Revegetation of Medusahead-Invaded Sagebrush Steppe

Medusahead (Taeniatherum caput-medusae [L.] Nevski) is an exotic annual grass invading western rangelands. Invasion by medusahead is problematic because it decreases livestock forage production, degrades wildlife habitat, reduces biodiversity, and increases fire frequency. Revegetation of medusahead-invaded sagebrush steppe is needed to increase ecosystem and economic productivity. Most efforts to revegetate medusahead-infested plant communities are unsuccessful because perennial bunchgrasses rarely establish after medusahead control. The effects of prescribed burning (spring or fall), fall imazapic application, and their combinations were evaluated for medusahead control and the establishment of seeded large perennial bunchgrasses. One growing season after treatments were applied, desert wheatgrass (Agropyron desertorum [Fisch. ex Link] Schult.) and squirreltail (Elymus elymoides [Raf.] Swezey) were drill seeded into treatment plots, except for the control treatment. Vegetation characteristics were measured for 2 yr postseeding (second and third year post-treatment). Medusahead was best controlled when prescribed burned and then treated with imazapic (P < 0.05). These treatments also had greater large perennial bunchgrass cover and density compared to other treatments (P < 0.05). The prescribed burned followed by imazapic application had greater than 10- and 8-fold more perennial bunchgrass cover and density than the control treatment, respectively. Prescribed burning, regardless of season, was not effective at controlling medusahead or promoting establishment of perennial bunchgrasses. The results of this study question the long-term effectiveness of using imazapic in revegetation efforts of medusahead-infested sagebrush steppe without first prescribed burning the infestation. Effective control of medusahead appears to be needed for establishment of seeded perennial bunchgrasses. The results of this study demonstrate that seeding desert wheatgrass and squirreltail can successfully revegetate rangeland infested with medusahead when medusahead has been controlled with prescribed fire followed by fall application of imazapic.     

A Common-Garden Study of Resource-Island Effects on a Native and an Exotic,Annual Grass After Fire

Plant-soil variation related to perennial-plant resource islands (coppices) interspersed with relatively bare interspaces is a major source of heterogeneity in desert rangelands. Our objective was to determine how native and exotic grasses vary on coppice mounds and interspaces (microsites) in unburned and burned sites and underlying factors that contribute to the variation in sagebrush-steppe rangelands of the Idaho National Lab, where interspaces typically have abiotic crusts. We asked how the exotic cheatgrass (Bromus tectorum L.) and native bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve) were distributed among the microsites and measured their abundances in three replicate wildfires and nearby unburned areas. We conducted a common-garden study in which soil cores from each burned microsite type were planted with seed of either species to determine microsite effects on establishment and growth of native and exotic grasses. We assessed soil physical properties in the common-garden study to determine the intrinsic properties of each microsite surface and the retention of microsite soil differences following transfer of soils to the garden, to plant growth, and to wetting/drying cycles. In the field study, only bluebunch wheatgrass density was greater on coppice mounds than interspaces, in both unburned and burned areas. In the common-garden experiment, there were microsite differences in soil physical properties, particularly in crust hardness and its relationship to moisture, but soil properties were unaffected by plant growth. Also in the experiment, both species had equal densities yet greater dry mass production on coppice-mound soils compared to interspace soils, suggesting microsite differences in growth but not establishment (likely related to crust weakening resulting from watering). Coppice-interspace patterning and specifically native-herb recovery on coppices is likely important for postfire resistance of this rangeland to cheatgrass.     

Bunchgrass Root Abundances and Their Relationship to Resistance and Resilience of Burned Shrub-Steppe Landscape

