Competition between cheatgrass and two native species after fire: Implications from observations and measurements of root distribution

Abstract

During 1987 and 1988, a study was conducted in northern Nevada to examine root growth of cheatgrass (Bromus tectorum L.) and 2 native species, needle-and-thread grass (Stipa comata Trin. & Rupr.) and rabbitbrush (Chrysothamnus viscidiflorus (Hook.) NW.), after fire. Profile wall maps were used to determine the distribution of roots in the soil profile for the 2 native species. Root morphology differed between the 2 species: needle-and-thread grass had a flabelliform root system, whereas rabbitbrush had a main tap root with 2-4 major lateral roots. Although total root biomass differed between the species, more than half the root biomass was in the top 0.2 m of soil for both needle-and-thread grass and rabbitbrush. Measurements of root length density were used to evaluate the interaction between root systems of cheatgrass and the native species. Root production of plots with only the native species was not significantly different from that of plots with both the native species and cheatgrass for the first 2 years after fire. Furthermore, root production of plots in a recently burned area was also not significantly different from that in an area burned 12 years prior to our study. Thus, root systems of these species rapidly occupied the belowground space and competed for soil resources after fire, and the presence of cheatgrass partially reduced the root systems of the native species.