Project Learning Tree uses the forest as a window on the world to increase students' understanding of the complex environment in the United States; to stimulate critical and creative thinking; to develop the ability to make informed decisions on environmental issues; and to instill the confidence and commitment to take responsible action on behalf of the environment. Project Learning Tree's Activity Guide is arranged under five major themes: Diversity, Interrelationships, Systems, Structure and Scale, and Patterns of Change. Each theme covers the areas of Environment, Resource Management and Technology, and Society and Culture. Each activity includes background information, procedures, recommended grade levels, subjects, concepts, skills, objectives, materials, time considerations, references, related activities. The activities integrate the themes within science, mathematics, language arts, social studies, art, music, and physical education and are based largely on constructivist learning theory and whole language teaching strategies. Appendices contain suggestions for teachers, resource list, and cross-reference indices for activities. (MKR)