Invasion of exotic annual grasses (EAG) and increased wildfire have led to an emphasis on managing rangeland plant communities for resistance to invasion and resilience to disturbances. In sagebrush steppe and similar rangelands, perennial bunchgrasses and particularly their roots are hypothesized to be primary contributors to resistance and resilience. We asked how bunchgrass root abundance relates to annual grass invasion and aboveground indicators of bunchgrass vigor that are more readily measured, such as plant height. We used a standardized US Department of Agriculture protocol for root measurement in 445 excavations made in 2016 ? 2018 across a topographically and ecologically varied region of sagebrush steppe burned in the 2015 Soda fire in the Northern Great Basin, United States. Nearly all (99%) bunchgrasses, including seedlings, had deeper roots than the surrounding annual grasses (mean depth of annuals = 6.8 ± 3.3 cm), and 88% of seedlings remained rooted in response to the “tug test” (uprooting resistance to ~ 1 kg of upward pull on shoot), with smaller plants (mean height and basal diameters < 20 cm and < 2 cm, respectively) more likely to fail the test regardless of their root abundance. Lateral roots of bunchgrasses were scarcer in larger basal gaps (interspace between perennials) but were surprisingly not directly related to cover of surrounding EAG. However, EAG cover increased with the size of basal gaps and decreased with greater basal diameter of bunchgrass (in addition to prefire EAG abundance), albeit with a low r². These results provide some support for 1) the importance of basal gaps and bunchgrass diameters as indicators of both vulnerability to annual grass invasion and bunchgrass root abundance and 2) the need for more detailed methods for root measurement than used here in order to substantiate their usefulness in understanding rangeland resistance and resilience.     

Postfire Seeding and Plant Community Recovery in the Great Basin

As wildland fire frequency increases around the globe, a better understanding of the patterns of plant community recovery in burned landscapes is needed to improve rehabilitation efforts. We measured establishment of seeded species, colonization of Bromus tectorum and other nonnative annual plants, and recovery of nonseeded native species in topographically distinct areas within five fires that burned Great Basin shrub-steppe communities in Elko County, Nevada. Plant density, frequency, and cover data were collected annually for 4 yr postfire. Vegetation composition varied among flat areas and north- and south-facing aspects, and changed over the course of the sampling period; recovery varied among sites. In general, B. tectorum densities were higher on south aspects, particularly 3 and 4 yr after fire, when densities increased dramatically relative to prefire conditions. Nonseeded native perennial grasses, forbs, and shrubs were abundant in three of the five fire sites, and were more likely to be present on north aspects and flat areas. Over time, nonseeded perennial grass densities remained relatively constant, and nonseeded forbs and shrubs increased. Seeded species were most likely to establish in flat areas, and the density of seeded perennial grasses, forbs, and shrubs decreased over time. Frequency and density measurements were highly correlated, especially for perennial species. Our results emphasize the value of considering site aspect and the potential for native regrowth when planning and monitoring restorations. For example, effective rehabilitation of south aspects may require the development of new restoration methods, whereas north aspects and flat areas in sites with a strong native component were not improved by the addition of seeded species, and may require weed control treatments, rather than reseeding, to improve recovery. Tailoring revegetation objectives, seed mixes, seeding rates, and monitoring efforts to conditions that vary within sites may lead to more cost effective and successful restoration.     

Fire Risk in Revegetated Bunchgrass Communities Infested with Bromus tectorum

In rangeland ecosystems, invasive annual grass replacement of native perennials is associated with higher fire risk. Large bunchgrasses are often seeded to reduce cover of annuals such as Bromus tectorum L. (cheatgrass), but there is limited information about how revegetation reduces fire risk over the long term. We assessed how revegetated community composition influences fire risk at three sites in Columbia National Wildlife Refuge in Grant County, Washington that were revegetated with large bunchgrasses 8 ? 18 years before the study. At each site, five replicates of 10 plots (10 × 10 m) were established. Fire risk was determined as the probability that a plot would completely burn following ignition at a randomly located point in each plot (i.e., if 8 of 10 plots burned, then fire risk was 80%). Preignition, cover of bunchgrasses, cheatgrass, forbs, and surface characteristics were determined for each plot. Fire risk was < 100%. However, fire risk was still relatively high around 73% and did not differ significantly among sites despite differences in cheatgrass and bunchgrass cover, which may have been attributable to other characteristics, such as high total fuels cover (> 80% at all sites) and unvegetated gap cover (soil and soil cryptogams, < 17%). This information can provide guidance for future studies with larger ranges of cover characteristics to develop robust fire risk models, which ultimately will be used to aid rangeland managers who need to specify reduction of fire risk after reestablishing large bunchgrasses in rangelands infested with cheatgrass.     

