Restoring riparian corridors with fire: Effects on soil and vegetation

In many riparian corridors of the semi-arid west, stream incision has resulted in lowered water tables, basin big sagebrush (Artemisia tridentata var. tridentata Nutt.) encroachment and the loss of the dominant herbaceous vegetation. To determine the potential for restoring basin big sagebrush-dominated riparian corridors to greater herbaceous cover, a fall prescribed burn on sites with relatively shallow (-153 to -267 cm) and deep (-268 to greater than or equal to -300 cm) water tables was conducted. We evaluated the separate and interacting effects of water table depth and burning on total soil C and N, soil nutrient availability, and soil enzyme activities by microsite (sagebrush subcanopy, sagebrush interspace), and soil depth (ash/liter, 0-2, 2-5, and 10-20 cm). Three years after the prescribed burn, tissue nutrient content in silvery lupine (Lupinus argenteus Pursh) and Douglas sedge (Carex douglasii Boott), by microsite, growing in burned and unburned areas of 1 shallow water table site was measured. Influence of fire on soil attributes was largely limited to the top 5 cm. As a consequence of prescribed burning, deep water table sites lost relatively more N and C from litter horizons and released more aqueous-soluble Ca+2 from 0-2 cm mineral horizons than did corresponding horizons from shallow water table sites. Overall, compared to unburned controls, burning: (1) increased aqueous-extractable SO4-2, K+, and KCl-extractable NH4+, (2) decreased activities of the enzymes asparaginase, urease and acid-phosphatase, and (3) decreased KCl-extractable NO3- and aqueous-soluble ortho-P. Out of 16 measured soil attributes reported, 7 were influenced by a microsite main effect and/or interaction. New tissue of silvery lupine on burned plots had greater N, greater Zn and Fe (only on subcanopy microsites) and less Ca than plants on control plots; new tissue of Douglas sedge had greater S and less Na, P, and Zn. The results indicate that burning alone is an appropriate restoration treatment for shallow water table sites because of minimal C and N loss and increased available nutrients for regrowth of understory herbaceous species. Deep water table sites require a burning prescription that minimizes tire severity because of higher potential C and N loss, and reseeding due to a lack of perennial understory herbaceous species and more xeric conditions.