Postfire Succession in Big Sagebrush Steppe With Livestock Grazing

Prescribed fire in rangeland ecosystems is applied for a variety of management objectives, including enhancing productivity of forage species for domestic livestock. In the big sagebrush (Artemisia tridentata Nutt.) steppe of the western United States, fire has been a natural and prescribed disturbance, temporarily shifting vegetation from shrub–grass codominance to grass dominance. There is limited information on the impacts of grazing to community dynamics following fire in big sagebrush steppe. This study evaluated cattle grazing impacts over four growing seasons after prescribed fire on Wyoming big sagebrush (Artemisia tridentata subsp. Wyomingensis [Beetle & Young] Welsh) steppe in eastern Oregon. Treatments included no grazing on burned and unburned sagebrush steppe, two summer-grazing applications after fire, and two spring-grazing applications after fire. Treatment plots were burned in fall 2002. Grazing trials were applied from 2003 to 2005. Vegetation dynamics in the treatments were evaluated by quantifying herbaceous canopy cover, density, annual yield, and perennial grass seed yield. Seed production was greater in the ungrazed burn treatments than in all burn–grazed treatments; however, these differences did not affect community recovery after fire. Other herbaceous response variables (cover, density, composition, and annual yield), bare ground, and soil surface litter did not differ among grazed and ungrazed burn treatments. All burn treatments (grazed and ungrazed) had greater herbaceous cover, herbaceous standing crop, herbaceous annual yield, and grass seed production than the unburned treatment by the second or third year after fire. The results demonstrated that properly applied livestock grazing after low-severity, prescribed fire will not hinder the recovery of herbaceous plant communities in Wyoming big sagebrush steppe.     

Ecological Scale of Bird Community Response to Piñon-Juniper Removal

Piñon (Pinus spp.) and juniper (Juniperus spp.) removal is a common management approach to restore sagebrush (Artemisia spp.) vegetation in areas experiencing woodland expansion. Because many management treatments are conducted to benefit sagebrush-obligate birds, we surveyed bird communities to assess treatment effectiveness in establishing sagebrush bird communities at study sites in Utah, Nevada, Idaho, and Oregon. Our analyses included data from 1 or 2 yr prior to prescribed fire or mechanical treatment and 3 to 5 yr posttreatment. We used detrended correspondence analysis to 1) identify primary patterns of bird communities surveyed from 2006 to 2011 at point transects, 2) estimate ecological scale of change needed to achieve treatment objectives from the relative dissimilarity of survey points to the ordination region delineating sagebrush bird communities, and 3) measure changes in pre- and posttreatment bird communities. Birds associated with sagebrush, woodlands, and ecotones were detected on our surveys; increased dissimilarity of survey points to the sagebrush bird community was characterized by a gradient of increased juniper and decreased sagebrush cover. Prescribed fires burned between 30% and 97% of our bird survey points. However, from 6% to 24% cover of piñon-juniper still remained posttreatment on the four treatment plots. We measured only slight changes in bird communities, which responded primarily to current vegetation rather than relative amount of change from pretreatment vegetation structure. Bird communities at survey points located at greater ecological scales from the sagebrush bird community changed least and will require more significant impact to achieve changes. Sagebrush bird communities were established at only two survey points, which were adjacent to a larger sagebrush landscape and following almost complete juniper removal by mechanical treatment. Our results indicate that management treatments that leave residual woodland cover and are not adjacent to extensive sagebrush stands are unlikely to establish sagebrush birds.     

