Christopher A. Call

Effects of targeted cattle grazing on fire behavior of cheatgrass-dominated rangeland in the northern Great Basin, USA

We evaluated the effectiveness of using targeted, or prescribed, cattle grazing to reduce the flame length and rate of spread of fires on cheatgrass (Bromus tectorum)-dominated rangeland in northern Nevada. Cattle removed 80–90% of B. tectorum biomass during the boot (phenological) stage in grazed plots in May 2005. Grazed and ungrazed plots were burned in October 2005 to assess fire behavior characteristics. Targeted grazing reduced B. tectorum biomass and cover, which resulted in reductions in flame length and rate of spread. When the grazing treatments were repeated on the same plots in May 2006, B. tectorum biomass and cover were reduced to the point that fires did not carry in the grazed plots in October 2006. Fuel characteristics of the 2005 burns were used to parameterize dry-climate grass models in BEHAVE Plus, and simulation modeling indicates that targeted grazing in spring (May) will reduce the potential for catastrophic fires during the peak fire season (July–August) in the northern Great Basin.

Elemental allelopathy: processes, progress, and pitfalls

Allelopathic interference between plants has generally been discussed in terms of the production of toxic complex biochemicals; however, complex biochemicals may not be the only substances plants use to interfere with one another. It has also been suggested that inorganic elements may be used in an allelopathic manner. If, through phytoenrichment or root exudates, a plant is able to increase the bioavailable levels of a particular element and tolerate the levels better than its neighbors, it can produce an allelopathic effect. Elemental allelopathy has been implicated as the cause for the success of a number of invasive weeds, including Acroptilon repens, Tamarix spp., Halogeton glomeratus, Salsola iberica, and Mesambryenthemum crystallinum. Phytoenrichment of elements can occur through hyperaccumulation and litter deposition and by altering rhizosphere chemistry. Reported cases of elemental allelopathy have involved three types of elements: heavy metals and soluble salts in terrestrial systems and elemental S in aquatic systems. For the most part, studies that have reported elemental allelopathy have been inconclusive. In order to prevent overreaching conclusions in the study of biochemical allelopathy, criteria were set that can be adapted to the study of elemental allelopathy. Of the studies reviewed, the most common criteria left uninvestigated were whether the plant was actually responsible for changing the concentration of the element and whether the increased levels of an element negatively affected other species. If the study of elemental allelopathy is to avoid the same problems often associated with the study of biochemical allelopathy, these criteria should be included in investigations of elemental allelopathy.

Predicting buffelgrass survival across a geographical and environmental gradient

This research was designed to identify relationships between T4464 buffelgrass (Cenchrus ciliaris L.) survival and climatic and soil characteristics. At 167 buffelgrass seeding sites in North America we collected climatic and soils data where the grass: 1) persisted over time and increased in area covered (spreads), 2) persisted over time but does not increase in area covered (persists), and 3) declined over time and all plants eventually died (dies). At 30 sites in Kenya we collected climatic and soils data in the area where T4464 seed was originally collected. Only total soil nitrogen and organic carbon differed among survival regimes. Total soil nitrogen and organic carbon concentrations were least where buffelgrass spreads, intermediate where the grass persists and greatest where the grass dies. To predict buffelgrass survival among the 3 survival regimes, and between areas where the grass spreads or dies, we used discriminant function analyses. A model including organic carbon, total soil nitrogen, sand, clay, potassium and cation exchange capacity correctly classified 78% (r2=0.8) of the seeding sites in the 3 survival regimes. A model including sand, total soil nitrogen, calcium, mean minimum temperature in the coldest month, annual precipitation and winter precipitation correctly classified 88% (r2 = 0.8) of the seedling sites between spreads and dies. Survival regime selection prior to brush control, seedbed preparation and sowing will reduce planting failure probabilities, soil erosion and economic losses, and enhance long-term beef production.

