Within Great Basin sagebrush communities, less than 25% remains intact with an Artemisia tridentata wyomingensis overstory and diverse understory of co-dominant perennial bunchgrasses.  In more than 60% of the remaining communities, Bromus tectorum either dominates the community or is a substantial component of the understory community. The competitive abilities of resident species are one of the primary mechanisms that determine a community's resistance to and resilience after invasion.  Plant establishment is limited primarily by soil water availability.  Competition for these resources takes place entirely belowground.  Belowground competitive ability is correlated with fine root biomass, lateral root spread, maximum rooting depth, etc. Several studies have shown that competition with bunchgrasses and sagebrush reduces cheatgrass establishment and population growth rates.  The objective of this study was to determine whether belowground openings in root neighborhoods of perennial natives are correlated with aboveground vegetation gaps.  The study site is located on the Hart Mountain National Antelope Range in Oregon. Over 1100 soil root core samples were taken in randomly selected basal gaps in vegetation at 0-15cm and 15-30cm depths.

Results/Conclusions

Preliminary findings indicate a significant reduction in root biomass at a threshold gap size of 50-100cm between Artemisia and Achnatherum thurberianum and Elymus elymoides and a smaller threshold gap size of 25-50cm between Artemisia and Poa secunda.  Regression analysis indicates a moderate correlation between root biomass and the aboveground distance from the base of perennial species at the 0-15cm depth.  Gaps in root networks may play an important role in Bromus establishment due to reduced competition for soil moisture. Mapping belowground root gap zones using aboveground basal gaps would allow managers to easily characterize the below-ground competition neighborhoods, monitor changes in response to different management actions or land uses, and identify areas particularly susceptible to cheatgrass invasion.