Soil Resources Influence Vegetation and Response to Fire and Fire-Surrogate Treatments in Sagebrush-Steppe Ecosystems

Current paradigm suggests that spatial and temporal competition for resources limit an exotic invader, cheatgrass (Bromus tectorum L.), which once established, alters fire regimes and can result in annual grass dominance in sagebrush steppe. Prescribed fire and fire surrogate treatments (mowing, tebuthiuron, and imazapic) are used to reduce woody fuels and increase resistance to exotic annuals, but may alter resource availability and inadvertently favor invasive species. We used four study sites within the Sagebrush Steppe Treatment Evaluation Project (SageSTEP) to evaluate 1) how vegetation and soil resources were affected by treatment, and 2) how soil resources influenced native herbaceous perennial and exotic annual grass cover before and following treatment. Treatments increased resin exchangeable NH₄⁺, NO₃^-, H₂PO₄^-, and K⁺, with the largest increases caused by prescribed fire and prolonged by application of imazapic. Burning with imazapic application also increased the number of wet growing degree days. Tebuthiuron and imazapic reduced exotic annual grass cover, but imazapic also reduced herbaceous perennial cover when used with prescribed fire. Native perennial herbaceous species cover was higher where mean annual precipitation and soil water resources were relatively high. Exotic annual grass cover was higher where resin exchangeable H₂PO₄^- was high and gaps between perennial plants were large. Prescribed fire, mowing, and tebuthiuron were successful at increasing perennial herbaceous cover, but the results were often ephemeral and inconsistent among sites. Locations with sandy soil, low mean annual precipitation, or low soil water holding capacity were more likely to experience increased exotic annual grass cover after treatment, and treatments that result in slow release of resources are needed on these sites. This is one of few studies that correlate abiotic variables to native and exotic species cover across a broad geographic setting, and that demonstrates how soil resources potentially influence the outcome of management treatments.     

Vegetation Response to Juniper Reduction and Grazing Exclusion in Sagebrush-Steppe Habitat in Eastern Oregon

Western juniper expansion is one of the largest threats to conserving sagebrush steppe ecosystems in the northwestern United States. Juniper expansion has degraded the sagebrush steppe by altering fire regimes and outcompeting shrubs and herbaceous vegetation for limited resources. We characterized the effect of juniper removal in a severely degraded sagebrush steppe habitat for 3 yr following juniper cutting. In addition, we measured the effect of low-intensity seasonal grazing on plant community recovery through cattle exclusion treatments. We monitored plant community composition (exotic annual grasses, preferred grasses, preferred forbs, and shrubs); fuel loads; and juniper recruitment in a factorial design of juniper removal and grazing exclusion. We found that although there were significant differences between cut and uncut juniper treatments, there were no consistent trends across all 3 yr. Our results suggest that other factors, such as timing of precipitation, may also have strong short-term effects on plant community composition. We detected no significant grazing effects during the study period, suggesting the current grazing regime is appropriate for the area. The cutting of juniper increased total fuel loads and herbaceous fuel loads. Compared with open interspace, a twofold increase in juniper seedlings and saplings was detected beneath juniper piles, which will act as sources for future juniper encroachment.     

Short-Term Butterfly Response to Sagebrush Steppe Restoration Treatments

As part of the Sagebrush Steppe Treatment Evaluation Project (SageSTEP), butterflies were surveyed pretreatment and up to 4 yr posttreatment at 16 widely distributed sagebrush steppe sites in the interior West. Butterfly populations and communities were analyzed in response to treatments (prescribed fire, mechanical, herbicide) designed to restore sagebrush steppe lands encroached by piñon-juniper woodlands (Pinus, Juniperus spp.) and invaded by cheatgrass (Bromus tectorum). Butterflies exhibited distinct regional patterns of species composition, with communities showing marked variability among sites. Some variation was explained by the plant community, with Mantel's test indicating that ordinations of butterfly and plant communities were closely similar for both woodland sites and lower-elevation treeless (sage-cheat) sites. At woodland sites, responses to stand replacement prescribed fire, clear-cutting, and tree mastication treatments applied to 10–20-ha plots were subtle: 1) no changes were observed in community structure; 2) Melissa blues (Plebejus melissa) and sulfurs (Colias spp.) increased in abundance after either burning or mechanical treatments, possibly due to increase in larval and nectar food resource, respectively; and 3) the juniper hairstreak (Callophrys gryneus) declined at sites at which it was initially present, probably due to removal of its larval food source. At sage-cheat sites, after prescribed fire was applied to 25–75-ha plots, we observed 1) an increase in species richness and abundance at most sites, possibly due to increased nectar resources for adults, and 2) an increase in the abundance of skippers (Hesperiidae) and small white butterflies. Linkages between woody species removal, the release of herbaceous vegetation, and butterfly response to treatments demonstrate the importance of monitoring an array of ecosystem components in order to document the extent to which management practices cause unintended consequences.     

