Exotic Forbs Research Articles

Vegetation, fuels, and fire-behavior responses to linear fuel-break treatments in and around burned sagebrush steppe: are we breaking the grass-fire cycle?

BackgroundLinear fuel breaks are being implemented to moderate fire behavior and improve wildfire containment in semiarid landscapes such as the sagebrush steppe of North America, where extensive losses in perennial vegetation and ecosystem functioning are resulting from invasion by exotic annual grasses (EAGs) that foster large and recurrent wildfires. However, fuel-break construction can also pose EAG invasion risks, which must be weighed against the intended fire-moderation benefits of the treatments. We investigated how shrub reductions (mowing, cutting), pre-emergent EAG-herbicides, and/or drill seedings of fire-resistant perennial bunchgrasses (PBGs) recently applied to create a large fuel-break system affected native and exotic plant abundances and their associated fuel loading and predicted fire behavior.ResultsIn heavily EAG-invaded areas, herbicides reduced EAG and total herbaceous cover without affecting PBGs for 2–3 years and reduced predicted fire behavior for 1 year (from the Fuel Characteristic Classification System). However, surviving post-herbicide EAG cover was still > 30%, which was sufficient fuel to exceed the conventional 1.2-m-flame length (FL) threshold for attempting wildfire suppression with hand tools. In less invaded shrubland, shrub reduction treatments largely reduced shrub cover and height by ~ half without increasing EAGs, but then redistributed the wood to ground level and increased total herbaceous cover. Herbicides and/or drill seeding after shrub reductions did not affect EAG cover, although drill seedings increased PBG cover and exotic forbs (e.g., Russian thistle). Fire behavior was predicted to be moderated in only one of the many yearly observations of the various shrub-reduction treatment combinations. Over all treatments and years, FLs were predicted to exceed 1.2 m in 13% of simulations under average (11 km h−1) or high (47 km h−1) wind speed conditions and exceed the 3.4-m threshold for uncontrollable fire in 11% of simulations under high-wind speeds only.ConclusionsPredicted fire-moderation benefits over the first 4 years of fuel break implementation were modest and variable, but, generally, increases in EAGs and their associated fire risks were not observed. Nonetheless, ancillary evidence from shrublands would suggest that treatment-induced shifts from shrub to herbaceous fuel dominance are expected to improve conditions for active fire suppression in ways not readily represented in available fire models.

Prescribed fire increases plant-pollinator network robustness to losses of rare native forbs.

Restoration efforts often focus on changing the composition and structure of invaded plant communities, with two implicit assumptions: (1) functional interactions with species of other trophic levels, such as pollinators, will reassemble automatically when native plant diversity is restored and (2) restored communities will be more resilient to future stressors. However, the impact of restoration activities on pollinator richness, plant-pollinator interaction network structure, and network robustness is incompletely understood. Leveraging a restoration chronosequence in Pacific Northwest prairies, we examined the effects of restoration-focused prescribed fire and native forb replanting on floral resources, pollinator visitation, and plant-pollinator network structure. We then simulated the effects of plant species loss/removal scenarios on secondary extinction cascades in the networks. Specifically, we explored three management-relevant plant loss scenarios (removal of an abundant exotic forb, removal of an abundant forb designated a noxious weed, and loss of the rarest native forb) and compared them to control scenarios. Pyrodiversity and proportion of area recently burned increased the abundance and diversity of floral resources, with concomitant increases in pollinator visitation and diversity. Pyrodiversity also decreased network connectance and nestedness, increased modularity, and buffered networks against secondary extinction cascades. Rare forbs contributed disproportionately to network robustness in less restored prairies, while removal of typical "problem" plants like exotic and noxious species had relatively small impacts on network robustness, particularly in prairies with a long history of restoration activities. Restoration actions aimed mainly at improving the diversity and abundance of pollinator-provisioning plants may also produce plant-pollinator networks with increased resilience to plant species losses.

Winner and losers: examining biotic interactions in forbs and grasses in response to changes in water and temperature in a semi-arid grassland.

