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Svejcar, Tony

Tausch, Robin

Rangelands

The University of Arizona

RANGELANDS 13(5), October 1991 233 Anaho Island, Nevada: A Relict Area Dominated by Annual Invader Species Tony Svejcar and Robin Tausch An increase in the presence and dominance of cheatgrass and red brome has been evident in more arid portions of the western Great Basin (Hunter 1990a, 1990b; Young et al. 1987). Beatley (1966) noted the pre- sence of cheatgrass above 5,100 ft and red brome at 3,600-5,100 ft at the Nevada Test Site in southern Nevada. They were primarily found on disturbed areas and red brome did not appear to be aggressive in the region. Recently the presence of these species has expanded to cover most of the Nevada Test Site (Hunter 1 990a, 1990b). These species are now found in undisturbed communities and red brome is more dominant than in pre- vious surveys. In 1988, introduced an- nuals were 81% of the ephemeral vegetation on disturbed areas and 61% on pristine areas on the Nevada Test Site. A similar increase has been noted for cheatgrass in the Lahontan Basin (Young and Tipton 1990). Similar changes have apparently occurred on Anaho Island in north- western Nevada. At 750 acres in size, Anaho is the largest island in Pyramid Lake, and rises to about 540 ft above lake level. Pyramid Lake is the rem- nant of the pluvial Lake Lahontan that once covered much of north- western Nevada and portions of southern Oregon. Precipitation for the Pyramid Lake area is 5 inches per year, and temperatures on Anaho Island are probably buffered by the surrounding water. The island was mentioned several times by Israel Cook Russell (1885) in his descrip- tion of Pyramid Lake. Russell found the island of interest as suggested from the following quote: "The island, although without fresh water, and but scantily clothed with vegetation, is one of the most instructive points about Pyramid Lake, and will well repay a visit from the geologist or the artist." Anaho Island was established as a National Wildlife Refuge in 1913 to protect bird populations (espe- cially pelicans) that depend on the island for safe nesting sites. As Beaz- ley (1977) suggested, given the lack of resources and abundances of rat- tlesnakes, the island has remained relatively undisturbed. The long history of minimal impact Fig. 2. The "halo" of greener grass around the shrubs is cheatgrass (18 April). Again, red brome dominates the interspaces. The arrow designates the cheatgrass halo. Fig. 1. General view of vegetation on the north side of Anaho Island on 18 April 1990. The bunch grass is desert needle- grass, the shrubs are primarily shadscale, and the inters paces are dominated by red brome and filaree, with a scattering of Russian thistle skeletons. Arrows point to cheat grass surrounding the shrubs. Authors are range scientist, USDA-Agricultural Research Service, 920 Valley Road, Reno, Nevada 89512; and Project Leader, Intermountain Research Station, USDA-Forest Service, 920 valley Road, Reno, Nevada 89512. Svejcar's current address is USDA-Agricultural Research Service, Eastern Oregon Agricultural Research Center, HC-71, 4.51 Hwy. 205, Burns, Oregon 97720. The authors wish to thank Bill Henry of the U.S. Fish and Wildlife Service for arranging the transporta- tion to the island, Al Bruner of the Forest Service for sampling the vegetation, and Drs. W. Burk- hardt, W.C. Krueger, and J.A. Young for sugges- tions on an earlier version of the manuscript. 234 RANGELANDS 13(5), October 1991 by humans makes Anaho Island an interesting place to view vegetation dynamics in response to the estab- lishment of annuals. There is no record of the island being grazed or intentionally burned since the turn of the century. In 1893, a brief descrip- tion of Anaho Island was given by Vernon Bailey of the Smithsonian Institute (on record with the U.S. Fish and Wildlife Service, Fallon, Nevada). In the report, Bailey men- tions that, "A few goats live on the island." Woodbury (1966) found the remains of sheep during his biologi- cal survey of the island. The only mammal he found on the island was the deer mouse. We traveled to Anaho Island on 18 April and 30 September 1990, with personnel from the U.S. Fish and Wildlife Service; pictures were taken and vegetation sampling was conducted. Current VegetatIon To quantify vegetation, 20 plots were sampled along a 300-foot tran- sect randomly located in the area depicted in Figure 1. This sample location is on the northwest side of Anaho Island and located above the high water line of the 19th century lake level. Thus, we sampled areas that had not been disturbed by rela- tively recent fluctuations in the lake level. Each plot was subdivided into 16, 8 by 16-inch subplots, and within each subplot, percentage cover by