Short-term Effects of Burning Wyoming Big Sagebrush Steppe in Southeast Oregon

Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis [Beetle & A. Young] S.L. Welsh) plant communities of the Intermountain West have been greatly reduced from their historic range as a result of wildfire, agronomic practices, brush control treatments, and weed invasions. The impact of prescribed fall burning Wyoming big sagebrush has not been well quantified. Treatments were sagebrush removed with burning (burned) and sagebrush present (control). Treatments were applied to 0.4-ha plots at 6 sites. Biomass production, vegetation cover, perennial herbaceous vegetation diversity, soil water content, soil inorganic nitrogen (NO-3, NH+4), total soil nitrogen (N), total soil carbon (C), and soil organic matter (OM) were compared between treatments in the first 2 years postburn. In 2003 and 2004, total (shrub and herbaceous) aboveground annual biomass production was 2.3 and 1.2 times greater, respectively, in the control compared to the burned treatment. In the upper 15 cm of the soil profile, inorganic N concentrations were greater in the burned than control treatment, while soil water, at least in the spring, was greater in the control than burned treatment. Regardless, greater herbaceous aboveground annual production and cover in the burned treatment indicated that resources were more available to herbaceous vegetation in the burned than the control treatment. Exotic annual grasses did not increase with the burn treatment. Our results suggest in some instances that late seral Wyoming big sagebrush plant communities can be prescribed fall burned to increase livestock forage or alter wildlife habitat without exotic annual grass invasion in the first 2 years postburn. However, long-term evaluation at multiple sites across a larger area is needed to better quantify the effects of prescribed fall burning on these communities. Thus, caution is advised because of the value of Wyoming big sagebrush plant communities to wildlife and the threat of invasive plants.     

Herbaceous Biomass Response to Prescribed Fire in Juniper-Encroached Sagebrush Steppe

Western juniper (Juniperus occidentalis Hook.) has expanded into sagebrush steppe plant communities the past 130 ? 150 yr in the northern Great Basin. The increase in juniper reduces herbage and browse for livestock and big game. Information on herbaceous yield response to juniper control with fire is limited. We measured herbaceous standing crop and yield by life form in two mountain big sagebrush communities (MTN1, MTN2) and a Wyoming/basin big sagebrush (WYOBAS) community for 6 yrs following prescribed fire treatments to control western juniper. MTN1 and WYOBAS communities were early-successional (phase 1) and MTN2 communities were midsuccessional (phase 2) woodlands before treatment. Prescribed fires killed all juniper and sagebrush in the burn units. Total herbaceous and perennial bunchgrass yields increased 2 to 2.5-fold in burn treatments compared with unburned controls. Total perennial forb yield did not differ between burns and controls in all three plant communities. However, tall perennial forb yield was 1.6- and 2.5-fold greater in the WYOBAS and MTN2 burned sites than controls. Mat-forming perennial forb yields declined by 80 ? 90% after burning compared with controls. Cheatgrass yield increased in burned WYOBAS and MTN2 communities and at the end of the study represented 10% and 22% of total yield, respectively. Annual forbs increased with burning and were mainly composed of native species in MTN1 and MTN2 communities and non-natives in WYOBAS communities. Forage availability for livestock and wild ungulates more than doubled after burning. The additional forage provided on burned areas affords managers greater flexibility to rest and treat additional sagebrush steppe where juniper is expanding, as well as rest or defer critical seasonal habitat for wildlife.     

