Dana M. Blumenthal’s research while affiliated with Agricultural Research Service and other places

Non‐native annual grasses can dramatically alter fire frequency and reduce forage quality and biodiversity in the ecosystems they invade. Effective management techniques are needed to reduce these undesirable invasive species and maintain ecosystem services. Well‐timed management strategies, such as grazing, that are applied when invasive grasses are active prior to native plants can control invasive species spread and reduce their impact; however, anticipating the timing of key phenological stages that are susceptible to management over vast landscapes is difficult, as the phenology of these species can vary greatly over time and space. To address this challenge, we created range‐wide phenology forecasts for two problematic invasive annual grasses: cheatgrass (Bromus tectorum), and red brome (Bromus rubens). We tested a suite of 18 mechanistic phenology models using observations from monitoring experiments, volunteer science, herbarium records, timelapse camera imagery, and downscaled gridded climate data to identify the models that best predicted the dates of flowering and senescence of the two invasive grass species. We found that the timing of flowering and senescence of cheatgrass and red brome were best predicted by photothermal time models that had been adjusted for topography using gridded continuous heat‐insolation load index values. Phenology forecasts based on these models can help managers make decisions about when to schedule management actions such as grazing to reduce undesirable invasive grasses and promote forage production, quality, and biodiversity in grasslands; to predict the timing of greatest fire risk after annual grasses dry out; and to select remote sensing imagery to accurately map invasive grasses across topographic and latitudinal gradients. These phenology models also have the potential to be operationalized for within‐season or within‐year decision support.

Active restoration often aims to accelerate ecosystem recovery. However, active restoration may not be worthwhile if its effects are overwhelmed by changes that occur passively. Moreover, it can be challenging to separate the effects of passive processes, such as dispersal and natural succession, from active restoration efforts. We assess the 24‐year impact of actively restoring a Minnesota old‐field grassland via seed addition of native tallgrass prairie species. We compared the abundance of four functional plant groups in actively restored plots against abundances in three reference classes: (1) unrestored plots undergoing passive recovery within the same old field, (2) passively recovering plots in two nearby old fields of similar age and (3) a chronosequence of 21 old fields within the same landscape. Active restoration led to a higher abundance of native grasses and forbs in the 36 m² treatment plots. Seed addition was more effective if the original vegetation was first removed using herbicide, burning and tilling. However, long‐term conclusions about the efficacy of active restoration varied widely depending on the choice of reference class. In our small‐scale restoration experiment, native abundance was similarly high in both the actively restored and reference plots after 24 years, suggesting either (1) passive recovery or (2) local dispersal of native species from nearby treatment plots (i.e. cross‐contamination). In contrast, a comparison with two nearby reference fields suggested active restoration resulted in much higher native abundance relative to passive recovery. A smaller, positive effect was detected when we compared actively restored plots to the chronosequence of old fields. In the chronosequence, many passively recovering old fields had transitioned to native grass dominance naturally, although active restoration appeared to increase native forb abundance. Synthesis and applications: Our findings highlight the importance of using scale‐appropriate references for assessing the efficacy and need for active restoration. Comparing actively restored plots with the surrounding landscape, we found that active restoration and passive recovery led to similar plant communities after 24 years. Because local dispersal from actively restored sites can nearby references, caution should be exercised when evaluating long‐term restoration projects using only small‐scale experiments.

Despite decades of research documenting the consequences of naturalized and invasive plant species on ecosystem functions, our understanding of the functional underpinnings of these changes remains rudimentary. This is partially due to ineffective scaling of trait differences between native and naturalized species to whole plant communities.Working with data from over 75,000 plots and over 5,500 species from across theUnited States, we show that changes in the functional composition of communities associated with increasing abundance of naturalized species mirror the differences in traits between native and naturalized plants. We find that communities with greater abundance of naturalized species are more resource acquisitive aboveground and below-ground, shorter, more shallowly rooted, and increasingly aligned with an independent strategy for belowground resource acquisition via thin fine roots with high specific root length. We observe shifts toward herbaceous-dominated communities but shifts within both woody and herbaceous functional groups follow community-level patterns for most traits. Patterns are remarkably similar across desert, grassland, and forest ecosystems.Our results demonstrate that the establishment and spread of naturalized species, likely in combination with underlying environmental shifts, leads to predictable and consistent changes in community-level traits that can alter ecosystem functions.