species was estimated. We averaged the subplots to obtain an estimate of percentage cover by species along the transect. Sampling was con- ducted on the 18 April visit. Current vegetation includes native species such as desert needlegrass, shadscale, Sandberg's bluegrass, and four-wing saltbush. However, the dom- inants in terms of group cover were the introduced species red brome and filaree. Percent cover was 9 for red brome, 3 for filaree, 3 for shads- cale, and less than 1 for other spe- cies. The dominance of red brome is shown in Figures 1 and 2. Filaree is less conspicuous, but is also com- mon in the interspaces. Cheatgrass dominates the more favorable microsites on the north end of Anaho Island. The "halo" of greener vegetation around the shrubs intheforegroundofFigurel isprim- arily cheatgrass. A closer view of the halo appears in Figure 2. Sites over- whelmed by cheatgrass are shown in Figures 3 and 4. The picture in Figure 3 was taken just below the rocky slope in the upper left corner of Fig- ure 1, and Figure 4 is a rocky location on the east side of the island. Pre- sumably, runoff from the rocky slopes increases the available moisture just below the slope even in the third year of a drought. We also noted that cheatgrass occurred around the edges of large boulders. Again we assume that water-shedding by the boulders increased available moisture around the edges. A similar pattern of domi- nance by annuals was observed over most of the rest of the island. The degree of annual grass dominance is suggested by the light color of the vegetation depicted in Figure 5. There was a tendency for litter buildups to occur in the interspaces. In a number of microsites there was an accumulation of up to 1 inch of litter (Figure 6). The accumulation of litter was greater than might be ex- pected in a perennial grass commun- ity in this rainfall regime. This may be related to absence of herbivores. Past VegetatIon Unfortunately, we could find no detailed records of vegetation on Anaho Island prior to the thesis of Fig. 3. A closeup of the base of the slope pictured at the top of figure 1 reveals a dense cover of cheatgrass (18 April). Fig. 4. Closeup of a cheatgrass-dominated site on the east side of the island (30 August). RANG ELANDS 13(5), October 1991 235 Woodbury (1966). He divided the island into 5 areas and rated plant species on a scale of 0 (absent) to 4 (very common). In the area we sam- pled he listed shadscale, four-wing saltbush, and spiny hopsage as very common. Russian thistle, and cheat- grass were common to occasionally very common. However, he did not list red brome as present on the area we sampled, and in fact found this species on only 2 of his 5 designated areas on the island. Red brome was listed as uncommon to common where it occurred. These results are con- sistent with other reports around the western Great Basin at the same time. Filaree and Russian thistle do not appear to have changed in abun- dance since Woodbury (1966) sur- veyed the vegetation in 1964. Red brome appears to have replaced cheat- grass as the dominant bromegrass over large areas of the island. Several native annuals listed by Woodbury (1966) as common in our sample area were not seen during our survey. Implications Areas that have been minimally impacted by human activities are of interest because they can serve as reference points for any changes in the dominance of annuals. Anaho Island would appear to be an ideal location for studying vegetation trends where direct human disturbance has been infrequent. Pelican nesting areas are the eastern shoreline, and there is no evidence the birds use the remainder of the island. Thus, they are not a direct source of distur- bance on most of the island, but they may carry seeds to the nesting area in from the mainland shoreline. It is possible that the introduction of com- petitive annuals may actually represent a major disturbance. Al- though plants of desert need legrass are evident on Anaho Island (Figure 1), we could not find evidence of either seedlings, or smaller plants of this species in the sampling area. Additionally, Russian thistle is still present as indicated in Figures 1-3. This species is generally considered a primary colonizer after disturbance (Young and Evans 1972), yet Anaho Island appears to have had minimal disturbance during this century (ex- ceptforthe invasion of annuals).The surrounding shoreline of the main- land has a full complement of the native herbivores for the region and has been continuously grazed by live- stock throughout the century. We observed the same annual species to be present on the mainland but with- out the dominance exhibited on the island. A major factor in the differ- ence appears to be the herbivory on the shoreline that is absent on the island. The invasions