Region-Wide Ecological Responses of Arid Wyoming Big Sagebrush Communities to Fuel Treatments

If arid sagebrush ecosystems lack resilience to disturbances or resistance to annual invasives, then alternative successional states dominated by annual invasives, especially cheatgrass (Bromus tectorum L.), are likely after fuel treatments. We identified six Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle & Young) locations (152–381 mm precipitation) that we believed had sufficient resilience and resistance for recovery. We examined impacts of woody fuel reduction (fire, mowing, the herbicide tebuthiuron, and untreated controls, all with and without the herbicide imazapic) on short-term dominance of plant groups and on important land health parameters with the use of analysis of variance (ANOVA). Fire and mowing reduced woody biomass at least 85% for 3 yr, but herbaceous fuels were reduced only by fire (72%) and only in the first year. Herbaceous fuels produced at least 36% more biomass with mowing than untreated areas during posttreatment years. Imazapic only reduced herbaceous biomass after fires (34%). Tebuthiuron never affected herbaceous biomass. Perennial tall grass cover was reduced by 59% relative to untreated controls in the first year after fire, but it recovered by the second year. Cover of all remaining herbaceous groups was not changed by woody fuel treatments. Only imazapic reduced significantly herbaceous cover. Cheatgrass cover was reduced at least 63% with imazapic for 3 yr. Imazapic reduced annual forb cover by at least 45%, and unexpectedly, perennial grass cover by 49% (combination of tall grasses and Sandberg bluegrass [Poa secunda J. Presl.]). Fire reduced density of Sandberg bluegrass between 40% and 58%, decreased lichen and moss cover between 69% and 80%, and consequently increased bare ground between 21% and 34% and proportion of gaps among perennial plants &spigt; 2 m (at least 28% during the 3 yr). Fire, mowing, and imazapic may be effective in reducing fuels for 3 yr, but each has potentially undesirable consequences on plant communities.     

Managing High-Elevation Sagebrush Steppe: Do Conifer Encroachment and Prescribed Fire Affect Habitat for Pygmy Rabbits?

Both fire and conifer encroachment can markedly alter big sagebrush communities and thus habitat quality and quantity for wildlife. We investigated how conifer encroachment and spring prescribed burning affected forage and cover resources for a sagebrush specialist, the pygmy rabbit. We studied these dynamics at spring prescribed burns in southwestern Montana and eastern Idaho during the summer of 2011. Within each spring prescribed burn, we established plots that described the habitat conditions for pygmy rabbits (forage plant biomass and habitat components that influence predation risk) in areas that were burned, adjacent areas of conifer encroachment, and areas that were neither burned nor encroached. We analyzed the data for significant differences in habitat conditions between the paired reference and encroachment plots and modeled when the burned areas would approximate the conditions on the paired reference plots. Biomass of forage plants and habitat components that reduce predation risk differed between undisturbed reference plots and areas that were either burned or encroached with > 30% conifer canopy. Our models estimated that 13–27 yr were required for a spring prescribed burn to provide levels of cover and forage resources similar to sagebrush steppe reference plots. We documented that vegetation composition was associated with the plot designations (burn, reference, or conifer encroachment), but not with other abiotic factors, such as soil texture, aspect, or study site; this suggested that the documented differences in habitat were related to the treatments, rather than being site-specific characteristics. The information from this study can contribute to habitat management plans for high-elevation mountain big sagebrush sites where conifer encroachment is altering habitat for sagebrush-dependent wildlife species.     