Warming and changing water amount can alter the outcome of biotic interactions in native and exotic plants between facilitation and competition. Exotic plants may adapt better to changing environmental conditions, such that they may compete better than native plants. We conducted competition trials for four plant species, two exotic forbs (Centaurea stoebe and Linaria vulgaris) and two grasses (exotic Poa compressa and native Pseudoroegneria spicata), commonly found in Southern interior British Columbia. We compared the effects of warming and changing water on target plant shoot and root biomass, and on pair-wise competitive interactions among all four species. We quantified interactions using the Relative Interaction Intensity index, which has values from -1 (complete competition) to +1 (complete facilitation). C. stoebe biomass was highest under low water and no competition. Facilitation of C. stoebe was found under high water and low temperatures but shifted to competition under low water and/or warming. Competition in L. vulgaris decreased due to reduced water and increased due to warming. Grasses were less competitively suppressed by warming but more competitively suppressed by reduced water input. The response of exotic plants to climate change can differ by plant species, moving in opposite directions for both forbs, but grasses appear to respond similarly. This has consequences for grasses and exotic plants in semi-arid grasslands.

Upland prairie adaptive management staged‐scale restoration practices for native plant and endangered butterfly reintroduction

Abstract The present practice insight derives from land manager requests to document current on‐site activity and provides a management planning reference for restoration on Violet Prairie. Start‐up restoration initiates from trial‐and‐error adaptive management practices in the Puget Sound region of western Washington, USA. Treatments used focus on the implementation of staged‐scale restoration. Preparation intends to meet reintroduction goals of establishing a native plant community that could potentially support the threatened endemic Castilleja levisecta (golden paintbrush). Reintroduction of the associated native plant community provides habitat for endangered Euphydryas editha taylori (Taylor's checkerspot butterfly). Known conventional agricultural use coupled to fire suppression since the 1800s altered regional prairie lands to an unfavourable state for native plant species. Local native prairie soil types were favoured for growing conventional grasses and exotic forb species common to grazing pastures. Land abandonment and degradation has lengthened the time of disturbance and complicated restoring to a generalized reference point prior to settlement. Persistent exotic species, encroaching housing development, coniferous forest and recent wildfire complicate converting back to native prairie. Threatened and endangered species and their habitat are targeted in a trial‐and‐error process of staged‐scale adaptive management within the goal of whole ecosystem and connectivity restoration. Land managers focus on exotics removal and intensive native reseeding while restoring the use of prescribed burning as a maintenance tool. Embedded monitoring and observation advises where future practices need to be adapted by focusing on treatments and outcomes. Past land use practices replaced native soil seed banks with exotic seed banks that further distort reference proxies. Unknowns interrupt the current implementation additionally to soil conversion issues, while short‐term adaptive management methods initiate conversion back to native prairie. Species reintroduction choices to develop community structure are complicated by the fact that historical reference point species may be missing altogether from existing native communities. An unanswered outcome of the restoration process is determining which set of treatments best prepares soil for the desired native plant community.

Plant community context controls short‐ versus medium‐term effects of pre‐emergent herbicides on target and non‐target species after fire

