Great Basin Naturalist Volume 49 Number 4 Article 14 10-31-1989 Arthropod community dynamics in undisturbed and intensively managed mountain brush habitats Tim A. Christiansen University of Wyoming, Laramie Jeffrey A. Lockwood University of Wyoming, Laramie Jeff Powell University of Wyoming, Laramie Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Christiansen, Tim A.; Lockwood, Jeffrey A.; and Powell, Jeff (1989) "Arthropod community dynamics in undisturbed and intensively managed mountain brush habitats," Great Basin Naturalist: Vol. 49 : No. 4 , Article 14. Available at: https://scholarsarchive.byu.edu/gbn/vol49/iss4/14 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. ARTHROPOD COMMUNITY DYNAMICS IN UNDISTURBED AND INTENSIVELY MANAGED MOUNTAIN BRUSH HABITATS 1 1 2 Christiansen A. Lockwood , and Jeff Powell Tim A. , Jeffrey Abstract. —The population dynamics of litter and foliage arthropods in undisturbed and intensively managed sagebrush (Artemisia tridentata ) and bitterbrush (Purshia tridentata ) habitats in southeastern Wyoming were assessed bv the measurement of density and the determination of indices of diversity, richness, and evenness. Brush manage- ment consisted of either mowing to a 20-cm stubble or applying the herbicide 2,4-D butyl ester. A total of 63 arthropod species were found in foliage and 150 species in litter. Mowing and herbicide applications resulted in significant changes in the density of 16 of the 46 major arthropod foliage species and 56 of the 70 major litter species. Diversity increased, except in Hymenoptera and Coleoptera, in both mowed and herbicide-treated foliage. In foliage, richness generally increased in all orders following mowing, and evenness tracked diversity. In litter, the diversity of Coleoptera decreased following mowing and herbicide application in Collembola, Homoptera, and Diptera. Evenness followed diversity in trends in both treatments. Soil arthropods were absent in this habitat before and after treatments. Although extensive studies of arthropod and succession, changes in plant diversity and ecology have been conducted in western resource availability affect insect diversities grasslands (Blocker et al. 1971, McDaniel (Murdoch et al. 1972, Southwood et al. 1979). 1971, and Kumar et al. 1976), virtually noth- Following a disturbance, early successional ing is known concerning the role of arthropods stages usually include plants with greater in mountain brush habitats. Sagebrush (Arte- palatability than in either the original habitat misia spp.)-dominated grasslands of the west- or later successional stages (Cates and Orians ern United States cover more than 100 million 1975). The amount and type of litter is also ha (Beetle 1960). Sagebrush is considerably affected by abiotic and biotic factors that may less palatable to livestock than other range be drastically altered by rangeland manage- plants such as annual grasses. For this reason, ment practices. A number of factors influence burning, herbicide applications, and mowing arthropod response to habitat disturbance, in- are commonly used to rid an area of undesir- cluding dispersal, host selection, resource able range plants and have been used in at- availability, litter composition, and vegeta- tempts to eradicate sagebrush (Wright et al. tion recovery (Schowalter 1985). The objec- 1979, Powell 1970). tives of this study were to determine the nor- In addition to direct eradication efforts, ap- mal arthropod taxa and population dynamics proximately 10% of the sagebrush habitat in and to ascertain the immediate impacts of the western United States has been cleared mowing and herbicide application on arthro- habitat. for cultivation and forage production since the pod communities in a mountain brush early 1900s (Beetle 1960). To this end, arthropod populations were mon- itored in the baseline (1985), treatment (1986), Rangeland management practices may and recovery (1987) years in sites that were have significant effects on the arthropod com- either undisturbed or intensively managed. munities in grassland habitats (Morris 1973, Lloyd and Kumar 1977). While it is clear that such disturbances in sagebrush communities Materials and Methods enable economically more desirable annuals to populate range areas, nothing is known This study was conducted on a sagebrush regarding the impact on arthropod popu- (Artemisia tridentata) and bitterbrush (Pur- lations. Habitat disturbance can influence shia tridentata) habitat, located at an eleva- arthropod densities, species distribution, tion of 2,400 m, 12 km southeast of Saratoga, and community diversity. During disturbance Carbon County, Wyoming. The soil is North 'Department of Plant, Soil and Insect Sciences, University of Wyoming. Laramie, Wyoming 82071. 