The Salt River, known to the Akimel O’Odham people as On’k Akimel, has been dammed, diverted, mined, clear-cut, restored, and ignored over more than a century of intensive manipulation. Although the Hohokam and their descendants irrigated fields with its waters for centuries, diversion intensified dramatically in the early 1900s when the Salt River Project, backed by federal funding, constructed dams and levees that isolated the river from its floodplain and left much of the channel dry. What water remains flows through a handful of reaches where human infrastructure unintentionally or deliberately sustains year-round inundation. In the Sonoran Desert, where riparian and wetland areas cover only about 0.4 percent of Arizona’s land yet support up to 80 percent of its wildlife species, these wet oases are disproportionately important for regional biodiversity.

The research team selected three perennially wet sites representing fundamentally different management philosophies. The first, called Tonto, sits upstream of the urban sprawl within Tonto National Forest, where Stewart Mountain Dam regulates flow and recreationists, kayakers, anglers, and growing herds of feral horses exert ongoing pressure on the ecosystem. The second, Price, is what ecologists call an accidental wetland: it formed beneath and around the intersection of two major highways in the early 2000s and is sustained largely by storm-drain runoff from the roads, agricultural fields on the Salt River Pima-Maricopa Indian Community reservation, and occasional reclaimed wastewater discharge. Beyond access restrictions and occasional harvests of culturally significant plants by Indigenous Elders, Price receives essentially no management. The third site, Rio Salado, is a former dumping ground in downtown Phoenix that the City of Phoenix, the US Army Corps of Engineers, and Audubon Southwest transformed in a restoration project exceeding 110 million dollars, involving litter removal, invasive plant eradication, groundwater wells, and native plantings.

The monitoring itself was methodical and demanding. Bird surveys were conducted seasonally at fixed points along transects crossing the river channel, with a trained observer recording all birds seen or heard within a 50-meter radius over fifteen minutes during calm, clear mornings. Herpetofauna were documented through visual encounter surveys in nine plots per site, conducted by two observers once morning temperatures reached about 21 degrees Celsius, the peak of reptile activity. Vegetation was sampled intensively at the study’s outset in 2012 and again in 2022, with researchers assessing plant cover by species across thirty plots per site using standard Daubenmire cover classes. The team analyzed species richness, abundance, and evenness using the Shannon Diversity Index and analysis of variance frameworks, treating the sites as case studies rather than statistical replicates, a candid acknowledgment that landscape-scale ecology often demands messy but necessary long-term observation.

The results paint a portrait of divergence between taxonomic groups. Bird communities along the river proved remarkably stable, and at the restored Rio Salado site, average annual bird abundance actually rose by 56.7 percent, from 68.5 individual observations in 2014 to 107.3 in 2022, with gains across every habitat preference guild. Aggregated across all three sites, bird species richness showed a statistically significant increase over the study period. Herpetofauna told a different and more troubling story: reptile and amphibian abundance and diversity both declined significantly, with the trend more pronounced at the urban sites. The researchers caution that COVID-19 pandemic disruptions reduced sampling effort and statistical power, but parallel analyses of the same data using different methods have detected similar declines, and the known hazards of urbanization for reptiles, including roads, free-roaming cats, contaminated soils and water, and intensifying heat, lend biological plausibility to the pattern.

The plant communities underwent the most dramatic transformation of all. At both urban sites, vegetation became substantially more abundant, increasing by roughly 50 percent in total cover, and more species-rich by 2022, yet also less evenly distributed, with a few prolific cosmopolitan species such as giant reed, California bulrush, and broadleaf cattail dominating the landscape. The non-urban Tonto site, by contrast, grew more evenly diverse even as drought and horse grazing reduced its obligate wetland plants by about half and its tall trees by roughly two-thirds. This contrast between homogenizing urban sites and diversifying non-urban ones aligns with the well-documented global phenomenon of biotic homogenization, in which cities worldwide increasingly share the same suite of urban-adapted species.

Perhaps the study’s most provocative finding concerns the unmanaged accidental wetland at Price. Despite being wedged beneath a highway interchange and receiving no ecological stewardship whatsoever, Price harbored the two rarest plant species encountered in the entire survey: Ammannia coccinea, a wetland plant more typical of higher elevations, and Ludwigia erecta, a tropical species found nowhere else within 1000 kilometers. Native plants increased from roughly 23 percent cover to 31 percent, and plants culturally significant to the Akimel O’Odham and Piipaash peoples climbed from about 1 percent to 4 percent cover, even as invasive giant reed and tamarisk proliferated. These observations suggest that accidental wetlands, often dismissed as degraded wastelands, may quietly complement formal restoration efforts and deserve consideration as legitimate components of urban ecological infrastructure.

