Exotic annual Brome fundamentally changes vegetation composition, and ecosystem function including fire regimes and biogeochemical cycling of ecosystem carbon. Native perennial herbaceous and woody vegetation in arid and semi-arid ecosystems is typically deep rooted and long lived resulting in relatively large and stable above and belowground carbon stocks. By contrast; annual Brome has lower above and belowground carbon allocation, and inter annual fluctuations in production can be dramatic depending on precipitation. Annual Brome is invading and replacing millions of hectares of native vegetation in the western US and has the potential in to influence regional carbon budgets and contribute significant quantities of CO2to the atmosphere. It is therefore critical to understand how invasion, wildfire, and landcover change influence carbon cycling in ecosystems prone to Brome invasion. We utilized a combination of field collected data from the Sagebrush Treatment Evaluation Project (SageSTEP) and remotely sensed data of landcover and wildfires to estimate standing stocks and fluxes of carbon in sagebrush-steppe ecosystems threatened by exotic Brome invasion.
Results/Conclusions
Exotic annual Brome invasion significantly reduces aboveground and belowground carbon stocks in both biomass and soil organic carbon pools. Belowground losses are potentially larger than from aboveground depending on the previously existing vegetation type. Although Brome dominated rangelands account for only 7% of the Great Basin land area; almost 30% of the land area affected by wildfires from 2000-2012 was burned because of fires starting in Brome dominated rangelands. Furthermore; greater than 20% of total wildfire CO2 emissions in the Great basin are due to fire originating in Brome dominated rangelands. Exotic Brome continues to invade degraded sagebrush-steppe ecosystems with and without fire as a disturbance, and Brome dominated rangelands account for a disproportionate number of acres burned and carbon emissions compared to intact native sagebrush-steppe. Each year the fires originating in Brome dominated rangelands consume additional sagebrush-steppe, and the likelihood that these burned areas becom Brome dominated is high. The pattern of invasion, burning, and Brome dominance is likely to create a large and persistent carbon source to the atmosphere until the invasion can be halted or reversed.