Contrasting Effects of Long-Term Fire on Sagebrush Steppe Shrubs Mediated by Topography and Plant Community

The role of fire in restoration of sagebrush plant communities remains controversial mainly because of paucity of information from long-term studies. Here, we examine 15-year post-fire responses of big sagebrush (Artemisia tridentata ssp wyomingensis) and broom snakeweed (Gutierrezia sarothrae), the two most abundant native shrubs at the John Day Fossil Beds National Monument, a protected area in north-central Oregon, USA. Fire effects were studied along gradients of topography and community type through time post-burn. Community types were distinguished as brush, plots dominated by big sagebrush and woodland, plots with a significant presence of Western juniper (Juniperus occidentalis) trees. Fire reduced big sagebrush cover in brush plots up to 100% and in woodland plots up to 86%. Broom snakeweed cover declined by 92% and 73% in brush plots and woodland plots, respectively. Big sagebrush did not show signs of recovery 15 years after burning regardless of topography and community type while broom snakeweed populations were clearly rebounding and prospering beyond pre-burn levels. Our results showed that an area initially dominated by big sagebrush (cover of big sagebrush 10-20%, cover of broom snakeweed 2-4%) dramatically shifted to an area dominated by broom snakeweed (cover of big sagebrush < 1%, cover of broom snakeweed 5%) in brush-dominated plots. Our results indicated that brush-dominated plots at lower elevation and southern exposures are the least post-fire resilient. We also observed a declining population of big sagebrush on unburned areas, suggesting the lack of post-fire recovery on burned areas was perhaps a result of low seeding potential by extant populations. Although more years of observation are required, these data indicate that recovery time, the encroachment of opportunistic competing shrubs, and the initial condition of vegetation are essential considerations by land managers when prescribing fire in big sagebrush communities.     

Influence of Land-Use Legacies Following Shrub Reduction and Seeding of Big Sagebrush Sites

Big sagebrush (Artemisia tridentata Nutt.) plant communities often require management to reduce shrub density and rehabilitate understory vegetation. We studied vegetation responses to a two-way chain harrow treatment and broadcast seeding of 12 herbaceous species at eight Wyoming big sagebrush (A. tridentata Nutt. subsp. wyomingensis Beetle & Young) sites. These sites differed in land-use history; five were cultivated for dryland wheat production during the 1950 ? 1980s and then seeded with introduced forage grasses (C-S), while three had not been exposed to this land-use legacy (non C-S). Our objective was to evaluate whether the C-S legacy influences the magnitude of vegetation change following contemporary treatment. Before treatment, C-S sites had lower sagebrush cover, higher dead sagebrush cover, and higher broom snakeweed (Gutierrezia sarothrae [Pursh] Britton & Rusby) cover than adjacent non C-S sites. Plant community change 3 years after treatment, determined with multivariate ordination analysis of species composition, varied between site histories, and response to treatment was most strongly correlated with reductions in sagebrush cover, increases in perennial grasses, and increases in 10 other herbaceous species—including some undesirable species and four that were seeded in 2010. Five years after treatment, mature sagebrush cover remained reduced for both land-use histories, yet density of sagebrush seedlings and broom snakeweed increased in C-S sites during the second and third years after treatment. In addition, perennial forb cover increased for C-S sites, while perennial grass biomass increased for non C-S sites. Our results emphasize that broad variability in plant community responses to sagebrush reduction and seeding is possible within the same ecological site classification and that legacy effects due to the combination of past cultivation and seeding should be considered when planning restoration projects, including the consideration that seeding may not always be necessary on C-S sites.     

Detection and measurement of benzimidazole resistance alleles in Haemonchus contortus using real-time PCR with locked nucleic acid Taqman probes

Benzimidazole resistance is a common problem in parasitic nematodes of ruminants and early detection is vital if its spread is to be monitored and controlled. Real time PCR offers a fast and reliable method for rapid detection and measurement of resistance allele frequencies. In Haemonchus contortus a single nucleotide polymorphism at codon 200 of the beta-tubulin gene (TTC to TAC), causing a phenylalanine to tyrosine amino acid substitution, has been shown to be involved in many cases of resistance. Locked nucleic acid (LNA) Taqman probes have been used in this work to detect and measure the frequency of resistance alleles in individual and multiple H. contortus. Detection of resistant genotypes using LNA Taqman probes in individual H. contortus is simpler and more reliable than with previously described assays. Measurement of the frequency of resistant alleles in populations of H. contortus was achieved by using the cycle threshold (C(t)) values and a standard curve derived from populations with known allele frequencies. Results using the LNA probes on individual and multiple worms gave similar results to the allele specific PCR. The sensitivity of the LNA assay on multiple nematodes allowed reliable detection of > or = 10% resistance allele frequency. Using the final fluorescence method, it was possible to differentiate populations with approximately 0, 5 and 10% resistance allele frequencies.     

