Research and Publications
Big sagebrush and scabland sagebrush communities responded uniquely to multiple fires, due to different fuel loadings, fire severities, succession and invasion dynamics. Big sagebrush experienced nearly complete shrub loss and conversion from exotic invaded‐shrubland to exotic annual grassland after only one fire. In contrast, scabland sagebrush retained a minor shrub component and higher relative cover of native herbaceous species, even after three fires. Both communities retained cover of native perennial grasses, including shallow‐ and deep‐rooted species, likely reflecting decreasing fire intensity with number of times burned.
Woodland encroachment is a global issue linked to diminished ecosystem services, prompting the need for restoration efforts. However, restoration outcomes can be highly variable, making it difficult to interpret the ecological benefits and risks associated with woodland-reduction treatments within semiarid ecosystems. We addressed this uncertainty by assessing the magnitude and direction of vegetation change over a 15-year period at 129 sagebrush (Artemisia spp.) sites following pinyon (Pinus spp.) and juniper (Juniperus spp.) (P–J) reduction. Pretreatment vegetation indicated strong negative relationships between P–J cover and the abundance of understory plants (i.e., perennial grass and sagebrush cover) in most situations and all three components differed significantly among planned treatment types. Thus, to avoid confounding pretreatment vegetation and treatment type, we quantified overall treatment effects and tested whether distinct response patterns would be present among three dominant plant community types that vary in edaphic properties and occur within distinct temperature/precipitation regimes using meta-analysis (effect size = lnRR = ln[posttreatment cover/pretreatment cover]). We also quantified how restoration seedings contributed to overall changes in key understory vegetation components. Meta-analyses indicated that while P–J reduction caused significant positive overall effects on all shrub and herbaceous components (including invasive cheatgrass [Bromus tectorum] and exotic annual forbs), responses were contingent on treatment- and plant community-type combinations. Restoration seedings also had strong positive effects on understory vegetation by augmenting changes in perennial grass and perennial forb components, which similarly varied by plant community type. Collectively, our results identified specific situations where broad-scale efforts to reverse woodland encroachment substantially met short-term management goals of restoring valuable ecosystem services and where P–J reduction disposed certain plant community types to ecological risks, such as increasing the probability of native species displacement and stimulating an annual grass-fire cycle. Resource managers should carefully weigh these benefits and risks and incorporate additional, appropriate treatments and/or conservation measures for the unique preconditions of a given plant community in order to minimize exotic species responses and/or enhance desirable outcomes.
This study evaluated the long-term (13 years post-treatment) effectiveness of prescribed fire and mechanical tree removal to re-establish sagebrush steppe vegetation and associated spatial patterns in ground surface conditions and soil hydrologic properties of two woodland-encroached sites. Specifically, we assessed the effects of tree removal on: (1) vegetation and ground cover at the hillslope scale (990 m2 plots) and (2) associated spatial patterns in point-scale ground surface conditions and soil hydrologic properties along transects extending from tree bases and into the intercanopy areas between trees. Both sites were in mid to late stages of woodland encroachment with extensive bare conditions (~60–80% bare ground) throughout a degraded intercanopy area (~75% of the domain) surrounding tree islands (~25% of domain, subcanopy areas). All treatments effectively removed mature tree cover and increased hillslope vegetation. Enhanced herbaceous cover (4–15-fold increases) in burned areas reduced bare interspace (bare area between plants) by at least 4-fold and improved intercanopy hydraulic conductivity (> than 2-fold) and overall ecohydrologic function. Mechanical treatments retained or increased sagebrush and generally increased the intercanopy herbaceous vegetation. Intercanopy ground surface conditions and soil hydrologic properties in mechanical treatments were generally similar to those in burned areas but were also statistically similar to the same measures in untreated areas in most cases. This suggests that vegetation and ground surface conditions in mechanical treatments are trending toward a significantly improved hydrologic function over time. Treatments had limited impact on soil hydrologic properties within subcanopy areas; however, burning did reduce the soil water repellency strength and the occurrence of strong soil water repellency underneath trees by three- to four-fold. Overall, the treatments over a 13-year period enhanced the vegetation, ground surface conditions, and soil hydrologic properties that promote infiltration and limit runoff generation for intercanopy areas representing ~75% of the area at the sites. However, ecological tradeoffs in treatment alternatives were evident. The variations in woodland responses across sites, treatments, and measurement scales in this long-term study illustrate the complexity in predicting vegetation and hydrologic responses to tree removal on woodland-encroached sagebrush sites and underpin the need and value of multi-scale long-term studies.
