Bromus Response to Climate and Projected Changes with Climate Change

Abstract

A prominent goal of invasive plant management is to prevent or reduce the spread of invasive species into uninvaded landscapes and regions. Monitoring and control efforts often rely on scientific knowledge of suitable habitat for the invasive species. However, rising temperatures and altered precipitation projected with climate change are likely to shift the geographic range of that suitable habitat. Here, we review experimental and modeling studies of climatic limits to exotic annual Bromus (Bromus hereafter) distribution in the Intermountain West in the context of projections of future climate change. We update empirical models of range shifts to test whether Bromus rubens L. (red brome) is likely to expand into ranges that become less suitable for Bromus tectorum L. (cheatgrass or downy brome). Warming temperatures are likely to create an advantage for Bromus species throughout much of the Intermountain West, potentially enhancing invasion into formerly resistant ecosystems if native species mortality increases with warming and drought. Bromus rubens is likely to expand into areas of the Southern Great Basin and Colorado Plateau as warmer winters reduce range constraints caused by cold intolerance. However, a primary limitation to exotic annual Bromus invasion and expansion is growing season precipitation. Projections for precipitation change are uncertain, but increased precipitation during periods critical for exotic annual Bromus germination and growth is forecast for the Northern Great Basin. Increased Bromus reproduction and biomass may exacerbate B. tectorum invasion and associated fire risk, especially if coupled with longer fire seasons and more extreme fire weather. Managers should anticipate both shifts in the overall distribution of Bromus species, as well as changes in relative abundance within its existing range.