AbstractQuestionsSelective herbicide application is a common restoration strategy to control exotic invaders that interfere with native plant recovery after wildfire. Whether spraying with pre‐emergent or bio‐herbicides releases native plants from competition with exotics (“spray‐and‐release” strategy) and makes communities resistant to reinvasion by exotic annual grasses (e.g. cheatgrass, medusahead), without risks to non‐target native plants or secondary invasion, is a major question for land managers of semiarid plant communities.LocationSagebrush steppe of southwest Idaho, USA.MethodsWe applied chemical herbicides (imazapic, rimsulfuron) and weed‐suppressive bacteria (Pseudomonas fluorescens strains MB906 and D7) to three sagebrush steppe communities after fire. We measured plant cover prior to burning and for four years (five for exotic annual grasses) post treatment.ResultsBoth chemical herbicides significantly reduced exotic annual grass cover in all communities in the first post‐spraying year, but rimsulfuron plots were re‐invaded after 1–2 years, while imazapic plots continued to resist reinvasion four and even five years post spraying, well after the herbicide should have degraded. We did not detect any increase in native perennial grass cover with either herbicide, and herbicides had both positive and negative effects on individual bunchgrass basal diameter, depending on species and plant community. Rimsulfuron was more damaging than imazapic to shallow‐rooted perennial bunchgrasses. Moss and lichen cover, key components of soil integrity, increased with chemical herbicide treatments in some communities. Both herbicides increased secondary invaders (exotic forbs or grasses), which varied by plant community and herbicide. Weed‐suppressive bacteria treatments had no significant effects on cover of any functional group.ConclusionsWhile short‐term effects of chemical herbicides that target exotic annual grasses were relatively consistent and predictable, longer‐term effects were specific to the herbicide and plant community. The “spray‐and‐release” strategy may confer resistance to re‐invasion by exotic annual grasses if herbicides prevent re‐invasion for an extended period.

Observations on the range expansion of Mecinus janthiniformis Toševski & Caldara, 2011 and Rhinusa neta (Germar, 1821) (Coleoptera: Curculionidae) into California

Dalmatian toadflax, Linaria dalmatica (L.) Mill., and yellow toadflax, Linaria vulgaris Mill. (Plantaginaceae), are exotic forbs that have become widespread in North America, including California. Both species have accumulated several exotic insects from accidental and intentional introductions. Until recently, Mecinus janthiniformis Toševski & Caldara, 2011 was known to occur at only one location in southern California. Recent surveys of L. dalmatica in northern California recovered M. janthiniformis and a second weevil, Rhinusa neta (Germar, 1821), the latter a new California record. From 2010–2015, M. janthiniformis was recovered at 24 of 27 sites in Lassen, Modoc, Plumas, Siskiyou, and Trinity Counties. After 2014, four locations in Trinity County and one in Sierra County were monitored annually through 2020, but no M. janthiniformis have been recovered to date suggesting this species has not extended its range since 2014. In 2018, R. neta was discovered in L. dalmatica seed capsules in Trinity and Sierra Counties. Later surveys found R. neta infesting L. dalmatica at five locations in four counties and Sairocarpus virga (A. Gray) D. A. Sutton (= Antirrhinum virga A. Gray) (Plantaginaceae), a native species, at one location in Colusa County. The intensity of attack of R. neta on L. dalmatica ranged from 9–70% of seed capsules infested. Being found 300 km south of the Oregon border suggests that R. neta spreads more readily than M. janthiniformis, which has only spread 190 km south of the Oregon border but no further since 2014. Repeated annual sampling at uninfested sites found R. neta to have spread 42 km in one year, an unusually high dispersal rate for exotic Coleoptera.

Positive interactions between an exotic invader and moss biocrusts vary across life stage and correspond with the effect of water pulses on soil nitrogen

Abstract The size and frequency of resource pulses can affect plant interactions and increase the abundance of invasive species relative to native species. We examined resource pulses generated during the desiccation and rehydration of communities of native biological soil crust (biocrust)‐forming mosses, in the context of positive associations between biocrusts and the invasive forb, Centaurea stoebe. We surveyed Centaurea and biocrust cover and evaluated how interactions among Centaurea, biocrusts and water pulses influenced plant biomass and soil nitrogen in a field experiment. Centaurea seedling and biocrust interactions were also compared in a greenhouse experiment to evaluate differences related to life stage. In field surveys, Centaurea and biocrusts were positively associated. Across water pulse treatments, biocrust biomass decreased when Centaurea was removed, indicating that Centaurea facilitated biocrusts. Biocrusts did not affect adult Centaurea in the field, but Centaurea seedling biomass was greater when grown with biocrusts in the greenhouse. Water pulses did not affect plant biomass, but interactions between Centaurea and biocrusts corresponded with variation in the effect of water pulses on soil nitrogen which were not evident when Centaurea or biocrusts were grown alone. Twenty‐four hours after large water pulses were added, soil was nine times higher in plots where biocrusts and Centaurea co‐occurred compared with small water pulse plots. In these same plots, soil tended to be lower at the end of the experiment. These results highlight positive interactions between an invasive exotic forb and native moss biocrust. Water pulses influenced soil nitrogen availability when both plants co‐occurred, but did not affect plant biomass, suggesting that resource pulses and species interactions can interact to affect ecosystem processes. A free Plain Language Summary can be found within the Supporting Information of this article.

