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Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4) Current High Risk Populations - By 2040, bull trout in Slate and Champion Creeks will be at a high risk of extinction, but for different reasons. Champion Creek is projected to see the loss of summer rearing habitat in the very lowest portion of the drainage from increased water temperatures above 15 o C and high risks from winter peak flows. The bull trout population is already “functioning at unacceptable risk” due to low densities (0.7 fish per 100m 2 ), high densities of brook trout (17.1 fish/100m 2 ), recent wildfire effects, and impacts to migration from irrigation diversions. Projected climate changes will likely increase winter peak flows enough to displace and kill newly emerged bull trout. Warmer water temperatures may also further decrease connectivity to migratory bull trout from the Salmon River. By 2080, risks from winter peak flows increase further (4.4 days), water temperatures are predicted to increase as far as the SF Champion confluence, leaving only 2.3 miles of habitat within optimal summer temperatures. Furthermore, baseflows are predicted to decrease by 33%, impacting rearing habitat and connectivity even further, especially if irrigation demands remain constant. By 2040, risks to summer baseflows in Slate Creek are expected to remain low, increases to winter peak flows increase moderately, and summer water temperatures remain high below Silver Rule Creek, due to irrigation diversions. These changes result in an overall low risk from climate change. However, the bull trout population was still projected to be at high risk of extinction due to very low population size and already-poor habitat conditions from grazing, historic mining, roads, irrigation diversions, and lingering impacts from the 1998 Labor Day flood. Thus, by 2040, climate change will add to cumulative effects but will not be the main driver of extinction risks. By 2080, risks from winter peak flows greatly increase (3.7 days), summer baseflows show a moderate decrease (27%), and summer water temperatures increase slightly, leaving 3.3 miles within the optimal temperature range. These risks will make it harder for an already-weak bull trout population to persist lower in this drainage. Subwatershed Name Management Threats Current Physical Condition Current Biological Condition Ecological Departure 176 Assessing the Vulnerability of Watersheds to Climate Change 2040 2080 Population Persistence Risk Ecological Departure Population Persistence Risk Alturas Lake Creek M FR FR M M M M Big Boulder Creek H FR FA L M M M Champion Creek M FR FUR M H M H Fishhook Creek M FA FR M M M M Fourth of July Creek M FR FR L M M M Germania Creek M FA FA L L M M Little Boulder Creek M FR FA L M H M Prospect-Robinson Bar M FA FA M M H M Slate Creek H FUR FUR L H M H Swimm-Martin L FA FA M L M L Upper EF Salmon M FR FR M M M M Upper Warm Spring Creek L FA FA L L M L West Pass Creek M FR FR L M M M Wickiup-Sheep H FR FR M M H H Table 5. Extinction risks and population persistence outcomes for bull trout-occupied subwatersheds
Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4) Overall, the predictions for bull trout do not seem promising for long-term persistence for many populations. The long-term climate patterns in tributary streams suggest both an expected decrease in the total amount of cold water stream habitat and fragmentation of some colder areas into disconnected “patches” of suitable habitat. Bull trout populations will likely increasingly retreat into these shrinking summer cold water refuges to avoid warming conditions. These restricted tributary populations may become more vulnerable to local extinction (Dunham et al. 1997; Dunham and Rieman 1999; Morita and Yamamoto 2002; Rich et al. 2003; Isaak et al. 2007). Many remaining patches will be subjected to more frequent winter peak flows, which will scour the streambed and destroy redds and/or kill newly emerged fry. Populations may also be subjected to larger, more severe wildfires (McKenzie et al. 2004; Westerling et al. 2006) that can remove riparian vegetation or catalyze severe channel disturbances such as debris flows (Luce, et al 2005). Conceivably, the combined effects of shrinking patch size and increasing frequency or magnitude of stream channel disturbance could chip away at what remaining resiliency these populations have, leaving them in a poorer condition to withstand the next series of disturbances, and accelerating the rate of local extinctions beyond that driven by temperature alone. Forest Infrastructure Developed recreation sites and trails within riparian conservation areas, water diversions, system roads, bridges, and ownership were categorized according to Forest Plan and literature criteria, histograms, and professional judgement, to determine the level of threat associated with each type of infrastructure (Table 6). Bayesian belief networks were then used to evaluate the overall amount of infrastructure and risk to facilities within each subwatershed from winter peak flows caused by rain-on-snow events on the Sawtooth NRA. Those subwatersheds that have moderate/high amounts of infrastructure and high risks from increased winter peak flows were considered to have a high risk of damage to road and trail drainage and facilities within riparian areas. Subwatersheds with less infrastructure were considered to have lower risks from winter peak flow events. Infrastructure Low Threat Moderate High Percent Federal Lands 85-100% 50-84% 8 sites/6 th Field Water Diversions No Diversions 1-2 diversions/6 th Field >2 sites/6 th System Road Density - Miles of Field road/sq. miles (within admin boundaries) < 0.7 mi/mi 2 0.71-1.7 mi/mi 2 >1.7 mi/mi 2 Road Stream Crossings - Number of road/stream crossings on perennial and intermittent streams based current road layer and NHD streams within total subwatershed regardless of ownership or administrative boundaries 0-11 crossings crossings >23 crossings Bridges No bridges present 1-2 Bridges >2 Bridges System Trails within RCAs < 0.7 mi/mi 2 0.71-1.7 mi/mi 2 >1.7 mi/mi 2 Table 6. Forest infrastructure and levels of risk 177 Assessing the Vulnerability of Watersheds to Climate Change
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AUTHORS AND CONTRIBUTORS Authors* M
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ASSESSSING THE VULNERABILITY OF WAT
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staff; the task group included repr
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Figure 2. Conceptual model for asse
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Figure 3. Density of springs and sm
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Using Historic Data One finding con
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NF (Region 8) relied on information
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level of uncertainty. Though there
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climate (Casola et al. 2005). Only
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sensitivity. Most were derived from
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The sensitivity evaluation typicall
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in exposure. The result of combinin
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highest priority for management act
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to information affected the assessm
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with and rely on in many resource d
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Pilot National Forest Reports Conte
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Assessment of Watershed Vulnerabili
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Gallatin National Forest Watershed
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Helena National Forest Watershed Vu
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