Resilience and Resistance of Sagebrush Ecosystems: Implications for State and Transition Models and Management Treatments

In sagebrush ecosystems invasion of annual exotics and expansion of piñon (Pinus monophylla Torr. and Frem.) and juniper (Juniperus occidentalis Hook., J. osteosperma [Torr.] Little) are altering fire regimes and resulting in large-scale ecosystem transformations. Management treatments aim to increase resilience to disturbance and enhance resistance to invasive species by reducing woody fuels and increasing native perennial herbaceous species. We used Sagebrush Steppe Treatment Evaluation Project data to test predictions on effects of fire vs. mechanical treatments on resilience and resistance for three site types exhibiting cheatgrass (Bromus tectorum L.) invasion and/or piñon and juniper expansion: 1) warm and dry Wyoming big sagebrush (WY shrub); 2) warm and moist Wyoming big sagebrush (WY PJ); and 3) cool and moist mountain big sagebrush (Mtn PJ). Warm and dry (mesic/aridic) WY shrub sites had lower resilience to fire (less shrub recruitment and native perennial herbaceous response) than cooler and moister (frigid/xeric) WY PJ and Mtn PJ sites. Warm (mesic) WY Shrub and WY PJ sites had lower resistance to annual exotics than cool (frigid to cool frigid) Mtn PJ sites. In WY shrub, fire and sagebrush mowing had similar effects on shrub cover and, thus, on perennial native herbaceous and exotic cover. In WY PJ and Mtn PJ, effects were greater for fire than cut-and-leave treatments and with high tree cover in general because most woody vegetation was removed increasing resources for other functional groups. In WY shrub, about 20% pretreatment perennial native herb cover was necessary to prevent increases in exotics after treatment. Cooler and moister WY PJ and especially Mtn PJ were more resistant to annual exotics, but perennial native herb cover was still required for site recovery. We use our results to develop state and transition models that illustrate how resilience and resistance influence vegetation dynamics and management options.     

Sage Grouse Groceries: Forb Response to Piñon-Juniper Treatments

Juniper and piñon coniferous woodlands have increased 2- to 10-fold in nine ecoregions spanning the Intermountain Region of the western United States. Control of piñon-juniper woodlands by mechanical treatments and prescribed fire are commonly applied to recover sagebrush steppe rangelands. Recently, the Sage Grouse Initiative has made conifer removal a major part of its program to reestablish sagebrush habitat for sage grouse (Centrocercus urophasianus) and other species. We analyzed data sets from previous and ongoing studies across the Great Basin characterizing cover response of perennial and annual forbs that are consumed by sage grouse to mechanical, prescribed fire, and low-disturbance fuel reduction treatments. There were 11 sites in western juniper (Juniperus occidentalis Hook.) woodlands, 3 sites in singleleaf piñon (Pinus monophylla Torr. & Frém.) and Utah juniper (Juniperus osteosperma [Torr.] Little), 2 sites in Utah juniper, and 2 sites in Utah juniper and Colorado piñon (Pinus edulis Engelm). Western juniper sites were located in mountain big sagebrush (A. tridentata ssp. vaseyana) steppe associations, and the other woodlands were located in Wyoming big sagebrush (A. tridentata ssp. wyomingensis) associations. Site potential appears to be a major determinant for increasing perennial forbs consumed by sage grouse following conifer control. The cover response of perennial forbs, whether increasing (1.5- to 6-fold) or exhibiting no change, was similar regardless of conifer treatment. Annual forbs favored by sage grouse benefitted most from prescribed fire treatments with smaller increases following mechanical and fuel reduction treatments. Though forb abundance may not consistently be enhanced, mechanical and fuel reduction conifer treatments remain good preventative measures, especially in phase 1 and 2 woodlands, which, at minimum, maintain forbs on the landscape. In addition, these two conifer control measures, in the short term, are superior to prescribed fire for maintaining the essential habitat characteristics of sagebrush steppe for sage grouse.     

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.     

