Passive Recovery of Wood Loads in Rivers

A growing worldwide body of literature is demonstrating the geomorphic and ecological roles played by wood in rivers. After more than a century of removing wood from rivers in many parts of the world, researchers and managers are now interested in returning the load of wood back to a more natural condition. The mechanical placement of wood in rivers is expensive, and so it is useful to know how long it will take for in‐stream wood loads to passively recover a target load by recruitment from riparian forests. Of fundamental interest to managers and researchers alike are the questions: (1) can a river passively recover to a preremoval load of wood, and (2) if so, how long will recovery take? We address these questions using the example of the anabranching King River, Northeast Victoria, Australia, which was desnagged twice: once in 1957 and again in 1980. We predict a recovery time of 255 ± 23 years using a complete census of recovering wood loads to develop and parameterize a mass balance delivery model run in a Monte Carlo simulation. Our results indicate that with a healthy supply of riparian vegetation and minimal interference from managers, rivers are likely to passively recover natural wood loads at least two and a half centuries after desnagging. Using the data and methods described in this paper, we develop a theory of recovery, conceptually describing the recovery process as a sequence of five stages that can be used to monitor and track wood loads through time. Key Points Desnagged rivers can recover a natural wood load but will take centuries rather than decades to passively return to presnagging loads Recovery time is a function of wood removal rates from the reach, while the volume of wood is a function of input/removal rates to the reach Desnagged rivers will typically go through five stages of recovery, with the final one depending on the storage of large key logs in the bed