Refuge or not: Do historic wildfire refugia remain unburned in recent fires?

Background/Question/Methods

Unburned patches and habitat refugia within wildfire perimeters serve as vital areas for the survival of species and regeneration of forest ecosystems. Camp et al. (1997) identified historic fire refugia in the Wenatchee National Forest of the east side Cascade Range based upon forest composition, structure, stand age, and topographic characteristics. In 2012, two wildfires burned through 34 refugial and 45 non-refugial sample plots identified by Camp et al., including over 500 surveyed trees. This provides an opportunity to re-visit and assess both the fire resilience of the previously-identified refugial plots and the accuracy of Camp et al.’s prediction of environmentally influenced wildfire refugia in general. Following Camp et al.’s hypothesis, refugial plots should have been less likely to burn in the 2012 fires, provided that no major forest characteristics changed in the succeeding years since the original study. Field work conducted in 2014 investigated the preliminary remote-sensing results of burn severity further by revisiting these 79 plots to assess actual refugial status from field observations of burn severity and forest structure change, while also characterizing fire impacts more generally across the landscape.

Results/Conclusions

Preliminary analysis of a differenced Normalized Burn Ratio (dNBR) spectral index derived from Landsat remotely-sensed data counterintuitively suggests that a higher percentage of identified refugial plots burned than non-refugial plots and that refugial plots experienced higher burn severity as well. Further field validation allows investigation into reasons why refugial plots may have burned at a differential severity than non-refugial plots.