Landscape Conservation Forecasting for Data-Poor at-Risk Species on Western Public Lands, United States

Managing vast federal public lands governed by multiple land use policies creates challenges when demographic data on at-risk species are lacking. The U.S. Bureau of Land Management Cedar City Field Office used this project in the Black Mountains (Utah) to inform vegetation management supporting at-risk greater sage-grouse and Utah prairie dog planning. Ecological systems were mapped from satellite remote sensing imagery and used to model species habitat suitability under two levels of management activity (custodial, preferred) and climate scenarios for historic and two global circulation models. Spatial state-and-transition models of ecological systems were simulated for all six scenarios up to 60 years while coupled with expert-developed habitat suitability indices. All ecological systems are at least moderately departed from reference conditions in 2012, whereas habitat suitability was 50.5% and 48.4% for sage-grouse and prairie dog, respectively. Management actions replaced non-native annual grasslands with perennial grasses, removed conifers, and controlled exotic forbs. The drier climate most affected ecological departure and prairie dog habitat suitability at 30 years only. Different climates influenced spatial patterns of sage-grouse habitat suitability, but nonspatial values were unchanged. Climate impacts on fire, vegetation succession, and restoration explain many results. Front-loading restoration is predicted to benefit under future drier climate.

Top-down and sideways: Herbivory and cross-ecosystem connectivity shape restoration success at the salt marsh-upland ecotone.

Wetland restoration provides remarkable opportunities to understand vegetation dynamics and to inform success of future projects through rigorous restoration experiments. Salt marsh restoration typically focuses on physical factors such as sediment dynamics and elevation. Despite many demonstrations of strong top-down effects on salt marshes, the potential for consumers to affect salt marsh restoration projects has rarely been quantified. Recently, major restoration projects at the Elkhorn Slough National Estuarine Research Reserve in central California, USA provided an opportunity to examine how herbivory influences restoration success. We quantified the strength of consumer effects by comparing caged to uncaged plantings, and compared effects among plant species and sites. We used camera traps to detect which herbivores were most common and how their abundance varied spatially. Beyond characterizing consumer effects, we also tested management strategies for reducing negative effects of herbivory at the restoration sites, including caging, mowing, and acoustic playbacks of predator sounds. We found extremely strong consumer effects at sites with extensive stands of exotic forbs upland of the high marsh; uncaged restoration plants suffered heavy herbivory and high mortality, while most caged plants survived. Brush rabbits (Sylvilagus bachmani) were by far the most frequent consumers of these high marsh plants. Our work thus provides the first evidence of mammal consumers affecting salt marsh restoration success. Mowing of tall exotic forb cover adjacent to the marsh at one restoration site greatly reduced consumption, and nearly all monitored plantings survived at a second restoration site where construction had temporarily eliminated upland cover. Playbacks of predator sounds did not significantly affect restoration plantings, but restoration efforts in marsh communities vulnerable to terrestrial herbivory may benefit from concurrent restoration of predator communities in the upland habitats surrounding the marsh. A landscape approach is thus critical for recognizing linkages between terrestrial and marine vegetation.

