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Seed‐based restoration is one of the most difficult challenges for dryland restoration. Identifying environmental conditions that drive variation in seed and seedling mortality across similar restoration efforts could increase understanding of when and where restoration outcomes are likely to be favourable and identify new tools and strategies to improve outcomes.We asked how variation in a suite of environmental predictors influenced germination, emergence, seedling establishment and juvenile survival of four commonly sown perennial grass species across 33 seeding experiments distributed over an ~160,000‐km2 area of the Great Basin, a cold desert system in the western United States.Across experiments, we observed wide variation in the rates of four demographic transitions and wide variation in environmental conditions experienced by plants at each stage. For all species, higher precipitation during the first 30 days following seeding was associated with an increase in germination. Conversely, higher soil temperature over this same time period was associated with a significant decrease in germination and emergence, and soil temperature was associated with a substantial portion of the variation in germination and emergence probabilities observed across our seeding experiments.Within the range of precipitation variation observed, we were unable to detect a significant relationship between seedling establishment the first growing season and cumulative precipitation the first year, precipitation during the first spring growing season or annual climatic water deficit (CWD) the first year. Higher CWD the second growing season reduced seedling survival over that time period.Synthesis and applications. Our results show higher soil temperature negatively impacts grass seedling establishment. Restoration efforts should be prioritized when seasonal or subseasonal temperature forecasts indicate likely periods of below average temperatures. These results also indicate that climate warming will make restoration even more difficult, with our model estimates suggesting the 2°C increase in temperature expected in the Great Basin over the coming decades will decrease germination and emergence by about 30%. Lastly, while our field‐based approach provided insight into short‐term drivers of mortality, it did not provide insight into drivers of longer term survival, suggesting a need for further work on predicting long‐term restoration outcomes. [ABSTRACT FROM AUTHOR]

Hydrothermal (HT) models can be used to characterize seed germination response to fieldvariable conditions of temperature (T) and water potential (Y). Hydrothermal response data are relatively difficult to generate, which limits their utility for large-scale comparisons of inter- and intraspecies germination response. Previous studies have hypothesized that HT germination response can be estimated using a simple model for thermal-time accumulation above a fixed threshold of environmental Y (wet-thermal [WT] model). The purpose of this study was to test this hypothesis by explicitly comparing HT and WT germination rates and estimated cumulative germination response of 13 rangeland grass seedlots under simulated conditions of field-variable T and Y. We used a 44-yr weather record to parameterize a seedbed-microclimate model for estimation of hourly T and Y at seeding depth for a sandy loam soil type at the Orchard field test site in southwestern Ada County, Idaho. Hydrothermal and WT germination responses for each hour of the simulation were estimated for 13 range grass seedlots. We found that overestimation of germination rate by thermal accumulation at low Y contributed relatively little to WT model error rates, and that >95% of the variability in predicted germination response could be explained by WT germination response above a Y threshold of -0.3 to -0.5 MPa. Given the pulse-like nature of favorable germination conditions in the field, this modeling approach may have immediate and wide potential application, as there are a relatively large number of thermal-germination datasets currently available for rangeland plant species. [ABSTRACT FROM AUTHOR]

Hydrothermal models used to predict germination response in the field are usually parameterized with data from laboratory experiments that examine the full range of germination response to temperature (T) and water potential (ψ). Inclusion of low-ψ and high- and low-T treatments, however, may not be necessary if their contribution to germination rate in the field is negligible. In this study, we simulated cumulative germination response of 13 range grass seedlots to a typical seasonal planting scenario used for rangeland restoration in the Great Basin region of the western United States. Given realistic estimates of actual time spent within the full hydrothermal range of these seedlots, >95% of germination response in the field could be predicted by models that only considered germination at ψ values less negative than -0.5 MPa and T values <25°C. Limiting laboratory treatments to a restricted hydrothermal range could greatly increase the efficiency of parameterizing hydrothermal models for predicting field response. Laboratory expenditures in this example could be reduced by 80 to 90% with only a relatively small reduction in the potential accuracy of field predictions. [ABSTRACT FROM AUTHOR]

