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Humans impact fire in many ways. They may reduce ignitions by implementing fire suppression protocols or increase fire incidence through accidental or prescriptive ignitions. Anthropogenic changes to climate affect wind speeds and temperature that in turn may translate to more dangerous fire behaviour. Importantly for this discussion, humans also change the species composition of plant communities either directly by moving plant propagules or indirectly by affecting climate which in turn affects the geographical distribution of plants. Largely because of human actions, Western United States have witnessed drastic increases in the geographic distribution and severity of several important fire-adapted exotic plant species including Bromus tectorum (cheatgrass), Cenchrus ciliaris (buffelgrass), Ventenata dubia (ventenata), Taeniatherum caput-medusae (medusahead), Arundo donax (giant reed), and others. A recent United Nations study finds "the management of invasive alien vegetation is crucial for the prevention of extreme wildfires". The increase of invasive plants that are fire-adapted has changed the fire regimes in the American West fundamentally leading to more frequent and intense fires. Altered fire regimes have significant human and environmental-health consequences and threaten the economic sustainability of communities broadly, especially in the wild-land-urban interface. In California, seven of the 20 deadliest fires on record and 11 of the 20 most destructive fires have occurred in the past five years. Exposure to smoke from wildfires can have severe health consequences broadly across the region. Environmental degradation and severe wildfire events associated with exotic plant invasion have had significant impacts on rare, threatened and endangered species.

Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs., Randomised controlled experiments are the gold standard for scientific inference, but environmental and social scientists often rely on different study designs. Here the authors analyse the use of six common study designs in the fields of biodiversity conservation and social intervention, and quantify the biases in their estimates.

Riparian areas—and the cottonwoods, water birch, bull berry, and currants that flourish within them—hold special significance for Tribes of the Intermountain American West. These species have served ceremonial and practical purposes for generations. Yet cottonwoods have experienced well-documented declines over the past several decades, and serve as indicators of overall riparian change. Research generally attributes this shift to the development of water control infrastructure, altered flood regimes, invasive species, and grazing, and rightfully so. Less attention has been paid to the cultural and historical geographies underlying these vectors of change. This research focuses on the Wind River as a case study to examine the cultural and historical factors related to riparian change. Using remote sensing, interviews and document analysis, we specifically examine boundaries between tribal/non-tribal lands along the Wind River and (1) heterogeneous patterns of riparian change, (2) significant differences in settlement patterns and the development of water infrastructure, and (3) distinct differences in water governance and its power relationships. We conclude that riparian change is heterogeneous; differs temporally, spatially, and between cultural boundaries; and relates to a socio-ecological interplay of values, practices, and policies that underlie water control, flood regime change, and proliferation of invasive species. Ultimately this research suggests that examinations of riparian change would benefit from additional in depth analyses of cultural and historical geographies, and their temporal and spatial relationships. Furthermore, tribal sovereignty over land and water may have significant impacts on overall landscape mosaics, particularly regarding the maintenance of species that support traditional lifeways.

Centaurea stoebe L. subsp. micranthos is native to Eurasia and is invasive in the western portion of the US. Negative impacts of C. stoebe micranthos present in the eastern US have not been recorded. In this study, we examine the effects of C. stoebe micranthos on species diversity on an eastern grassy bald, compare the competitive abilities of plant species from eastern and western grasslands against C. stoebe micranthos, and assess the production of allelopathic compounds in an eastern population of C. stoebe micranthos. Field observations indicated that increasing C. stoebe micranthos abundance was not associated with decreasing abundance or diversity of species. In a greenhouse experiment, C. stoebe micranthos growing with plant species from an eastern grassland were smaller than C. stoebe micranthos growing with species from western grasslands, suggesting that species from the eastern grassland are more competitive against C. stoebe micranthos. We found no evidence that the eastern population of C. stoebe micranthos has allelopathic effects. While the invasion dynamics may change over time, the possibility that C. stoebe micranthos may never become invasive in the studied grassy bald should be weighed when considering control measures here and throughout the eastern US. This study illustrates that invasion dynamics can vary geographically and that land managers need relevant information to gauge an appropriate and economical response.