SDAS 2001 Vol 80
Total Page:16
File Type:pdf, Size:1020Kb
Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) 283 EFFECTS OF GRAZING AND HAYING ON ARTHROPOD DIVERSITY IN NORTH DAKOTA CONSERVATION RESERVE PROGRAM GRASSLANDS Courtenay K. Hoernemann and Paul J. Johnson Plant Science Department South Dakota State University Brookings, SD 57007 Kenneth F. Higgins SD Cooperative Fish and Wildlife Research Unit USGS/BRD South Dakota State University Brookings, SD 57007 ABSTRACT A study of arthropod populations in North Dakota CRP grasslands was con- ducted to determine the impact of grazing and haying management practices on the arthropod fauna. Four sampling methods were used to collect arthro- pods: flight intercept traps, pitfall traps, sweep net, and soil samples. The three study sites occurred in Bowman, Ward, and Stutsman counties, North Dakota. Each site consisted of three pastures under a twice-over rotation grazed system, one pasture grazed seasonlong, a hayed field, and an idle area which served as a control. Shannon’s Index showed there were no significant differences in diversity among pastures or county sites. Correspondence anal- ysis (COA) showed Diplopoda (millipedes) and Formicidae (ants) were corre- lated to idle and hayed treatments in which both groups had a higher mean abundance. Stutsman County had the highest mean abundance of millipedes. Two beetle families, Elateridae (click beetles) and Curculionidae (weevils), showed a trend toward the idle area from COA, but neither group had a sig- nificantly higher mean abundance in idle areas. Ward County had the highest mean abundance of both click beetles and weevils. Miridae (plant bugs) showed a strong trend to hayed fields where they had a significantly higher mean abundance. A significantly higher mean abundance of plant bugs was found in Bowman County. Acrididae (grasshoppers) were found equally abun- dant in all pasture types in 1995, but fewer were found in idle areas in 1996. The lowest mean abundance of grasshoppers was collected in Ward County. Grasshopper densities did not reach threatening levels in either year of this study. Based on the overall results grazing and haying appear to be viable op- tions for post-contract uses of CRP lands with regard to management of arthro- pod populations. 284 Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) INTRODUCTION The Conservation Reserve Program (CRP) was created under the Food and Security Act of 1985 and was a 10-year cropland retirement program designed to protect the nation’s most highly erodible and fragile cropland. About 2.9 million acres were retired in North Dakota. The objectives of the CRP were to reduce water and wind erosion, improve water quality, create better habitat for fish and wildlife through improved food and cover, and provide income sup- port for participants in the program (Blackburn et al. 1991). As the CRP con- tracts expire, landowners will be faced with the decision of converting the acreage back to cropland or sustaining the existing cover for grazing or haying production. A grazing and haying demonstration was set up in 1992 enabling researchers to investigate the potential of these as post-contract uses of CRP. A limited number of studies have been conducted on the effects of graz- ing and haying management on insect communities. Total insect abundance can increase under grazing pressure (Smith 1940) and mowing or haying (Dun- widdie 1991). However, an increase in abundance may be accompanied by a decrease in species richness (Gibson et al. 1992). Faunal differences occur be- tween grazed and ungrazed areas (Morris 1968; Horn & Dowell 1974) even though there are no significant differences in insect diversity. Phytophagous species tend to benefit from grazing pressure, while predatory species favor lack of management (Morris & Rispin 1988; DeBano 1994) due to complex trophic level interactions. This demonstrates that the effects of grazing will vary depending on the group of insect studied. Thus, it is necessary to evalu- ate specific groups of insects separately in response to grazing treatments. One group of phytophagous insects which shows an increase in abun- dance from grazing (Smith 1940; Horn & Dowell 1974) and mowing (Morris & Lakhani 1979; Morris 1981b; Dunwiddie 1991) treatments is Heteroptera (plan- thoppers and true bugs). Grassland management practices that include graz- ing and haying alter the sward structure and floristic composition which is im- portant for determining the fauna of Heteroptera. Due to their plant commu- nity associations and response to management practices, leafhoppers and oth- er Auchenorrhyncha are used as indicators of prairie reserve quality (Hamilton 1995). Another group of phytophagous insects that is given much consideration by grassland managers is Orthoptera (grasshoppers). Orthoptera respond sim- ilarly to planthoppers and plant bugs with an increase in abundance from graz- ing (Horn & Dowell 1974; Smith 1940) and mowing (Dunwiddie 1991). This effect lead Capinera and Sechrist (1982a) to suggest modification of grasshop- per abundance through regulation of