Soil Seed Banks of the Exotic Annual Grass Bromus rubens on a Burned Desert Landscape

Red brome (Bromus rubens), an exotic annual grass, can dominate soil seed banks and poses serious threats to mature native plant communities in the Mojave Desert by competing with native species and providing fine fuels that facilitate widespread wildfire. By exploring how seed bank density and composition in burned areas change over time since fire (TSF), we can improve our understanding of how the seed banks are affected by fire. Samples of the 5-cm-deep soil seed bank were collected from two microsites (under shrubs, in open interspaces) within paired burned and unburned areas on 12 fires ranging from 5–31 yr TSF. Seed bank samples were assayed using the emergence method and seed densities were compared among TSFs, burn status (burned, unburned), and microsites for the species that emerged. Red brome soil seed bank density was spatially variable and TSF rarely predicted abundance. Overall, undershrub seed densities did not differ between burned and unburned areas. However, at some fire sites, seed densities in interspaces were greater in burned than unburned areas. Although native seed densities were low overall, they did not appear to differ according to burn status. Studies have shown that red brome plant and seed bank densities can be greatly reduced immediately after fire. Management efforts that focus on this initial colonization window may be able to take advantage of diminished red brome seed densities to limit its reestablishment while facilitating the establishment of native species. However, this window is brief, as our findings indicate that once reestablished, red brome soil seed densities in burned areas can be similar to those in unburned areas within 5 yr.     

Vegetation Response to Mowing Dense Mountain Big Sagebrush Stands

A decrease in fire frequency and past grazing practices has led to dense mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) stands with reduced herbaceous understories. To reverse this trend, sagebrush-reducing treatments often are applied with the goal of increasing herbaceous vegetation. Mechanical mowing is a sagebrush-reducing treatment that commonly is applied; however, information detailing vegetation responses to mowing treatments generally are lacking. Specifically, information is needed to determine whether projected increases in perennial grasses and forbs are realized and how exotic annual grasses respond to mowing treatments. To answer these questions, we evaluated vegetation responses to mowing treatments in mountain big sagebrush plant communities at eight sites. Mowing was implemented in the fall of 2007 and vegetation characteristics were measured for 3 yr post-treatment. In the first growing season post-treatment, there were few vegetation differences between the mowed treatment and untreated control (P > 0.05), other than sagebrush cover being reduced from 28% to 3% with mowing (P < 0.001). By the second growing season post-treatment, perennial grass, annual forb, and total herbaceous vegetation were generally greater in the mowed than control treatment (P < 0.05). Total herbaceous vegetation production was increased 1.7-fold and 1.5-fold with mowing in the second and third growing seasons, respectively (P < 0.001). However, not all plant functional groups increased with mowing. Perennial forbs and exotic annual grasses did not respond to the mowing treatment (P > 0.05). These results suggest that the abundance of sagebrush might not be the factor limiting some herbaceous plant functional groups, or they respond slowly to sagebrush-removing disturbances. However, this study suggests that mowing can be used to increase herbaceous vegetation and decrease sagebrush in some mountain big sagebrush plant communities without promoting exotic annual grass invasion.     

Interspace/Undercanopy Foraging Patterns of Beef Cattle in Sagebrush Habitats

Forage selection patterns of cattle in sagebrush (Artemisia L.) communities are influenced by a variety of environmental and plant-associated factors. The relative preference of cattle for interspace versus under-sagebrush canopy bunchgrasses has not been documented. Potential preferences may indirectly affect habitat for sage-grouse and other ground-nesting birds. Our objectives were to investigate grazing patterns of cattle with respect to undercanopy (shrub) and interspace tussocks, determine the influence of cattle grazing on screening cover, and relate shrub morphology to undercanopy grazing occurrence. Eighteen-day replicated trials were conducted in the summers of 2003 and 2004. Findings suggest cattle initially concentrate grazing on tussocks between shrubs, and begin foraging on tussocks beneath shrubs as interspace plants are depleted. Grazing of undercanopy grass tussocks was negligible at light-to-moderate utilization levels (< 40% by weight). Grass tussocks under spreading, umbrella-shaped shrub canopies were less likely (P < 0.001) to be grazed than those beneath erect, narrow canopies. Horizontal screening cover decreased (P < 0.001) with pasture utilization. At the trial’s end, removal of 75% of the herbaceous standing crop induced about a 5% decrease in screening cover in all strata from ground level to 1 m with no differences among strata (P = 0.531). This implied that shrubs constituted the majority of screening vegetation. Our data suggest that conservative forage use, approaching 40% by weight, will affect a majority (about 70%) of interspace tussocks and a lesser proportion (about 15%) of potential nest-screening tussocks beneath sagebrush. Probability of grazing of tussocks beneath shrubs, however, is also affected by shrub morphology. These findings will help managers design grazing programs in locales where habitat for ground nesting birds is a concern.     

