Graduate Thesis Or Dissertation
 

Spatial and temporal patterns of forest cover in the central western Cascades of Oregon and southeast Zaire : a test of distance decay and deforestation models

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  • The Central Western Cascades and southeast Zaire were selected to test the distance decay and deforestation models on forest environments. Distance gradients included away from cities, and away from highways/roads. Two forest definitions were used in each study site. The "extended-forest" definition included areas with at least 30 percent canopy cover in the central western Cascades, and with at least 10 percent canopy cover in southeast Zaire. The "restricted-forest" definition included at least 80 years old conifer forests in the central western Cascades, and forested areas least affected by human activities in southeast Zaire. Additional variables included land ownership, population growth rates, per capita gross national products/money income. The distance decay model assumed increasing forest cover with distance. Extended-forest cover was predicted to increase more rapidly than restricted-forest cover. Forest cover was also hypothesized to increase more rapidly with distance away from highways/roads than away from cities, and more rapidly in southeast Zaire than in the central Western Cascades. Furthermore, it was hypothesized that forest loss rates were higher in southeast Zaire than in the Central Western Cascades. Resulting distance decay curves varied with study sites, land ownership, and forest types. The impact of distance was more identifiable in the restricted than the extended forest definition in the central western Cascades. Forests with at least 30 percent canopy cover increased more rapidly than unmanaged forests. Slope values in the away-from-highways gradient were also higher than in the away-from-cities gradient. There was no significant difference between forest types, and distance gradients in southeast Zaire. The distance was a constraint in private non-industrial lands in the central western Cascades and in all lands in southeast Zaire. This was not always the case with lands owned by United States Forest Service, Bureau of Land Management, and private industrial. The deforestation model was not validated in the central western Cascades. The average forest loss rate was 0.5 percent per year (1972-1988), and it was 1.3 in southeast Zaire (1973-1989). Differences in results were due to natural variability of forest environments, external demands, forest cut policy, socio economic reasons, and population density.
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