Although island attributes such as size and accessibility to colonizing organisms can influence community structure, the consequences of these for ecosystem functioning are little understood. A study of the suspended soils of spatially discrete epiphytes or treetop "islands" in the canopies of New Zealand rainforest trees revealed that different components of the decomposer community responded either positively or negatively to island size, as well as to the tree species that the islands occurred in. This in turn led to important differences between islands in the rates of ecosystem processes driven by the decomposer biota. This system serves as a model for better understanding how attributes of both real and habitat islands may affect key ecosystem functions through determining the community structure of organisms that drive these functions.