This study reports ethnographic and experimental analyses of inter-generational changes in native Itza' Maya and immigrant Ladino populations of Guatemala's Petén rainforest concerning understanding of ecological relationships between plants, animals, and humans, and the perceived role of forest spirits in sustaining these relationships. We find dramatic changes in understanding ecological relationships and the perceived role of forest spirits. Itza' Maya conceptions of forest spirits (arux) are now more often confounded with Ladino spirits (duendes), with Itza' spirits no longer reliably serving as forest guardians. These changes correlate with a shift in personal values regarding the forest, away from concern with ecologically central trees and towards monetary incentives. More generally, we describe how economic, demographic, and social changes relate to the loss of a system of beliefs and behaviours that once promoted sustainable agro-forestry practices. These changes coincide with open access to common pool resources.In this study we describe an ongoing research project on how different groups of agro-foresters in the lowland rainforest of Guatemala deal with a resource dilemma involving the forest itself. Using ethnographic and experimental methods we describe inter-generational changes in Itza' Maya and Ladino understandings of ecological relationships between plants, animals, and humans, and the perceived role of forest spirits in sustaining these relationships.While dealing with the conception of environment, this study also contributes to the perennial debate of nature versus culture. The subfield of ecological anthropology or French anthropologie de la nature is mainly interested in understanding the concept of nature as well as people's relation to nature. In recent years, ecological anthropology has been especially concerned theoretically and practically with environment policies, bs_bs_banner