Where Have the Native Grasses Gone?: What a Long-Term, Repeat Study Can Tell Us about California’s Native Prairie Landscapes

Much of the foothill and valley areas of coastal southern California are covered by stands of non-native grasses with occasional scattered patches of native bunch grasses. For decades, the dominant view held that these native bunchgrasses, particularly Stipa pulchra, once covered these lands and that grazing practices were a key cause of their decline. The so-called bunchgrass dominant paradigm (BDP) put forth by Clements influenced thinking on grassland ecology and biogeography for decades until it was discredited. Recent research suggests that grazing and related disturbances might have supported native bunchgrasses, but results are mixed and most studies cover only a short time frame. This research uses a long-term, repeat study design to analyze and compare data from three surveys of 15 permanent quadrats in La Jolla Valley, California, to determine changes in grassland cover over 34 years. A unique aspect of the study is that the site was selected by researchers precisely because it contained excellent ‘relic’ stands of Stipa pulchra (in accordance with the BDP) and the baseline study was conducted shortly after the area was released from grazing and placed under conservation management. We compared data on species frequency and percent cover collected using the same sampling routine for three periods: 1981, 1994, and 2015, to document the shifts in vegetation. We found that native grass cover decreased dramatically (especially on the valley floor), exotic grass cover fluctuated widely over time, while both native and exotic forb cover increased over time. The findings support the notion that prior grazing management practices may have supported the former stands of Stipa pulchra.

Repeat burning affects species composition in degraded Cumberland Plain Woodland

Cleared areas in Scheyville National Park, New South Wales, that formerly supported Cumberland Plain Woodland (CPW) now have a long unburnt mixed native and exotic grassland. To test whether re-introducing fire to these sites would benefit native species composition, and drive it towards that of neighbouring remnant woodland, an experiment was established in three grassy areas (grassy blocks) with prior agricultural land use, and one block in a remnant woodland. Replicate plots were established within blocks, and assigned to a repeat fire treatment, or unburnt controls. Plots in the fire treatment were burnt on all blocks in 2001, and in the grassy blocks only in 2005. Although the two fires did not result in recruitment of new native species on the grassy blocks, the successive fires had other beneficial effects. More native species were apparent in the above-ground vegetation on burnt than unburnt plots after both fires, and more summer-growing native grasses were apparent above ground and increased in abundance after the second fire. The large flush of exotic forbs that appeared after the first fire was not repeated after the second fire; many of these forbs had an obligate seeder fire response, and the short inter-fire interval may not have allowed replenishment of their seed bank. Burning did not result in recruitment of new native species in the grassy areas, and did not make the grassy areas more similar to the woodland in species composition. In the woodland, the first fire did not significantly affect species composition. Re-instating fire to degraded grassy sites will not by itself return the site to good quality CPW in the short term, but may contribute positively in the longer term through beneficial effects on natives and adverse effects on exotics.

Fire controls annual bromes in northern great plains grasslands—Up to a point

Concern about the impacts of two invasive annual brome grasses (cheatgrass and Japanese brome, Bromus tectorum L. and B. japonicus Thunb. ex Murray) on the mixed-grass prairie of North America's northern Great Plains (NGP) is growing. Cheatgrass is well known west of the NGP, where replacement of fire-intolerant, native sagebrush steppe by fire-prone, exotic annual grasslands is widespread. Consequently, fire is often not considered as a tool for controlling annual bromes. This should not be the case in the NGP, where mixed-grass prairie is adapted to frequent fires. Fire's efficacy may vary with the degree of invasion, though; suppressing postfire annual brome populations or enhancing the native plant community may improve postfire annual brome control in highly invaded areas. To test this, we performed an experiment at two sites to evaluate the relative effectiveness of prescribed fire alone, fire followed by imazapic application and fire followed by native seeding across a pretreatment invasion gradient of annual brome-to-native species cover ranging from 0.05 to 2.35. Fall-prescribed fire alone greatly reduced annual bromes, but by the second yr after treatment the effect was significant only at invasion ratios < 1.2. Postfire imazapic application reduced annual bromes even further than fire alone, but only for 1 yr at the less invaded site and only at invasion ratios > 1.2 in yr 2 at the other site. Native species cover and total species richness responded positively to all treatments, but the degree of their response varied along the invasion gradient, between sites, with time since treatment and among treatments. Also, at one site, fire yielded a lagged stimulation of short-lived, exotic forbs. Seeding had little effect. Fire is an effective tool for reducing annual bromes in the NGP at lower invasion levels, but more tools are needed for long-term, effective control at highly invaded sites.

