Year of Award
Dissertation - Campus Access Only
Doctor of Philosophy (PhD)
Organismal Biology and Ecology
Department or School/College
Division of Biological Sciences
Ragan Callaway, Elizabeth Crone, Tom DeLuca, Emily Heyerdahl
University of Montana
Mixed ponderosa pine forests are widespread in the western United States and are experiencing less frequent wildfire today than they did historically. Higher stand densities associated with lack of fire raise concerns that trees in these forests are under physiological stress due to increased competition for resources, and that current wildfires are more likely to harm trees than fires of prior centuries because of higher fuel loads today. However, little research has addressed effects of wildfire and lack of fire by comparing contemporary unburned stands to frequently burned stands in forests that have not been logged.
The main focus of this research is to understand how wildfire and lack of fire affect ponderosa pine communities and individual ponderosa pine trees in forests that were never logged or directly managed. I utilized sites in old-growth ponderosa pine/Douglas-fir forests in Montana and Idaho, each with at least two stands, one not burned for at least 70 years and one burned at approximately the historical fire frequency. I found higher overall tree densities and densities of shade-tolerant tree species (Douglas- fir and grand fir) in unburned stands, although overstory and understory community composition and structure varied from site to site. Surprisingly, there were no significant biological differences between mature ponderosa pine trees in burned versus unburned stands in a suite of physiological variables. I found a trend of increasing negative growth responses to wildfire (reduced stemwood (basal area) growth in the burned stand compared to the unburned stand) in recent fire years that had drier winters.
I was able to study very old trees that are otherwise extremely rare across landscapes. Recent investigations on “age-related’' growth in trees have led to the common assumption that old trees grow slowly due to negative effects of age or height on growth. In contrast, I found that tree age and height have little effect on basal area growth, and I present evidence that slow growing trees may be more likely to reach old age. These findings highlight the potential importance of old-growth ponderosa pine/Douglas-fir forests as reservoirs and sinks for carbon in a future with novel fire regime and climate.
Keeling, Eric G., "Wildfire responses and tree longevity in old-growth ponderosa pine/Douglas-fir forests" (2009). Graduate Student Theses, Dissertations, & Professional Papers. 10835.
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© Copyright 2009 Eric G. Keeling