Seedling Interference and Niche Differentiation Between Crested Wheatgrass and Contrasting Native Great Basin Species

Abstract Interference from crested wheatgrass (Agropyron cristatum [L.] Gaertn.) seedlings is considered a major obstacle to native species establishment in rangeland ecosystems; however, estimates of interference at variable seedling densities have not been defined fully. We conducted greenhouse experiments using an addition-series design to characterize interference between crested wheatgrass and four key native species. Crested wheatgrass strongly interfered with the aboveground growth of Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young), rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G. L. Nesom & Baird subsp. consimilis [Greene] G. L. Nesom & Baird), and to a lesser extent with bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). Alternatively, bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey subsp. californicus [J. G. Sm.] Barkworth) and crested wheatgrass had similar effects on each others growth, and interference ratios were near 1.0. Results indicate that the native grasses more readily establish in synchrony with crested wheatgrass than these native shrubs, but that once established, the native shrubs are more likely to coexist and persist with crested wheatgrass because of high niche differentiation (e.g., not limited by the same resource). Results also suggest that developing strategies to minimize interference from crested wheatgrass seedlings emerging from seed banks will enhance the establishment of native species seeded into crested wheatgrass–dominated communities.

Economic feasibility of controlling tall larkspur on rangelands.

Larkspur (Delphinium spp.) poisoning of cattle poses a serious economic problem on many western rangelands. Losses varied from 1.5% to 12.3% of the grazing cattle over a 15-year period on the Manti Canyon grazing allotment. Three herbicides and different application methods were compared for control of tall larkspur. The 3 herbicides were: glyphosate [N-(phosphonmethyl) glycine]; picloram (4-amino-3,5,6- trichloro-2-pyridine carboxylic acid); and metsulfuron 2[[[[(4-methyoxy-6-methly-1,3,5-triaxin-2-yl) amino] carbonyl] amino] sulfonyl] benzoic acid. A boom type sprayer and a carpeted roller applicator were tested for the selective herbicides. Spot treatment and backpack sprayers were tested for the nonselective herbicide (metsulfuron). The internal rate of return was used to evaluate the economic feasibility of each alternative control method. A treatment was considered economically feasible if the internal rate of return was equal to or higher than the cost of borrowing money. Each treatment was evaluated for an assumed cattle death loss of 4.5% and 2.25%. A 10-year life was considered for each treatment. All of the herbicides and application methods tested were economically feasible. The internal rates of return varied from 14.23% to 133.38%. An internal rate of return above 100% occurs when the benefits in a single year exceeds the total cost of control. The cost of herbicides have increased considerably over the past few years, but they can still be used economically if treatment results in death loss reductions described in this study.

Effects of Targeted Grazing and Prescribed Burning on Community and Seed Dynamics of a Downy Brome (Bromus tectorum)–Dominated Landscape