Toward Improving Pollinator Habitat: Reconstructing Prairies with High Forb Diversity

Reconstructed prairies can provide habitat for pollinating insects, an important ecosystem service. To optimize reconstructions for pollinators, goals may include enhancing flowering plant cover and richness and increasing bloom availability early and late in the growing season. Resistance to invasive exotic species must also be a goal in any reconstruction, but it is unclear how increasing forb richness and dominance may affect susceptibility to invasion. We compared planted forb richness and cover, cover of planted grasses, and persistence of exotic species 10 y post-planting of reconstructions with 58 species (extra-high richness), 34 species (high), 20 species (medium), and 10 species (low) planted at the same time in the same fields, and using the same methods and overall seeding rate at Neal Smith National Wildlife Refuge in Iowa, USA. Planted forb richness and cover were higher and planted warm-season, but not cool-season, grass cover was lower in the extra-high richness plots. Mean Coefficient of Conservatism was higher and there was less cover of exotic forbs in the extra-high richness plots. Cover of exotic cool-season grasses was greater in the extra-high richness plots than in the lower-richness plots and this trend was still increasing at the last sample date. Our results are encouraging in that we increased cover of pollinator-friendly habitat, but invasive grasses are a concern as they may reduce forb cover and opportunities for ground-nesting bees in the long term.

All systems are equal: In defense of undervalued ecosystems

On The Ground • We introduce the concept of biodiversity potential to assign equal biodiversity value among socially valued and undervalued ecosystems. • Widespread greasewood (Sarcobatus vermiculatus) ecosystems were examined as a case study of biodiversity potential of an undervalued ecosystem at the sodic end of soil salinity. • Groundwater pumping could drop the water table below greasewood taproots, which could degrade wildlife habitat through decreased canopy cover, increased mineral soil, invasive flammable non-native annual species, and exotic forbs. • State-and-transition simulation models and field studies can be used to assess degraded greasewood ecosystems.

Species differences in exhibit use by antelope: addax (Addax nasomaculatus) and sable (Hippotragus niger)

Some conservation breeding centres provide semi-natural conditions for hoofstock herds, to achieve the goal of maintaining genetic and behavioural resilience suitable for eventual reintroduction of conservation-reliant species. Little is known about mixed-species grazing by allopatric herbivores outside their native ranges (ex situ), although species and breed differences have been documented for domestic livestock as well as for sympatric wildlife species. The grazing and resting activities of two species of horse antelope (Hippotraginae) were examined in a central Texas ecoregion characterised by wooded and open grass patches. Theoretically, the mesic-adapted sable antelope Hippotragus niger, would prefer high productivity patches more than the desert-adapted addax Addax nasomaculatus. At three times of the day, behavioural activity and locations of sable (n=28) and addax (n=37) relative to three types of vegetation patches were recorded. It was predicted that sable would more likely (1) forage in locations with higher biomass and (2) rest in shade during midday. Ranked by decreasing forage biomass, the vegetation patch types included introduced exotic grass species (improved), forbs and grasses (native), and woody shrubs or trees (juniper). Shade was greatest in the juniper patches, and temperature was highest during midday. Sable were more likely to be in improved patches (overall and while foraging) and addax were more likely located in native patches. Both species rested in shady juniper patches, primarily during morning and midday. Based on hierarchical analyses using logistic regression models, individual use of patch types was a complex interaction of species, time of day and activity. Use of patches changed significantly during the day, species used patches differently, and foraging behaviour differed among the patches. Better understanding of species differences in use of an ex-situ landscape can contribute to maintaining herd health and behavioural resilience, as needed to meet goals of in-situ population restoration.