Developing land-use practices that lead to sustainable net primary productivity in rangelands are important, but understanding their consequences to population and community processes is not often accounted for in basic ecosystem studies. Grazed and ungrazed upland ecosystems generally do not differ in net ecosystem CO2 exchange (NEE), but the underlying mechanisms and the concurrent effects of defoliation to vegetative and reproductive biomass allocation are unclear. To address this, we measured evapotranspiration (ET), NEE, and its constituent fluxes of ecosystem respiration (Reco) and gross ecosystem photosynthesis (GEP) with live canopy leaf area index (LAIlive; m² live leaf area/m² ground area) and aboveground leaf, culm, and reproductive biomass in plots of clipped and unclipped squirreltail (Elymus elymoides) and bluebunch wheatgrass (Pseudoroegneria spicata) growing in intact sagebrush steppe. Clipping reduced LAIlive by 75%, but subsequent re-growth rates in clipped plots was similar to LAIlive accumulation in unclipped plots. Concurrently, ET and NEE was similar between clipped and unclipped plots, with NEE primarily determined by GEP. GEP was initially lower in clipped plots, but then converged with unclipped GEP even as LAIlive continued to increase in both treatments. GEP convergence was driven by higher whole-plant photosynthesis (GEPlive = GEP/LAIlive) in clipped plots. Ecosystem water use efficiency (GEP/ET) was reduced by 16% with clipping, due to low GEP/ET 2 weeks following defoliation, but GEP/ET converged before GEP levels did. Proportional reproductive biomass was higher in E. elymoides (21.4% total biomass) than in P. spicata (0.5% total biomass) due to lower allocation to specific leaf and culm mass. Clipping reduced reproductive effort in E. elymoides, in terms of total reproductive biomass (-56%), seed mass per unit leaf area (-64%), and seed mass per flowering head (-77%). We concluded defoliation increased canopy-level light penetration, facilitating rapid Recovery of ecosystem fluxes, but that allocation to vegetative regrowth supporting this led to lower reproductive effort in these range grasses. Insights from studies such as this will be useful in formulating systems-based land management strategies aimed at maintaining annual productivity and long-term population and community goals in semiarid rangeland ecosystems. [ABSTRACT FROM AUTHOR]

Seeding native plants is a key management practice to counter land degradation across the globe, yet the majority of seeding efforts fail, limiting our ability to accelerate ecosystem recovery., Recruitment requires transitions through several seed and seedling stages, some of which may have overriding influences on restoration outcomes. We lack, however, a general framework to understand and predict differences in these critical demographic processes across species. Functional traits influence fitness, and consequently, trait variation could provide the basis for a framework to explain and predict variation in life stage transition probabilities., We used seed and seedling traits, and field probabilities of germination, emergence, seedling establishment, and survival for 47 varieties of drylands grasses under two watering treatments to identify critical life stage transitions and quantify the effect of traits on cumulative survival through the first growing season., Variation in germination and emergence probabilities explained over 90% of the variation in cumulative survival regardless of seedling survival probabilities or watering treatment, with emergence probability being the strongest predictor of cumulative survival., Coleoptile tissue density and seed mass had significant effects on emergence and germination, respectively, explaining 10-23% of the variation in transition probabilities., Synthesis and applications. While the majority of functional trait work has centred on linking leaf and root traits to resource acquisition and utilization, our study demonstrates that traits associated with germination and emergence may have prevailing influences on restoration outcomes. A portion of these traits have been examined, but there is substantial opportunity to identify other key traits driving these demographic processes. These advancements will underpin our ability to develop trait-based frameworks for overcoming recruitment barriers and facilitating recovery of degraded systems across the globe. [ABSTRACT FROM AUTHOR]

Functional differences between native and exotic species potentially constitute one factor responsible for plant invasion. Differences in trait values between native and exotic invasive species, however, should not be considered fixed and may depend on the context of the comparison. Furthermore, the magnitude of difference between native and exotic species necessary to trigger invasion is unknown. We propose a criterion that differences in trait values between a native and exotic invasive species must be greater than differences between co-occurring natives for this difference to be ecologically meaningful and a contributing factor to plant invasion. We used a meta-analysis to quantify the difference between native and exotic invasive species for various traits examined in previous studies and compared this value to differences among native species reported in the same studies. The effect size between native and exotic invasive species was similar to the effect size between co-occurring natives except for studies conducted in the field; in most instances, our criterion was not met although overall differences between native and exotic invasive species were slightly larger than differences between natives. Consequently, trait differences may be important in certain contexts, but other mechanisms of invasion are likely more important in most cases. We suggest that using trait values as predictors of invasion will be challenging. [ABSTRACT FROM AUTHOR]

