Transition Monitoring for Riparian Vegetation in the Colorado River Corridor of Grand Canyon National Park Michael J.C. Kearsley and Tina J. Ayers Department of Biological Sciences Northern Arizona University Flagstaff, AZ 86011 Starting Date: 1 October 1995 Duration: 12 Months Submitted To: U.S. Department of the Interior Bureau of Reekunation Glen Canyon Environmental Studies Flagstaff, Az 86002-2459 ‘1 24 MI D. Henry 0. Hooper, Ph.D. Co-Princip Investigator Associate Vice President for Academic Affairs, - 4 Research and Graduate Tina .7. Ayers, StucUes Co-Principal Investigator ABSTRACT Riparian plants in marsh, channel margin, and back beach environments downstream of Glen Canyon Dam are strongly affected by the timing, magnitude, and duration of water releases. During the Bureau of Reclamation's Interim Flows, the number of channel margin marshes has increased, but their total area has decreased. Also, there has been a riverward displacement of wet marsh (Typha, Juncus, Phragmites) species in return current channel marshes. Water stress in coyote willow, Salix exigua, and dieback of cattails, Typha domingensis, are inversely related to discharge volumes. Here we propose monitoring of riparian and wetland plant assemblages using aerial photographs and ground-truthing as outlined in the Transition Monitoring Plan strategy document. We will track the development of these assemblages, paying special attention to fluvial marshes and newly exposed habitats in the zone between 20,000 cfs stage elevation and 28,000 cfs stage elevation (the 'New Dry Zone'). We will use mapping and census methods developed and refmed in the last two years of Interim Flows monitoring. In addition to providing broad scale patterns of vegetation change, the data will reveal patterns of species loss and turnover and the establishment and spread of important exotic plant species This information is important for both land- and water- management agencies because riparian plant assemblages are continuing to change rapidly under Interim Flows. For example, the higher elevation areas of marshes lost significant numbers of obligate wetland species during the first three years of Interim Flows. These same species colonized the New Dry zone during that same time. Also, riparian and wetland vegetation have special significance for wildlife in and near the river corridor. )(earsley and Ayers 2 INTRODUCTION Problem Statement The timing, magnitude, and duration of water releases from Glen Canyon Dam have had strong effects on new high water zone plant assemblages in the river corridor of Glen Canyon National Recreation Area and Grand Canyon National Park (Campbell and Green 1968, Carothers and Aitchison 1976, Phillips et al 1977, Johnson et al. 1985, Koslowski 1984, Stevens et al. 1995). Through physical effects of substrate deposition and scouring and indirect, groundwater-mediated influences, dam operations can determine the identity, diversity, and productivity of riparian plant assemblages (Stevens and Ayers 1992, Stevens 1989, Turner and Karpisak 1980). These vegetation characters, in turn, determine the suitability of these settings for wildlife. Given these effects, vegetation monitoring must continue, even at a minimal level. Although Interim Flows (IF) discharge criteria were mandated at Glen Canyon Dam to minimize the effects on downstream resources, riparian habitats have continued to change rapidly since their implementation. Fluvial marshes have become drier, measured either by changes in assemblage-wide ordinations or basal area of obligate wetland species (Kearsley and Ayers 1995). Habitats in the 'New Dry' zone (between the maximum stage discharge elevations of Interim Flows and pre-IF normal flows) have been colonized rapidly by a diverse group of species. Specific Objectives We propose to continue monitoring the composition and successional trajectories of plant assemblages in the river corridor. The data will describe plant assemblages and will provide updates on exotic plant species. We cannot overemphasize too strongly the importance of data continuity to the monitoring effort, given the dynamic nature of riparian plant assemblages and the importance of riparian vegetation to other species in the river corridor. Our work will be directed towards answering the following questions: 1. Are riparian plant assemblages below the old high water zone continuing to change during the extension of interim flows? This question breaks down to specific questions: a). Are there losses of species or a change in the abundance of important wetland and riparian species in our study areas? We will be testing the null hypothesis of no change in either species composition or species abundance. b). Are the areas in which obligate wetland species occur continuing to shrink or changing position as a result of water release patterns? Our null hypothesis is that the areal extent and location of areas in which these species will not change. c). Are populations of exotic species growing and expanding into new areas during the study period? We will test hypotheses of no changes in foliar cover of specific exotic species in our study sites and no movement into new areas in the study sites. 