The Vegetation and Flora of the Lower Verde River, Arizona

For this study, the flora of the northern section of the Lower Verde River, within the Tonto National Forest in Yavapai and Gila Counties, Arizona was documented and analyzed. The study site, part of the northern leading edge of the Sonoran Desert, encompasses about 16,000 hectares and is located approximately 45 miles north-northeast of Phoenix. The area, extends roughly 28 river miles from the East Verde River in the north to Chalk Mountain in the south and is largely only accessible by foot, or by boat, and as a result was previously extremely under-collected. Over a three-year study period, from August, 2017 to May, 2020, 835 plant specimens were collected and identified, representing 360 species which, combined with earlier herbarium specimens collected by others, resulted in 427 plant species found in the study area. The plant diversity of this remote region reflects three distinct vegetation communities: upland Sonoran Desert, perennial riparian corridor, and semi-desert grasslands. Together, these communities act as an important transition zone between the Sonoran Desert and higher elevation habitats. Perennial streams are biodiversity hotspots within the study area. For example, the 400 hectares of Red Creek that falls within the study boundaries contain 28% of the total species. The study site contains several plants of conservation importance including 12 species endemic to Arizona, 22 vulnerable or imperiled species, five US Forest Service sensitive species, and one Federally Endangered species. In order to compare the diversity of the Lower Verde River Flora to nine other similar/related floras in Arizona, a species-area curve using five different models was generated. The resulting models showed the Lower Verde River flora to be very close to, although slightly below, the species-accumulation curve which may indicate that roughly 50-100 species may yet be added to the flora. This prediction seems realistic, as there were several locations that could not be collected due to remoteness and excessive heat.