Drylands support over 2 billion people and are major providers of critical ecosystem goods and services across the globe. Drylands, however, are one of the most susceptible biomes to degradation. International programmes widely recognize dryland restoration as key to combating global dryland degradation and ensuring future global sustainability. While the need to restore drylands is widely recognized and large amounts of resources are allocated to these activities, rates of restoration success remain overwhelmingly low., Advances in understanding the ecology of dryland systems have not yielded proportional advances in our ability to restore these systems. To accelerate progress in dryland restoration, we argue for moving the field of restoration ecology beyond conceptual frameworks of ecosystem dynamics and towards quantitative, predictive systems models that capture the probabilistic nature of ecosystem response to management., To do this, we first provide an overview of conceptual dryland restoration frameworks. We then describe how quantitative systems framework can advance and improve conceptual restoration frameworks, resulting in a greater ability to forecast restoration outcomes and evaluate economic efficiency and decision-making. Lastly, using a case study from the western United States, we show how a systems approach can be integrated with and used to advance current conceptual frameworks of dryland restoration., Synthesis and applications. Systems models for restoration do not replace conceptual models but complement and extend these modelling approaches by enhancing our ability to solve restoration problems and forecast outcomes under changing conditions. Such forecasting of future outcomes is necessary to monetize restoration benefits and cost and to maximize economic benefit of limited restoration dollars. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the grassland natives exhibiting long-term coexistence with an invader, and determines whether herbicide use can affect invasive species. One-time herbicide use made two native forbs exceedingly rare for the entire study period. It was found that the dominant invader became more abundant in response to the decreases in native-forb abundances. However, some applications are not warranted because they target small invader patches or larger areas with no remaining natives.

Establishing native forbs is crucial for invasive plant management and restoring a desirable plant community. Our objectives were to determine (1) if increasing forb seed density results in increased forb establishment; (2) if a species-rich mixture of forbs has greater establishment and survivorship than a single species; and (3) if mixtures of forbs are more competitive with Spotted knapweed ( Centaurea maculosa) than a forb monoculture. To test our first two objectives, we seeded monocultures of Purple coneflower ( Echinacea angustifolia), Arrowleaf balsamroot ( Balsamorhiza sagittata), Annual sunflower ( Helianthus annuus), Dotted gayfeather ( Liatris punctata), Western white yarrow ( Achillea millefolium), Sticky geranium ( Geranium viscosissimum), as well as a mixture of all forbs. Pots were seeded at 800 or 2,000 seeds/m2 and watered twice or thrice weekly. The highest seed density produced the highest plant density, which averaged 4.35 plants/pot. The density of the mixture was similar to the mean density seen for individual species, and it doubled in response to the highest seed density. To test our third objective, Spotted knapweed and Purple coneflower were arranged in an addition series matrix with a maximum total density of 4,000 seeds/pot. We found that the forb mixture was seven times more competitive with Spotted knapweed than Purple coneflower alone. Using a mixture of forbs rather than a single species enhances forb establishment in various and unpredictable environments because the mixture possesses a variety of traits that may match year–year and site–site conditions. Once established, the mixture may have a greater chance of persisting than a monoculture. [ABSTRACT FROM AUTHOR]

Ecologists are searching for models, frameworks, and principles that provide a bridge between theory and the practice of restoration. Successional management has been proposed as a useful model for managing and restoring invasive-plant-dominated rangeland because it provides a framework in which ecological processes can be manipulated by managers to achieve a desired plant community. Successional management identifies three general causes of succession (site availability [disturbance], species availability [colonization], and species performance) and suggests that managers address the ecological process influencing each general cause in a coordinated fashion to direct plant community dynamics. We tested successional management using various techniques to restore invasive-weed-dominated rangeland. Our hypothesis was that successively modifying the factors influencing the causes of succession in an integrated fashion would favor the establishment and abundance of native grasses over singularly applied treatments. Thus, we anticipated that the majority of responses to multiple treatments would be explained by higher order interactions, especially in the final year of the study (2004). To test this hypothesis; we used a model system within a Festuca campestris/Pseudoroegneria spicata habitat among pothole wetlands dominated by Centaurea maculosa and Potentilla recta, two invasive species. We used three herbicide treatments (none, 2,4-D, and picloram) to influence species performance; two seeding methods (imprinting, i.e., creating a small depression and broadcasting, and no-till drilling) to influence disturbance; three seeding rates (977, 1322, and 1557 seeds/m2) to influence colonization; and two cover crop treatments (with and without Triticum aestivum) to influence soil N and favor native grasses. Treatments were factorially arranged and replicated four times in a randomized complete block design in 2001 and sampled in 2002 and 2004. As predicted, plant response to treatments was dominated by two- and three-way interactions in 2004. The highest seeding rate (colonization) combined with no-till drilling (disturbance) produced the highest native grass density in 2002. These effects persisted into 2004 for P. spicata. but not for F. campestris or F. idahoensis. Combining picloram with no-till drill seeding also produced a high density of P. spicata. Drill seeding at 977 seeds/m2 favored F. idahoensis density, while no-till drilling at 1322 seeds/m2 favored its biomass in 2004. F. idahoensis established well after drill seeding with a cover crop and applying 2,4-D. Herbicides reduced native forb density and/or biomass, with early season forbs being more sensitive topicloram and summer forbs being more sensitive to 2,4-D. Herbicides increased exotic grasses’ density and biomass but had no effect on native grasses. In most cases, integrating treatments that addressed multiple causes of succession favored a desired plant community. Thus, we accomplished our goal of using successional management to direct plant communities toward native desired species, but the treatments used did not improve species richness. Since naturally occurring native forbs did not respond favorably to any treatment combination, ecological restoration using successional management may best be thought of as an iterative procedure where various components and processes of the system are methodically repaired or replaced over time. [ABSTRACT FROM AUTHOR]