Abstract Downy brome (Bromus tectorum L.)—dominated communities can remain as stable states for long periods, even with frequent disturbance by grazing and fire. The objective of this study was to determine the effectiveness of using targeted cattle grazing and late-season prescribed burning, alone and in combination, to reduce B. tectorum seed bank input and seed bank density and thus alter aboveground community dynamics (species composition) on a B. tectorum–dominated landscape in northern Nevada. Cattle removed 80 to 90% of standing biomass in grazed plots in May of 2005 and 2006 when B. tectorum was in the boot (phenological) stage. Grazed and ungrazed plots were burned in October 2005 and 2006. The combined grazing–burning treatment was more effective than either treatment alone in reducing B. tectorum seed input and seed bank density, and in shifting species composition from a community dominated by B. tectorum to one composed of a suite of species, with B. tectorum as a component rather than a dominant. This study provides a meso-scale precursor for landscape-scale adaptive management using grazing and burning methodologies. Nomenclature: Downy brome; Bromus tectorum L. BROTE. Management Implications: Livestock grazing, the invasion of downy brome, and the resulting grass-fire cycle have played major roles in the conversion of sagebrush–grassland and other native plant communities to downy brome–dominated landscapes. Grazing and fire, if properly managed, can also play major roles in suppressing downy brome and changing plant community composition. This investigation was aimed at determining if targeted cattle grazing and prescribed burning, alone and in combination, could reduce downy brome reproductive potential, and thus its dominance in a degraded sagebrush–grassland community. In this study, we found that intensive cattle grazing in May, when downy brome was in the boot stage (just before inflorescence emergence from the culm), reduced seed input into the seed bank (Figures 1 and 2). Prescribed burning in October consumed much of the litter on the soil surface, killing or damaging many downy brome seeds suspended in the litter and reducing the number of favorable microsites for germination and establishment of surviving seeds in the soil. The integration of targeted grazing with prescribed burning was more effective than either treatment alone in reducing downy brome seed bank density and changing species composition from a community dominated by downy brome to one dominated by less flammable species such as Sisymbrium altissimum (Figures 1 and 3). Although S. altissimum is less flammable than downy brome the potential for fire spread is still present because of the tumbling nature of S. altissimum. Thus, our methodologies created a less fire-prone plant community, not a fireproof community. These findings are encouraging; the required stocking density for intensive grazing and the short temporal window for grazing during the boot stage will limit the use of targeted grazing to relatively small scales, i.e., about 42 ha during one growing season for a herd of 500 cow–calf pairs. And, managers must recognize that the effects of grazing and prescribed burning treatments are short-lived (1 to 2 yr); thus, treatments must be integrated with other management methods (herbicide or mechanical) and repeated to have the greatest impact on downy brome. These treatments could be used to create or maintain fuel-break strips and possibly to prepare patches of downy brome–dominated areas for revegetation. We have laid the groundwork for further studies at larger scales.

Comparison of Herbicides for Reducing Annual Grass Emergence in Two Great Basin Soils

Abstract Reducing seed germination and seedling emergence of downy brome (Bromus tectorum L.) improves the success of revegetating degraded shrubland ecosystems. While pre-emergence herbicides can potentially reduce these two processes, their impact on germination and emergence of downy brome and revegetation species in semiarid ecosystems is poorly understood and has not been comprehensively studied in soils with potentially contrasting herbicide bioavailability (i.e., residual plant activity). We designed a greenhouse experiment to evaluate the effects two pre-emergence acetolactate synthase–inhibiting herbicides (rimsulfuron and imazapic) on germination and emergence of downy brome and two revegetation grass species (crested wheatgrass [Agropyron cristatum {L.} Gaertn.] and bottlebrush squirreltail [Elymus elymoides {Raf.} Swezey]) that were grown in representative soils from salt desert and sagebrush shrublands. Pre-emergence herbicides significantly (P < 0.05) reduced seedling emergence and biomass production of downy brome and crested wheatgrass and increased mortality more so in sagebrush compared to salt desert soil, suggesting that these common Great Basin soils fundamentally differ in herbicide bioavailability. Also, germination and emergence of the two highly responsive species (crested wheatgrass and downy brome) were clearly more impacted by rimsulfuron than imazapic. We discuss these results in terms of how the specific soil physiochemical properties influence herbicide adsorption and leaching. Our results shed new light on the relative performance of these two promising herbicides and the importance of considering soil properties when applying pre-emergence herbicides to reduce germination and emergence of invasive annual grasses and create suitable seedbed conditions for revegetation.