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Shifts from longer seasonal snowpacks to shorter, ephemeral snowpacks (snowpacks that persist for <60 days) due to climate change will alter the timing and rates of water availability. Ephemeral snowmelt has less predictable timing and lowers soil water availability during the growing season. The Great Basin, United States is an ideal system to study snow ephemerality across a broad climate gradient. To identify the climatic controls on snow ephemerality, we analysed moderate resolution imaging spectroradiometer (MODIS) snow‐covered products from water years 2001–2015 using an object‐based mapping approach and a random forest model. Winter temperature and precipitation were the most influential variables on the maximum snow duration. We predict that warming the average winter air temperature by 2 and 4°C would reduce the areal extent of seasonal snow by 14.7 and 47.8%, respectively (8.8% of the Great Basin’s areal extent is seasonal in the historical record), with shifts to ephemeral snowpack concentrated in lower elevations and warmer regions. The combination of warming and interannual precipitation variability (i.e., reductions of 25%) had different effects on vegetation types. Vegetation types that have had consistent seasonal snow cover in their historical record are likely to have lower resilience to a new hydrologic regime, with earlier and more intermittent snowmelt causing a longer but drier growing season. Implications of increased snow ephemerality on vegetation productivity and susceptibility to disturbance will depend on local topography, subsurface water storage, and physiological adaptations. Nevertheless, patterns found in this study can help target management intervention to species that are most at risk.
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What may appear at first glance as a sea of sagebrush is in reality a complex and diverse ecosystem with a wide variety of plants and animals. The sagebrush steppe teems with life, but threats such as wildfire, grazing and invasive species are affecting the resilience of rangeland across the Northwest. Learn more about the groups of plants that make up a healthy rangeland ecosystem.
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Grazing by domestic livestock is a ubiquitous land use in the sagebrush (Artemisia spp.) biome of western North America. Widespread, long‐term population declines in greater sage‐grouse (Centrocercus urophasianus) have elicited concern about potential negative effects of livestock management practices on sage‐grouse populations. We evaluated how recently implemented rotational grazing systems affected sage‐grouse nesting habitat quality as part of a large‐scale, replicated, natural experiment in central Montana, USA. We used Bayesian methods to assess support for effects of rotational grazing management and rest from grazing on daily survival rates of nearly 500 sage‐grouse nests monitored over 6 years, and mixed effects models to test for effects of rotational grazing and rest on vegetation structure. Though nests on rotationally grazed ranches displayed a trend toward greater daily survival rates, the evidence for an effect was weak. There was no evidence that rest from grazing (≥12 months) increased daily survival rates. Furthermore, rotational grazing systems and rest had negligible effects on herbaceous vegetation height and cover relative to other grazing strategies used in the study area. Results do not support the hypothesis that rotational grazing systems or rest from grazing increase nest success in the northern Great Plains. Estimated nest success, however, was comparable to range‐wide averages, suggesting concealing cover for nests is unlikely to be limiting growth of this population regardless of grazing strategy. In light of these results and recent research questioning reported relationships between grass height and nest survival, maximization of hiding cover may be overemphasized in grazing management guidelines and policies. Rather, our findings suggest a variety of locally appropriate grazing strategies focused on fundamental range health principles may provide adequate habitat quality for nesting sage‐grouse.
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In coniferous western forests, recent widespread tree mortality provided opportunities to test the long-held theory that forest cover loss increases water yield. We reviewed 78 studies of hydrologic response to standing-replacing (severe wildfire, harvest) or nonstand-replacing (drought, insects, low-severity wildfire) disturbances, and reassessed the question: Does water yield or snowpack increase after forest disturbance? Collective results indicate that postdisturbance streamflow and snowpack may increase, not change, or even decrease, and illuminate factors that may help improve predictability of hydrologic response to disturbance. Contrary to the expectation that tree mortality reduces evapotranspiration, making more water available as runoff, postdisturbance evapotranspiration sometimes increased—particularly following nonstand-replacing disturbance—
because of (a) increased evaporation resulting from higher subcanopy radiation, and (b) increased transpiration resulting from rapid postdisturbance growth. Postdisturbance hydrologic response depends on vegetation structure, climate, and topography, and new hypotheses continue to be formulated and tested in this rapidly evolving discipline.
