The many functions of Puerto Rico and the Luquillo Experimental Forest (the Forest) were evaluated in units of solar EMERGY, an energy-based measure of resource contribution and influence, defined as the energy of one type required to produce a flow or storage of another type. Rainfall and tectonic uplift are the largest environmental inputs into the Forest. The interaction of these inputs results in an erosional landscape where the EMERGY of biological processes is less than the EMERGY associated with the physical and chemical sculpturing of the landscape. The environmental work that built the natural capital of these forests is 9 to 50 times their current dollar market values. Of the investments evaluated in this study, the effects associated with water extraction are the largest. Tectonic inputs and the hydrologic cycle also provide most of the environmental EMERGY flows in the island of Puerto Rico. The ratio of societal inputs to environmental inputs, however, is 45 for Puerto Rico and 3.5 for the Forest. Per capita EMERGY- use is typical of moderately developed economies, but the island has one of the most investment-intensive, least self-sufficient economies known and an EMERGY signature that resembles a city-state.