A commonly cited mechanism for invasion resistance is more complete resource use by diverse plant assemblages with maximum niche complementarity. We investigated the invasion resistance of several plant functional groups against the nonindigenous forb Spotted knapweed ( Centaurea maculosa). The study consisted of a factorial combination of seven functional group removals (groups singularly or in combination) and two C. maculosa treatments (addition vs. no addition) applied in a randomized complete block design replicated four times at each of two sites. We quantified aboveground plant material nutrient concentration and uptake (concentration × biomass) by indigenous functional groups: grasses, shallow-rooted forbs, deep-rooted forbs, spikemoss, and the nonindigenous invader C. maculosa. In 2001, C. maculosa density depended upon which functional groups were removed. The highest C. maculosa densities occurred where all vegetation or all forbs were removed. Centaurea maculosa densities were the lowest in plots where nothing, shallow-rooted forbs, deep-rooted forbs, grasses, or spikemoss were removed. Functional group biomass was also collected and analyzed for nitrogen, phosphorus, potassium, and sulphur. Based on covariate analyses, postremoval indigenous plot biomass did not relate to invasion by C. maculosa. Analysis of variance indicated that C. maculosa tissue nutrient percentage and net nutrient uptake were most similar to indigenous forb functional groups. Our study suggests that establishing and maintaining a diversity of plant functional groups within the plant community enhances resistance to invasion. Indigenous plants of functionally similar groups as an invader may be particularly important in invasion resistance. [ABSTRACT FROM AUTHOR]

Abstract Centaurea maculosa (Lam.) (spotted knapweed) reduces wildlife and livestock habitat biodiversity and increases erosion. Nutrient availability to plants may be used to accelerate succession away from spotted knapweed. Early-successional plant communities often have high nutrient availability, whereas late-successional communities are often found on lower nutrient soils. We hypothesized that removal of nutrients would change the competitive advantage from spotted knapweed to Pseudoroegneria spicatum (bluebunch wheatgrass) (late seral). In two addition series matrices, background densities of Secale cereale (annual rye) and Elymus elimoides (bottlebrush squirreltail) (3,000 seeds/m2) were used to remove nutrients from the soil. In another set of addition series matrices, nitrogen (33 kg/ha) or phosphorus (33 kg/ha) were added to the soil. Nutrient analysis of soil and vegetation indicated that annual rye and bottlebrush squirreltail reduced nutrient availability in soils. In another matrix, neither a background density nor nutrients were added. Data were fit into Watkinson's curvilinear model to determine the competitive relationship between bluebunch wheatgrass and spotted knapweed. This allowed comparison of the equivalence ratios (C) generated from each addition series. The C parameters are the per-plant equivalent of bluebunch wheatgrass or spotted knapweed and can be interpreted as the ratio of intra-to-interspecific competition. The C parameters are also the equivalence ratio of the number of spotted knapweed it takes to have equivalent effect on bluebunch wheatgrass or the number of bluebunch wheatgrass having the equivalent effect on spotted knapweed. Without nutrient manipulation, spotted knapweed was more competitive than bluebunch wheatgrass. The C for bluebunch wheatgrass was 0.17, indicating that 0.17 knapweed plants were competitively equivalent to one wheatgrass. Annual rye changed the competitive balance in favor of bluebunch... [ABSTRACT FROM AUTHOR]