This thesis compares farmers' and researchers' interpretation of ecological adaptation based on studies of farmers' knowledge associated with taro and rice grown under varying temperatures and moisture regimes. Farmers' knowledge was acquired through different socio-metric techniques and household surveys. The scientific basis of farmers' knowledge was examined through field testing and laboratory analyses. Wide and narrow adaptation of taro cultivars was experimentally tested at different altitudes and cultivation practices. Similarly, rice varieties were tested reciprocally under different moisture regimes, independent on agro-ecological zones. The persistence of crop diversity and local knowledge are primarily affected by environmental factors. Compared to stress environments, more diversity and knowledge persist under favourable environments. Similarly, the amount of diversity was always high where improved and traditional varieties were grown together. The richness of diversity and the amount of local knowledge that farmers hold are directly related. In the Mid Hills where varietal diversity was rich, farmers’ knowledge was also rich.