Fine‐scale variables associated with the presence of native forbs in natural temperate grassland

AbstractBroad‐scale threats to floristic diversity in native temperate grasslands are well‐documented and include elevated soil nutrients, changes in disturbance regimes and exotic species. However, fine‐scale variables associated with the presence of native forbs, such as gap size and biomass cover, have received relatively little attention. We conducted a case–control study to determine the relative influence of physical structural dimensions and other fine‐scale variables associated with the presence of native forbs in a modified temperate grassland previously used for domestic grazing. We matched 145 case plots centred on 27 different species of native forbs with 290 control plots not centred on a native forb. For each percentage increase in ground litter cover, dead biomass cover, grass cover or exotic forb cover, or the area of bare ground within 30 cm, the relative odds that a native forb was present vs absent declined by a mean of 10–13%. Living and dead biomass reduces light availability, and the former can also reduce nutrient and water availability. Declines in the presence of native forbs associated with increasing total bare ground may suggest that gap sizes were too small or the soil surface condition too degraded. Our results add to a body of evidence suggesting that native forbs in temperate native grassland are likely to benefit from periodic removal of living and dead grass biomass and a reduction in the cover of exotic forbs.

Long‐term monitoring of a highly invaded annual grassland community through drought, before and after an unintentional fire

AbstractQuestions(a) How did seedling numbers and species composition change in the first year after a wildfire during drought, relative to pre‐fire variation? (b) Has the community returned to pre‐fire composition after five years? (c) Has the degree of dominance by exotic annual grasses changed? (d) Is there any evidence that drought conditions affected community cover, before or after fire?LocationExotic‐dominated annual grassland in southern California, USA.MethodsWe monitored community cover and native annual forb densities for four years before and four (cover) to five (densities) years after an unintentional fire (fall 2013) coinciding with the spring 2012–2019 California drought. We also measured seedling emergence both before and during the first year post‐fire. We assessed post‐fire changes in cover and density relative to pre‐fire variation, and tested correlations between community cover and annual rainfall measures.ResultsSeedling emergence declined strongly after fire for exotic grasses, but remained stable for exotic forbs. Seedling densities of the most common native forbs declined, but several previously‐rare natives increased. Community cover initially shifted towards the exotic forbs Erodium spp., then returned to higher exotic grass densities. Yet the previously dominant Bromus diandrus declined steeply, even as other exotic grasses and some native forbs increased. Up to five years after fire, relative cover and abundance of the most common exotic and native species still differed from pre‐fire composition. Common species were uncorrelated with annual precipitation, but several may have responded to shorter growing seasons.ConclusionsImmediate post‐fire conditions favoured exotic and native forbs over grasses, as predicted. Yet in contrast to many previous studies, the community did not return quickly to pre‐fire composition but showed persistent changes that favoured neither natives nor exotics. Our results suggest post‐fire recovery in this habitat may be contingent on abiotic conditions, with drought one potential explanation for changes.

Evaluation of soil treatment techniques on remediated brine spill sites in semi-arid rangelands

Unconventional oil and gas development (UOG) generates high volumes of flowback and produced water, byproducts of hydraulic fracturing operations, that are often released or spilled on the soil surface. Soil contamination with these wastewaters, commonly referred to as brine, has the potential to inhibit vegetation growth indefinitely. Natural attenuation of brine is not expedient in arid and semi-arid regions where most United States UOG developments are located, including the Bakken region of North Dakota. In situ (at-site) and ex situ (off-site) soil treatment techniques are commonly employed to remediate brine-contaminated soils in the Bakken. However, little is known regarding each technique's efficacy despite differences in application, cost, and efficiency. We selected 10 sites previously remediated with chemical amendments (in situ) and 11 sites with topsoil excavation (ex situ) in the United States Forest Service Little Missouri National Grasslands. We paired each remediated site with a reference to examine the ability of each strategy to return brine-contaminated sites to conditions reflective of the current state of the surrounding semi-arid rangeland ecosystem. At each site, we quantified soil electrical conductivity (ECe) as an indicator of soil salinity and measured vegetation cover, biomass production, bare ground, and litter. The difference between paired reference and remediated sites was used for analysis. Brine contamination was still evident as soil ECe was similarly increased on chemical amendment and topsoil excavation remediated sites over paired references at all soil depths tested. Due to the nature of the topsoil excavation treatment, elevated ECe in the 0–15 cm depth suggested resalinization of the new topsoil. Remediation techniques also resulted in similar plant community composition marked by an increase in exotic forb biomass, largely due to the invasion of kochia (Bassia scoparia) which was absent from reference sites. However, remediation techniques differed substantially in vegetation establishment. We found 15% more bare ground on sites remediated with chemical amendment treatment than paired references and 55% more with topsoil excavation. Our results indicate that in situ strategies may be more suitable than ex situ strategies for brine-spill remediation in semi-arid rangelands like the Bakken in North Dakota as they cause less disturbance and likely require less post-remediation management to establish adequate vegetation cover to protect the soil from further erosion.

