• Are Early Summer Wildfires an Opportunity to Revegetate Exotic Annual Grass-Invaded Plant Communities?

      Davies, Kirk W.; Nafus, Aleta M.; Johnson, Dustin D. (Society for Range Management, 2013-03-01)
      Medusahead (Taeniatherum caput-medusae [L.] Nevski) is an exotic annual grass invading western rangelands. Successful revegetation of invaded-plant communities can be prohibitively expensive because it often requires iterative applications of integrated control and revegetation treatments. Prescribed burning has been used to control medusahead and prepare seedbeds for revegetation, but burning has been constrained by liability concerns and has produced widely varying results. Capitalizing on naturally occurring wildfires could reduce revegetation costs and alleviate liability concerns. Thus, our objective was to determine if early summer wildfires and fall drill seeding could be used as a treatment combination to decrease medusahead and increase perennial and native vegetation. Treatments were evaluated pretreatment and for 3 yr postfire at six sites and included 1) an early summer wildfire combined with a seeding treatment (burn and seed) and 2) a nontreated (no burn, no seed) control. Perennial grass density was 4.6- to 10.0-fold greater in the burn-and-seed treatment compared to the control in the first 3 yr posttreatment (P<0.05). Exotic annual grass density and cover in the third year posttreatment were lower in the burn-and-seed treatment than in the control (P<0.05). However, exotic annual grass density was still 130 individuals m-2 in the burn-and seed treatment. The density of exotic annual grass is of concern because over time medusahead may displace perennial grasses and annual forbs that increased with the burn-and-seed treatment. Though not directly tested in this study, we suggest that, based on other research, the burn-and-seed treatment may need to incorporate a preemergent herbicide application to further suppress medusahead and increase the establishment of seeded vegetation. However, it appears that early summer wildfires may provide an opportunity to reduce the cost of integrated programs to revegetate medusahead-invaded plant communities.
    • Mowing Wyoming Big Sagebrush Communities With Degraded Herbaceous Understories: Has a Threshold Been Crossed?

      Davies, Kirk W.; Bates, Jonathan D.; Nafus, Aleta M. (Society for Range Management, 2012-09-01)
      Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle A. Young] S.L. Welsh) plant communities with degraded native herbaceous understories occupy vast expanses of the western United States. Restoring the native herbaceous understory in these communities is needed to provide higher-quality wildlife habitat, decrease the risk of exotic plant invasion, and increase forage for livestock. Though mowing is commonly applied in sagebrush communities with the objective of increasing native herbaceous vegetation, vegetation response to this treatment in degraded Wyoming big sagebrush communities is largely unknown. We compared mowed and untreated control plots in five Wyoming big sagebrush plant communities with degraded herbaceous understories in eastern Oregon for 3 yr posttreatment. Native perennial herbaceous vegetation did not respond to mowing, but exotic annuals increased with mowing. Density of cheatgrass (Bromus tectorum L.), a problematic exotic annual grass, was 3.3-fold greater in the mowed than untreated control treatment in the third year posttreatment. Annual forb cover, largely consisting of exotic species, was 1.8-fold greater in the mowed treatment compared to the untreated control in the third year posttreatment. Large perennial grass cover was not influenced by mowing and remained below 2%. Mowing does not appear to promote native herbaceous vegetation in degraded Wyoming big sagebrush plant communities and may facilitate the conversion of shrublands to exotic annual grasslands. The results of this study suggest that mowing, as a stand-alone treatment, does not restore the herbaceous understory in degraded Wyoming big sagebrush plant communities. We recommend that mowing not be applied in Wyoming big sagebrush plant communities with degraded understories without additional treatments to limit exotic annuals and promote perennial herbaceous vegetation./Las comunidades de plantas de artemisia Wyoming big sagebrush (Artemisia tridentate ssp. Wyomingensis [Beetle & A. Young] S.L. Welsh) con degradadas coberturas herbáceas ocupan una gran extensión del oeste de los Estados Unidos. El restablecimiento de la cobertura herbácea nativa en estas comunidades es necesario para mejorar la calidad del hábitat para fauna silvestre, mitigar el riesgo de la invasión de plantas exóticas e incrementar la producción de forraje para ganado. A pesarde que comúnmente se hacen cortes en comunidades de artemisia con el objetivo de incrementar la vegetación nativa, se desconoce la respuesta de la vegetación al tratamiento en áreas con comunidades degradadas de Wyoming big sagebrush. Se compararon parcelas segadas y áreas control sin tratamientos en cinco comunidades de Wyoming big sagebrush con cobertura herbácea degradada en el este de Oregón durante tres años posteriores a la aplicación de los tratamientos. La vegetación perenne herbácea no respondió a la siega, pero las plantas exóticas anuales se incrementaron con esta práctica. La densidad de cheatgrass (Bromus tectorum L.), una especie problemática exótica fue tres veces mayor en áreas segadas que en áreas control sintratamiento tres años después de la aplicación de los tratamientos. La cobertura herbácea anual en gran parte formada por especies exóticas fue 1.8 veces mayor en las zonas segadas que en las áreas control sin tratamiento tres años posteriores a la aplicación de tratamientos. La gran cobertura de pastos perennes no fue influenciada por la siega y permaneció debajo del 2%.La siega parece no promover la vegetación herbácea nativa en comunidades degradadas de Wyoming big sagebrush y podría facilitar el cambio de áreas de matorrales a pastizales anuales exóticos. Los resultados de este estudio sugieren que la siega, como un tratamiento independiente, no restablece la cobertura herbácea en comunidades de Wyoming big sagebrush. Nosotros recomendamos que la siega no se practique en comunidades de Wyoming big sagebrush con cobertura degradada sin tratamientos adicionales para limitar la presencia de plantas anuales exóticas y estimular la vegetación herbácea perenne.
    • Multispecies Allometric Models Predict Grass Biomass in Semidesert Rangeland

