Tuolumne River Report - U.S. Fish and Wildlife Service
Tuolumne River Report - U.S. Fish and Wildlife Service
Tuolumne River Report - U.S. Fish and Wildlife Service
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LINKING PHYSICAL PROCESSES AND SALMON LIFE HISTORYLarge floods also deposited considerable volumesof fine sediment on floodplains, <strong>and</strong> less frequentlyon terraces, creating seed beds thatencouraged riparian initiation. New fine sedimentdeposits imported nutrients, improving plantgrowth <strong>and</strong> regeneration on floodplain <strong>and</strong>terraces. Again, initiation success also dependedon local soil moisture conditions. To avoidsuffocation from deep silt <strong>and</strong> s<strong>and</strong> deposited atthe base of established plants, many speciesdeveloped the ability to sprout adventitiousroots further up the trunk, closer to the newdepositional surface, to preserve gas exchangefunctions.Each woody riparian species <strong>and</strong> life stageresponds differently to hydrologic <strong>and</strong> fluvialprocesses, but particular plant life stages aremore vulnerable to the effects of flow variation<strong>and</strong> fluvial processes. Initiating <strong>and</strong> early establishingplants are especially susceptible tomortality agents because substrate composition<strong>and</strong> water availability are vital during early lifestages. If they survive the summer, they aresusceptible to scour-induced mortality duringrelatively small winter <strong>and</strong> spring floods. Once theplant escapes a two to four year window <strong>and</strong>develops deeper <strong>and</strong> more extensive root system,the risk of mortality decreases. Ultimately,mortality to maturing plants depends on channelmigration, being pushed over by flood debris, ordisease. These periodic <strong>and</strong> spatially variabledisturbance patterns <strong>and</strong> mortality agents perpetuatethe plant series diversity historically foundalong the <strong>Tuolumne</strong> <strong>River</strong>.2.4.1.2. Pre-settlement riparian vegetationcompositionPrior to the gold rush era, the riparian corridorextended miles wide in places where the riverlacked confinement. Pre-settlement riparianvegetation in the s<strong>and</strong>-bedded reaches wascomparable to a lush jungle “gallery forest” wherelianas (vines) connected the canopy to denseundergrowth (Bakker 1984) (Figures 2-17, 2-27,2-28). Throughout the corridor, western sycamore,Fremont cottonwood, Oregon ash, <strong>and</strong>CHAPTER 251
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