Longer-Term Evaluation of Revegetation of Medusahead-Invaded Sagebrush Steppe

Medusahead (Taeniatherum caput-medusae [L.] Nevski) and other exotic annual grasses have invaded millions of hectares of sagebrush (Artemisia L.) steppe. Revegetation of medusahead-invaded sagebrush steppe with perennial vegetation is critically needed to restore productivity and decrease the risk of frequent wildfires. However, it is unclear if revegetation efforts provide long-term benefits (fewer exotic annuals and more perennials). The limited literature available on the topic questions whether revegetation efforts reduce medusahead abundance beyond 2 or 3 yr. We evaluated revegetation of medusahead-invaded rangelands for 5 yr after seeding introduced perennial bunchgrasses at five locations. We compared areas that were fall-prescribed burned immediately followed by an imazapic herbicide treatment and then seeded with bunchgrasses 1 yr later (imazapic-seed) with untreated controls (control). The imazapic-seed treatment decreased exotic annual grass cover and density. At the end of the study, exotic annual grass cover and density were 2-fold greater in the control compared with the imazapic-seed treatment. The imazapic-seed treatment had greater large perennial bunchgrass cover and density and less annual forb (predominately exotic annuals) cover and density than the untreated control for the duration of the study. At the end of the study, large perennial bunchgrass density average 10 plant ? m^? 2 in the imazapic-seed treatment, which is comparable with intact sagebrush steppe communities. Plant available soil nitrogen was also greater in the imazapic-seed treatment compared with the untreated control for the duration of the study. The results of this study suggest that revegetation of medusahead-invaded sagebrush steppe can provide lasting benefits, including limiting exotic annual grasses.     

Long-Term Effects of Aeration and Fire on Invasion of Exotic Grasses in Mixed-Brush Plant Communities

Invasion of exotic grasses into grasslands dominated by native plants changes fire cycles and reduces biodiversity. Brush management practices that create soil disturbance, such as aeration, may potentially result in invasion of exotic grasses and replacement of native vegetation. We tested the hypothesis that a long-term effect of aeration and prescribed burning is an increase in exotic grasses. The study was conducted at the Chaparral Wildlife Management Area in the western south Texas plains where four treatments were evaluated: aeration, warm-season burn, aeration followed by a warm-season burn, and no treatment (control). The experimental design was a randomized complete block with four replicates. We estimated percentage canopy cover of exotic grasses, native grasses, forbs, litter, bare ground, and woody and succulent plants in 2007. There was a multivariate main effect among treatments for the dependent variables absolute canopy cover of exotic grasses, native grasses, forbs, litter, and bare ground (Wilks's Lambda F_15,179.84 = 2.78, P = 0.001). Variables that contributed to the significant overall effect included litter (F_3,69 = 4.32, P = 0.008) and native grasses (F_3,69 = 6.11, P = 0.001). The multivariate main effect of treatment was significant (Wilks's Lambda F_9,180.25 = 2.04, P = 0.038) for the relative canopy cover of herbaceous species. Relative cover of exotic grasses was 31% higher (P = 0.024) in control than in the prescribed burn treatment. Native grasses relative cover was 30% higher (P = 0.003) in prescribed burn than in the control treatment. We did not detect differences among treatments in the percentage of total woody and succulent plants canopy cover (P = 0.083). Under the environmental conditions at the time of the study, aeration and/or prescribed burning do not increase exotic grasses.     

