Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2013
Publication Date: 7/22/2013
Citation: Harmon, D.N., Clements, C.D. 2013. Forecasting Bromus tectorum and fire threat: site soil type versus population traits [abstract]. Soil and Water Conservation Society International meeting. 68:120.
Technical Abstract: Cheatgrass (Bromus tectorum), is an exotic invasive annual grass that increases the chance, rate, spread and season of wildfires. Cheatgrass truncates secondary succession by out-competing native perennial seedlings for limited moisture and resources. Habitats that historically burned every 60-110 years now burn every 5-10 years, simply too short of a period of time to allow for critical browse species like big sagebrush to return to the site. Cheatgrass is native to central Asia where humans are first thought to have domesticated animals in environments very similar to the Intermountain West. The success of cheatgrass can be attributed to it’s ability to produce many more seeds than is needed to sustain the population, germinate at a wide range of constant and alternating temperatures present in the Intermountain West, build persistent seed banks, and is very competitive at the seedling stage. As few as 4 cheatgrass/ft² can out-compete most competitive native species, and it is not uncommon to record more than 100 cheatgrass plants/ft². In 2009, we began monitoring 15 cheatgrass populations. Five habitats were chosen: 1) big sagebrush understory, 2) post burn, 3) silt salt desert, 4) sandy salt desert, and 5) pine forest. Habitats were discerned by soil types (nitrogen and water capacity) and consisted of three replications each. Based on field observations and a controlled greenhouse experiment using field soils, germination and biomass as well as seed bank densities were all affected by soil type, whereas, flowering was determined by the parent seed. One population however, pine forest, had a heritable larger biomass (e.g. increased fire threat) (0.76g –vs- 0.56g per plant for the other habitats) and delayed flowering (73 days -vs- 32 days). Silty salt desert sites had the only summer (June) germination observed, most likely due to water holding potential of fine soils. Sandy salt desert populations lacked establishment during drought years and had the smallest average seed bank (sand = 7, silt = 11, understory = 15, pine forest = 18, post burn = 26 seeds/ft2). Sagebrush understory soils were the most productive, resulting in larger biomass (fire threat) and seed production (understory soil = 1.14g biomass/0.84g seed -vs- 4 other soil types = 0.45g biomass/0.30g seed per plant). Frequent wildfires fueled by cheatgrass continue to cause resource managers and land owners management problems associated with loss of wildlife habitat (e.g. sage grouse) and sustainable forage to manage grazing systems. This research can aid resource managers and land owners by defining the threat of cheatgrass based on soil type to improve the efficacy and predictability of restoration/rehabilitation efforts so that prioritization of fire prevention and land management can occur.