Stand dynamics and fire effects in a subalpine Pinus longaeva ecosystem

Background/Question/Methods

Fire and its associated effects on stand composition have never been studied in Great Basin bristlecone pine (Pinus longaeva D.K. Bailey). We aimed to study fire in Pinus longaeva by examining a high-severity fire that occurred in fall 2000 on Mt. Washington, Nevada. This fire provides an opportunity to assess fire effects on regeneration and stand dynamics in Pinus longaeva, which we assessed using vegetation plots located throughout both burned and unburned areas. We collected georeferenced measurements of stem characteristics to assess vegetation structure and its relationship to fire effects on 40 randomly located 0.1-ha circular plots. Relationships between fire occurrence and bristlecone regeneration were examined with regard to topography (elevation, aspect, and slope), stand basal area, stem density, tree diameter and height.

Results/Conclusions

Mean tree basal area in burned plots (n=22; 24.8 m²) was not significantly different from unburned plots (n=18; 25.1 m²). Stand basal area and density, as well as tree diameter and height, correlated inversely with elevation. Total basal area dropped precipitously above 3400 m, as the treeline is reached. Abundance of seedlings and saplings was negatively correlated with elevation, but positively with live stem abundance. Bristlecone pine height and diameter were less affected by elevation than those of other conifers (Picea Engelmannii and Pinus flexilis). Regeneration abundance of Pinus longaeva was not significantly different in burned and unburned plots (p > 0.06), indicating that fire did not produce lasting negative effects on regeneration.