Overstory composition and stand structure shifts within inter-mixed ponderosa pine and lodgepole pine stands of the south-central Oregon pumice zone Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4x51hn09n

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  • Ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta var. murrayana) forests of south-central Oregon have been extensively researched over the last century. However, little information has been reported on overstory composition and stand structure shifts associated with fire exclusion within inter-mixed ponderosa pine and lodgepole pine stands of the south-central Oregon pumice zone. In recent time, the lack of disturbance history and quantitative information needed to reconstruct historic stand conditions has become a growing concern for many ecologists. The need to collect quantitative information from remnant old-growth stands is imperative to improve restoration activities, incorporate stand-level diversity, identify the degree of successional departure, and to ensure valuable data is archived for future reference and ecological analysis. In Chapter 1, an exhaustive search for published information on early land-use practices specific to our study area was performed to: (1) identify the degree of Native American influence on vegetation; (2) identify direct and indirect Euro-American disturbances involving the loss of natural processes; and (3) establish a reference period for appropriate representation of historic conditions. In Chapter 2, remnant old-growth stands were analyzed using dendrochronological techniques and statistical comparisons to quantify: (1) shifts in overstory composition and stand structure; (2) growth and development of ponderosa pine and lodgepole pine across time; and to (3) characterize the influence of climate and fire on species recruitment. Our analysis indicated successional trajectory shifts occurred shortly after the loss of Native American influence beginning around 1850 and associated affects of intensive grazing following 1880. Age reconstruction displayed an exponential pattern of recruitment between 1880 and 1950. Since 1850, our analysis revealed a reduction in average tree basal area growth and height development of understory ponderosa pine and lodgepole pine. Ponderosa pine greater than 150 years old accounted for less than 5.0% of the total contemporary density, but composed 45.0% of the total basal area. Lodgepole pine greater than 100 years old accounted for approximately 3.0% of the total contemporary density and composed 12.8% of the total basal area. Stand density for our study area averaged 25.3 trees per hectare for ponderosa pine greater than 53.3 centimeters diameter at 1.4 meters. We report low levels of lodgepole pine recruitment (2/hectare/decade) prior to 1880 and suggest the long-term development of less fire-resistant lodgepole pine has been favored since fire exclusion. Furthermore, contemporary settings support conditions associated to atypical mountain pine beetle outbreaks and fire behavior known to cause mortality of large diameter ponderosa pine. Restoration of remnant inter-mixed stands requires the aggressive removal of lodgepole pine and re-introduction of fire to provide long-term sustainability of ecosystem health and preservation of large diameter ponderosa pine.
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