Topographic variation in structure of mixed-conifer forests under an active-fire regime

Abstract

Management efforts to promote forest resiliency as climate changes have often used historical forest conditions to provide general guidance for fuels reduction and forest restoration treatments. However, it has been difficult to identify what stand conditions might be fire and drought resilient because historical data and reconstruction studies are generally limited to accurate estimates only of large, live tree density and composition. Other stand features such as smaller tree densities, dead wood, understory conditions, regeneration and fuel loads have been difficult to quantify, estimate how they may vary across a landscape, or assess how they would be affected by fire under current climate conditions. We sampled old-growth, mixed-conifer forests with at least two low-intensity fires within the last 65 years in 150 plots at 48 sample sites ranging over 400 km of the Sierra Nevada. Recent fire history had the strongest influence on understory conditions with small tree density decreasing and shrub cover increasing with the increased severity and frequency of fire associated with upper slope and ridge-top locations. In contrast, stand structures associated with large, overstory trees such as total basal area, canopy cover, and the abundance of large snags and logs increased in topographic locations associated with more mesic, productive sites regardless of fire history. Our results suggest that topography, fire history and their interaction affect forest conditions by directly influencing fire intensity, and indirectly by differences in productivity, leading to heterogeneous forest conditions across a landscape.

Citation

Lydersen, Jamie; North, Malcolm. 2012. Topographic variation in structure of mixed-conifer forests under an active-fire regime. Ecosystems 15: 1134-1146.