The nocturnal, arboreal Marbled Gecko, Christinus marmoratus, is a common reptile in urban areas in southern Australia. This study compared the demographics and the distribution of geckos occupying different tree species in a modified urban park, the Adelaide Parklands, with those of a population occurring in Ferguson Conservation Park, a nearby native vegetation remnant surrounded by suburbia. The geckos in the modified urban and native remnant parks demonstrated different demographic characteristics. These differences were explained by tree circumference and the amount and type of bark cover on the tree trunk. In the Parkland, geckos were limited by the availability of thick exfoliating bark, its clearly preferred microhabitat as demonstrated by a laboratory choice experiment. The preference for trees with larger circumference, more cover, and thick bark were probably linked to thermoregulation, predator avoidance, and food resources. This study supports the premise that to support populations of urban animals, tree species selection needs careful consideration with regard to its microhabitat capabilities as well as food provision and other resource supports it can provide.