of Bromus species into the Great Basin are generally well documented (Mack 1981; Mor- row and Stahlman 1984). Russian thistle occurred in much of the west- ern U.S. by the turn of the century (Young and Evans 1977), but the introduction and spread of red brome was not well documented until the early 1960's (Hunter 1990a, 1990b). At least in the case of cheatgrass and Russian thistle, the seeds were intro- duced as contaminants in crop seeds (e.g., Mack 1981) but the period of introduction coincided with the set- tling of the western U.S. During this period, excessive grazing, road build- ing, farming of marginal lands, and general expansion of the human pop- ulation all probably contributed to the rapid spread of these species. The evidence from Anaho Island and the Nevada Test Site suggests these introduced species are more com- petitive than the native perennials, even if human and livestock impacts on the site are minimal. This compet- itive ability has been documented in FIg. 5. View of north side of Anaho Island on 30 August 1990. Coloration reveals the extent of annual grass dominance. 236 RANG ELANDS 13(5), October 1991 other studies from the region (Bil- lings 1990, Melgoza et al. 1990). The presence of significant disturbance does not appear to have been a necessary precursor for either the establishment, or the development of dominance of annual grass on the island. It appears that the absence of disturbance will not favor a return to dominance of native species. Hunter (1990a) concluded tnat reu brome and cheatgrass will slowly reduce populations of native ephe- merals on the Nevada Test Site. This will occur through shading, competi- tion for water and nutrients, and changes in fire regimes. Increasing fire frequency (and a potential change in the timing of fires) from the in- creased cover of annuals has a sub- stantial negative impact on the per- ennials (Young et al. 1987). Similar changes appear to be occurring on Anaho Island. Annuals are now suf- ficiently dominant on the island for a fire to potentially eliminate much of its remaining perennial salt desert vegetation, and the chances of a return to pristine conditions appear minimal. Literature Cited Beatley, J.C. 1966. Ecological status of introduced Brome grasses (Bromus spp.) indesertvegetation of southern Nevada Ecology 47:548-554. BeazIey, B. 1977. Anaho Island—its for the birds. Nevada State Journal. July 17. Billings, W.D. 1990. Bromus tectorum, a bio- tic cause of ecosystem impoverishment in the Great Basin. In: G.M. Woodwell (ed.), the earth in transition: patterns and pro- cesses of biotic impoverishment. Cam- bridge Univ. Press, NY (In press). Hunter, R. 1990a. Recent increases in Bro- mus on the Nevada test site. In: ED. McArthur, E.M. Rummey, S.D. Smith, and P.T. Tueller (eds.). Proceedings Sympo- sium on cheatgrass invasion, shrub dieoff, and other aspects of shrub biology and management. USDA Forest Serv. Gen. Tech. Rep. INT-276 p. 22-25. Hunter, R. 1990b. Progress of Bromus inva- sions of the Nevada test site. Great Basin Naturalist (In press). Mack, R.N. 1981. The invasion of Bromus tectorum L. into western North America: an ecological chronicle. Agro-Ecosystems 7:145-1 65. Melgoza, G., R.S. Nowak, and R.J. Tausch. 1990. Soil water exploitation after fire: competition between Bromus tectorum (cheatgrass) and two native species. Oecologia 83:7-13. Morrow, L.A., and P.W. Stahiman. 1984. The history and distribution of downy brome (Bromus tectorum) in North America. Weed Sd. 32:Supplement 1:2-7. Russell, I.C. 1885. Geological history of Lake Lahontan, a quaternary lake of north- western Nevada. USGS Monograph Xl. Woodbury, W.V. 1966. The history and pres- ent status of the biota of Anaho Island, Pyramid Lake, Nevada. Thesis, Univ. of Nevada, Reno. 175 p. Young, J.A., and F. Tipton. 1990. Invasion of cheatgrass into arid environments of the Lahontan Basin. In: E.D. McArthur, E.M. Rummey, S.D. Smith, and PT. Tueller (eds.) Proceedings Symposium on cheat- grass invasion, shrub dieoff, and other aspects of shrub biology and manage- ment. USDA Forest Serv. Gen. Tech. Rep. INT-276 p. 37-40. Young, J.A., R.A. Evans, R.E. Eckert, Jr., and B.L. Kay. 1987. Cheatgrass. Range- lands 9:266-270. Young, J.A., and R.A. Evans. 1972. Germi- nation and establishment of Salsola in relation to seedbed environment. Part 1. Temperature, afterripening, and moisture relations of Salsola seeds as determined by laboratory studies. Agron. J. 64:214-218. Fig. 6. A buildup of litter from the annual species is suggested in this photo. 

Anaho Island, Nevada: A Relict Area Dominated by Annual Invader Species

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Anaho Island, Nevada: A Relict Area Dominated by Annual Invader Species

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