Local adaptation may facilitate range expansion during invasions, but the mechanisms promoting destructive invasions remain unclear. Cheatgrass ( Bromus tectorum ), native to Eurasia and Africa, has invaded globally, with particularly severe impacts in western North America. We sequenced 307 genotypes and conducted controlled experiments. We found that diverse lineages invaded North America, where long-distance gene flow is common. Ancestry and phenotypic clines in the native range predicted those in the invaded range, indicating pre-adapted genotypes colonized different regions. Common gardens showed directional selection on flowering time that reversed between warm and cold sites, potentially maintaining clines. In the Great Basin, genomic predictions of strong local adaptation identified sites where cheatgrass is most dominant. Preventing new introductions that may fuel adaptation is critical for managing ongoing invasions.

Uncertainty persists within trait‐based ecology, partly because few studies assess multiple axes of functional variation and their effect on plant performance. For 55 species from two semiarid grasslands, we quantified: (1) covariation between economic traits of leaves and absorptive roots, (2) covariation among economic traits, plant height, leaf size, and seed mass, and (3) relationships between these traits and species' abundance. Pairs of analogous leaf and root traits were at least weakly positively correlated (e.g. specific leaf area (SLA) and specific root length (SRL)). Two pairs of such traits, N content and DMC of leaves and roots, were at least moderately correlated (r > 0.5) whether species were grouped by site, taxonomic group and growth form, or life history. Root diameter was positively correlated with seed mass for all groups of species except annuals and monocots. Species with higher leaf dry matter content (LDMC) tended to be more abundant (r = 0.63). Annuals with larger seeds were more abundant (r = 0.69). Compared with global‐scale syntheses with many observations from mesic ecosystems, we observed stronger correlations between analogous leaf and root traits, weaker correlations between SLA and leaf N, and stronger correlations between SRL and root N. In dry grasslands, plant persistence may require coordination of above‐ and belowground traits, and dense tissues may facilitate dominance.

Covering approximately 40% of land surfaces, grasslands provide critical ecosystem services that rely on soil organisms. However, the global determinants of soil biodiversity and functioning remain underexplored. In this study, we investigate the drivers of soil microbial and detritivore activity in grasslands across a wide range of climatic conditions on five continents. We apply standardized treatments of nutrient addition and herbivore reduction, allowing us to disentangle the regional and local drivers of soil organism activity. We use structural equation modeling to assess the direct and indirect effects of local and regional drivers on soil biological activities. Microbial and detritivore activities are positively correlated across global grasslands. These correlations are shaped more by global climatic factors than by local treatments, with annual precipitation and soil water content explaining the majority of the variation. Nutrient addition tends to reduce microbial activity by enhancing plant growth, while herbivore reduction typically increases microbial and detritivore activity through increased soil moisture. Our findings emphasize soil moisture as a key driver of soil biological activity, highlighting the potential impacts of climate change, altered grazing pressure, and eutrophication on nutrient cycling and decomposition within grassland ecosystems.

