Length and Timing of Grazing on Postburn Productivity of Two Bunchgrasses in an Idaho Experimental Range

Plant mortality and productivity in semiarid grasslands may be affected by the length of time grazing is excluded during the postfire regeneration period. The degree of grazing tolerance for the semiarid bunchgrass species, Festuca idahoensis and Agropyron spicatum, exposed to fire, and how the variation in grazing tolerance was affected by the length of time allowed for undisturbed plant regeneration after fire, were central questions addressed in this study. We examined the degree of plant mortality and productivity that resulted from the interaction of fire and grazing. Plants exposed to fire alone, i.e., without subsequent defoliation, exhibited low plant mortality, although culm production was reduced relative to unburned plants. An early-season-defoliation treatment after fire resulted in the plant mortality as high as 50% for Festuca and 70% for Agropyron bunchgrasses. Plant height and the number of vegetative and reproductive culms were also most affected by this defoliation treatment. These detrimental effects were lessened when defoliation was delayed by one growing season after the fire. Although our results suggest that one growing season seems to be enough for both species to recover after the fire, more studies will be necessary to confirm these trends, and induce changes in current grazing management policies.

Effect ofSclerotinia sclerotiorumon the Interference between Bluebunch Wheatgrass (Agropyron spicatum) and Spotted Knapweed (Centaurea maculosa)

Effectiveness of the common soil fungusSclerotinia sclerotiorumas a biological control for spotted knapweed and its effect on competitive interactions between spotted knapweed and bluebunch wheatgrass were evaluated in a growth chamber study using addition series methods. Total seeding densities ranged from 2000 to 60 000 seeds/m2. Mean bluebunch wheatgrass plant weight was 3.5 times greater than spotted knapweed weight per plant, respectively. Coefficient ratios estimating species interaction showed bluebunch wheatgrass density had a greater influence than spotted knapweed density on both bluebunch wheatgrass and spotted knapweed weights (2.11 and 0.51, respectively) when not under the influence ofS. sclerotiorum. Niche differentiation ratios indicated a lack of resource partitioning between species (1.11).S. sclerotiorumreduced spotted knapweed density by 68 to 80% without reducing bluebunch wheatgrass density. Spotted knapweed weight per plant also was reduced by the addition of 5.sclerotiorum(1.4 to 1.2 mg) but there was not a corresponding increase in bluebunch wheatgrass weight.S. sclerotiorumdecreased competition between spotted knapweed and bluebunch wheatgrass. This study provides evidence that establishment of bluebunch wheatgrass on spotted knapweed infested rangeland may be improved by combiningS. sclerotiorumwith high grass seeding rates.

The Relative Sensitivity of Two Bunchgrass Species to Fire

The response of two bunchgrass species, Festuca idahoensis and Agropyron spicatum, to fire was examined under three levels of fire severity. The fire treatment was applied with an instrument system that allowed precise control over the intensity and duration of fire, and full documentation of the temperatures experienced in various regions of each plant during the fire and postfire cooling phases. A quantitative index of fire exposure, or severity, for each plant was obtained by integrating the temperature curve for the meristematic crown region over the fire and postfire cooling periods. No significant plant mortality was observed at any fire severity level. Although tissue damage in newly initiated culms was observed for Festuca, this did not significantly affect culm or biomass productivity. Culm production was initiated earlier and more rapidly in Festuca than Agropyron, and within 60 days after fire exposure the total number of culms produced in Festuca was nearly that of unburned plants. Above ground biomass for both species was significantly less than that of unburned plants at the end of this 60-day period. Agropyron exhibited significantly less culm and biomass production at a moderate fire severity, whereas high fire severity was required for this reduction in Festuca. Contrary to previous studies, Festuca thus appears less sensitive to fire injury than Agropyron.

Responses of Nematodes to Ungulate Herbivory on Bluebunch Wheatgrass and Idaho Fescue in Yellowstone National Park

Above- and belowground biomass of Idaho fescue Festuca idahoensis and bluebunch wheatgrass Agropyron spicatum and nematode densities under these plant species were sampled during the growing season inside and outside a 2-year old exclosure on Crystal Bench in Yellowstone National Park. Early in the growing season, grazed plants of both species had lower shoot and root biomass than ungrazed plants. Standing biomass of grazed plants was equal to ungrazed plants at the end of the growing season. Densities/g root biomass of phytophagous and bacterial feeding nematodes were higher under grazed than ungrazed plants of both plant species only early in the growing season. Foliar concentrations of nitrogen in grazed plants were higher than ungrazed plants but there was no difference in root nitrogen between grazed and ungrazed plants. The effects of ungulate grazing on the Northern winter range of Yellowstone National Park has recently received considerable attention (Frank 1990, Coughenour 1991, Singer 1992, Wallace submitted). Early interest in this topic centered around the question to cull or not to cull elk in the Park. However, as the concepts of "maintaining ecological processes" (Houston 1982) and "ecosystem management" (Keiter 1991) have gained acceptance in Park management, understanding the dynamics and interactions of a broader array of herbivores inhabiting the Park have become increasingly important. In this paper, we describe the results of a study which focused on the effects of aboveground herbivory on nematode density and trophic structure. Root-feeding nematodes are major herbivores in other grassland systems and may consume twice as much biomass as aboveground consumers (Ingham and Detling 1984, Stanton 1988). Houston (1982) reported that nothing is known about the effects of nematodes on the native grasses of the northern range especially in combination with aboveground grazers. We hypothesized that if spring grazing is intense, grazed plants would initially show a decline in root growth and phytophagous nematodes. Cessation of root growth is a common response of plants to grazing and may occur within the first 2-24 hours (Hodgkinson and Baas Becking 1977). Evidence to date supports the idea that phytophagous nematode densities are highest under moderate levels of grazing and low under heavily grazed and ungrazed plants (Stanton 1983, Stanton et al. 1984, Seastedt 1985, Seastedt et al. 1988). Because senescing roots, subsequent to grazing, provide increased substrates for decomposers, we also hypothesized that microbial activity and nitrogen mineralization should increase (Stanton et al. 1984). As a result, we expected to detect an increase in microbial feeding nematodes. As root regrowth occurred, we expected phytophagous nematodes to increase. However, we predicted that populations would not reach levels found under ungrazed plants because plants in grazed areas experience higher levels of nitrogen mineralization (Holland and Detling 1990) than ungrazed plants and may produce proportionally fewer numbers of root hairs (nutrient absorption organs) which serve as feeding sites for nematodes. Because of reduced densities of phytophagous nematodes and increased mineralization rates under grazed plants, we expected grazed plants to recoup their losses rapidly. The net result we predicted would be no detectable differences in aboveground or belowground biomass during years of normal rainfall. Thus, our study addressed 3 null hypotheses. First, root and shoot biomass of grazed and ungrazed plants will be similar at the end of the growing season. Second, density of phytophagous and microbial feeding nematodes will not differ between grazed and ungrazed plants. Finally, nitrogen concentration of roots and aboveground foliage will not be higher in grazed than in ungrazed plants. We focused our attention on bluebunch wheatgrass Agropyron spicatum and Idaho fescue Festuca idahoensis because of their importance as winter range forages and because Mueggler (1975) reported that bluebunch wheatgrass was more sensitive and recovered more slowly to heavy clipping than Idaho fescue.

