Influence of a native legume on soil N and plant response following prescribed fire in sagebrush steppe

Abstract

Woodland expansion affects grasslands and shrublands on a global scale. Prescribed fire is a potential restoration tool, but recovery depends on nutrient availability and species responses after burning. Fire often leads to long-term losses in total nitrogen, but presence of native legumes can influence recovery through addition of fixed nitrogen. We examined the effects of prescribed fire in the central Great Basin, Nevada, USA, on density, biomass and nutrient content of a native legume, Lupinus argenteus (Pursh), and the effects of Lupinus presence and prescribed fire on soil inorganic nitrogen and on neighboring plant functional groups. We examined three treatments – 1 year post-burn, 3 years post-burn and unburned control in three replicate blocks. Extractable soil inorganic nitrogen was variable and, despite a tendency towards increased inorganic nitrogen 1 year post-burn, differences among treatments were not significant. Extractable soil inorganic nitrogen was higher in Lupinus presence regardless of time since fire. Lupinus density increased after fire mainly owing to increased seedling numbers 3 years post-burn. Fire did not affect Lupinus tissue N and P concentrations, but cover of perennial grasses and forbs was higher in Lupinus presence. The invasive annual grass Bromus tectorum had low abundance and was unaffected by treatments. Results indicate that Lupinus has the potential to influence succession through modification of the post-fire environment.