The elevational ascent and spread of exotic annual grasslands in the Great Basin, USA

In the Great Basin of the U.S., sagebrush (Artemisia spp.) and salt desert shrublands are rapidly transitioning to exotic annual grasslands, a novel and often self-reinforcing state that threatens the economic sustainability and conservation value of western grazing lands. Climate change is predicted to directly and indirectly favor annual grasses, potentially pushing annual grassland transitions into higher elevations. We used recently developed remote sensing-based rangeland vegetation data to retrospectively quantify expansion and elevational range shift of annual grassland transitions in the Great Basin from 1986–2019. During this period, we document an alarming six-fold increase in annual grassland area (to >75,000 km2) occurring at a rate of 1,950 km2 yr-1. Annual grasslands now occupy one fifth of Great Basin rangelands. This rapid expansion has been in part facilitated by a broadening of elevational range limits, with the leading edge of annual grassland transitions moving upslope at 60–110 m decade-1. Accelerated intervention is critically needed to conserve the fragile band of rangelands being compressed between annual grassland transitions at lower elevations and woodland expansion at higher elevations.SignificanceExotic annual grasses became widespread throughout the western U.S. Great Basin in the last century and now rank among the most vexing challenges facing western rangelands. Once established, these invaders can transform native sagebrush (Artemisia spp.) and salt desert shrublands into virtual monocultures of highly flammable exotic annual grasses with severely diminished biological and economic value. Capitalizing on a recently developed remote sensing vegetation product providing continuous spatial and annual temporal coverage of western US rangelands, we map the expansion of exotic annual grasslands over the past three decades. Our analysis reveals the alarming pace at which native shrublands are transitioning to annual grasslands, and confirms the movement of these transitions into ever higher elevations as the climate of the western U.S. warms.

Diversity and Community Structure

Similar drivers across mediterranean-type climate (MTC) regions have selected for plants with comparable traits (Chapters 3 and 6). This has resulted in the assembly of MTC region plant communities (groups of interacting populations of organisms) that are broadly similar, both structurally and functionally. However, there are also many different types of communities within MTC regions that may be quite divergent from one another even though they occur within a single region. These differences in community types also reveal both similarities and differences among the different MTC regions. This chapter briefly introduces and describes the composition and structure of the main types of plant communities that are found within MTC regions, including the iconic evergreen sclerophyllous shrublands, known as mediterranean-type vegetation (MTV), and other types of shrublands (drought-deciduous soft-leaved shrubs, desert shrublands along arid margins), grasslands, woodlands, and forests.

A diamond in the rough desert shrublands of the Great Basin in the Western United States: A new cryptic toad species (Amphibia: Bufonidae: Bufo (Anaxyrus)) discovered in Northern Nevada

We describe a new species of toad from the Great Basin region of northern Nevada belonging to the Bufo (Anaxyrus) boreas species complex. This cryptic species was detected through genetic analyses of toad populations sampled throughout the Great Basin and the morphological evidence was quantified through extensive sampling of live toads within the region. The new species has the smallest body size in the species complex, and can be further diagnosed from other species in the complex by its large tibial glands and unique coloration. The known distribution of the new species is restricted to an area less than 6 km2 in Dixie Valley, Churchill Co., Nevada. The Great Basin is an arid region where aquatic resources are both rare and widely scattered, making habitat suitable for anuran populations highly vulnerable to anthropogenic change. The habitat occupied by this newly described species is threatened by the incipient installation of geothermal and solar power development projects that require the water that defines its habitat.