Cattle Grazing and Vegetation Succession on Burned Sagebrush Steppe

There is limited information about the effects of cattle grazing to longer-term plant community composition and herbage production following fire in sagebrush steppe. This study evaluated vegetation response to cattle grazing over 7 yr (2007–2013) on burned Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & Young] Welsh) steppe in eastern Oregon. Treatments, replicated four times and applied in a randomized complete block design, included no grazing on burned (nonuse) and unburned (control) sagebrush steppe; and cattle grazing at low (low), moderate (moderate), and high (high) stocking on burned sagebrush steppe. Vegetation dynamics were evaluated by quantifying herbaceous (canopy and basal cover, density, production, reproductive shoot weight) and shrub (canopy cover, density) response variables. Aside from basal cover, herbaceous canopy cover, production, and reproduction were not different among low, moderate, and nonuse treatments. Perennial bunchgrass basal cover was about 25% lower in the low and moderate treatments than the nonuse. Production, reproductive stem weight, and perennial grass basal cover were greater in the low, moderate, and nonuse treatments than the control. The high treatment had lower perennial bunchgrass cover (canopy and basal) and production than other grazed and nonuse treatments. Bunchgrass density remained unchanged in the high treatment, not differing from other treatments, and reproductive effort was comparable to the other treatments, indicating these areas are potentially recoverable by reducing stocking. Cover and production of Bromus tectorum L. (cheatgrass) did not differ among the grazed and nonuse treatments, though all were greater than the control. Cover and density of A.t. spp. wyomingensis did not differ among the burned grazed and nonuse treatments and were less than the control. We concluded that light to moderate stocking rates are compatible to sustainable grazing of burned sagebrush steppe rangelands.     

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.     

Disturbance Type and Sagebrush Community Type Affect Plant Community Structure After Shrub Reduction

Treatments to reduce shrub cover are commonly implemented with the objective of shifting community structure away from shrub dominance and toward shrub and perennial grass codominance. In sagebrush (Artemisia L.) ecosystems, shrub reduction treatments have had variable effects on target shrubs, herbaceous perennials, and non-native annual plants. The factors mediating this variability are not well understood. We used long-term data from Utah’s Watershed Restoration Initiative project to assess short-term (1 − 4 yr post-treatment) and long-term (5 − 12 yr post-treatment) responses of sagebrush plant communities to five shrub reduction treatments at 94 sites that span a range of abiotic conditions and sagebrush community types. Treatments were pipe harrow with one or two passes, aerator, and fire with and without postfire seeding. We analyzed effect sizes (log of response ratio) to assess responses of sagebrush, perennial and annual grasses and forbs, and ground cover to treatments. Most treatments successfully reduced sagebrush cover over the short and long term. All treatments increased long-term perennial grass cover in Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle & Young) communities, but in mountain big sagebrush (ssp. vaseyana [Rydb.] Beetle) communities, perennial grasses increased only when seeded after fire. In both sagebrush communities, treatments generally resulted in short-term, but not long-term, increases in perennial forb cover. Annual grasses (largely invasive cheatgrass, Bromus tectorum L.) increased in all treatments on sites dominated by mountain big sagebrush but stayed constant or decreased on sites dominated by Wyoming big sagebrush. This result was unexpected because sites dominated by Wyoming big sagebrush are typically thought to be less resilient to disturbance and less resistant to invasion than sites dominated by mountain big sagebrush. Together, these results indicate some of the benefits, risks, and contingent outcomes of sagebrush reduction treatments that should be considered carefully in any future decisions about applying such treatments.     

Mowing Wyoming Big Sagebrush Communities With Degraded Herbaceous Understories: Has a Threshold Been Crossed?

Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis &lsqb;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.     