Decadal plant composition changes in grazed native grassland

SummaryMost high value grasslands of south‐eastern Australia are restricted to small fragmented areas of public land. However, a significant proportion of native grassland is privately owned, managed with grazing rather than fire and is rarely monitored. Hence, a better understanding of grassland management and conservation on the private estate is required. Eco‐markets are policy instruments that incentivise private landholders to effectively manage and conserve native vegetation. However, short funding cycles restrict the capacity of monitoring programs to assess long‐term vegetation changes. In this study, 17 native grassland remnants on private land managed with livestock grazing were monitored before and during a 4‐year eco‐market and 6 years after it ended to determine how composition had changed over 10 years of monitoring. Numerous grassland attributes were either maintained or improved over the 10‐year period, which coincided with one of the most severe and long‐lasting droughts in recent history (i.e. the Millennium drought). In addition, several threatened species were identified as part of the program. A decline in exotic forb richness, native grass cover and native forb richness suggests there is also some impact of the Millennium drought on plant mortality as evidenced by altered litter dynamics. Inherent variability year‐to‐year for most measures of grassland attributes over the monitoring period indicates that climatic conditions have a strong influence on grassland dynamics. Our ability to determine the driver(s) of grassland composition was limited by monitoring program design. Future eco‐market monitoring programs should have adequate resources allocated to enable effective monitoring designs, that incorporate reference information and control sites, and should aim to be long‐term (i.e. &gt;10 years). This will provide clearer insights into the drivers of grassland dynamics and allow for refinement of management options for conservation of this threatened community.

Prescribed Summer Fire and Seeding Applied to Restore Juniper-Encroached and Exotic Annual Grass-Invaded Sagebrush Steppe

Western juniper (Juniperus occidentalis Hook.) encroachment and exotic annual grass (medusahead [Taeniatherum caput-medusae L. Nevski] and cheatgrass [Bromus tectorum L.]) invasion of sagebrush (Artemisia L.) communities decrease ecosystem services and degrade ecosystem function. Traditionally, these compositional changes were largely confined to separate areas, but more sagebrush communities are now simultaneously being altered by juniper and exotic annual grasses. Few efforts have evaluated attempts to restore these sagebrush communities. The Crooked River National Grassland initiated a project to restore juniper-encroached and annual grass-invaded sagebrush steppe using summer (mid-July) applied prescribed fires and postfire seeding. Treatments were unburned, burned, burned and seeded with a native seed mix, and burned and seeded with an introduced seed mix. Prescribed burning removed all juniper and initially reduced medusahead cover but did not influence cheatgrass cover. Neither the native nor introduced seed mix were successful at increasing large bunchgrass cover, and 6 yr post fire, medusahead cover was greater in burned treatments compared with the unburned treatment. Large bunchgrass cover and biological soil crusts were less in treatments that included burning. Exotic forbs and bulbous bluegrass (Poa bulbosa L.), an exotic grass, were greater in burned treatments compared with the unburned treatment. Sagebrush communities that are both juniper encroached and exotic annual grass invaded will need specific management of both juniper and annual grasses. We suggest that additional treatments, such as pre-emergent herbicide control of annuals and possibly multiple seeding events, are necessary to restore these communities. We recommend an adaptive management approach in which additional treatments are applied on the basis of monitoring data.