Influence of fire on a rare serpentine plant assemblage: a 5-year study of Darlingtonia fens.

PREMISE OF THE STUDY Serpentine soils have attracted the attention of evolutionary biologists for decades because of 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 ha in California and Oregon's Klamath Mountains in 2002. We established permanent plots in eight unburned and eight 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 2 yr after the fire. Average species density was ∼10% lower in burned fens 1 yr after the fire but ∼4-8% higher for the next 4 yr. Burned fens exhibited greater evenness but not until 4 yr 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.