Selected factors affecting the pattern of agricultural land conversion in Washington County, Oregon, 1963-1973

Graduation date: 1979In recent years the conversion of agricultural lands to more\ud intensive non-rural land uses has become a focus of increasing public\ud awareness and concern. The growing attention to farmland conversion\ud is manifested in increasing public policies and legilsation to protect\ud agricultural and forestry land uses. Nevertheless, our understanding\ud of the farmland conversion process is restricted. Although agricultural\ud land conversion has been descriptively addressed, little consideration\ud has been given to defining and analyzing the factors affecting the spatial\ud pattern of rural land conversion.\ud The purpose of this investigation was to analyze the impact of\ud selected variables on agricultural land transition to more intensive\ud non-agricultural uses. The research tested the reliability of a composite\ud site characteristic model, and individual submodels for explaining\ud land conversion patterns in Washington County, Oregon. Within the framework of the site characteristic model, specific objectives were:\ud (1) to determine those site factors which exhibited a significant\ud influence on agricultural land conversion,\ud (2) to estimate empirically the influence of each factor on agricultural\ud land conversion, and\ud (3) to determine differences in the effect of individual factors and\ud composite models on agricultural land conversion in areas with\ud varying stages of urbanization.\ud The site characteristic model examined in the investigation\ud included twenty-three predictor variables drawn from four sets of\ud site factors. These four broad categories of site characteristics are\ud accessibility indices, infrastructural-policy factors, social factors,\ud and environmental factors. Individual regression models were\ud developed for each set of site characteristic variables, as well as,\ud for the composite site characteristic model. Published government\ud documents, planning reports, and manually calculated information\ud from aerial photographs provided the primary sources of these data.\ud Following the collection of farmland conversion data from 1963\ud and 1973 aerial photography for Washington County, a series of multiple\ud regression analyses were undertaken. The results of these analyses\ud showed that the hypothesized site characteristics proved important\ud factors in explaining farmland conversion patterns. The composite\ud site characteristic model, with fourteen predictor variables, accounted for 78 percent of the variation in farmland conversion for\ud the county. Geographically, the composite model was most effective\ud in explaining land conversion in urban sections of the county\ud (R² = . 676), while achieving its lowest precision in urban-rural\ud fringe areas (R2 = . 627).\ud As expected, the effectiveness of individual submodels varied\ud extensively with respect to explaining land conversion. Several of\ud the hypothesized variables were consistently strong performers\ud accounting for much of the variation in farmland transition. Conversely,\ud numerous variables proved of only peripheral value during the\ud modeling. The modeling results showed the most powerful set of\ud variables to be the infrastructural-policy factors. This submodel,\ud with four significant variables, was able to explain 70.7 percent of\ud the variation in farmland transition for the entire county. Conversely,\ud the weakest set of site characteristics were the environmental factors.\ud With five significant variables the environment submodel accounted for\ud 49.2 percent of the farmland conversion in the study area. As in the\ud case of the composite model, the relative effectiveness of the submodels\ud varied extensively between urban, urban-rural fringe, and\ud rural portions of Washington County.\ud The research results of the investigation found that the site\ud characteristic model provided a consistently powerful tool for understanding\ud farmland transition in all sections of Washington County, Oregon. The strong measure of reliability associated with the site\ud characteristic methodology, viewed within the framework of concern\ud for farmland conversion, suggests that the conclusions of this investigation\ud may have broad policy implications. The linkage between\ud farmland development and site characteristics provide insight regarding\ud the operation of agricultural land conversion process. Drawing\ud on the relationships pointed out in the investigation, Washington\ud County and other governmental units may find that the study findings\ud can assist in improving mechanisms for controlling land conversion