Understorey plant community dynamics following a large, mixed severity wildfire in aPinus ponderosa–Pseudotsuga menziesiiforest,Colorado,USA

Abstract

AbstractQuestionHow do understorey plant communities ofPinus ponderosa–Pseudotsuga menziesiiforests respond during the first 5 yrs following wildfire, and do responses vary with fire severity?LocationColoradoFrontRange,USA.MethodsIn 2002, theHaymanFire burned across 55 800 ha ofColoradoFrontRangeP. ponderosa–P. menziesiiforest. Also burned in the fire were 20 upland and five riparian plots within a 400‐ha study area. These plots had been surveyed for understorey plant composition and cover 5–6 yrs prior. We re‐measured all plots annually from 2003 to 2007, 1–5 yrs post‐fire. Changes in the occurrence of common understorey plant species and in metrics of understorey plant richness and cover were analysed with regard to fire severity and time since fire using repeated measuresANOVA. Compositional changes were explored using ordination.ResultsFire severity (defined in terms of overstorey mortality, overstorey canopy consumption, and forest floor consumption) in upland plots was highly variable, with 50%, 30% and 20% of plots burning with low, moderate and high severity, respectively. For all severities, total cover in uplands declined in the first post‐fire year relative to pre‐fire levels, but met or exceeded pre‐fire levels by post‐fire year five. Total richness in uplands, however, did not similarly decline immediately following fire, due largely to a high return rate of pre‐fire species, and exceeded pre‐fire levels for all severities from post‐fire years 3–5 due to new species recruitment. Over 90% of the common upland species either were found in a similar number of plots before and after the fire, regardless of fire severity or time since fire, or were found in more plots following the fire in at least 1 yr and one severity class. Temporal changes in upland composition occurred for all severities but were most pronounced following moderate and severe fire. In contrast, riparian plots largely burned with low severity, and the understorey plant communities within them exhibited little change in richness, cover and composition over the 5 yrs.ConclusionsOur results suggest that theHaymanFire had largely neutral or stimulatory impacts on understorey plant communities following the first five post‐fire years.