A 10,000-curie ¹³⁷Cs gamma source was placed by helicopter at the center of a selected site in the Luquillo Experimental Forest in Puerto Rico. The source was operated for three months after which it was retracted into its shield and eventually removed. Immediately upon termination of the irradiation, detailed effects studies began with quantitative comparisons of the status of the main site before irradiation with that developing subsequently. The studies described in this volume deal with the impact of gamma radiation on species and also with the more abstract phenomenology associated with the modification of ecological systems.