Postfire Defoliation Response of Agropyron spicatum and Sitanion hystrix

Prescribed fire is an important management tool to increase herbaceous productivity and maintain seral communities of Intermountain sagebrush grasslands. Currently, pastures treated with prescribed fire are rested from livestock grazing before burning to allow fine fuel accumulation, and rested a full year following burning to restore bunchgrass vigor. This study examined the post-fire defoliation response of Agropyron spicatum and Sitanion hystrix to three different defoliation treatments: an early season defoliation during the boot phenological stage, late season defoliation after seedset, and non-defoliation. Plant response to these defoliation timings was compared to determine the amount of non-use required to restore vigor to these species following fire. Mortality was low for late and non-defoliated plants of both species. Results indicate no differences between late season and non-defoliated plants for biomass production, basal area, or culm number for Agropyron. No differences in Sitanion culm number resulted between the late and non defoliated treatments. Sitanion biomass production differed between late and non-defoliated treatments at Emmett, but not at Craters of the Moon. Basal area and culm number of late and non-defoliated plants of both species increased as compared to the first post-burn season.

TEMPORAL VARIATION IN RANGELAND GRASSHOPPER (ORTHOPTERA: ACRIDIDAE) COMMUNITIES IN THE STEPPE REGION OF MONTANA, USA

A study was conducted to evaluate changes in rangeland grasshopper communities over a 5-year period in the Agropyron spicatum (Pursh) Scribn. and Smith and Bouteloua gracilis (H.B.K.) Lag. provinces of the steppe region of Montana, USA. Results showed that it was possible to categorize years into outbreak, non-outbreak, and transitional based on rangeland grasshopper intensity. Nearly twice as many species were observed in outbreak versus non-outbreak years. Of the 57 total grasshopper species collected over the entire study period, 16 species were found only during outbreak years and only two were found exclusively during non-outbreak years. Of the remaining 39 species collected during outbreak and non-outbreak years, 27 species showed no significant differences in the percentage of the community that they represented and 11 species showed significant increases. The only species that made up proportionately less of the community as densities declined from outbreak to non-outbreak was Melanoplus sanguinipes (F.). Although M. sanguinipes, Ageneotettix deorum (Scudder), and Aulocara elliotti (Thomas) were the three top-ranked species in both outbreak and non-outbreak years, M. sanguinipes contributed most to overall shifts in grasshopper intensity. Results support the hypothesis that grasshopper communities overall are sensitive to temporal changes in resources, even though responses of individual species differed.

De-awning of Agropyron spicatum cultivator for use as an understory grass on erosive sites

South-facing, semi-arid slopes supporting sagebush (Artemisia tridentata) with scant understory are difficult sites for establishment of perennial vegetative cover in Central Washington. Blue-bunch wheatgrass (Agropyron spicatum) is the most ubiquitous, widely distributed native perennial where exotic annuals are a competitive problem. It can be found as an understory associate or in open stands.Secar is a cultivar, of A. spicatum developed in the Pacific Northwest. Unfortunately, the percent germination of secar seed has been found to be low. It was suspected that a possible inhibitor exists in the awn and mechanical removal may result in earlier and greater germinative ability for increased establishment on Conservation Reserve Program lands.It was found that total germination was not significantly affected by temperature treatment but an apparent difference in rate was determined. A significant increase in germination occurred with awn removal. Specific location of an inhibitor(s) was not statistically apparent. Key words: Agropyron spicatum, germination, seedling vigor, reseeding

Responses of Nematodes to Ungulate Herbivory on Bluebunch Wheatgrass and Idaho Fescue in Yellowstone National Park

The effects of ungulate grazing on the Northern winter range of Yellowstone National Park has recently received considerable attention. Early interest in this topic centered around the question to cull or not to cull elk in the Park. However, as the concepts of "maintaining ecological processes" (Houston 1982) and "ecosystem management" (Keiter 1991) have gained acceptance in Park management, understanding the dynamics and interactions of a broader array of herbivores inhabiting the Park will become increasingly important. In 1990, we studied the responses of Idaho fescue (Festuca idahoensis) and bluebunch wheatgrass (Agropyron spicatum) and their associated nematode communities to ungulate herbivory.