2 Department of Range Management, University of Wyoming, Laramie, Wyoming 82071. 570 October 1989 Christiansen et al. : Arthropod Community Dynamics 571 Park Formation of brown, sandy loams devel- taken from both open and closed areas. Sepa- oped of loess, limestone, sandstone, and tuff. ration of arthropods from the soil was accom- The average yearly precipitation is 48 cm, plished by flotation in a 20% dilute magne- with most of the moisture being provided by sium sulfate solution (Salt and Hollick 1944) or snow. The mean annual temperature is 10.2 a heptane solution (Walter et al. 1987). Also, C, with a range of 21.0 to 27.0 C during the each sample was subdivided and examined sampling period of this study. under a dissecting microscope at 20X to detect Habitat manipulation consisted of either soil arthropods. mowing to a 20-cm stubble height or applying Samples were pooled between seasons and 2,4-D butyl ester in water at a rate of 0.91 kg blocks to provide estimates of ecological in- per acre in June of 1986. Within each treat- dices and the density of each major species ment and control, four blocks of at least 8 ha (i.e., those that accounted for at least 5% of were randomly chosen from sites with similar an order) in foliage, litter, or soil in each vegetation and soil characteristics. treatment and control site. The densities Arthropod samples from foliage, litter, and across treatments were compared using the soil in the control and treatment blocks were protected least significant difference post- collected every 10 days from the end of May ANOVA test. Differences were considered through mid-September in 1985, 1986, and significant at P < .05. Diversity was expressed 1987. Samples were taken along three 100-m using the natural logarithm form of the Shan- transects in each block. The location of the non-Weaver index; evenness was calculated first transect in each block was randomly de- using Pielou's J, and richness was expressed as termined, and the other two transects were the number of species present (Poole 1974). placed 70 m from and parallel to the first transect. The sequence of sampling each Results block was also randomly determined in every sampling period in order to eliminate any The brush management procedures re- chance of systematic errors as a consequence sulted in significant decreases in the total of block location and time of day. shrub cover. Herbicide application reduced Five samples of foliage arthropods were shrub cover to 59% and 57% of the baseline collected from both closed (canopy/shrub- level (which was 30% of the total area before covered) and open (grass-covered) areas along treatment) in the treatment and recovery each transect. Arthropods were collected by years, respectively. Mowing reduced shrub enclosing foliage in a 114 1 plastic container cover to 75% and 72% of the baseline level into which carbon dioxide was released for (which was 32% of the total area before treat- several minutes. A D-vac was then used to ment) in the treatment and recovery years, collect the specimens, which were subse- respectively. Sagebrush was generally re- quently stored at —5 C. duced to a greater extent than bitterbrush. Litter arthropods were collected on the A total of 150 arthropod species were col- same days as foliage arthropods. Five open lected in litter, of which 70 were considered areas and five closed areas were sampled major species (Table 1). Mowing and herbi- along the same transects as were used for cide applications resulted in significant chang- foliage samples. Sampling consisted of collect- es in the density of 57 of these 70 species in the ing all loose litter in a 0.5-m" quadrant. The treatment year. Following mowing, 17 spe- arthropods were separated from the litter in cies significantly decreased and 22 species the laboratory by use of Berlese funnels and significantly increased in density. After herbi- then stored in 70% ethanol. cide treatment, 16 species significantly de- Soil cores for each treatment and block creased and 27 species significantly increased were taken along the same transects as foliage in density. All orders included species that and litter collections. These cores were taken were significantly impacted by management. several days before foliage and litter collec- A total of 63 arthropod species were found tions so that the arthropods would not be dis- in foliage, of which 46 were considered major turbed for foliage collection. A core