Hydrologic Response to Mechanical Shredding in a Juniper Woodland

We investigated soil compaction and hydrologic responses from mechanically shredding Utah juniper (Juniperus ostesperma [Torr.] Little) to control fuels in a sagebrush/bunchgrass plant community (Artemisia nova A. Nelson, Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young/Pseudoroegneria spicata [Pursh] A. Löve, Poa secunda J. Presl) on a gravelly loam soil with a 15% slope in the Onaqui Mountains of Utah. Rain simulations were applied on 0.5-m² runoff plots at 64 mm · h^?1 (dry run: soil initially dry) and 102 mm · h^?1 (wet run: soil initially wet). Runoff and sediment were collected from runoff plots placed in five blocks, each containing four microsites (juniper mound, shrub mound, vegetation-free or bare interspace, and grass interspace) with undisturbed or tracked treatments for each microsite type and a residue-covered treatment for grass and bare interspace microsites. Soil penetration resistance was measured at the hill slope scale, and canopy and ground cover were measured at the hill slope and runoff plot scale. Although shredding trees at a density of 453 trees · ha^?1 reduced perennial foliar cover by 20.5%, shredded tree residue covered 40% of the ground surface and reduced non–foliar-covered bare ground and rock by 17%. Tire tracks from the shredding operation covered 15% of the hill slope and increased penetration resistance. For the wet run, infiltration rates of grass interspaces were significantly decreased (39.8 vs. 66.1 mm · h^?1) by tire tracks, but infiltration rates on juniper mounds and bare interspaces were unchanged. Bare interspace plots covered with residue had significantly higher infiltration rates (81.9 vs. 26.7 mm · h^?1) and lower sediment yields (38.6 vs. 313 g · m^?2) than those without residue. Because hydrologic responses to treatments are site- and scale-dependent, determination of shredding effects on other sites and at hill slope or larger scales will best guide management actions.     

Herbicide Protection Pods (HPPs) Facilitate Sagebrush and Bunchgrass Establishment under Imazapic Control of Exotic Annual Grasses

Revegetation of exotic annual grass−invaded rangelands is a primary objective of land managers following wildfires. Controlling invasive annual grasses is essential to increasing revegetation success; however, preemergent herbicides used to control annual grasses prohibit immediate seeding due to nontarget herbicide damage. Thus, seeding is often delayed 1 yr following herbicide application. This delay frequently allows for reinvasion of annual grasses, decreasing the success of revegetation efforts. Incorporating seeds into herbicide protection pods (HPPs) containing activated carbon (AC) permits concurrent high preemergent herbicide application and seeding because AC adsorbs and renders herbicides inactive. While HPPs have, largely in greenhouse studies, facilitated perennial bunchgrass emergence and early growth, their effectiveness in improving establishment of multiple species and functional groups in the field has not been assessed. Five bunchgrass species and two shrub species were seeded at two field sites with high imazapic application rates as bare seed and seed incorporated into HPPs. HPPs significantly improved establishment of sagebrush (Artemesia tridentata Nutt. Spp. wyomingensis Beetle & Young) and crested wheatgrass (Agropyron cristatum [L.] Gaertn.) over the 2-yr study. Three native perennial grass species were protected from herbicide damage by HPPs but had low establishment in both treatments. The two remaining shrub and grass species did not establish sufficiently to determine treatment effects. While establishment of native perennial bunchgrasses was low, this study demonstrates that HPPs can be used to protect seeded bunchgrasses and sagebrush from imazapic, prolonging establishment time in the absence of competition with annual grasses.     

Can Imazapic and Seeding Be Applied Simultaneously to Rehabilitate Medusahead-Invaded Rangeland? Single vs. Multiple Entry

It has recently been proposed that the cost of rehabilitating medusahead (Taeniatherum caput-medusae [L.] Nevski)–invaded rangelands may be reduced by concurrently seeding desired vegetation and applying the preemergent herbicide imazapic. However, the efficacy of this “single-entry” approach has been inconsistent, and it has not been compared to the multiple-entry approach where seeding is delayed 1 yr to decrease herbicide damage to nontarget seeded species. We evaluated single- and multiple-entry approaches in medusahead-invaded rangelands in southeastern Oregon with seeding for both approaches occurring in October 2011. Before seeding and applying herbicide, all plots were burned to improve medusahead control with imazapic and prepare the seedbed for drill seeding–introduced perennial bunchgrasses. Both approaches effectively controlled medusahead during the 2 yr postseeding. However, almost no seeded bunchgrasses established with the single-entry treatment (< 0.5 individals · m^-2), probably as a result of nontarget herbicide mortality. Perennial grass cover and density in the single-entry treatment did not differ from the untreated control. In contrast, the multiple-entry treatment had on average 6.5 seeded bunchgrasses · m^-2 in the second year postseeding. Perennial grass (seeded and nonseed species) cover was eight times greater in the multiple-entry compared to the single-entry treatment by the second year postseeding. These results suggest that the multiple-entry approach has altered the community from annual-dominated to perennial grass–dominated, but the single-entry approach will likely be reinvaded and dominated medusahead without additional treatments because of a lack of perennial vegetation.     