2. Have the previous year's flows affected the physical layout of return-current channel marshes in our study sites? We will combine our efforts with the NAU sandbar studies Kearsley and Ayers 3 group to test the hypothesis that the morphologies of return current channels have been unaffected by flows during water year 1995. In addition, we will be refilling the integration of previous vegetation studies' data into the GCES GIS. Although most data from 1992 onward were collected in ways which allow them to be integrated in a very gross manner (i.e. references to data files), a better integrated set of data would allow easier access to the information and better use of the capabilities of the GIS. Process of Integration with Transition Monitoring Plan. The work outlined in questions 1 through lc above directly address Item IV: A(1) in the Transition Monitoring Plan. Question 2 above addresses Item IV: A(2) BACKGROUND Review of Literature and Previous Work Turner and ICarpisak (1980) and Pucherelli (1988) reported a rapid increase in riparian vegetation cover in the new (post-dam) high water zone (NHWZ) between 1965 and 1982. Cover was significantly reduced in this new riparian zone in wide reaches during spillover flooding in 1983-1984. Brian (1982, 1988) and Stevens and Waring (1988) reported significant loss of riparian vegetation in the NHWZ as a result of spillover flooding. The latter authors noted that spillover flooding degraded substrate, decreased riparian plant cover and diversity, and stimulated germination. Stevens (1989) compared the impacts of flooding on riparian vegetation in tributaries and along the river corridor. He concluded that dam-induced substrate changes in soil texture, water availability, and nutrient status were largely responsible for the successional development of the phreatophyte community. He also reported that the river corridor was structurally more similar to the sparsely-vegetated ephemeral tributaries than to the richly- vegetated perennial tributaries. Stevens and Waring (1988) studied post-1983 development of woody riparian vegetation along the Colorado River in Grand Canyon National Park from 1984 through 1988, reporting that germination of dominant riparian species was induced by flooding, and exotic Tamarix ramosissima density appeared to have increased as a result of dam operations. GCES Phase II studies on riparian vegetation were conducted by Ayers and co- workers (Stevens and Ayers 1993, Stevens et al. 1995). Their data defmed several impacts of discharge on riparian vegetation relevant to this proposal: 1. Reduced flooding frequency after completion of Glen Canyon Dam in 1963 allowed fluvial marshes to form in low velocity channel margin environments in wide reaches. Kearsley and Ayers 4 Marshes were scoured by spillover flooding in 1983 and have redeveloped since 1987. Approximately 253 wet and 850 dry marshes were found in the Colorado River corridor in the park in 1991. Total marsh area was conservatively estimated at 25.0 ha, with 30% as wet marsh (Typha domingensis, Juncus spp. and Scimus spp) and 70% as dry marsh (Phragmites australis and Equisetum X ferrissiz). Marshes in this system were generally small (< 0.5 ha), with wet marshes significantly larger than dry marshes. Marsh assemblage composition and succession was related to sediment distribution and daily inundation frequency (0.4 to 0.9 for wet marshes). More than 95% of the wet marsh vegetation in this system lay between the 283 m3/sec (10,000 cfs) and 566 m3/sec (20,000 cfs) stages. Fluvial marshes can re-develop rather quickly after flooding events (e.g. 1983-1986). 2. Riparian seedling establishment was greatest in the New High Water Zone and was dominated by herbaceous species there. Seedling density varied as a function of particle size, and differed between plant groups (xerophytes and phreatophytes) in wide versus narrow channels. Tamarix ramosissima seedling density was low in 1991, but limited establishment suggests that this species is capable of continuing to colonize the river corridor under fluctuating flow regimes. 3. Several previously unrecorded non-native species colonized the river corridor. Erianthus ravennae (a large Eurasian bunchgrass) and Lepidium latifolium, a clonal herb had rapidly colonized riparian habitats in the river corridor. Prompt action