Event Title

Tree Size and Species Influence Snag Retention Rates Following Severe Wildfires in Dry Coniferous Forests

Event Website

http://www.nafew2009.org/

Start Date

22-6-2009 11:30 AM

End Date

22-6-2009 11:50 AM

Description

Recent debates over post-fire logging practices and their impacts have highlighted the need for a greater understanding of snag dynamics and the relative importance of snags as potential wildlife habitat and as the source of future fuels that influence the severity of subsequent wildfires. This debate is especially relevant in fire-prone dry coniferous forests, where fire exclusion has often altered forest structure and fuel loadings and increased the incidence of stand-replacing wildfires. To address these issues, we sampled fire-killed trees at 126 sites within a chronosequence of 49 wildfires that burned dry coniferous forests of eastern Washington and Oregon from 1970-2007. We sampled a total of 6851 fire-killed trees, recording their species, diameter, and status. Logistic regression analysis showed that snag fall rates varied by species and size. Snag retention times increased with tree diameter. For any given size class, ponderosa pines fell more rapidly than true firs (Abies spp) and Douglas-firs. More than half of small ponderosa pines (< 30 cm dbh) fell within 10 years after wildfire. Fire-killed ponderosa pines had at least a 50% chance of falling within 20 years after wildfire across all size classes. Large true firs and Douglas-firs (> 45 cm diameter) were retained longer, with fall rates less than 50% during the first 30 years after wildfire. Stand level attributes (tree density and basal area, elevation, slope) did not significantly influence snag fall rates. These results suggest that large fire-killed Douglas-fir and true fir trees are most likely to persist for long periods as standing snags, while fire-killed ponderosa pines fall relatively rapidly, increasing downed coarse woody debris and surface fuels. However, the same decay processes that produce earlier snag fall in ponderosa pines may also accelerate suitability of fire-killed trees for cavity nesting birds.

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Jun 22nd, 11:30 AM Jun 22nd, 11:50 AM

Tree Size and Species Influence Snag Retention Rates Following Severe Wildfires in Dry Coniferous Forests

Recent debates over post-fire logging practices and their impacts have highlighted the need for a greater understanding of snag dynamics and the relative importance of snags as potential wildlife habitat and as the source of future fuels that influence the severity of subsequent wildfires. This debate is especially relevant in fire-prone dry coniferous forests, where fire exclusion has often altered forest structure and fuel loadings and increased the incidence of stand-replacing wildfires. To address these issues, we sampled fire-killed trees at 126 sites within a chronosequence of 49 wildfires that burned dry coniferous forests of eastern Washington and Oregon from 1970-2007. We sampled a total of 6851 fire-killed trees, recording their species, diameter, and status. Logistic regression analysis showed that snag fall rates varied by species and size. Snag retention times increased with tree diameter. For any given size class, ponderosa pines fell more rapidly than true firs (Abies spp) and Douglas-firs. More than half of small ponderosa pines (< 30 cm dbh) fell within 10 years after wildfire. Fire-killed ponderosa pines had at least a 50% chance of falling within 20 years after wildfire across all size classes. Large true firs and Douglas-firs (> 45 cm diameter) were retained longer, with fall rates less than 50% during the first 30 years after wildfire. Stand level attributes (tree density and basal area, elevation, slope) did not significantly influence snag fall rates. These results suggest that large fire-killed Douglas-fir and true fir trees are most likely to persist for long periods as standing snags, while fire-killed ponderosa pines fall relatively rapidly, increasing downed coarse woody debris and surface fuels. However, the same decay processes that produce earlier snag fall in ponderosa pines may also accelerate suitability of fire-killed trees for cavity nesting birds.

http://digitalcommons.usu.edu/nafecology/sessions/fire_effects/3