This thesis develops and tests a conceptual framework for assessing the changes in agroecosystem health from the perspective of agricultural land use. To understand the dynamic relationships in agroecosystems, a general conceptual model is developed with reference to patterns, processes, and forces of change in agricultural land use at different spatial scales. The definition of agroecosystem health adopted for this research is defined as the system's ability to realize its functions desired by society and to maintain its structure needed both by its functions and by society over a long time period. General criteria for characterizing the structural, functional, organizational, and dynamic health of agroecosystems are identified, and their potential utility assessed. The identified general criteria are further developed as five agroecosystem health indicators relating to different aspects of changes in agricultural land use. They are changes in agricultural land resource availability, land use diversity, productivity, self-dependence, and land use stability. A conceptual framework is then developed to further an understanding of the stress-response relationships involved in these aspects of changes in agricultural land use. The framework also facilitates the identification of driving factors/attributes related to macro-level environments. The proposed framework for assessing agroecosystem health is tested in two case studies. The first case study investigates the changes in agricultural land use to southern Ontario over a twenty year period from 1971 to 1991, and the second in Wellington County over the period 1986-91. Using four measurable indicators of land use change and secondary census data, the macro-scale study identifies that both structural and organizational health of the southern Ontario agroecosystem have deteriorated noticeably while the functional health has improved greatly. The macro-scale case study also concludes that the changes in agroecosystem health are significantly associated with the various forces related to biophysical conditions, changes in technology, changes in economic conditions, and modifications in institutional and social settings. According to two indicators of land resource availability and diversity, the county level study identifies that the structural health of the agroecosystem has also undergone a decline. The study reveals that the level of decline in the structural health is higher in northeastern Wellington than in the southwestern part of the county. Also, the changes are associated with different processes of land use conversion among agricultural land, forest, scrubland, and urban related uses. The analytical approach in the first case study demonstrates the utility of censuses and other secondary information for assessing the dynamics of agroecosystem health at a macro scale. It shows how the specific health indicators can be measured, and how GIS and statistical methods can be used to analyze the relationships in the changes of agroecosystem health. The second case study illustrates the utility and limitation of the remote sensing approach for studying the short term change in agroecosystem health at a meso-scale. (Abstract shortened by UMI.)