As cities expand, river floodplains have become increasingly endangered ecosystems, and thus, the target of restoration projects. Studies show that restoration or rehabilitation of riparian areas can make habitat and microhabitat available for species, and it is beneficial for bird survival and reproduction rates. However, until now, few studies have examined how riparian rehabilitation programs influence non-bird species.
Amphibians and reptiles are often good indicators of ecosystem function, playing important ecological roles within riparian ecosystems. Yet, previous studies show that amphibian and reptile decline is related to human activities. Thus, restoration programs that promote amphibian and reptile abundance in urbanized areas may reestablish or improve ecosystem functions as well as contribute to long-term ecosystem stability. Two scientists at Arizona State University evaluated reptilian and amphibian communities at various levels of urbanization and restoration along the Salt River in Arizona. Writing in Urban Ecosystems, the scientists report on how river sites with varying degrees of urbanization impacted reptilian and amphibian species.
The surveyed urbanized areas were predominantly parts of the Salt River surrounded by built environments that were rehabilitated and restored in the last 10 years by having garbage removed, establishing a deep low flow channel, and building terraces. Wildland survey areas were in a national forest. The authors performed visual surveys, recording species and location of each reptile and amphibian spotted, checking for indicators of declining reptile population health. The authors also measured vegetative characteristics of survey areas.
The authors were able to compare wildland areas that had never been urbanized with urban disturbed areas and urban rehabilitated areas. The scientists found that wildland sections of the Salt River had the healthiest populations, while the urban disturbed had the lowest population health of the surveyed sites. The urban rehabilitated parts of the river exhibited some similar indicators of population health to the wildland areas, suggesting the success of restoration projects. Despite displaying dissimilar health markers, rehabilitated and disturbed urban sections of the river contained similar measures of species diversity.
The conclusion from the research suggests that restoration positively influences both abundance and diversity, but that diversity from restoration may benefit more slowly. Habitat generalists may adapt easily to urban environments—some may even thrive there. More specialized species, such as arboreal species, may have a harder time in urban environments and may be slower to colonize rehabilitated sites.
By measuring variables at all the sites, the scientists determined key differences in habitat between the different survey locations. Habitats that had complex vegetation structures—those involving several different vegetation species with various growth patterns, ages, and sizes—were positively linked to at least one lizard species. Sites with high densities of mesquite, willow, and cottonwood also were linked to high amphibian and reptile abundance, as were sites with a high density of non-reptilian animal burrows.
The authors suggest that natural resource managers who aim to rehabilitate southwestern degraded riparian ecosystems increase vegetation structural complexity and woody debris to improve habitat for reptiles and amphibians. By planting a diversity of vegetative layers—in size, shape, age, and species—reptiles and amphibians will have a diversity of food and shelter sources. This study also suggests that planting mesquite, willow, and cottonwood will benefit amphibian and reptile species. Natural resource managers should keep woody debris on site and introduce woody debris if none exists in the area. By taking steps to rehabilitate degraded riparian areas, natural resource managers can improve the southwestern riparian population health and ecosystems.