This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Invasion of Alien Annuals and Ecological Consequences in Salt Desert Shrublands of Western Utah Kimball T. Harper Renee Van Buren Stanley G. Kitchen Abstract-Vegetation plots in experimentally grazed pastures at species on better managed ranges. In years of above-average the Desert Experimental Range in west-central Utah have been precipitation, native annual species such as sixweeks grama mapped periodically since 1935. The pastures have been grazed at (Bouteloua barbata), Hooker's eriogonum (Eriogonum the same intensity and in the same season by sheep from 1935 to the hookeri), Palmer's buckwheat (E. palmerianum), thymeleaf present. Records show that Bromus tectorum and Salsola pestifer spurge (Euphorbia serpyllifolia), broadlobe gilia (Gilia were observed on mapped plots in 1958, although the latter species hutchinsifolia), western stickseed (Lappula occidentalis), was reported from the range in 1937. Halogeton glomeratus ap­ desert pepperplant (Lepidium montanum var. montanum), peared first in 1969. All of these species had become common on both false buffalograss (Munroa squarrosa), and crenulate grazed and ungrazed plots by 1989, although plant density and phacelia' (Phacelia crenulata) were a conspicuous part of the vigor of these aliens were reduced on ungrazed sites. Frequency of vegetation prior to the advent of aggressive alien annuals. occurrence of these species has increased steadily since their first Long-term (1951-1980) precipitation records at the DER appearance. Experimental studies suggest that soils from areas show an average annual total of 6.12 inches. Average annual 0 dominated by Halogeton and Salsola are associated with lower temperature for that period was 49.0 OF with means of 26.4 survival of Ceratoides lanata seedlings than soils from healthy and 73.8° for January and July, respectively. About 53% of Ceratoides stands. the annual precipitation was received during the growing season (May 1 and Sept. 30) in the period 1951 to 1980 (National Oceanic and Atmospheric Administration 1982). The Desert Experimental Range (DER) is a 55,000 acre experimental area in Millard County, west-central Utah. Methods Sheep grazing trials were initiated there in experimental ----------------------------------- pastures in 1935 and have continued uninterrupted and The grazing trials considered here have been applied to 20 with only minor changes to the present (Clary and Holmgren fenced pastures (240-360 acres in size). Three grazinginten­ 1982). The grazing treatment design and early results were sities (arbitrarily referred to as light, moderate, or heavy) described by Hutchings and Stewart (1953). More recently, that have averaged about 10, 14, and 17 sheep days per acre grazing effects on shrubby species have been reported by have been applied to various pastures. Stocking rates have Harper and others (1990). This paper represents an attempt been varied annually within the foregoing limits depending to evaluate the role of annual plant species in the salt desert upon annual forage production in order to achieve a some­ shrublands that dominate the DER. Prior to this study what uniform degree of utilization from year-to-year for key annual species had been pooled together without reference forage species (Hutchings and Stewart 1953). Each grazing to individual species. Hutchings and Stewart (1953) show intensity class was applied in each ofthree seasons (Nov. 15- that all minor herbaceous species including annuals rarely Jan. 3, Jan. 4-Feb. 23, and Feb. 24-Apr. 10). Every grazing contributed more than 18% of the above ground production. intensity-season of use combination was replicated at least The vegetation under consideration was initially domi­ twice, except for moderate use in midwinter which is repre­ nated by shrubs, primarily shadscale (Atriplex confertifolia) sented but once in the research design. The preceding and winterfat (Cera to ides lanata). Perennial grasses includ­ statement assumes that split season use in which pastures ing Indian ricegrass (Stipa hymenoides), galleta grass are grazed in the early and midwinter season is not signifi­ (Hilariajamesii), three-awn (Aristida purpurea), and sand cantly different from early winter or midwinter grazing dropseed (Sporobolus cryptandrus) occur as subordinate alone. It is further assumed that any split season combina­ tion of early or midwinter use with late winter use does not differ significantly from late season grazing alone. Both of In: Barrow, Jerry R.; McArthur, E. Durant; Sosebee, Ronald E.; Tausch, the preceding assumptions are compatible with conclusions Robin J., comps. 