Terrestrial Resources
Terrestrial resources of interest to stakeholders in the adaptive management program include riparian vegetation, riparian breeding birds and waterfowl, invertebrates including Kanab ambersnail, small mammals, and reptiles associated with the river corridor. Monitoring approaches for terrestrial biologic resources underwent review in late 1999 (KAS expert panel) and 2000 (Urquhart, 2000). Recommendations from these reviews were incorporated into 2001 monitoring and research plans and continue to be evaluated and implemented through 2005.
A review of previous riparian studies and their applicability to monitoring, as well as the information that these studies provide for assessing change, was completed in 2001 (Kearsley and Ayers, 2001). Power analysis of historic data indicates that change detection of vegetation attributes varied by vegetation type and parameter measured (e.g., species richness, density). For example, changes in cover can be detected within a year’s time for mixed scrub, but changes in diversity for the same community type may take over 20 years. Kearsley and Ayers (2001) analysis also indicated that the minimum number of sites needed to detect change in species richness and cover is between 30 and 70, depending on the type of vegetation (Kearsley and Ayers, 2001), and that previous approaches and sites over-represented some types of vegetation (e.g., tamarisk) and under-represented others (e.g., seep willow). Areas of high density, single species composition were more likely to show little change compared to mixed communities and would require longer time periods for change detection. In most cases, change was detectable within five years of measurement. The temporal and spatial scale as well as number of sites needed to detect change was taken into account in the development of monitoring approaches for terrestrial resources.
Currently monitoring includes yearly field-based assessment of vegetation cover, species richness and diversity at 60 sites that are linked to stage/discharge changes up to 60,000 cfs, and five-year change detection at the landscape scale using GIS and image processing. The basemap of vegetated areas initiated in FY2003 and to be completed in FY2004 serves as a template for past and future large-scale change detection, as well as for randomized selection of monitoring sites for vertebrates including bird patches. Results from the monitoring project for vegetation indicate measures of plant abundance, species richness, diversity, and distribution all showed a decline in 2002 compared to 2001 (Kearsley, 2002), data from 2003 is still to be provided. Herbaceous desert annuals and perennial grasses and herbs like cheat grass, sand dropseed and spiny aster showed the greatest decline and are affected by yearly precipitation. Compositional shifts did not occur for zones below 35k cfs, but at sites of 45k and 60 k cfs, species composition did change significantly compared to 2001, again the change is associated more with a loss of annual and rarely encounter plant species. The mean wetland score, which most closely tracks operational effects on vegetation and available groundwater, showed no change within zones between years, but an increase in value for all zones compared to 2001 (Kearsley, 2002). As long-term data accumulate we will be better able to see how yearly operations and weather patterns affect vegetation.
Monitoring for riparian breeding birds, including southwest willow flycatcher, and over-wintering waterfowl continues. Power analysis by Spence et al. 2003 indicates that approximately 64 sites visited three time in the spring provides sufficient power to detect change in bird abundances between years for the 18 most common bird species. In FY2001, this program was combined with vegetation monitoring and insect, reptile and mammal inventories to provide an integrated picture of the terrestrial resources and long-term patterns associated with these resources and Glen Canyon Dam operations. Surveys to assess riparian bird abundance and distribution were done in April, May and June of 2002. 64 vegetation patches were surveyed in 2002 and 17 of these sites were repeated from the previous year. A total of 2627 passerine birds of 66 species were detected in the three surveys. Bird detections were highest in May when birds are both migrating through and establishing nests. Bird abundance and density, which included migrants and permanent winter and summer residents, was greater in the New High Water Zone (t=3.4, p=0.001) (Yard and Blake, 2002). Species richness was also higher in the New High Water Zone. This was in contrast to 2001 where species abundance was greater in the Old High Water Zone. Comparison of 15 common species between years showed a significant difference in abundance for only 2 species: Black-chinned Hummingbirds had increased in abundance in 2002 and Mourning Doves had decreased in abundance in 2002. The shift in bird abundance between Old and New High Water Zones may be associated with lower abundance and diversity of arthropods or seeds from annual grasses and herbs in the Old High Water Zone related to the drought conditions. Synthesis of invertebrate data will take place in 2003-04 and it is anticipated that trophic level interactions will be more developed by 2004.
Lastly, Kanab ambersnail monitoring at Vasey’s Paradise has continued to follow the protocols begun 1997. Data collection efforts continue at two trips per year: one in spring and one in fall. Population estimates for the snail indicate that the snail numbers vary widely throughout the year (10,000 in the spring to 100,000+ in the fall), influenced by climatic and concomitant habitat variability (SWCA, 1999). Measured snail habitat at Vasey’s Paradise increased 6 % in area between spring and fall of 2002. Total surveyed habitat changed from 270.01 m2 in April to 288.36 m2 by August 24, 2002. Yearly average total habitat has increased steadily and significantly since 1998 (p = 0.014; F=5.19 4,5) from 176 m2 in 1998 to 279 m2 in 2002.
Estimated snail numbers have not changed significantly since 1998, but numbers have shown a decline to a value of 7,444 snails in August 2002. Curiously, while habitat has increased, snail numbers have not had a correlated increase. The lack of increase in snail numbers may be associated with soil moisture rather than the amount of habitat available. The discharge from the spring at Vasey’s Paradise was lower in 2003, and the habitat was also visited by bighorn sheep. Tramping by sheep may have been a contributor to lower snail numbers recorded for 2002.