Effects of Long-Term Livestock Grazing on Fuel Characteristics in Rangelands: An Example From the Sagebrush Steppe

Livestock grazing potentially has substantial influence on fuel characteristics in rangelands around the globe. However, information quantifying the impacts of grazing on rangeland fuel characteristics is limited, and the effects of grazing on fuels are important because fuel characteristics are one of the primary factors determining risk, severity, continuity, and size of wildfires. We investigated the effects of long-term (70+ yr) livestock grazing exclusion (nongrazed) and moderate levels of livestock grazing (grazed) on fuel accumulations, continuity, gaps, and heights in shrub-grassland rangelands. Livestock used the grazed treatment through 2008 and sampling occurred in mid- to late summer in 2009. Nongrazed rangelands had over twofold more herbaceous standing crop than grazed rangelands (P < 0.01). Fuel accumulations on perennial bunchgrasses were approximately threefold greater in nongrazed than grazed treatments. Continuity of fuels in nongrazed compared to grazed treatments was also greater (P < 0.05). The heights of perennial grass current year’s and previous years’ growth were 1.3-fold and 2.2-fold taller in nongrazed compared to grazed treatments (P < 0.01). The results of this study suggest that moderate livestock grazing decreases the risk of wildfires in sagebrush steppe plant communities and potentially other semi-arid and arid rangelands. These results also suggest wildfires in moderately grazed sagebrush rangelands have decreased severity, continuity, and size of the burn compared to long-term nongrazed sagebrush rangelands. Because of the impacts fuels have on fire characteristics, moderate levels of grazing probably increase the efficiency of fire suppression activities. Because of the large difference between fuel characteristics in grazed and nongrazed sagebrush rangelands, we suggest that additional management impacts on fuels and subsequently fires need to be investigated in nonforested rangelands to protect native plant communities and prioritize management needs.     

Immature Seedling Growth of Two North American Native Perennial Bunchgrasses and the Invasive Grass Bromus tectorum

Pseudoroegneria spicata (Pursh) A. Löve and Elymus wawawaiensis J. Carlson & Barkworth are two native perennial grasses widely used for restoration in the Intermountain West. However, the rapid establishment and spread of Bromus tectorum L., an invasive annual grass, has led to a decline in the abundance of native perennial grasses. Proliferation of B. tectorum has been attributed to its early germination, superior cold-temperature growth, profuse root production, and high specific leaf area (SLA). To enhance restoration success, we compared B. tectorum to commercially available plant materials of two perennial rangeland bunchgrasses, P. spicata (cv. Whitmar, cv. Goldar, and Anatone Germplasm) and E. wawawaiensis (cv. Secar), for germination, seedling morphological traits, and growth rates at the immature seedling stage. We monitored germination and immature seedling growth in a growth chamber in two separate experiments, one under low (5/10°C) and the other under high (15/20°C) day/night temperatures. Compared to the average of the two perennials, B. tectorum was 93% (77%) greater at high (and low) temperature for root∶shoot length ratio, but only 14% (14%) greater for root∶shoot biomass ratio and 12% (19%) lower for SLA. This suggests that B. tectorum’s substantial investment in surface area of roots, rather than in shoot length, root biomass, or leaf area, may be responsible for the annual’s success at the early seedling stage. Compared to E. wawawaiensis, P. spicata averaged 65% (41%) higher shoot biomass, 39% (88%) higher root biomass, and 70% (10%) higher absolute growth rate, but 25% (15%) lower SLA and 15% (36%) lower specific root length (SRL) at high (and low) temperatures, respectively. Although P. spicata’s greater productivity may initially make for better seedling establishment than E. wawawaiensis, it may also prove disadvantageous in competitive or highly resource-limited environments where high SLA or SRL could be an advantage.     

