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Monitoring woodland expansion in a loess mixed prairie in central Nebraska

Jose-Juvenal Gutierrez-Castillo, University of Nebraska - Lincoln

Abstract

Natural populations of deciduous trees before settlement in the Great Plains region were generally restricted to steep sides of deep valleys, along small creeks and ravines, and along floodplains and other wetlands. Coniferous forest were highly restricted to local sites. Reduction of wildfires, changes in wildlife populations, alteration of streams, introduction of windbreaks, and management changes, an interacting with other physical factors have been recognized as important causes for woodland expansion. Only a limited number of studies have assessed woodland expansion for extended periods, but these studies are not commonly spatially referenced. The purpose of this study was to evaluate woodland change and to develop a model for estimating final cover of woodland in a loess mixed prairie of central Nebraska. It was performed through the analysis of aerial photographs from 1938 to 1994 using image analysis and GIS. Specific objectives were to: (1) document change of woody plant species, (2) estimate changes in woodland spread rates, (3) locate microsite variability in woodland spread rates based in topographic conditions (slope and aspect), (4) evaluate if distance to seed sources affects woodland expansion, (5) estimate the influence of human disturbance and birds in seed dispersal of woody plants measured as an indirect effect in closeness to physical features, (6) document woodland expansion in terms of its edaphic composition, (7) develop a model to predict woodland expansion. Results in this study showed that distance to seed source was the most important variable affecting woodland expansion. Spread rates decreased exponentially from seed source. A second outstanding variable was aspect. Spread rates increased when sites were located close to north-facing positions. A model based on distance to seed source, aspect and slope was built-using logistic regression. A total accuracy of 78.6 percent was reached using this model. It was difficult to predict final cover based on initial cover, distance to seed source and aspect, in a period of about 50 years. The model obtained only an R-square of 26 percent. ^

Subject Area

Agriculture, Agronomy|Biology, Ecology|Physical Geography|Agriculture, Forestry and Wildlife|Agriculture, Range Management

Recommended Citation

Gutierrez-Castillo, Jose-Juvenal, "Monitoring woodland expansion in a loess mixed prairie in central Nebraska" (1999). ETD collection for University of Nebraska - Lincoln. AAI9942124.
http://digitalcommons.unl.edu/dissertations/AAI9942124

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