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Restoration of degraded drylands is urgently needed to mitigate climate change, reverse desertification and secure livelihoods for the two billion people who live in these areas. Bold global targets have been set for dryland restoration to restore millions of hectares of degraded land. These targets have been questioned as overly ambitious, but without a global evaluation of successes and failures it is impossible to gauge feasibility. Here we examine restoration seeding outcomes across 174 sites on six continents, encompassing 594,065 observations of 671 plant species. Our findings suggest reasons for optimism. Seeding had a positive impact on species presence: in almost a third of all treatments, 100% of species seeded were growing at first monitoring. However, dryland restoration is risky: 17% of projects failed, with no establishment of any seeded species, and consistent declines were found in seeded species as projects matured. Across projects, higher seeding rates and larger seed sizes resulted in a greater probability of recruitment, with further influences on species success including site aridity, taxonomic identity and species life form. Our findings suggest that investigations examining these predictive factors will yield more effective and informed restoration decision-making., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Trait–environment correlations can arise from local adaptation and can identify genetically and environmentally appropriate seeds for restoration projects. However, anthropogenic changes can disrupt the relationships between traits and fitness. Finding the best seed sources for restoration may rely on describing plant traits adaptive in disturbed and invaded environments, recognizing that while traits may differ among species and functional groups, there may be similarities in the strategies that increase seedling establishment. Focusing on three grass genera, two shrub species, and two forb genera, we collected seeds of all taxa from 16 common sites in the sagebrush steppe of the western United States. We measured seed and seedling characteristics, including seed size, emergence timing, and root and shoot traits, and compiled a suite of environmental variables for each collection site. We described trait–environment associations and asked how traits or environment of origin were associated with seedling survival in invaded gardens. Sampling seven taxa from the same sites allowed us to ask how trait–environment–performance associations differ among taxa and whether natural selection favors similar traits across multiple taxa and functional groups. All taxa showed trait–environment associations consistent with local adaptation, and both environment of origin and phenotypes predicted survival in competitive restoration settings, with some commonalities among taxa. Notably, rapid emergence and larger seeds increased survival for multiple taxa. Environmental factors at collection sites, including lower slopes (especially for grasses), greater mean annual temperatures (especially for shrubs and forbs), and greater precipitation seasonality were frequently associated with increased survival. We noted one collection site with high seedling survival across all seven taxa, suggesting that conditions within some sites may result in selection for traits that increase establishment for multiple species. Thus, choosing native plant sources with the most adaptive traits, along with matching climates, will likely improve the restoration of invaded communities. [ABSTRACT FROM AUTHOR]

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]

Questions How does performance of a native early seral seed mix during early life stages compare to that of a late seral mix when seeded with Bromus tectorum or Taeniatherum caput-medusae? Does either mix reduce survival of exotic annual grasses during early life stages, and does this effect differ with soil type? Is exotic performance stronger in one soil type, and does native performance when growing with exotics differ between soil types as a result of exotic preference? Location University of Nevada Agricultural Research Station, Reno, NV, US. Methods We compared seedling emergence and early survival (Nov through May) of two native seed mixes, each composed of grass, forb and shrub functional groups, when growing with B. tectorum or T. caput-medusae in soils of contrasting texture (sandy loam and clay loam). Natives were also seeded without exotics. Performance of an early seral mix was compared with that of a late seral mix representative of species commonly used in Great Basin restoration. Results Comparing emergence and survival probabilities, early seral natives generally outperformed late seral natives when growing with exotics and had earlier emergence timing, although results differed among functional groups and soil types. In contrast, survival probabilities did not differ between the early and late seral mixes when growing without exotics. Within each seed mix, native grasses exhibited the highest emergence probabilities of the functional groups. Natives did not suppress exotics in early life stages. Performance of B. tectorum was higher on sandy loam, while T. caput-medusae was highly successful in both soil types. Performance of native functional groups differed by soil type when growing with exotics but did not differ when growing without exotics. Survival of native grasses, in particular, was generally higher on sandy loam when growing with exotics. Conclusions Findings suggest that the use of early seral natives in areas invaded by exotic annual grasses may improve early seedling survival in the Great Basin, in comparison to the use of later seral species in traditional seed mixes. Variation in native performance in the two soil types may be helpful in tailoring seed mixes to different sites. [ABSTRACT FROM AUTHOR]

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Abstract: Restoration is challenging in systems invaded by competitive, disturbance oriented plants, but greater success may be achieved by mimicking natural successional processes and including disturbance-oriented natives in a seed mix. We asked whether seven native annual forbs from the Great Basin Desert, USA, were capable of reducing biomass of the invasive annual grass Bromus tectorum, and if competition between forbs and B. tectorum could indirectly promote establishment of the native perennial grass Elymus multisetus. Some annual forbs were highly competitive with B. tectorum. For example, in a field experiment, Amsinckia tessellata reduced B. tectorum biomass by 97%, and Amsinckia intermedia, A. tessellata, and Descurainia pinnata reduced seed output between 79 and 87%. Adding native forbs to interacting B. tectorum and E. multisetus increased E. multisetus seedling growth rates in the greenhouse, but had no significant positive effects in the field. Strong suppressive effects of native forbs on B. tectorum might lead to indirect enhancement of perennial native species in subsequent years. While native colonizing species are often themselves considered “weedy”, they may be able to serve a transitory role in community recovery, allowing restoration in invaded systems to progress towards more desirable vegetation. [Copyright &y& Elsevier]

Restoration is an opportunity to study natural selection: One can measure the distribution of traits in source propagules used to found populations, compare this with the distribution of traits in successful recruits, and determine the strength and direction of selection on potentially adaptive traits. We investigated whether natural selection influenced seedling establishment during postfire restoration in the Great Basin, an area where large-scale restoration occurs with a few widely available cultivars planted over a large range of environmental conditions. We collected seeds from established plants of the perennial grass Elymus elymoides ssp. californicus (squirreltail) at two restoration sites and compared the distribution of phenotypic traits of surviving plants with the original pool of restoration seeds. Seeds were planted in common gardens for two generations. Plants grown from seeds that established in the field were a nonrandom subset of the original seeds, with directional selection consistently favoring a correlated suite of traits in both field sites: small plant and seed size, and earlier flowering phenology. These results demonstrate that natural selection can affect restoration establishment in strong and predictable ways and that adaptive traits in these sites were opposite of the current criteria used for selection of restoration material in this system. [ABSTRACT FROM AUTHOR]

Widespread invasion by Bromus tectorum (cheatgrass) in the Intermountain West has drastically altered native plant communities. We investigated whether Elymus multisetus (big squirreltail) is evolving in response to invasion and what traits contribute to increased performance. Seedlings from invaded areas exhibited significantly greater tolerance to B. tectorum competition and a greater ability to suppress B. tectorum biomass than seedlings from adjacent uninvaded areas. To identify potentially adaptive traits, we examined which phenological and phenotypic traits were correlated with seedling performance within the uninvaded area, determined their genetic variation by measuring sibling resemblance, and asked whether trait distribution had shifted in invaded areas. Increased tolerance to competition was correlated with early seedling root to shoot ratio, root fork number, and fine root length. Root forks differed among families, but none of these traits differed significantly across invasion status. Additionally, we surveyed more broadly for traits that varied between invaded and uninvaded areas. Elymus multisetus plants collected from invaded areas were smaller, allocated more biomass to roots, and produced a higher percentage of fine roots than plants from uninvaded areas. The ability of native populations to evolve in response to invasion has significant implications for the management and restoration of B. tectorum-invaded communities. [ABSTRACT FROM AUTHOR]