      Nafus, Aleta M.; McClaran, Mitchel P.; Archer, Steven R.; Throop, Heather L. (Society for Range Management, 2009-01-01)
      Multispecies allometric models to predict grass biomass may increase field study efficiency by eliminating the need for species- specific data. We used field measurements during two growing seasons to develop single-species and multispecies regression models predicting the current year’s aboveground biomass for eight common cespitose grass species. Simple and stepwise regression analyses were based on natural log expressions of biomass, basal diameter, and height, and a dummy variable expression of grazing history. Basal diameter had the strongest relationship with biomass among single-species (adjusted R2 = 0.80 to 0.91) and multispecies (adjusted R2 = 0.85) models. Regression slopes (b) for diameter among single-species (b = 1.01 to 1.49) and the multispecies (b = 1.25) models suggests that biomass will double when diameter increases <75%. Height and grazing history added little predictive value when diameter was already in the model. When applied to actual populations, biomass estimates from multispecies models were within 3-29% of estimates from the single-species models. Although the multispecies biomass-size relationship was robust across the cespitose life-form, users should be cautious about applying our equations to different locations, plant sizes, and population size-structures. 
    • Restoring the Sagebrush Component in Crested Wheatgrass-Dominated Communities

      Davies, Kirk W.; Boyd, Chad S.; Nafus, Aleta M. (Society for Range Management, 2013-07-01)
      Monotypic stands of crested wheatgrass (Agropyron cristatum [L] Gaertm. and Agropyron desertorum [Fisch.] Schult.), an introduced grass, occupy vast expanses of the sagebrush steppe. Efforts to improve habitat for sagebrush-associated wildlife by establishing a diverse community of native vegetation in crested wheatgrass stands have largely failed. Instead of concentrating on a diversity of species, we evaluated the potential to restore the foundation species, Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis [Beetle A. Young] S. L. Welsh), to these communities. We investigated the establishment of Wyoming big sagebrush into six crested wheatgrass stands (sites) by broadcast seeding and planting seedling sagebrush across varying levels of crested wheatgrass control with glyphosate. Planted sagebrush seedlings survived at high rates (~70% planted sagebrush survival 3 yr postplanting), even without crested wheatgrass control. However, most attempts to establish sagebrush by broadcast seeding failed. Only at high levels of crested wheatgrass control did a few sagebrush plants establish from broadcasted seed. Sagebrush density and cover were greater with planting seedlings than broadcast seeding. Sagebrush cover, height, and canopy area were greater at higher levels of crested wheatgrass control. High levels of crested wheatgrass control also created an opportunity for exotic annuals to increase. Crested wheatgrass rapidly recovered after glyphosate control treatments, which suggests multiple treatments may be needed to effectively control crested wheatgrass. Our results suggest that planting sagebrush seedlings can structurally diversify monotypic crested wheatgrass stands to provide habitat for sagebrushassociated wildlife. Though this is not the full diversity of native functional groups representative of the sagebrush steppe, it is a substantial improvement over other efforts that have largely failed to alter these plant communities. We also hypothesize that planting sagebrush seedlings in patches or strips may provide a relatively inexpensive method to facilitate sagebrush recovery across vast landscapes where sagebrush has been lost.