Aim Native biodiversity is threatened by the spread of non‐native invasive species. Many studies demonstrate that invasions reduce local biodiversity but we lack an understanding of how impacts vary across environments at the macroscale. Using ~11,500 vegetation surveys from ecosystems across the United States, we quantified how the relationship between non‐native plant cover and native plant diversity varied across different compositions of invading plants (measured by non‐native plant richness and evenness) and environmental contexts (measured by productivity and human activity). Location Continental United States. Time Period Surveys from 1990s‐present. Major Taxa Studied Terrestrial plant communities. Methods We fit mixed effects models to understand how native plant richness, diversity and evenness varied with non‐native cover. We tested how this relationship varied when non‐native cover interacted with non‐native plant richness and evenness, and with productivity and human activity. Results Across the United States, communities with greater cover of non‐native plants had lower native plant richness and diversity but higher evenness, suggesting rare native plants can be lost while dominant plants decline in abundance. The relationship between non‐native cover and native community diversity varied with non‐native plant richness and evenness but was not associated with productivity and human activity. Negative associations were strongest in areas with low non‐native richness and evenness, characterizing plant communities that were invaded by a dominant non‐native plant. Main Conclusions Non‐native plant cover provides a first approximation of invasion impacts on native community diversity, but the magnitude of impact depended on non‐native plant richness and evenness. Relationships between non‐native cover and native diversity were consistent in strength across continental scale gradients of productivity and human activity. Therefore, at the macroscale, invasive plant impacts on native plant communities likely depend more on the characteristics of the invading plants, that is the presence of a dominant invader, than on the environmental context.

The U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists have worked in agricultural and natural ecosystems, including agronomic and horticultural crops, pastures, forests, wild lands, aquatic habitats, wetlands, and riparian areas. Through strong partnerships with academia, state agencies, private industry, and numerous federal programs, ARS weed scientists have made contributions to discoveries in the newest fields of robotics and genetics, as well as the traditional and fundamental subjects of weed–crop competition and physiology and integration of weed control tactics and practices. Weed science at ARS is often overshadowed by other research topics; thus, few are aware of the long history of ARS weed science and its important contributions. This review is the result of a symposium held at the Weed Science Society of America’s 62nd Annual Meeting in 2022 that included 10 separate presentations in a virtual Weed Science Webinar Series. The overarching themes of management tactics (IWM, biological control, and automation), basic mechanisms (competition, invasive plant genetics, and herbicide resistance), and ecosystem impacts (invasive plant spread, climate change, conservation, and restoration) represent core ARS weed science research that is dynamic and efficacious and has been a significant component of the agency’s national and international efforts. This review highlights current studies and future directions that exemplify the science and collaborative relationships both within and outside ARS. Given the constraints of weeds and invasive plants on all aspects of food, feed, and fiber systems, there is an acknowledged need to face new challenges, including agriculture and natural resources sustainability, economic resilience and reliability, and societal health and well-being.

Invasive species science has focused heavily on the invasive agent. However, management to protect native species also requires a proactive approach focused on resident communities and the features affecting their vulnerability to invasion impacts. Vulnerability is likely the result of factors acting across spatial scales, from local to regional, and it is the combined effects of these factors that will determine the magnitude of vulnerability. Here, we introduce an analytical framework that quantifies the scale‐dependent impact of biological invasions on native richness from the shape of the native species–area relationship (SAR). We leveraged newly available, biogeographically extensive vegetation data from the U.S. National Ecological Observatory Network to assess plant community vulnerability to invasion impact as a function of factors acting across scales. We analyzed more than 1000 SARs widely distributed across the USA along environmental gradients and under different levels of non‐native plant cover. Decreases in native richness were consistently associated with non‐native species cover, but native richness was compromised only at relatively high levels of non‐native cover. After accounting for variation in baseline ecosystem diversity, net primary productivity, and human modification, ecoregions that were colder and wetter were most vulnerable to losses of native plant species at the local level, while warmer and wetter areas were most susceptible at the landscape level. We also document how the combined effects of cross‐scale factors result in a heterogeneous spatial pattern of vulnerability. This pattern could not be predicted by analyses at any single scale, underscoring the importance of accounting for factors acting across scales. Simultaneously assessing differences in vulnerability between distinct plant communities at local, landscape, and regional scales provided outputs that can be used to inform policy and management aimed at reducing vulnerability to the impact of plant invasions.