature regulation, air pollution regulation, and green space accessibility) at 250 study sites in Montreal across a range of building densities (ranging from 0-100%) and population densities (number of households). Using data derived from Landsat-8 and SENTINEL 5P images as well as GIS based analyses, this study addresses the questions: 1) How does building density and its associated landscape features affect multiple health-based ecosystem service indicators? And 2) Is population density related to the provision of ecosystem services at the scale of investigation once building density is accounted for? Results indicate that higher building densities lead to decreases in temperature regulation, but do not impact air quality regulation. High population density sites tend to be more exposed to high temperatures, but are not more exposed to high levels of air pollution. We did not find a statistically significant relationship between household density and distance to public green space, and although marginally significant, the relationship between building density and distance to public green space was weak. Area of private green space per household is negatively correlated with both building density and population density. These results indicate that while some ecosystem services are unaffected by densification, maintenance of multiple services may require creative solutions at the interface of ecology, planning and design