Longer-Term Evaluation of Sagebrush Restoration After Juniper Control and Herbaceous Vegetation Trade-offs

Degradation of shrublands around the world from altered fire regimes, overutilization, and anthropogenic disturbance has resulted in a widespread need for shrub restoration. In western North America, reestablishment of mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) is needed to restore ecosystem services and function. Western juniper (Juniperus occidentalis ssp. occidentalis Hook) encroachment is a serious threat to mountain big sagebrush communities in the northern Great Basin and Columbia Plateau. Juniper trees can be controlled with fire; however, sagebrush recovery may be slow, especially if encroachment largely eliminated sagebrush before juniper control. Short-term studies have suggested that seeding mountain big sagebrush after juniper control may accelerate sagebrush recovery. Longer-term information is lacking on how sagebrush recovery progresses and if there are trade-offs with herbaceous vegetation. We compared seeding and not seeding mountain big sagebrush after juniper control (partial cutting followed with burning) in fully developed juniper woodlands (i.e., sagebrush had been largely excluded) at five sites, 7 and 8 yr after seeding. Sagebrush cover averaged ~ 30% in sagebrush seeded plots compared with ~ 1% in unseeded plots 8 yr after seeding, thus suggesting that sagebrush recovery may be slow without seeding after juniper control. Total herbaceous vegetation, perennial grass, and annual forb cover was less where sagebrush was seeded. Thus, there is a trade-off with herbaceous vegetation with seeding sagebrush. Our results suggest that seeding sagebrush after juniper control can accelerate the recovery of sagebrush habitat characteristics, which is important for sagebrush-associated wildlife. We suggest land manager and restoration practitioners consider seeding sagebrush and possibly other shrubs after controlling encroaching trees where residual shrubs are lacking after control.     

Understory Cover Responses to Piñon–Juniper Treatments Across Tree Dominance Gradients in the Great Basin

Piñon (Pinus spp.) and juniper (Juniperus spp.) trees are reduced to restore native vegetation and avoid severe fires where they have expanded into sagebrush (Artemisia tridentata Nutt.) communities. However, what phase of tree infilling should treatments target to retain desirable understory cover and avoid weed dominance? Prescribed fire and tree felling were applied to 8–20-ha treatment plots at 11 sites across the Great Basin with a tree-shredding treatment also applied to four Utah sites. Treatments were applied across a tree infilling gradient as quantified by a covariate tree dominance index (TDI = tree cover/&lsqb;tree + shrub + tall perennial grass cover]). Mixed model analysis of covariance indicated that treatment × covariate interactions were significant (P &spilt; 0.05) for most vegetation functional groups 3 yr after treatment. Shrub cover was most reduced with fire at any TDI or by mechanical treatment after infilling resulted in over 50% shrub cover loss (TDI &spigt; 0.4). Fire increased cheatgrass (Bromus tectorum L.) cover by an average of 4.2% for all values of TDI. Cutting or shredding trees generally produced similar responses and increased total perennial herbaceous and cheatgrass cover by an average of 10.2% and 3.8%, at TDIs ≥ 0.35 and ≥ 0.45. Cheatgrass cover estimated across the region was &spilt; 6% after treatment, but two warmer sites had high cheatgrass cover before (19.2% and 27.2%) and after tree reduction (26.6% and 50.4%). Fuel control treatments are viable management options for increasing understory cover across a range of sites and tree cover gradients, but should be accompanied by revegetation on warmer sites with depleted understories where cheatgrass is highly adapted. Shrub and perennial herbaceous cover can be maintained by mechanically treating at lower TDI. Perennial herbaceous cover is key for avoiding biotic and abiotic thresholds in this system through resisting weed dominance and erosion.     