Postfire Invasion Potential of Rush Skeletonweed (Chondrilla Juncea)

North American sagebrush steppe communities have been transformed by the introduction of invasive annual grasses and subsequent increase in fire size and frequency. We examined the effects of wildfires and environmental conditions on the ability of rush skeletonweed (Chondrilla juncea L.), a perennial Eurasian composite, to invade degraded sagebrush steppe communities, largely dominated by cheatgrass (Bromus tectorum L.). Recruitment of rush skeletonweed from seed and root buds was investigated on 11 burned and unburned plot pairs on Idaho's Snake River Plain following summer 2003 wildfires. Emergence from soil seedbanks was similar on burned and unburned plots in 2003 and 2004 (P = 0.37). Soils from recently burned plots (P = 0.05) and sterilized field soil (P &spilt; 0.01) supported greater emergence than did unburned field soils when rush skeletonweed seeds were mixed into the soils in the laboratory. These decreases may indicate susceptibility of this exotic invasive to soil pathogens present in field soils. Seeds in bags placed on field soil in late October 2003 reached peak germination by mid-January 2004 during a wet period; 1% remained viable by August 2004. Seedling emergence from sown plots or the native seedbank and establishment of new rosettes from root sprouts in 2003–2005 indicate that seed germination of rush skeletonweed on the Snake River Plain may be facultative, occurring in fall or spring if soil moisture is adequate, although many germinants may not survive. Stand development results primarily from root sprouting. Establishment from seed is episodic but provides for dispersal, with increasing fire frequency and size expanding the areas of disturbance available for new invasions.     

Long-Term Response Patterns of Tallgrass Prairie to Frequent Summer Burning

Knowledge of how tallgrass prairie vegetation responds to fire in the late growing season is relatively sparse and is based upon studies that are either spatially or temporally limited. To gain a more robust perspective of vegetation response to summer burning and to determine if repeated summer fire can drive vegetational changes in native tallgrass prairie, we evaluated species cover and richness over a 14-yr period on different topographic positions from ungrazed watersheds that were burned biennially in the growing season. We found that annual forbs were the primary beneficiaries of summer burning, but their fluctuations varied inconsistently among years. Concomitantly, species richness and diversity increased significantly with summer burning but remained stable through time with annual spring burning. After 14 yr, species richness was 28% higher in prairie that was burned in the summer than in prairie burned in the spring. Canopy cover of big bluestem (Andropogon gerardii Vitman) and Indiangrass (Sorghastrum nutans [L.] Nash) increased significantly over time with both summer and spring burning, whereas heath aster (Symphyotrichum ericoides [L.] Nesom), aromatic aster (Symphyotrichum oblongifolium [Nutt.] Nesom), and sedges (Carex spp.) increased in response to only summer burning. Kentucky bluegrass (Poa pratensis L.) cover declined in both spring-burned and summer-burned watersheds. Repeated burning in either spring or summer did not reduce the cover or frequency of any woody species. Most perennial species were neutral in their reaction to summer fire, but a few species responded with large and inconsistent temporal fluctuations that overwhelmed any clear patterns of change. Although summer burning did not preferentially encourage spring-flowering forbs or suppress dominance of the warm-season grasses, it is a potentially useful tool to increase community heterogeneity in ungrazed prairie.     

Potential of Kochia prostrata and Perennial Grasses for Rangeland Restoration in Jordan

Six varieties of forage kochia (Kochia prostrata [L.] Schrad.), two Atriplex shrubs native to North America, and four drought-tolerant perennial grass varieties were seeded and evaluated under arid rangeland conditions in Jordan. Varieties were seeded in December 2007 and evaluated in 2008 and 2009 at two sites. Conditions were dry with Qurain receiving 110 mm and 73 mm and Tal Rimah receiving 58 mm and 43 mm of annual precipitation during the winters of 2007/2008 and 2008/2009, respectively. Plants were more abundant and taller (P < 0.001) at Qurain than Tal Rimah in 2008. Forage kochia frequency was 48% and 30% in 2008 at Qurain and Tal Rimah, respectively. However, no seeded plants were observed at Tal Rimah in 2009, suggesting that 58 mm and 43 mm of annual precipitation are insufficient to allow plants to persist over multiple years. At the wetter site, forage kochia abundance in 2009 was similar (P = 0.90) to that observed in 2008 and plant height increased (P < 0.001) from 2008 (14.4 cm ± 1.1 SE) to 2009 (38.4 cm ± 1.1 SE). Sahro-select and Otavny-select were the most abundant forage kochia varieties (P < 0.05), suggesting that these experimental lines could be more adapted to the environmental conditions of Jordan than the commercially available cultivar Immigrant. Frequency of perennial grass varieties declined (P < 0.001) at Qurain from 82% ± 4 SE to 39% ± 4 SE between 2008 and 2009, respectively. Among grasses, Siberian wheatgrass had better stands than crested wheatgrass, with Russian wildrye being intermediate. Based on this study, forage kochia appears to have great potential for establishing palatable perennial shrubs in arid rangeland conditions in Jordan if annual precipitation is at least 70 mm. Arid-adapted perennial grass varieties might also be useful in rangeland restoration if annual precipitation is over 100 mm.     

