Modelling root reinforcement in shallow forest soils

A hypothesis used to explain the relationship between timber harvesting and landslides is that tree roots add mechanical support to soil, thus increasing soil strength. Upon harvest, the tree roots decay which reduces soil strength and increases the risk of management -induced landslides. The technical literature does not adequately support this hypothesis. Soil strength values attributed to root reinforcement that are in the technical literature are such that forested sites can't fail and all high risk, harvested sites must fail. Both unstable forested sites and stable harvested sites exist, in abundance, in the real world thus, the literature does not adequately describe the real world. An analytical model was developed to calculate soil strength increase due to root reinforcement. Conceptually, the model is composed of a reinforcing element with high tensile strength, i.e. a conifer root, embedded in a material with little tensile strength, i.e. a soil. As the soil fails and deforms, the reinforcing element also deforms and stretches. The lateral deformation of the reinforcing element is treated analytically as a laterally loaded pile in a flexible foundation and the axial deformation is treated as an axially loaded pile. The governing differential equations are solved using finite-difference approximation techniques. The root reinforcement model was tested by comparing the final shape of steel and aluminum rods, parachute cord, wooden dowels, and pine roots in direct shear with predicted shapes from the output of the root reinforcement model. The comparisons were generally satisfactory, were best for parachute cord and wooden dowels, and were poorest for steel and aluminum rods. A parameter study was performed on the root reinforcement model which showed reinforced soil strength increased with increasing root diameter and soil depth. Output from the root reinforcement model showed a strain incompatibility between large and small diameter roots. The peak increase in soil strength attributed to roots was controlled by the small (<4mm) diameter root fraction. These results were used to calculate the effect of timber harvesting on a small, approximately 7.6 m^3 (10 yd^3), hypothetical landslide in a shallow, cohesionless, forest soil. The root reinforcement model predicted a post-harvest reduction in soil strength of 14 and 19 percent for a soil with and without 5 kPa (105 lbs/ft^2) of cohesion, respectively

The role of the geophysical template and environmental regimes in controlling stream-living trout populations

The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream's geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish-habitat relationships in streams

Local Variability Mediates Vulnerability of Trout Populations to Land Use and Climate Change

Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. Here we applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in modifying responses of Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) to scenarios simulating identical changes in temperature and stream flows linked to forest harvest, climate change, and their combined effects over six decades. We parameterized the model for four neighboring streams located in a forested headwater catchment in northwestern Oregon, USA with multi-year, daily measurements of stream temperature, flow, and turbidity (2007–2011), and field measurements of both instream habitat structure and three years of annual trout population estimates. Model simulations revealed that variability in habitat conditions among streams (depth, available habitat) mediated the effects of forest harvest and climate change. Net effects for most simulated trout responses were different from or less than the sum of their separate scenarios. In some cases, forest harvest countered the effects of climate change through increased summer flow. Climate change most strongly influenced trout (earlier fry emergence, reductions in biomass of older trout, increased biomass of young-of-year), but these changes did not consistently translate into reductions in biomass over time. Forest harvest, in contrast, produced fewer and less consistent responses in trout. Earlier fry emergence driven by climate change was the most consistent simulated response, whereas survival, growth, and biomass were inconsistent. Overall our findings indicate a host of local processes can strongly influence how populations respond to broad scale effects of land use and climate change

An annotated bibliography of selected guides for stream habitat improvement in the Pacific Northwest

This annotated bibliography is a response to widespread interest in stream habitat improvement in the Pacific Northwest by land managers, governmental and nongovernmental organizations, and the lay public. Several guides to stream habitat improvement have been written in the past, but may not be easily accessible to people from diverse backgrounds. This annotated bibliography reviews 11 guides to stream habitat improvement so that readers can find literature appropriate to their needs. All reviews begin with summaries of the contents, stated audiences, and goals of each guide. Reviews also include subjective comments on the strengths and weaknesses of each guide. Finally, this bibliography includes recommendations of guides and combinations of guides judged most useful for a range of purposes.Keywords: aquatic habitat, fisheries, restoration, salmonids, stream managemen

Alsea watershed study revisited: unpublished temperature datasets from pre-harvest 2006 to 2010

These data contain temperature readings from dataloggers launched in Deer Creek, Flynn Creek, and Needle Branch from 2006 to 2010. These loggers were apart of the Alsea Watershed Revisisted Study Revisited articles, but the data was incomplete due to logging gaps, temperature spikes, or other issues. The "Thermistor Functionality" datasets indicate whether dataloggers launched in each stream have complete datasets or not. Despite these data not being complete, they help tell the data collection story for the Alsea Watershed Study Revisited

An Approach to Study the Effect of Harvest and Wildfire on Watershed Hydrology and Sediment Yield in a Coast Redwood Forest

The Little Creek watershed, within California State Polytechnic University’s Swanton Pacific Ranch, is the location of a paired and nested watershed study to investigate the watershed effects of coast redwood forest management. Streamflow, suspended sediment, and stream turbidity have been collected during storms at two locations on the North Fork Little Creek and at the outlet of South Fork Little Creek from 2002 until present. In 2008, the watershed area between the two monitoring stations on the North Fork Little Creek watershed was harvested with an individual tree selection silvicultural system within the Santa Cruz County Rules of the California Forest Practice Rules. The South Fork Little Creek was left unharvested to serve as a control. In 2009, the Little Creek watershed was burned by a wildfire. The wildfire eliminated our control watersheds for the proposed Before After Control Intervention (BACI) study design. We present an alternative approach at detecting harvest and fire effects that uses rainfall/runoff models, soil erosion models, and sediment runoff relations to simulate runoff and sediment yield from the watersheds. The models and sediment runoff relationships will be developed within the framework of an uncertainty assessment to simulate pre-harvest and pre-fire conditions for the North and South Forks of Little Creek. The modeled results will be used as the control for the study which had been eliminated due to the wildfire in 2009. We use the HBV hydrologic model and sediment runoff relations to demonstrate our approach. An example of post-harvest and post-fire runoff and sediment changes within the uncertainty of the approach are demonstrated

