For ecologists who study the budgets of as nutrients such nitrogen, phosphorus, or calcium, one of the first steps is to inventory their distribution within an ecosystem. Invento. Nalini Nadkarni(1981, 1984a, 1984b) changed our ries by ideas of how tropical and temperate rain forests are structured and how they function. With the aid of mountain-climbing equipment, Nadkarni slowly made her first ascent into the canopy of the Costa Rican rain forest, a world explored by few others and where she was to become a pioneer(fig. 1.5) She stood on the rain forest floor and wondered about the diversity of organisms and ecological relationships that might be hidden in the canopy high above. Her wonder soon gave way to determination, and she not only visited the canopy but was among the first to explore the ecology of this unseen world. Because of leaching by heavy rains, many rain forest o soils are poor in nutrients such as nitrogen and phosphorus The low availability of n can the prodigious produced one of ecology's puzzles. How life of rain forests be maintained on such nutrient-poor soils? Many factors contribute to the maintenance of this intense biological activity. Nadkarni's research in the treetops uncovered one of those factors, a significant store of nutrients in the rain forest canopy. associ- The nutrient stores in the rain forest canopy are ated with epiphytes. Epiphytes are plants, such as many