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Grassland restoration efforts typically aim to recover lost biodiversity, guided by biologically diverse old‐growth grasslands as a benchmark. In most old‐growth grasslands, forbs greatly outnumber grasses in terms of richness and therefore contribute most to diversity, but globally, restoration practitioners continue to disproportionately focus on increasing perennial grass cover. While such grass‐centric restoration approaches might be appropriate for meeting some restoration goals, an increasing number of studies reveal negative effects of perennial grass cover on forb and total plant diversity in restored grasslands—with cascading consequences for other trophic levels and grassland functionality. To that end, we urge restoration practitioners to recognize the biodiversity costs of grass‐centric approaches and embrace forb‐centric approaches to meet the goal of increasing biodiversity in restorations. Transferring knowledge between well‐studied and understudied grassland systems around the world will facilitate the shared vision of conserving and restoring global grassland biodiversity. [ABSTRACT FROM AUTHOR]

Restoration outcomes are variable, which impairs our ability to plan projects, meet goals, and predict restoration outcomes. Understanding the drivers of this variation is an important research need, especially within urban ecosystems, which support altered abiotic and biotic conditions and face higher rates of loss and degradation than non‐urban areas. Despite the importance of urban areas for restoration, research and practice have largely focused on non‐urban areas. It is unclear if we can extend current knowledge from restoration ecology to urban systems. Here, we surveyed 30 urban prairie restoration plantings across southern Michigan. We collected plant community and site condition data (e.g. soil attributes) and we quantified landscape context as the percentage of urban land surrounding each site. Variation in plant community composition among restorations was related primarily to site‐level factors, such as soil compaction, texture, and water‐holding capacity, rather than landscape context. Non‐prairie species were structured primarily by the local site conditions. There was an increase in non‐prairie richness for sites that experienced warmer local climate conditions, while there was a decrease in non‐prairie richness for sites where soils were less compacted, sandier, and had elevated water‐holding capacity. Prairie species richness responded oppositely. Overall, our study revealed specific factors structuring restoration outcomes in urban contexts and illustrated the importance of local site conditions, not surrounding landscape context, for shaping plant community composition. Restoration practices developed in non‐urban areas should be extended to urban contexts to better understand the impact of local site conditions on plant community development. [ABSTRACT FROM AUTHOR]

A central goal of ecological restoration is to promote diverse ecosystems dominated by native species, but restorations are often plagued by exotic species. A better understanding of factors underlying positive correlations between native and exotic species richness, a pattern that is nearly ubiquitous at large scales in plant communities, may help managers modify these correlations to favor native plant species during restoration. Across 29 tallgrass prairie sites restored through seed sowing onto former agricultural lands, we examined whether the relationship between native and exotic richness is (1) altered by management, such as seed additions and prescribed fire; (2) controlled instead by environmental conditions and successional processes; or (3) altered by management in certain environments and not in others. As is commonly found, native and exotic richness were positively correlated at large scales (i.e., across sites) in this study. Management actions explained much of the remaining variation in native richness, while environmental conditions explained very little. Sites sown with more species at higher seeding rates, especially forb species, had higher native richness than predicted by the native–exotic richness relationship. In contrast, native richness was lower in older restorations than predicted by the native–exotic richness relationship, because native richness, and not exotic richness, declined with restoration age. We show that management actions such as seed sowing can modify the native–exotic richness relationship to favor native species during restoration. The development of management actions that mitigate native species richness declines over time will further benefit native species restoration. [ABSTRACT FROM AUTHOR]

Ecological restoration is critical for recovering degraded ecosystems but is challenged by variable success and low predictability. Understanding which outcomes are more predictable and less variable following restoration can improve restoration effectiveness. Recent theory asserts that the predictability of outcomes would follow an order from most to least predictable from coarse to fine community properties (physical structure > taxonomic diversity > functional composition > taxonomic composition) and that predictability would increase with more severe environmental conditions constraining species establishment. We tested this "hierarchy of predictability" hypothesis by synthesizing outcomes along an aridity gradient with 11 grassland restoration projects across the United States. We used 1829 vegetation monitoring plots from 227 restoration treatments, spread across 52 sites. We fit generalized linear mixed‐effects models to predict six indicators of restoration outcomes as a function of restoration characteristics (i.e., seed mixes, disturbance, management actions, time since restoration) and used variance explained by models and model residuals as proxies for restoration predictability. We did not find consistent support for our hypotheses. Physical structure was among the most predictable outcomes when the response variable was relative abundance of grasses, but unpredictable for total canopy cover. Similarly, one dimension of taxonomic composition related to species identities was unpredictable, but another dimension of taxonomic composition indicating whether exotic or native species dominated the community was highly predictable. Taxonomic diversity (i.e., species richness) and functional composition (i.e., mean trait values) were intermittently predictable. Predictability also did not increase consistently with aridity. The dimension of taxonomic composition related to the identity of species in restored communities was more predictable (i.e., smaller residuals) in more arid sites, but functional composition was less predictable (i.e., larger residuals), and other outcomes showed no significant trend. Restoration outcomes were most predictable when they related to variation in dominant species, while those responding to rare species were harder to predict, indicating a potential role of scale in restoration predictability. Overall, our results highlight additional factors that might influence restoration predictability and add support to the importance of continuous monitoring and active management beyond one‐time seed addition for successful grassland restoration in the United States. [ABSTRACT FROM AUTHOR]