Effects of Fire Exclusion on Previously Fire-Managed Semiarid Savanna Ecosystem

Long-term (> 100 yr) fire exclusion is associated with numerous ecological consequences in grasslands and savannas, including transitions into shrub- or tree-dominated systems. Several studies have reported differences in woody vegetation after multiple fires among burned and unburned rangelands, but none have reported the impacts of fire exclusion after a period of fire management. We evaluated effects of fire exclusion on herbaceous and woody canopy cover and herbaceous biomass in semiarid savanna of southwest Texas in pastures with known burn histories. Pastures were burned in summer and winter in 1994, 2000, and 2006, followed by 11 yr of fire exclusion. Between 2006 and 2017, woody subcanopy increased (5–21%) in all treatments while overstory canopy remained unchanged. Herbaceous cover decreased (5–18%) in all treatments but remained higher in burned treatments. From 2006 to 2017, herbaceous biomass declined in all treatments by > 650 kg·ha⁻¹ and was not statistically different among treatments. These trends support other research demonstrating the importance of historical mean fire return interval in maintaining grasslands and savannas.     

Vegetation,Hydrologic, and Erosion Responses of Sagebrush Steppe 9 Yr Following Mechanical Tree Removal

Land managers across the western United States are faced with selecting and applying tree-removal treatments on pinyon (Pinus spp.) and juniper (Juniperus spp.) woodland-encroached sagebrush (Artemisia spp.) rangelands, but current understanding of long-term vegetation and hydrological responses of sagebrush sites to tree removal is inadequate for guiding management. This study applied a suite of vegetation and soil measures (0.5 ? 990 m²), small-plot rainfall simulations (0.5 m²), and overland flow experiments (9 m²) to quantify the effects of mechanical tree removal (tree cutting and mastication) on vegetation, runoff, and erosion at two mid- to late-succession woodland-encroached sagebrush sites in the Great Basin, United States, 9 yr after treatment. Low amounts of hillslope-scale shrub (3 ? 15%) and grass (7 ? 12%) canopy cover and extensive intercanopy (area between tree canopies) bare ground (69 ? 88% bare, 75% of area) in untreated areas at both sites facilitated high levels of runoff and sediment from high-intensity (102 mm ? h^? 1, 45 min) rainfall simulations in interspaces (~ 45 mm runoff, 59 ? 381 g ? m^? 2 sediment) between trees and shrubs and from concentrated overland flow experiments (15, 30, and 45 L ? min^? 1, 8 min each) in the intercanopy (371 ? 501 L runoff, 2 342 ? 3 015 g sediment). Tree cutting increased hillslope-scale density of sagebrush by 5% and perennial grass cover by twofold at one site while tree cutting and mastication increased hillslope-scale sagebrush density by 36% and 16%, respectively, and perennial grass cover by threefold at a second more-degraded (initially more sparsely vegetated) site over nine growing seasons. Cover of cheatgrass (Bromus tectorum L.) was < 1% at the sites pretreatment and 1 ? 7% 9 yr after treatment. Bare ground remained high across both sites 9 yr after tree removal and was reduced by treatments solely at the more degraded site. Increases in hillslope-scale vegetation following tree removal had limited impact on runoff and erosion for rainfall simulations and concentrated flow experiments at both sites due to persistent high bare ground. The one exception was reduced runoff and erosion within the cut treatments for intercanopy plots with cut-downed-trees. The cut-downed-trees provided ample litter cover and tree debris at the ground surface to reduce the amount and erosive energy of concentrated overland flow. Trends in hillslope-scale vegetation responses to tree removal in this study demonstrate the effectiveness of mechanical treatments to reestablish sagebrush steppe vegetation without increasing cheatgrass for mid- to late-succession woodland-encroached sites along the warm-dry to cool-moist soil temperature ? moisture threshold in the Great Basin. Our results indicate improved hydrologic function through sagebrush steppe vegetation recruitment after mechanical tree removal on mid- to late-succession woodlands can require more than 9 yr. We anticipate intercanopy runoff and erosion rates will decrease over time at both sites as shrub and grass cover continue to increase, but follow-up tree removal will be needed to prevent pinyon and juniper recolonization. The low intercanopy runoff and erosion measured underneath isolated cut-downed-trees in this study clearly demonstrate that tree debris following mechanical treatments can effectively limit microsite-scale runoff and erosion over time where tree debris settles in good contact with the soil surface.