Even as studies have shown that the uneven distribution of urban heat islands, urban tree canopy cover, and urban environmental hazards, for example, are strongly dictated by structural racism and classism in cities, relatively few studies have addressed the varied contributions of social factors like race to ecological heterogeneity in cities. Here, Christopher J. Schell and colleagues integrate findings from ecology, evolution, and the social sciences to underscore such relationships. Their findings, they say, are necessary to conserve biodiversity, improve human health, and promote justice in nature and society. They start with a well-known hypothesis called the luxury effect - which suggests that urban biodiversity, and plant diversity in particular, is positively correlated with neighborhood wealth. A direct effect of the luxury effect is that poorer-income neighborhoods usually have less tree cover - and thus more heat. These neighborhoods are also typically located closer to pollution sources. "Work on heat islands and pollution support the idea that inequality in neighborhood wealth leads not only to a diversity of environmental hazards," the authors say, "but that these hazards compound to create unique, challenging environmental patches." They also cite research that has shown that neighborhood racial composition can be a stronger predictor of urban socio-ecological patterns than wealth. Neighborhoods that were "redlined" decades ago - by a policy that segregated urban residential neighborhoods principally by race - have on average 21 percent less tree canopy, for example. Knowing where these cities are could help to identify and predict geographic regions with compounding anthropogenic disturbances that require more sustained stewardship, the authors say. "Our capacity to understand urban ecosystems and non-human organisms necessitates a more thorough integration of the natural and social parameters of our cities," Schell and colleagues write. "We cannot generalize human behavior in urban ecosystems without dealing with systemic racism and other inequities."