cattle grazing intensity. However, changes in abundance could be accompanied by a shift in the grasshopper species complex (Quinn & Walgenbach 1990; DeBano 1994). Differences in grasshopper species complexes are a result of the differences in plant com- munity composition. Fielding and Brusven (1993) determined plant commu- nities composed of annual vegetation may have low species diversity, where- as sites dominated by introduced perennial grasses have higher species diver- sity. Fielding & Brusven (1993) suggest that rehabilitation of annual grasslands Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) 285 with perennial grasses would support more diverse grasshopper communities with lower proportions of pest species, thus reducing outbreaks. In contrast to phytophagous insects, predatory beetles favor lack of man- agement when comparing grazed and ungrazed areas (DeBano 1994). Preda- cious species of beetles also favor lack of management when comparing hay fields to control areas (Morris & Rispin 1987). In a second study by Morris & Rispin (1988), predacious beetles once again favored lack of management, while haying tended to benefit phytophagous species of beetles. Grassland management decision-making needs to consider these options with regard to their impacts on the arthropod fauna. Morris (1971) suggested that the insect fauna must be relatively well known, taxonomically and eco- logically, if its consideration is to be a factor in management of grasslands. Arthropod diversity should be maintained in order to prevent the potential population outbreak of one or a few pest species. Rotational management has been suggested by several researchers as a way to meet manager’s goals and maintain arthropod diversity (Smith 1940; Morris 1968). Rotational manage- ment through cutting has also been proposed as a way to reach economic goals and maintain insect species richness and diversity (Morris & Lakhani 1979; Morris 1979, 1981a, 1981b; Morris & Rispin 1987, 1988). Rotational graz- ing would enable removal of the maximum amount of vegetative material each season and maintain the pasture in its most productive condition. There are concerns among landowners that CRP may be serving as a reser- voir for pest species, such as wireworms and grasshoppers, which would lead to possible outbreaks if the land is returned to cropland. In 1992 and 1993, Kennedy (1994) evaluated the effects of management on nongame birds, veg- etation structure, and insect biomass in the CRP lands of the same demonstra- tion project as this study. A more detailed study of the arthropod populations of the CRP demonstration sites was conducted in 1995 and 1996 in order to gain an understanding of the insect fauna present and to address questions re- garding potential pest species. The objectives of this study were to: (1) tax- onomically identify the fauna present, (2) determine arthropod abundances, (3) determine which groups responded to grazing and haying treatments, (4) iden- tify any potential pest species, and (5) make recommendations for post-con- tract uses of CRP lands with regard to maintaining high arthropod diversity. STUDY SITES The three study sites for this project were located in Bowman, Ward, and Stutsman counties, North Dakota. These sites were enrolled in the Conserva- tion Reserve Program in 1987 and have been in a grazing and haying demon- stration since 1992. There were six experimental tracts per site, each with five treatments: three pastures in a twice-over rotation system (TOR-A, TOR-B, and TOR-C), one pasture grazed seasonlong (SL), and one hayed field (H). An idle field (I) that had been undisturbed since enrollment in the program served as a control plot. For a detailed illustration of the study plots on each site see Harris (1996: Figs. 1-4). Cattle in the twice-over rotation system were rotated 286 Proceedings of the South Dakota Academy of Science,Vol. 80 (2001) between pastures every 21 days and completed the cycle twice each season. Hayed fields were mowed twice, once in June and again in July. The Bowman County site is 16 km (10 mi) south of Bowman, North Dako- ta. It is located on the Missouri Plateau which is a gently sloping plain with buttes and hills having a semiarid, continental climate (USDA-SCS 1975). Most of North Dakota is characterized by mixed grassland containing both medium and tall grass species. Bowman County occurs in the region where the domi- nant grasses are wheatgrass (Agropyron and Elytrigia spp.) and needlegrass (Stipa spp.) (GPFA 1986). The soil association of the region is Rhoades-More- au with well drained, loamy soils with a claypan (USDA-SCS 1975). At this site 150 ha (370 acres) were planted in the fall of 1988 with a mixture of crested wheatgrass, intermediate wheatgrass, and alfalfa (See Appendix A for botani- cal nomenclature of CRP planting mixtures). The grazing schedule for the Bowman County site is listed in Table 1. The Ward County site is 48 km (30 mi) southwest of Minot, North Dakota. It is located on the Missouri Coteau (Bluemle 1991) with rolling morainic hills in a subhumid, continental climate (USDA-SCS 1974).