Prescribed Fire,Soil, and Plants: Burn Effects and Interactions in the Central Great Basin

Pinyon and juniper expansion into sagebrush ecosystems results in decreased cover and biomass of perennial grasses and forbs. We examine the effectiveness of spring prescribed fire on restoration of sagebrush ecosystems by documenting burn effects on soil nutrients, herbaceous aboveground biomass, and tissue nutrient concentrations. This study was conducted in a central Nevada woodland and included control and burn treatment plots sampled before and after a prescribed fire. Six native understory plant species (Crepis acuminata, Eriogonum umbellatum, Eriogonum elatum, Poa secunda secunda, Festuca idahoensis, and Lupinus argenteus) important for native sagebrush obligate foragers were chosen to represent the understory plant community. L. argenteus is also important for system nutrient cycling and nitrogen fixation. Plants were collected from three microsites (under tree canopy, under shrub canopy, and interspace) common in transitional woodlands during peak growth the summer before a spring prescribed burn and each of two summers following the burn. Soils were collected from corresponding locations at two depth intervals (0–8 and 8–52 cm) to determine the relationships between soil and plant nutrients following fire. Microsite affected soil nutrients but did not influence plant tissue concentrations with the exception of F. idahoensis. Burning resulted in increases in soil surface NH+4, NO₃⁻, inorganic N, Ca²⁺, Mn²⁺, and Zn²⁺. Increases in NO₃⁻, inorganic N, and Zn²⁺ were also observed in deeper horizons. Burning did not affect aboveground plant biomass or nutrient concentrations in the first year with the exception of F. idahoensis, which had increased tissue P. By the second year, all species had statistically significant responses to burning. The most common response was for increased aboveground plant weight and tissue N concentrations. Plant response to burning appeared to be related to the burn treatment and the soil variables surface K⁺, NO₃⁻, and inorganic N.     

Response of Planted Sagebrush Seedlings to Cattle Grazing Applied to Decrease Fire Probability

Restoration of non-sprouting shrubs after wildfire is increasingly becoming a management priority. In the western U.S., Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) restoration is a high priority, but sagebrush establishment from seed is sporadic. In contrast, planting seedlings often successfully restores sagebrush, but is expensive and time consuming. After planting, hence, there is a need to protect the investment from disturbances such as fire that will erase gains in sagebrush recovery. Grazing is likely the only tool that can be applied feasibly across the landscape to decrease wildfire probability, but there are concerns that grazing and associated activities (e.g. trampling) may negatively impact sagebrush seedlings. We investigated effects of grazing by cattle, applied as a fine fuel management strategy, on planted sagebrush seedlings at five blocks for five years. Grazing substantial reduced exotic annual grasses, large perennial bunchgrasses, and total herbaceous cover, thus achieving fuel management goals. Sagebrush cover and reproductive efforts were almost 2-fold greater in grazed compared to non-grazed areas in the final year of the study. This suggests that grazing favored sagebrush, a generally unpalatable shrub, recovery, likely by reducing competition from highly palatable herbaceous vegetation. Density of sagebrush, however, was similar between grazed and non-grazed areas. This research demonstrates that grazing can be strategically applied to reduce the probability of wildfire in areas with planted sagebrush seedlings; thereby, protecting the investment in sagebrush recovery. With more refinement, it also appears that grazing can be utilized to accelerate the recovery of sagebrush and potentially other woody vegetation habitat by modifying the competitive relationship between herbaceous and woody vegetation.