• Linked disturbance interactions in South-Central Alaska: implications for ecosystems and people

      Hansen, Winslow D. (2013-05)
      Communities and ecosystems in the Alaskan boreal forest are undergoing substantial change. People contribute to this change. They are also impacted by the consequences. For example, wildfire and spruce bark beetle (Dendroctonus rufipennis) outbreaks have increased in frequency and severity due to warming trends, affecting the ecosystem and services important to people. I conducted a study to explore the social and ecological implications of changing natural disturbances. I evaluated how the occurrence of spruce bark beetle outbreak has altered the probability of wildfire between 2001 and 2009 on the Kenai Peninsula, Alaska. Modeling the effects of bark beetle outbreak on the probability of large wildfire (> 500 ha) and small wildfires (<500 ha), I found that the influence of the outbreak differed as a function of wildfire size. The occurrence and length of outbreak increased large wildfire probability. Small wildfires were mediated by human influence and less so by bark beetle outbreak. I also used spatial econometric techniques to estimate how wildfires and the bark beetle outbreak affected property values on the Kenai Peninsula in 2001 and 2010. I found that wildfires> 3.3 ha and the bark-beetle outbreak increased property values. Wildfires <3.3 ha decreased property values.
    • Temporal and spatial variation of broadleaf forest flammability in boreal Alaska

      Wehmas, Maija I.; Verbyla, David; Mann, Daniel; Hollingsworth, Teresea (2018-08)
      The boreal forest is a carbon reservoir containing roughly 40% of the world's reactive soil carbon, which is mainly cycled by wildland fires. Climate warming in boreal Alaska has changed the wildfire regime such that an increase in broadleaf forest relative to conifer forest is likely, which may reduce landscape flammability. However, the current and future flammability of broadleaf forest in a warming climate is not well understood. We used pre-fire and post-fire geospatial data to investigate the flammability of upland boreal forest patches in Interior Alaska in relation to summer weather conditions. Our objectives were to assess burning of broadleaf forest patches during "Normal" vs. "Large Fire Years", by week within a fire season, and by topographic position. Using 30-meter land-cover and fire-severity grids, we estimated the flammability of upland broadleaf forest patches during Large and Normal Fire Years. We then tested for topographic effects using a solar radiation index to eliminate potential deviations within the vegetation. Finally, Moderate Resolution Imaging Spectroradiometer (MODIS) hotspots were used to track the spatial extent of burns during the fire season by examining the periods of fire activity and intensity. Flammability of broadleaf forest patches varied both in time and space. Even during Normal Fire Years, broadleaf forest patches exhibited substantial flammability, with a mean of over 50% patch area burned. Patch flammability was significantly higher during Large Fire Years. Burning of broadleaf patches varied with topographic position and correlated with potential insolation. Broadleaf forest patches burned most frequently in late June-early July. Contrary to "conventional wisdom", broadleaf forest patches in boreal Alaska are susceptible to burning even during Normal Fire Years. With climate warming, the flammability of broadleaf forest is likely to increase due to more extreme fire weather events. Thus, although the frequency of broadleaf forest patches on the landscape is likely to increase with more frequent and severe wildfires, their effectiveness as a fire break may decrease in the future.