Historic disturbance legacies to anadromous salmon habitat

Natural disturbance regimes are an integral component of the development and maintenance of aquatic habitat in river ecosystems of the Pacific Northwest. Over the past 150 years, these systems also have been  impacted by anthropogenic disturbances that often differ from natural events in frequency, severity, and patterns of recovery. A disturbance index was developed that through time combines both natural and anthropogenic disturbance in five rivers in the Willamette Valley of Oregon. The disturbance index, focusing on anadromous salmon spawning and rearing habitat, is calculated from the impact of three types of disturbance: fire, floods and associated landslides, and logging practices. Disturbances associated with logging practices include both log transport and riparian forest removal. Each disturbance was scaled by spatial extend and intensity and the index calculated annually.  Disturbance indices for the past 200 years are presented as decadal means. The index illustrates that disturbance occurrence and duration of disturbed conditions varies among watersheds. While current index values continue to decline, the overall legacy of logging practices on anadromous salmon spawning and rearing habitat will continue without substantial restoration as the processes and natural materials required to re-establish productive conditions will take decades to recover.