Chemically and genetically immunocompromised mice are not more susceptible than immunocompetent mice to infection with Cryptosporidium muris

The prevailing paradigm is that immunosuppressed individuals are more susceptible to infection and are at higher risk of infection from Cryptosporidium oocysts if present in drinking water. To test this hypothesis, three immune conditions were examined: genetically immunocompromised T cell deficient CD-1 nude mice, B and T cell deficient Fox Chase CB-17/IcrClB SCID mice, and chemically immunosuppressed C57Bl/6 mice. Chemical immunosuppression was induced with a single subcutaneous injection of methylprednisolone acetate (MPA) at 600 mg/kg. The MPA immunosuppressed C57Bl/6 mice were characterized by a sustained decrease in circulating CD3, CD4 and CD8 T-lymphocytes of greater than 80% and a similar decrease in B-lymphocytes. A sharp rise in circulating mature segmented neutrophils followed MPA injection, dropping sharply after 10-14 days, mirroring the decrease in lymphocytes. The cessation of oocyst production after MPA was not accompanied by a radical rise in circulating CD3 or CD4 T-lymphocytes, but rather a rise in CD8 T-lymphocytes. The ID50 for the MPA immunosuppressed C57Bl/6 mice was 122 oocysts, whereas the ID50 for the C57Bl/6 immunocompetent group was 44. The genetically immunocompromised mice showed similar differences. The ID50 for CD-1 nude mice was 166 oocysts compared to 64 in CD-1 immunocompetent mice. For Fox Chase CB-17/IcrClB SCID and the immunocompetent CB-17 mice, the ID50's were 83 and 60 oocysts, respectively. These results suggest that the lack of an immune response does not increase the ability of C. muris to establish a productive infection and produce oocysts.     

Methylprednisolone acetate immune suppression produces differing effects on Cryptosporidium muris oocyst production depending on when administered

At different times after inoculation with Cryptosporidium muris, infected CF-1 female mice were immunosuppressed with a single subcutaneous dose of methylprednisolone acetate (MPA; 600 mg/kg). MPA immunosuppression decreases circulating CD3, CD4 and CD8 T-lymphocytes and B-lymphocytes by greater than 90% for approximately 14 days with numbers not returning to pre-suppression levels until after 41 days post-suppression. Immunosuppression was initiated at selected times before, during, and after oocyst production. Immunosuppression initiated prior to oocyst production delayed the start of production by 4-5 days and extended oocyst shedding by 16 days. Initiation of immunosuppression during oocyst production both extended oocyst shedding and greatly increased the number of oocysts shed per day over most of the extended shedding period. Immunosuppression during the decline of oocyst production resulted in only a moderate extension of shedding and a moderate increase in oocyst numbers. Immunosuppression initiated soon after oocyst shedding had ceased resulted in the re-initiation of limited oocyst production for only a few days. Suppression initiated on days 40 and 46 post-infection, 11 and 17 days after oocysts could no longer be detected in the feces, did not result in a resumption of oocyst production. In all cases, where oocyst production was extended or reinitiated, the shedding of oocysts halted between days 45 and 53 post-oocyst inoculation. These studies demonstrate that the effect of MPA immunosuppression depends on the immunologic conditions existing in the host at the time immunosuppression was initiated. Immunosuppression initiated during oocyst production allows an overwhelming parasitism to exist, implying that T- and B-lymphocytes play an important role in moving the host immune process along during this period of the infection. Conversely, severe suppression of T- and B-lymphocytes initiated as oocyst production is decreasing does not result in a complete relapse of the disease suggesting that T- and B-lymphocytes are not critical to the continuation of the immune process after this point. These studies also show that the C. muris infection persists beyond the end of the detection of oocysts in the feces.     

The Effectiveness of Capillary Barriers to Hydraulically Isolate Salt Contaminated Soils

The use of capillary barriers overlayed with topsoil to hydraulically isolate highly saline soils was investigated in a greenhouse study. Capillary barriers of 8 cm or greater thickness effectively prevented salt from migrating upward into the topsoil, thus allowing vegetation to be established. The water which drained from the capillary barrier had electrical conductivities on the order of one third that of the underlying saline soil, and should be acceptable for stream discharge. The capillary barriers reduced the flux of water and salt to the groundwater to about one third of that of the control. The results of the study show that capillary barriers can be used effectively to contain salt contaminated soils.