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In recent years restoration project efforts in arid grasslands of the Pacic Northwest have increased; however, little isknown about the bee communities in these areas or how restoration affects them. Native bees provide an essential ecosystemservice through pollination of crops and native plants and understanding their response to restoration is a high priority. Toaddress this issue, we conducted a three-year study in an arid bunchgrass prairie with three objectives: (1) describe the beecommunity of this unique grassland type and its temporal variability; (2) investigate environmental variables inuencing thecommunity; and (3) examine effects of restoration on the community. We identified 62 bee species and found strong seasonaland inter-annual variation in bee abundance, richness, diversity, and species composition. Unexpectedly, these temporaltrends did not correspond with patterns in floral resources; however, several variables were associated with variation inbee abundance, richness, and diversity among sites. Sites with high levels of litter cover had more bees, while sites withtaller vegetation or more blooming flowers had greater species richness but lower diversity. We found no detectable effectof restoration on bee abundance, richness, diversity, or composition. Species composition at native sites differed from those inactively and passively restored sites, which did not differ from each other. Restored sites also had fewer flowers and differingfloral composition relative to native sites. These results suggest that if grassland restoration is to benefit bees, efforts shouldfocus on both expanding floral resources and enhancing variables that influence nesting habitat.
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Water-holding soil amendments such as super-absorbent polymer (SAP) may improve native species establishment in restoration but may also interact with precipitation or invasive species such as Bromus tectorum L. to influence revegetation outcomes.We implemented an experiment at two sites in Colorado, U.S.A., in which we investigated the interactions of drought (66% reduction of ambient rainfall), B. tectorum seed addition (BRTE, 465 seeds/m2), and SAP soil amendment (25 g/m2) on initial plant establishment and 3-year aboveground and belowground biomass and allocation. At one site, SAP resulted in higher native seeded species establishment but only with ambient precipitation. However, by the third year, we detected no SAP effects on native seeded species biomass. Treatments interacted to influence aboveground and belowground biomass and allocation differently. At one site, a SAP × precipitation interaction resulted in lower belowground biomass in plots with SAP and drought (61.7±7.3 g/m2) than plots with drought alone (91.6±18.1 g/m2). At the other site, a SAP × BRTE interaction resulted in higher belowground biomass in plots with SAP and BRTE (56.6±11.2 g/m2) than BRTE alone (35.0±3.7 g/m2). These patternswere not reflected in aboveground biomass. SAP should be used with caution in aridland restoration because initial positive effects may not translate to long-term benefits, SAP may uniquely influence aboveground versus belowground biomass, and SAP can interact with environmental variables to impact developing plant communities in positive and negative ways.
As we approach the Decade of Ecosystem Restoration (2021–2030), there is renewed focus on improving wetland restoration practices to reestablish the habitat and climate mitigation functions and services that wetlands provide. A first step in restoring these functions and services is to reestablish the native vegetation structure and composition through strategic seed-based approaches. These approaches should be driven by ecological, genetic, and evolutionary principles, along with consideration for economics, logistics, and other social constraints. Effective seed-based approaches must consider the chosen species, seed sourcing, dormancy break and germination requirements, seed enhancement technologies, potential invaders, seeding densities, and long-term monitoring. Choice of species should reflect historical plant communities and future environmental conditions, species that support functional goals including invasion resistance, and seed availability constraints. Furthermore, seeds should be sourced to ensure ample genetic diversity to support multifunctionality and evolutionary capacity while also considering the broad natural dispersal of many wetland species. The decision to collect wild seeds or purchase seeds will also impact species choice and genetic diversity, which can have cascading effects for functional goals. To ensure seedling establishment, seed dormancy should be addressed through dormancy breaking treatments and the potentially narrow germination requirements of some species will require targeted sowing timing and location to align with safe sites. Other seed enhancements such as priming and coatings are poorly developed for wetland restoration and their potential for improving establishment is unknown. Because wetlands are highly invasion prone, potential invaders and their legacies should be addressed. Seeding densities should strike a balance between outcompeting invaders and preserving valuable seed resources. Invader control and long-term monitoring is key to improving revegetation and restoration. Here, we review scientific advances to improve revegetation outcomes, and provide methods and recommendations to help achieve the desired goals. Gaps in knowledge about seed-based wetland restoration currently exist, however, and untested practices will certainly increase risks in future efforts. These efforts can be used to better understand the ecological, genetic, and evolutionary processes related to wetland seeds, which will bring us one step closer to seed-based restoration of functions and services needed for human and ecological communities.