1996. Proceedings: shrubland ecosystem dynamics in a drawn by Blaisdell and Holmgren (1984) and Harper and changing environment; 1995 May 23-25; Las Cruces, NM. Gen. Tech. Rep. INT-GTR-338. Ogden, UT: U.S. Department of Agriculture, Forest Service, others (1990). Anyone pasture has been grazed at the same Intermountain Research Station. intensity and in the same season throughout the 54 year Kimball T. Harper is Professor of Botany and Range Science, Department period covered by this study (1935-1989) (Hutchings and of Botany and Range Science, Brigham Young University, Provo, UT 84606. Renee Van Buren is Assistant Professor of Biology, Department of Biology, Stewart 1953). Utah Valley State College, Orem, UT 84058. Stanley G. Kitchen is Botanist, Two 1 acre exclosures were constructed in'16 of the 20 Shrub Sciences Laboratory, U.S. Department of Agriculture, Forest Service, pastures in 1935. Two permanently marked monitoring Intermountain Research Station, Provo, UT 84606. 58 plots were placed in each exclosure at time of construction. 1970 on winterfat seedling establishment. Surface soil These plots are 100 ft2 (5 ft by 20 ft) in area. At least two samples were collected from an area where flood waters additional plots were established at the same time on sites resulted in the death of winterfat in 1969. The dieoffarea is of comparable terrain, soils, and vegetation in grazed areas located in the southeast Y4 of section 11, T.25 S., R.17W. (the near each exclosure. Most plots in and adjacent to exclosures 4 unnumbered pastures, fig. 4 of Hutchings and Stewart were mapped in 1935 using a 1.0 ft2 grid marked offin .01 ft2 1953). A large stand of nearly pure winterfat occupied the subunits (Clary and Holmgren 1987). The mapping grid area prior to the flooding event. Minor local differences in frame was secured to heavy steel pegs permanently driven elevation resulted in the flood waters overflowing winterfat into the soil at the corners ofthe 100 ft2 monitoring plots. The plants on an irregularly shaped area across the extreme plots considered in this paper were chosen because they southeasterly corner of the quarter section of concern. The appeared to belong to a range site type with the potential of winterfat plants thus irrigated by the July 1969 flood greened supporting similar vegetation under uniform grazing use. up and grew vigorously until cold weather arrived in late The 48 plots used in this study were remapped periodically autumn. For unknown reasons, the flood irrigated plants did using the same procedures as in 1935 and a standardized not survive the 1969-70 winter. The dieoffarea was immedi­ form for recording results. The plots were reinventoried in ately invaded by halogeton and Russian thistle. Those spe­ 1935, 1936, 1937, 1959, 1968, 1975, and 1989. For our cies have continued to dominate the site from 1970 to the summary analyses, each map was subdivided into ten 2 ft x present. Although winterfat still exists in healthy stands 5 ft subunits. The number of individuals (density) of each along the margins of the dieoff area, that species has not annual plant species was determined for each 10.0 ft2 sub­ reoccupied the flooded area. plot for each year of record. Our summary analyses also In 1987, workers familiar with the dieoff event initiated a report the percentage of all 2 ft x 5 ft subplots that contain study to determine why winterfat was not reoccupying the any individuals of each species (frequency of occurrence). area from which it had been displaced. Soil samples (top 2.0 The location of plots and grazing treatments applied to the inches of the profile) were taken at 10 locations within the plots and subplots used in this paper are reported in table 1. dieoffzone and the adjacent, intact winterfat stands in May In an attempt to learn something ofthe separate effects of 1987. Subsamples were analyzed for texture, pH, electrical grazing intensity and season of grazing, all grazed plots are conductivity and exchangeable sodium by the Soil Analysis analyzed in two different ways. In a first analysis, plots were Laboratory, Department of Agronomy and Horticulture, sorted into two groups: (1) light or moderate grazing inten­ Brigham Young University. The remainder of each soil sity with season of use being ignored and (2) heavy grazing sample was placed directly into 5.0 inch diameter, drained intensity again with season of use ignored. In a second pots for winterfat seeding trials under greenhouse condi­ analysis, all plots were sorted into two groups: (1) plots tions. Seed used for these initial trials was obtained from grazed in early or midwinter or (2) plots grazed in late field collections at the DER. winter. These groupings were suggested by results of earlier We also attempted to determine whether