Fine organic debris and dissolved oxygen in streamed gravels in the Oregon Coast Range

Intragravel organic loading and intragravel dissolved oxygen were studied to determine the relationship between timber harvesting adjacent to first-, second-, and third-order streams and intragravel water quality. Twenty watersheds in the central Coast Range of western Oregon were studied of which five were undisturbed, nine were partially harvested, and six were completely harvested. Intragravel dissolved oxygen was sampled by accessing intragravel water with a small, steel probe and dissolved oxygen was determined with a membrane electrode and dissolved oxygen meter. Streambed gravels were sampled with a liquid nitrogen freeze-core technique and the organics were separated from the inorganics by elutriation. Intragravel organic loading averaged 6.6 gms/ℓ core volume and ranged from 0.2 to 79.5. Intragravel dissolved oxygen averaged 6.5 mg/ℓ and ranged from 2.2 to 10.8 while iritragravel dissolved oxygen depression averaged 34% and ranged from 0% to 74%. Partially harvested watersheds had significantly ([alpha] = .01) lower intragravel organic loading than the undisturbed or completely harvested Gravels in the Oregon Coast Range. watersheds which were not significantly different. A reduction of large organic debris was observed in the partially harvested watersheds. This could have modified the stream's retention capacity for fine organic debris and in turn reduced intragravel organic loading. The most significant variables associated with intragravel organic loading in the multiple linear regression equations were: sample depth, streambed porosity, percent inorganic fines, and large organic debris loading. An increase in any of these variables indicated increased intragravel organic loading. When percent area harvested and length of streambank with harvesting adjacent were included in a regression equation, they explained a small, but significant amount of the variation in intragravel organic loading. Increased harvesting activities as indicated by these variables were associated with decreased intragravel organic loading. There was no significant difference in intragravel dissolved oxygen depression between the undisturbed, partially harvested, and completely harvested watersheds. Percent inorganic fines was the single most significant variable correlated with intragravel dissolved oxygen depression in the multiple linear regression equations. An increase in inorganic fines was associated with decreased intragravel dissolved oxygen. Another group of variables which were indicators of watershed size was correlated with intragravel dissolved oxygen depression. The relationship indicated that larger watersheds were associated with higher intragravel dissolved oxygen. The general conclusion drawn from this study is that timber harvesting in the Oregon Coast Range has not had an adverse impact upon intragravel dissolved oxygen by increasing intragravel organic loading

Uncertainty Assessment of Forest Road Modeling with the Distributed Hydrology Soil Vegetation Model (DHSVM)

We used a generalized likelihood uncertainty estimation procedure with the Distributed Hydrology Soil Vegetation Model (DHSVM) for two streamflow and 11 road ditchflow locations. We observed considerable uncertainty in DHSVM simulations of forest road and stream runoff. The accuracy of simulations decreased as the size of the area modeled decreased. For streamflow, 44% of attempted model structures exceeded a 0.5 Nash–Sutcliffe efficiency threshold for a 630 ha catchment; 12% of attempted model structures exceeded a 0.5 Nash–Sutcliffe efficiency threshold for a 55 ha catchment. DHSVM simulations produced behavioral model structures for only six of the 11 road ditchflow sites (ha). Cumulative distribution functions of parameter values did not indicate specific parameter ranges of parameter values across all locations, indicating that parameter values in DHSVM are influenced by their interaction with other parameters. The sensitivity of parameters and the range of that sensitivity varied across simulations of road ditchflow and streamflow. DHSVM simulations for two streamflow locations varied outside the uncertainty bounds for 10%–22% of storm volumes and 12%–22% of peak flows, respectively. Twenty-eight percent to 52% of storm volumes and 28%–48% of peak flows were outside the uncertainty bounds for the six road ditchflow locations

Road Runoff and Sediment Sampling for Determining Road Sediment Yield at the Watershed Scale

In this study, we demonstrate that watershed-scale estimates of road sediment production are improved if field measurements of road runoff and sediment production are used in the analysis. We used several techniques to spatially extrapolate measurements of road runoff and sampled sediment: comprehensive road runoff measurements, runoff estimates derived from the Distributed Hydrology Soil Vegetation Model (DHSVM), and adjustment of the road erosion models WARSEM and SEDMODL2.The sediment yield for the Oak Creek, Oregon, road network based on measured road runoff and sediment was 6.5 tons/year. When DHSVM was used to simulate road runoff, the estimated sediment from roads was similar, 6.9 tons/years. The road sediment production estimated by SEDMODL2 and WARSEM, adjusted with field-measured road runoff and sediment, was 28% and 34% less, respectively, than using the models with the default parameters. When applied to a road network in commercial forest land with frequent road use, the sediment yield estimated by SEDMODL2 and WARSEM without adjustment from field measurements was 480% and 610% higher, respectively, than with adjustments. We found that measuring runoff and sediment from one large storm event (≥1 year recurrence) provided a statistically significant relationship with the annual sediment yield