A Biological Inventory and Hydrological Assessment of the Cave Springs Riparian Area, Tonto National Monument, Arizona

Albrecht, Eric; Halvorson, William; Guertin, Phillip; Powell, Brian; Schmidt, Cecilia

This report gives geohydrology details on the Cave Canyon watershed and the springs in Cave Canyon that give rise to a riparian woodland at Tonto National Monument, located in east-central Arizona. It also summarizes the results of the first biological inventory of plants and vertebrates. The inventory focused on the riparian area in Cave Canyon and included some surveys in other areas as well. Cave Canyon is steep and bedrock dominated, resulting in relatively rapid run-off and frequent high water events. Sediment transport is also a frequent event which leads to specific areas of the stream alternately experiencing periods of accretion and sediment flushing. We created GIS coverages of the watershed and then created flow models to simulate flooding events. There are two active springs in Cave Canyon. An upper, larger spring, near where the trail to the Upper Cave Dwelling crosses the main channel, and a smaller spring approximately 100 meters down stream from the upper spring. The upper spring is an artesian-type spring with highest flows in the winter and decreased flows in the spring and summer when the riparian trees and shrubs are in full leaf. This spring has perennial flows while the smaller, lower spring does exhibit dry periods during droughts. From 2001 to 2003, we surveyed for vascular plants and vertebrates (amphibians, reptiles, birds, and mammals) at Tonto NMON to record species presence. We recorded 149 species in the riparian area, and 369 species overall in the monument, including 65 plant species and four bird species that were previously unrecorded for the monument. The number of new species recorded in the riparian area is unknown because previous studies and collections have not listed comprehensive results by vegetation type or locality. We recorded 78 plant species in the riparian area that previous studies had not indicated were present there. Several species of each taxonomic group were found only in the riparian area, suggesting that because of their concentration in this small area, these populations are vulnerable to disturbance and may be of management concern. Four of the bird species that we recorded (Bell’s vireo, yellow warbler, summer tanager, and Abert’s towhee) have been identified as riparian “obligate” species by other sources. Bird species that are obligated to riparian areas are targets of conservation concern due to widespread degradation of riparian areas in the desert southwest over the last century. We recommend a continued conservative approach in limiting public access to the riparian area, and careful monitoring and management of the source spring and associated surface flow. We also recommend that managers incorporate monitoring protocols developed by the Sonoran Desert Network Vital Signs Inventory and Monitoring program rather than initiating a separate program for the riparian area. Park managers should encourage the Vital Signs program to address the unique monitoring challenges presented by small spatial areas such as this riparian area, and request specific monitoring recommendations. We suggest that repeat inventories for vertebrates, and census (rather than sampling) of perennial vegetation may be the most effective long-term monitoring strategies in the riparian area to verify species persistence through time in this unique and spatially limited environment.