Many of the streams and aquifers that sustain Interior riparian deciduous forests in the US Southwest are being dewatered, yet we know little about how the plant communities are being affected by these hydrologic changes. This study found that several measures of biotic integrity, including Platanus wrightii xylem water potential, P. wrightii radial growth rate, tree species diversity, and woody plant wetland indicator scores, varied significantly with ground water depth and fluctuation among nine sites in Arizona. P. wrightii trees had highest productivity, and the forests had greatest compositional diversity, where ground water averaged less than 2 m below the tree base during the growing season and less than 0.5 m below the stream thalweg, and where ground water fluctuated annually by less than a meter. Where ground water was at a depth of 3 to 5 m, trees had low growth rates and low, seasonally fluctuating stem water potentials. Ground water tolerance ranges differ between juvenile and adult life stages, and P. wrightii seedlings were largest and most abundant where ground water was less than 0.5 m below the flood plain surface. Productivity and diversity generally were highest in perennial stream reaches; however, values also were high at the one ephemeral-flow site (Garden Canyon) that had high and stable ground water tables. The ground water thresholds identified in this study could be incorporated into monitoring plans and used as management 'triggers' to prevent ground water mining activities from causing loss of biotic integrity in this riparian forest type.
- Biotic integrity
- Ephemeral stream flow
- Ground water
- Platanus wrightii
ASJC Scopus subject areas
- Nature and Landscape Conservation
- Management, Monitoring, Policy and Law