A Characterization of Vegetation in the Alvord Basin, Southeastern Oregon Using Two Sampling Methods


	Characterizing Vegetation in the Alvord Basin, Using Two Sampling Methods John Brinda, Brooke Budnick, Kristi Wiegand Summer Session 2000 Field Biology Course, Biol 417a Department of Biology, Western Washington University Bellingham, WA 98225 Introduction Methods Results Conclusions Introduction The Alvord Basin, near the northern boundary of the Great Basin, is in the rain shadow of Steens Mountain making it one of the most arid regions in Oregon (OSU 1981). The area is host to a variety of plant, reptile, and insect species inhabiting three main substrate types: dunes, hardpan, and sandy flats. The study sites were located just south of Borax Lake in the Alvord Basin (42°18'N, 118°37'W) (Figure 1). Our objective was to characterize the late June vegetation on the two study plots where lizards and insects were simultaneously studied. Two plant sampling methods were used to determine plant distribution and abundance as well as species composition and diversity. Back To Top Methods The north study plot was 80 m (west-east) by 130 m (north-south). The south plot was 150 m (west-east) by 150 m (north-south). Stakes and labeled flags were placed every 10 meters within the plots. We further divided the plots into subplots which were 25 m by 50 m. We randomly selected 6 subplots in the north plot and 12 subplots in the south plot to sample. There was one line and one quadrat in each subplot. Using randomly generated numbers, start points for each line and the southwest corner of each quadrat were determined. Lines were run 20 m to the north and quadrats were a 5 m by 5 m square. Line transect method: The start and end points for all plants and bare ground falling directly beneath the meter tape were recorded. The species name, length, width, and height of each plant intersected were also recorded. This information was then used to determine the percentage of the line covered by each species (Sutherland 1996). To get a typical vegetation profile, the beginning, middle, and end height of the intersected plants were measured (Figure 2). Quadrat method: The species name, length, width, and height of every plant within the boundary of the quadrat were recorded. If plants were transected by the quadrat boundary, only the portion inside the quadrat was measured. Percent cover and species diversity data was compared between the quadrat and line transect methods. Back To Top Results A total of 33 plant, 1 fungus, and 1 moss species were found using both the line transect and quadrat methods (Table 1). The mean species richness per quadrat was 8.9 compared to 4.7 for line transects. (t-test, P <0.01). The mean percent cover for all species using the quadrat method was 30.3% compared to 18.7% using the line transect method (t-test, P <0.01). Percent plant cover on the sandy flats using the line transect method ranged between 12.7% and 36.3% with a mean of 24.5% (s = 8.1). Shrubs were the dominant type of plant cover followed by grasses. Other types of plant cover were rare (Figure 3). According to line transect method, the two most common shrubs were Artemisia tridentata and Sarcobatus vermiculatus (Figure 4). The average distance between two patches of shrubs on the sandy flats using the line transect method was 1.84 m and there was no difference between the north and south plots (t-test, P = 0.21). The average shrub patch size on the sandy flats using the line transect method was 0.58 m and there was no difference between the north and south plots (t-test, P = 0.11). Back To Top Conclusions Shrub species such as Basin Big Sagebrush (A. tridentata) and Greasewood (S. vermiculatus) are the dominant form of vegetation. Percent plant cover using the line transect method averaged 18.7% over both plots with an average distance between shrubs of 1.84 m on the sandy flats. Lines gave a better estimation of percent cover because the lines more closely followed the perimeter of the plants, excluding large spaces between branches. Also, in our quadrat calculations, we estimated the plants to be rectangular rather than elliptical. The quadrats gave better estimates of species diversity than lines because the rarer plants were often small and less likely to fall on a line. Back To Top Home Course Description Course Application Practical Information Class Projects Photo Gallery