Prescribed burning may produce refugia for invasive forb, Oncosiphon pilulifer

Abstract

Prescribed burning is a common management technique to reduce non-native grass cover and seed availability in temperate forests and grasslands; however, its effectiveness in reducing non-native forbs is unclear. Litter of invasive forbs like Oncosiphon pilulifer are not consumed by fire like invasive grass litter is, resulting in residual singed stands and high heterogeneity in the postburn landscape. We investigated the potential for this incomplete burning to alter postfire establishment of native and non-native plant species by conducting a field experiment in a prescribed burn in Lake Perris State Park, CA. We investigated the role of microclimate and seed availability on establishment for 2 years following a prescribed burn in both singed stands and completely burned patches by adding or removing litter and adding native seed in a factorial design. Litter presence reduced soil temperatures and light availability, while singed stands had lower soil moisture and temperature. Litter present treatments had 5.6 ± 5.9% (mean ± SE) greater Oncosiphon cover yet doubled Oncosiphon viable seeds in the seedbank. Singed stands had 22.6 ± 4.9% greater Oncosiphon cover and more than doubled Oncosiphon viable seeds. Native seed addition did not influence native or Oncosiphon cover. These results suggest that residual singed stands within the prescribed burn landscape can create a favorable microclimate and allow Oncosiphon to retain seed, increasing reinvasion. Our experiment suggests that litter increased establishment of non-native species as these species may better utilize postburn establishment opportunities impacting overall community recovery. Management of invasive forbs with prescribed burns may require secondary treatments to reduce reinvasion.