The Influence of Fire on a Rare Serpentine Plant Assemblage: A Five Year Study of Darlingtonia Fens

Abstract

Premise of the study: Serpentine soils have attracted the attention of evolutionary biologists for decades due to their high number of rare and endemic taxa, though less is known about the ecological factors that govern the diversity and composition of serpentine communities. Theory suggests that vegetation on these low-productivity soils will be relatively resilient to fire, the most common natural disturbance in serpentine systems. Methods: We studied the recovery of vegetation in Darlingtonia fens, a unique habitat dominated by herbaceous perennials, from a major fire that burned ~202,000 hectares in California and Oregon’s Klamath Mountains in 2002. We established permanent plots in 8 unburned and 8 burned fens in 2003 and recorded percent cover of vascular plant species. We re-sampled plots each year through 2007. Key results: Burned fens had less plant cover than unburned fens for two years after the fire. Average species density was ~10% lower in burned fens one year after the fire but ~4-8% higher for the next four years. Burned fens exhibited greater evenness, but not until four years after the fire. Differences in community composition were detected between the two fen types, but species ranks were similar, and species neither were added to, nor removed from, the burned assemblages. Conclusions: Burning of Darlingtonia fens has detectable, albeit modest effects on serpentine communities. Because fens have little or no canopy cover, fire has little influence on light availability in this system. This relatively small resource change, combined with high soil moisture and well-developed underground organs of fen plants, produces a highly resilient assemblage.