The findings also complicate the conventional wisdom surrounding invasive species management. At Rio Salado, managers invested heavily in eradicating species such as chaste tree, giant reed, globe chamomile, and floating water primrose, yet these plants recolonized from the surrounding urban matrix despite the costly efforts. Meanwhile, the authors found no evidence that introduced plants were suppressing native or culturally important species, which increased in abundance even at sites dominated by invaders. The team argues that management rationales should be critically evaluated before expensive eradication campaigns are launched, and that holistic goals such as increasing habitat complexity, supporting culturally significant plant populations, and protecting accidental wetlands may deliver greater conservation value than reactive removal programs.

The project’s most visible innovation may be its art. Working with City of Phoenix land managers, the researchers harvested the three most abundant marsh plants targeted for removal, which would otherwise have been sent to landfills, and pulped their biomass using field retting, caustic cooking, and a Hollander beater to create handmade paper. Each study site was represented by two sheets, one made from the dominant marsh species of 2012 and one from 2022, and the team hand-carved linoleum blocks to print community composition graphics directly onto the paper, with each icon representing one percent of annual plant cover. The resulting artworks were exhibited at the Nina Mason Pulliam Rio Salado Audubon Center, a university, and an art center between 2023 and 2025, reaching more than 2000 people and sparking public conversations about the river’s ecological past and future. For the researchers, this embodied mode of science communication demonstrates that ecological data, ecosystem stewardship, and community engagement can be woven together, and that the plants managers routinely discard may hold unexpected value as both scientific evidence and cultural material. As the United Nations Decade on Ecosystem Restoration unfolds, the Phoenix wetlands offer a compelling lesson: in social-ecological systems, surprises thrive where humans least expect them, and listening to a decade of data, sometimes printed on cattail paper, is the first step toward stewarding them wisely.

The study’s framing draws on a social-ecological perspective in which large-scale pressures, such as damming and urban expansion, interact with rapid pulses like drought, recreation, and management interventions to shape what lives in a given reach of river. The authors constructed a Press-Pulse diagram to situate their case studies within this broader context, treating community composition as a visible clue to underlying ecosystem processes that are otherwise difficult to observe directly.

The research also addresses a recognized gap in the urban wetland literature. A review cited by the team identified the mitigation of urban wetlands acting as ecological traps, where animals are attracted to habitats that ultimately reduce their survival, as one of the field’s largest unresolved questions. By monitoring birds, herpetofauna, and vegetation simultaneously rather than focusing on a single taxonomic group, the study captures some of the trophic complexity that single-group surveys miss, since vegetation structure creates habitat for animals while animals, including humans, disperse seeds that reshape the landscape. Invertebrates and fungi, however, were excluded from the analysis.

The authors emphasize that urban wetlands deliver a wide array of ecosystem services in arid settings where such features are spatially rare, including flood mitigation, water quality improvement, phytoremediation, carbon storage, heat reduction, denitrification, and habitat corridors, and even shelter for people experiencing houselessness. Infrastructure itself can generate habitat, as bridge overpasses create shaded niches for plants and animals seeking respite from the sun. Because long-term monitoring and citizen engagement are considered essential for managing these systems rather than working against them, the project’s blend of decade-scale surveys, collaboration with land managers, and public art exhibitions offers a model for how ecological research can remain connected to the communities it studies.

Subject of Research: Long-term changes in bird, herpetofauna, and plant community composition across managed, restored, and accidental urban wetlands of the Salt River in Phoenix, Arizona

Article Title: A portrait of changing community composition in three urban wetlands of the Salt River, Phoenix AZ USA

Article References: Ramsey-Wiegmann, L., Bateman, H. L., Childers, D. L., Green, H., & Makings, E. (2026). A portrait of changing community composition in three urban wetlands of the Salt River, Phoenix AZ USA. Discover Ecology, 2(1), Article 18. https://doi.org/10.1007/s44396-026-00030-3

Image Credits: AI Generated

DOI: 10.1007/s44396-026-00030-3

Keywords: urban ecology, wetlands, Salt River, Phoenix, biodiversity, herpetofauna, invasive species, restoration ecology, accidental wetlands, plant communities, long-term monitoring, science art