Scholarship & Research
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Item Conifer cover increase in the Greater Yellowstone Ecosystem : rates, extent, and consequences for carbon(Montana State University - Bozeman, College of Letters & Science, 2004) Powell, Scott Lael; Chairperson, Graduate Committee: Andrew J. HansenIncreases in the extent and density of woody vegetation have been observed in many locations worldwide. Conifer cover increase in the Greater Yellowstone Ecosystem (GYE) has been documented by historical photos, but the rate and extent remain unquantified. Elevated atmospheric CO2 levels have focused research attention on carbon budgeting. Carbon sinks associated with conifer cover increase are believed to account for a fraction of the βmissing carbon sink,γ although estimates of the fraction are highly uncertain. I examined changes in conifer cover and aboveground carbon across biophysical gradients in the GYE using a combination of aerial photos, satellite imagery, field data, allometric equations, and statistical techniques. I quantified the percent conifer cover for samples in 1971 and 1999 to determine the frequency and rate of conifer cover increase. I used satellite image change detection to map the extent of conifer cover increase and aerial photo interpretation to quantify the rates of conifer cover increase. I then estimated aboveground carbon stocks for 1985 and 1999 and quantified the source/sink dynamics associated with conifer cover increase and other trajectories of forest change. I determined that the area of conifer forest increased by 7% during the period 1971-1999, at highly variable rates depending upon elevation, aspect, vegetation type, and proximity to conifer forest. Much of the variation in the rates of change was associated with gradients of soil moisture. Conifer cover increased across 685,075 ha between 1985-1999 and was responsible for the aboveground sequestration of 369 Gg C yr-1, offsetting 34% of the carbon source associated with widespread fire and logging during that time period. Climate variability, fire suppression, grazing dynamics, and elevated atmospheric CO2 levels are the hypothesized determinants of conifer cover increase. Although it is likely that no single factor is singularly responsible, fire frequency has been sufficiently reduced throughout the GYE, and the majority of carbon uptake occurred in forest types adapted to frequent fire. The temporal duration of a carbon sink associated with conifer cover increase therefore remains in question.Item Remote sensing of wetlands in Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2004) Wright, Christopher Kevin; Chairperson, Graduate Committee: Daniel GoodmanAs part of the Amphibian Research and Monitoring Initiative, satellite remote sensing was used to identify potential wetland amphibian habitat in Yellowstone National Park. Landsat Thematic Mapper imagery was combined with ancillary predictors of wetland occurrence including habitat type, cover type, landform type, bedrock geology, soil attributes, terrain measures, and climate data. Classification trees were used to predict the likelihood of palustrine wetland occurrence across the Yellowstone landscape. Wetland maps generated by this study are intended to address shortcomings of the National Wetland Inventory in Yellowstone; namely, errors-of-omission and the temporally invariant nature of the inventory. Relative importance of Thematic Mapper imagery, image texture information, terrain measures, and thematic spatial data were assessed by comparing the accuracy of classification trees trained with different subsets of predictors. In general, classification trees using all available predictors exhibited the greatest accuracy. Classification tree structure was similar in models generated with satellite imagery from different years. Also, similar accuracy rates were found across years. The results indicate that the method could be applied to annual wetland monitoring. Average producer's accuracy for the palustrine wetland class was approximately 0.92. Five palustrine wetland classes were discriminated with an average overall accuracy of approximately 0.83. A wetland map derived from a 1 August, 2003 Thematic Mapper image was field-verified in late-summer and early-autumn of 2003. The classification tree methodology appears to be sensitive to within-season wetland condition and yearly wetland variability. Satellite remote sensing located wetlands not mapped by the National Wetland Inventory and also identified upland sites erroneously classified as wetland. Methods developed by this study are general enough to be applied in other physiographic settings and should prove to be useful to amphibian conservation efforts over large geographic extents.