Controls on leaf processing in streams from spatial-scaling and hierarchical perspectives

The importance of leaf litter to streams is well known, as is the series of events involved in leaf decay (leaf processing). What is currently missing, however, is an understanding of how the numerous, interacting variables controlling leaf-processing rates in streams can be organized. We suggest that leaf processing is scale-dependent and that factors controlling processing rates will largely depend on the spatial scale of study. Such factors may interact across spatial scales, creating problems in extrapolating results beyond the scale at which the study was conducted. We present a hierarchical framework that relates constraints on leaf processing to specific spatial scales. This framework reveals a predictable structure regarding the factors controlling leaf processing, providing a means for explicit incorporation of spatial scale into studies of leaf processing. Our framework also allows for developing scale-specific predictions of how various environmental changes might affect rates of leaf processing in streams.