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hypothesis. Connell suggested that biodiversity is maximized by ecosystems that are "adapted" to disturbance events of intermediate intensity and duration. Intermediate might be loosely quantified in catchment terms as less than a 100 year flood event and more dynamic than constant flow, for example, from a spring or a storage reservoir. In other words, it is intuitive that a most probable state of quasi-equilibrium can be maintained by natural, intermediate disturbances until a major disturbance event on the scale of a volcanic eruption or hurricane eventuates. Events of that magnitude can completely restructure ecosystems. However, recovery is more rapid than once thought (e.g., recovery of streams following the 1980 eruption of Mount St. Helens in the Cascade Range, USA, is occurring decades sooner than expected). In many ways the idea of natural disturbance controls on stream ecosystem structure and function, however intuitive, remains hypothetical for lack of long-term data sets to test inferences. Indeed, the National Science Foundation decided nearly a decade ago to support long-term ecological research (LTER) at a variety of sites in different biomes so that accurate data describing interannual variation and ecosystem responses to environmental change could be evaluated quantitatively. The objective was to initiate work on hypotheses requiring data sets of five years or more and at the same time setting up a network of sites where basic biophysical data would be systematically gathered for decades (Likens 1989, Franklin et al. 1990). These studies have already greatly contributed to understanding ecosystem connectivity, although data are not yet of sufficient scope to resolve many of the landscape- and patch- specific hypotheses proposed in the LTER program (Swanson and Sparks 1990). Moreover, these data are very site specific and tied to falsefication of hypotheses that are clearly of great scientific importantance but may also be rather narrow in scope from the point of view of many managers. Even though the scientific community has a long way to go before ecosystem response to natural environmental changes is fully understood, frequency, intensity and duration of human disturbances of catchments are often more extreme than natural events. In case after case, ecosystems in the catchment sense presented herein have been essentially uncoupled by the cummulative impacts and interactions of human disturbances (Table 1) (see also Ward and Stanford 1989). Perhaps the most pervasive disturbance is encompassed by the combined effects of channelization, revetment and harvest of riparian timber within major river corridors. It has often. been written that we may never know the true nature of channel-floodplain connectivity of large (> 8th order) rivers in the temperate latitudes because cultural development of the industrial nations was so dependent on these rivers as commercial waterways and 9