Premise: In 1879, Dr. William Beal buried 20 glass bottles filled with seeds and sand at a single site at Michigan State University. The goal of the experiment was to understand seed longevity in the soil, a topic of general importance in ecology, restoration, conservation, and agriculture, by periodically assaying germinability of these seeds over 100 years. The interval between germination assays has been extended and the experiment will now end after 221 years, in 2100. Methods: We dug up the 16th bottle in April 2021 and attempted to germinate the 141‐year‐old seeds it contained. We grew germinants to maturity and identified these to species by vegetative and reproductive phenotypes. For the first time in the history of this experiment, genomic DNA was sequenced to confirm species identities. Results: Twenty seeds germinated over the 244‐day assay. Eight germinated in the first 11 days. All 20 belonged to the Verbascum genus: Nineteen were V. blattaria according to phenotype and ITS2 genotype; and one had a hybrid V. blattaria × V. thapsus phenotype and ITS2 genotype. In total, 20/50 (40%) of the original Verbascum seeds in the bottle germinated in year 141. Conclusions: While most species in the Beal experiment lost all seed viability in the first 60 years, a high percentage of Verbascum seeds can still germinate after 141 years in the soil. Long‐term experiments such as this one are rare and invaluable for studying seed viability in natural soil conditions. [ABSTRACT FROM AUTHOR]

Ecological restoration outcomes are highly variable, undermining efforts to recover biodiversity and ecosystem functions. One poorly understood source of variability is 'year effects'—interannual variation in environmental conditions during the first year of restoration that alter successional trajectories of plant communities.There have been few experimental tests disentangling planting years from other differences among restoration projects (e.g. edaphic conditions, restoration approach), particularly those resolving mechanisms for year effects such as planting‐year rainfall. Moreover, past year effect studies focused almost exclusively on species‐level consequences. Therefore, the extent to which year effects influence the traits of communities is unknown.To address these gaps and provide a mechanistic test of how precipitation contributes to year effects, we conducted an experiment where we manipulated rainfall (drought, average and high levels) during the first growing season, replicated across three establishment year treatments to disentangle the effects of precipitation from other drivers of year effects. In each establishment year, we seeded the same species mix to initiate grassland restoration. We then surveyed plant community compositions annually for 5 years to quantify trait responses of restored communities to planting year rainfall.We found that variation in planting‐year precipitation altered community assembly trajectories by influencing community‐weighted mean (CWM) trait composition, and these effects persisted for at least 5 years. Over time, CWM specific leaf area and CWM seed mass decreased and CWM plant height increased. The effect of age on CWM plant height was stronger in plots that received mean and high watering treatments compared to drought treatments. This effect was also observed for CWM seed mass, albeit weaker.We also found some evidence for planting year effects unrelated to planting‐year rainfall for the three CWM traits, illustrating how interannually varying environmental conditions besides rainfall can generate persistent year effect on plant communities through their traits.Synthesis and applications. Our results provide evidence for planting year rainfall interacting with community assembly to alter the functional trait composition of restored grasslands. This suggests that interannual variation in rainfall during establishment is an important source of divergent biodiversity and functional outcomes in restored grasslands. [ABSTRACT FROM AUTHOR]

Human activities are altering ecological communities around the globe. Understanding the implications of these changes requires that we consider the composition of those communities. However, composition can be summarized by many metrics which in turn are influenced by different ecological processes. For example, incidence‐based metrics strongly reflect species gains or losses, while abundance‐based metrics are minimally affected by changes in the abundance of small or uncommon species. Furthermore, metrics might be correlated with different predictors. We used a globally distributed experiment to examine variation in species composition within 60 grasslands on six continents. Each site had an identical experimental and sampling design: 24 plots × 4 years. We expressed compositional variation within each site—not across sites—using abundance‐ and incidence‐based metrics of the magnitude of dissimilarity (Bray–Curtis and Sorensen, respectively), abundance‐ and incidence‐based measures of the relative importance of replacement (balanced variation and species turnover, respectively), and species richness at two scales (per plot‐year [alpha] and per site [gamma]). Average compositional variation among all plot‐years at a site was high and similar to spatial variation among plots in the pretreatment year, but lower among years in untreated plots. For both types of metrics, most variation was due to replacement rather than nestedness. Differences among sites in overall within‐site compositional variation were related to several predictors. Environmental heterogeneity (expressed as the CV of total aboveground plant biomass in unfertilized plots of the site) was an important predictor for most metrics. Biomass production was a predictor of species turnover and of alpha diversity but not of other metrics. Continentality (measured as annual temperature range) was a strong predictor of Sorensen dissimilarity. Metrics of compositional variation are moderately correlated: knowing the magnitude of dissimilarity at a site provides little insight into whether the variation is driven by replacement processes. Overall, our understanding of compositional variation at a site is enhanced by considering multiple metrics simultaneously. Monitoring programs that explicitly incorporate these implications, both when designing sampling strategies and analyzing data, will have a stronger ability to understand the compositional variation of systems and to quantify the impacts of human activities. [ABSTRACT FROM AUTHOR]