Spatiotemporal Variations in the Fire Regimes of Whitebark Pine (\u3cem\u3ePinus albicaulis\u3c/em\u3e Engelm.) Forests, Western Montana, USA, and Their Management Implications

Abstract

Whitebark pine (Pinus albicaulis) is a long-lived tree species that exists throughout high elevation forest communities of western North America. It is the foundation of a diminishing ecosystem that supports Clark’s nutcrackers, red squirrels, grizzly bears, and black bears. The decline of this species is directly related to mortality from widespread mountain pine beetle outbreaks and infestation by the invasive white pine blister rust, and may be exacerbated by fire suppression. Prescribed fire will be a primary management tool in efforts to preserve whitebark pine on the landscape. My research used dendrochronology to investigate the fire history of whitebark pine stands on three mountains in the Lolo National Forest, Montana, via fire-scar and age structure analyses. I then used these data to assess the USDA Fire Regime Condition Classification (FRCC) fire regime types for my sites. Additionally, I utilized traditional superposed epoch analysis techniques in a novel manner to develop a multi-decadal superposed epoch analysis for fire-climate and fire-tree establishment analyses. I sampled between 40 and 50 fire-scarred trees, snags, and remnants, and collected age structure data in two 0.5 ha plots at each site. Samples at all sites recorded a frost event in AD 1601 related to southern hemisphere volcanic activity. The fire-history and stand-structure data indicate all three sites were characterized by mixed-severity fire regimes and generally agreed with the FRCC classifications. However, fires occurred with greater frequency than previously found in whitebark pine forests and distinct differences existed between the fire regimes of each of the three sites that are likely related to topography, forest cover, and climate conditions. A period of widespread fire activity at all three sites occurred from the mid-1700s to the early 1800s and may be the expression of interactions between several climate variables. Fire suppression led to a decline in fire activity in the 1900s, but subalpine fir trees began establishing between 300 and 140 years ago at all three sites. This suggests fire suppression may not be responsible for the advanced succession found in these whitebark pine forests and management decisions based on that assumption are inappropriate for these sites. In addition, the spatial and temporal variability in fire activity between these sites requires a refinement in the Fire Regime Condition Classification methods if they are to be used for managing whitebark pine forests