Riparian Vegetation Rectuitment Tool for Assessing River Management Flexibility

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Existing hydraulic and ecological models for the South Fork Boise River have provided detailed information on flow, elevation, and connectivity that promote areas of native cottonwood recruitment. However, little data exists to validate the model results owing to little pre-fire disturbance that would allow for seedling recruitment and growth. A fire in 2013 has provided a unique opportunity to examine the reduction in competition and subsequent success of riparian seed recruitment along the river corridor. This proposal seeks to leverage the recovery of a riparian vegetation community subject to a recent forest fire and the existing numerical models along the South Fork Boise River to provide a rule-based decision-making tool for native riparian species in a post-fire setting. Field surveys of native riparian plants with similar life histories, like cottonwood and willows, will be used to validate a seedling recruitment model for the characteristic bioclimate region. This tool will then be used to evaluate average flow conditions based on irrigation deliveries, as well as extreme flood conditions from a recent record snowpack. The University of Idaho’s activities to be funded through this action include: 1. Employ the existing burn severity maps to identify areas prone to vegetative regrowth vs. seedling recruitment within the riparian corridor. 2. Validate a riparian seedling recruitment model through field surveys of the dominant substrate and various age classes of native willows and cottonwoods along a study reach of the South Fork Boise River. 3. Establish new rules for the bioclimatic region to assess cottonwood recruitment success. 4. Calibrate the model to assess the success of each year’s hydrograph since the 2013 fire in recruiting seedlings within the burned riparian area. 5. Evaluate the role of last year’s record flood in reestablishing floodplain and riparian recruitment outside the narrow band available during average hydrologic years. 6. Assess historic aerial photos for historic vs. current field conditions and compare with model results.

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