Fire History and Forest Structure along an Elevational Gradient in the Southern Cascade Range, Oregon, USA

We examined stand structure, demography, and fire history using tree cores and fire scar data across an approximately 7000-hectare study area over an elevational gradient in the southern Cascade Range, Oregon, USA. Our plots were located in mountain hemlock (Tsuga mertensiana [Bong.] Carr), red fir (Abies magnifica A. Murr.), lodgepole pine (Pinus contorta Loudon), and mixed conifer forest types. Stand demography from high elevation mountain hemlock forests showed continuous regeneration since the early 1600s and no fire scars present. Red fir forests showed both continuous and episodic regeneration over the past several centuries, providing evidence for a mixed-severity fire regime. Lodgepole pine stands were even-aged with no fire scar evidence and likely established following high severity fire events. Mixed conifer forests were uneven-aged. The majority of trees that we sampled established between 1880 and 1920. Interpretation of our data is limited by a small number of fire scars and relatively small sample size. However, our study highlights the spatial complexity of forest types and concomitant fire regimes on this landscape.