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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

Weeds and invasive plants know no borders and have collectively impacted many ecosystems worldwide, including croplands, forests, grasslands, rangelands, wetlands, and riparian areas. Losses continue to mount, affecting yield and productivity, species diversity, and ecosystem services, with both short- and long-term repercussions on the sustainability of plant and animal communities and the livelihoods of many. New and emerging invasive plants, along with many of the most intractable weeds, have undermined even the best control efforts, serving as a reminder of the constant need for improvements in science, application, and technology. One of the main reasons for the success of weeds and invasive plants is their ability to adapt to abiotic and biotic conditions, and research suggests that this will continue with minimal change. Despite the challenges posed by weeds and invasive plants, integrated management techniques, several effective chemistries, and the development of new technology are a signal that ongoing and renewed efforts are worthwhile. National coordination is needed across the sectors of weed and invasive plant sciences to achieve common goals. Federal agencies have the largest land holdings—which are infested with weeds and invasive plants—and work with a diverse group of stakeholders comprising managers, researchers, and regulators. Thus, there is an urgent and pressing need to facilitate dialogue between federal agencies specific to weed and invasive plant science to (1) serve as a starting point for summarizing current knowledge and identifying information gaps and (2) re-engage national program leaders and representatives to better coordinate programs in addressing common challenges. Federal departments and agencies with expertise in weed and invasive plant science were brought together at a symposium held during the Weed Science Society of America’s 63rd Annual Meeting in Washington, DC. Individuals from the Animal and Plant Health Inspection Serv

Climate change and biological invasions by plant pests (weeds), agriculture and forest insect pests (insects), and microbial pests (plant pathogens) are complex interactive components of global environmental change. The influence of pest distribution and prevalence across landscapes are challenging the conservation and sustainability of natural resources, agricultural production, native biological diversity, and the valuable ecosystem services they provide (Huenneke 1997; Vitousek 1997; Juroszek and von Tiedemann 2013; Ziska and Dukes 2014). Since 2000, numerous scientific studies indicate accelerating climate change is posing substantial risks to natural and managed systems in North America (IPPC 2022). Intensified droughts, largescale wildfires, and increased demands for limited surface and groundwater water supplies in arid regions are threatening the sustainability of irrigated agriculture and contributing to economic losses (Stewart et al. 2020), while extreme rainfall events are contributing to severe riverine and urban flooding across the United States. Climate change affects crops, rangelands, forests, and natural areas directly through the immediate effects of temperature, precipitation, and atmospheric carbon dioxide (CO2) levels and thereby impacts production and management systems. These effects are amplified by climatedriven increases in weed, insect, and plant pathogen problems that further complicate related factors such as water, nutrient, and pest management (Walthall et al. 2013). Changing climates also alter physiological, ecological, and evolutionary processes that can support increased establishment, invasiveness, local spread, and geographic range changes of weeds, insects, and plant pathogens (Chidawanyika et al. 2019; Gallego-Tevár et al. 2019; Ziska et al. 2019) that have cascading effects on soil and water quality, and human livelihoods. Joshua W. Campbell is a research ecologist studying basic insect and pollinator behavior in managed and

For nearly a century, invasive annual grasses have increasingly impacted terrestrial ecosystems across the western United States. Weather variability associated with climate change and increased atmospheric carbon dioxide (CO2) are making even more difficult the challenges of managing invasive annual grasses. As part of a special issue on climate change impacts on soil and water conservation, the topic of invasive annual grasses is being addressed by scientists at the USDA Agricultural Research Service to emphasize the need for additional research and future studies that build on current knowledge and account for (extreme) changes in abiotic and biotic conditions. Much research has focused on understanding the mechanisms underlying annual grass invasion, as well as assessing patterns and responses from a wide range of disturbances and management approaches. Weather extremes and the increasing occurrences of wildfire are contributing to the complexity of the problem. In broad terms, invasive annual grass management, including restoration, must be proactive to consider human values and ecosystem resiliency. Models capable of synthesizing vast amounts of diverse information are necessary for creating trajectories that could result in the establishment of perennial systems. Organization and collaboration are needed across the research community and with land managers to strategically develop and implement practices that limit invasive annual grasses. In the future, research will need to address invasive annual grasses in an adaptive integrated weed management (AIWM) framework that utilizes models and accounts for climate change that is resulting in altered/new approaches to management and restoration.

The United Nations Decade on Ecosystem Restoration aims to prevent, halt, and reverse the degradation of ecosystems on every continent. Disturbances stemming from anthropogenic or natural causes make plant community restoration challenging. The introduction of fast-growing weeds that generate high biomass and produce copious seed is most threatening to plant communities. A paradigm shift in ecosystem restoration is needed that emphasizes traits and affected ecological processes similar to weeds. The repeated introduction of seed from native plants with weedy characteristics follows the propagule pressure and evolution of invasiveness hypotheses. In targeting areas with heavy weed populations, native plants could establish and more successfully develop into functioning plant communities.

Due to numerous human activities, organisms have been transported and either accidentally or deliberately introduced all around the globe. Biological invasions are now considered to be one of the main drivers of global change because many invasive plants have severe ecological, economic, and health consequences. Thus, there is an ever-growing need to better understand invasions to determine how specific plant species are able to establish in communities and, in many cases, expand their range. Here, we describe the invasion process and how it contributes to the invasion of plant communities. We present an invasion-factor framework (IFF) model that uses three factors (climate dynamics, ecosystem resistance, and invader fitness) to explain how each plays a role in the introduction of plants and their ultimate failure or success (i.e., becoming invasive). The invasion of plant communities starts with the uptake of propagules from the native range, followed by their transport to and release into a new territory, where they become established and can spread or expand. Propagule pressure, prior adaptation, anthropogenically induced adaptation to invade, and post-introduction evolution are several theories that have been posed to explain the establishment of invasive plants. Further, traits of invasive plants, either before (existing) or after (developed) introduction, provide a mechanistic understanding with direct ties to the three factors of the IFF. The IFF is a general guide with which to study the invasion process based on specific factors for individual invaders and their target communities. The IFF combines (a) climatic dynamics, analogous to environmental filters; (b) ecosystem resistance, which prevents invasive plants from becoming established even if they are able to overcome the climate factor; and (c) invader fitness, relating to the genetic diversity of invasive plants, which allows them to become established after overcoming climate and ecosystem resistance