Invasion of Broom Snakeweed (Gutierrezia sarothrae) Following Disturbance: Evaluating Change in a State-and-Transition Model

Abstract Broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) is an aggressive native invasive species that thrives after disturbance in semiarid rangelands of the western United States. A 5-yr (2002–2006) study was initiated following grazing and fire disturbances on an Upland Gravelly Loam ecological site in the sagebrush steppe of northern Utah, to evaluate broom snakeweed invasion in different plant communities. The study site originally had two plant communities: a sagebrush/bunchgrass community that received alternate-year, fall cattle grazing, and was dominated by bluebunch wheatgrass (Elymus spicatus) and an open stand of Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis), and a sagebrush community that received continuous, annual, spring cattle grazing that removed the bunchgrasses, leaving a dense stand of Wyoming big sagebrush with an understory of Sandberg bluegrass (Poa secunda). Portions of these two plant communities were burned in a wildfire in 2001, removing the sagebrush, and creating two additional communities. The burned portion of the sagebrush/bunchgrass community became a bluebunch wheatgrass–dominated community, and the burned portion of the sagebrush community became a snakeweed-dominated community. Foliar cover, aboveground biomass, and sagebrush and snakeweed densities were compared among the four communities. Mature snakeweed plants that existed in the sagebrush/bunchgrass community were eliminated in 2003, because of drought conditions. Snakeweed was eliminated in the bluebunch wheatgrass community by the wildfire in 2001, and there was no reestablishment. Snakeweed density and cover remained constant in the sagebrush community. Snakeweed cover increased from 2% to 31% in the snakeweed community, despite the presence of Sandberg bluegrass. The data were used to evaluate and update the current Upland Gravelly Loam (Wyoming big sagebrush) ecological site description in the Great Salt Lake Major Land Resource Area and its state-and-transition model to reflect vegetation changes associated with snakeweed invasion.

RECOVERY AND GERMINABILITY OF NATIVE SEED FED TO CATTLE

Abstract Using livestock as seed dispersal agents may be an effective method for increasing species diversity on degraded and previously seeded rangelands. We quantified seed passage and recovery rates, and post-passage germinability of Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young), bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey), and gooseberry globemallow (Sphaeralcea grossulariaefolia [H. & A.] Rydb.) by feeding Holstein heifers seeds of each species at 3 levels (15,000; 30,000; and 60,000 seeds) over a period of 3 weeks. One-kg fecal samples were collected 1, 2, 3, and 4 days after seed ingestion. Undamaged seeds were extracted from the samples and tested for germinability. Globemallow had the highest percentage of recovered, undamaged seed, followed by squirreltail and sagebrush. Globemallow and sagebrush seed passage was highest on Day 1, after which seed numbers dropped sharply. Squirreltail passage and recovery were more consistent through time, with higher seed recovery at lower seed feeding levels. Post-passage germinability was highest for squirreltail and globemallow on Day 1. Sagebrush germination was negligible. Differences in physical seed properties (size, shape, and seed coat) likely influenced interspecies variation in passage, recovery, and germinability. Globemallow and squirreltail seeds may be suited for livestock dispersal, but sagebrush seeds are not.

Mycorrhizae, survival and growth of selected woody plant species in lignite overburden in Texas.

Abstract Seedlings of live oak ( Quercus virginiana (Mill.)), Chinese tallow tree ( Sapium sebiferum (L.) Roxb.), and Texas mountain laurel ( Sophora secundiflora (Ort.) Lag.) were inoculated with either ectomycorrhizal fungi ( Pisolithus tinctorius (Mich. ex Pers.) Ckr. and Couch) or vesicular-arbuscular mycorrhizal (VAM/endomycorrhizal) fungi ( Glomus fasciculatum (Thaxter) Gerd. & Trappe, Gigaspora margarita (Becker & Hall), and Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe) in a containerized system and transplanted into lignite overburden at two separate mine sites in the Post Oak Savannah region of Texas. Ectomycorrhizal Q. virginiana and endomycorrhizal S. sebiferum exhibited greater growth, and endomycorrhizal S. secundiflora showed greater survival and growth than noninoculated controls. Overburden at one site was low in P, while the second site was moderately high in P; however, root colonization levels of inoculated plants were high at both sites, while non inoculated plants had low levels of colonization. Both ecto- and endomycorrhizal fungi enhanced growth of the three woody species in these nitrogen-deficient overburden sites, independent of overburden P.