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

The central western Cascades of Oregon and southeast Zaire were selected to test the distance decayand deforestation models on forest environments. Distance gradients included away from cities, andaway 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 westernCascades, 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 forestedareas least affected by human activities in southeast Zaire. Additional variables included landownership, population growth rates, per capita gross national products/money income.The distance decay model assumed increasing forest cover with distance. Extended-forest cover waspredicted to increase more rapidly than restricted-forest cover. Forest cover was also hypothesizedto increase more rapidly with distance away from highways/roads than away from cities, and morerapidly in southeast Zaire than in the central Western Cascades. Furthermore, it was hypothesizedthat 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. Theimpact of distance was more identifiable in the restricted than the extended forest definition in thecentral western Cascades. Forests with at least 30 percent canopy cover increased more rapidly thanunmanaged forests. Slope values in the away-from-highways gradient were also higher than in theaway-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 thecentral western Cascades and in all lands in southeast Zaire. This was not always the case withUnited States Forest Service, Bureau of Land Management, private industrial, and Wilderness.
The deforestation model was not validated in the central western Cascades. The average forest lossrate 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.