Modeling the dynamic responses of riparian vegetation and salmon habitat in the Oregon Coast Range with state-and-transition models

Abstract

Interactions between landuse and ecosystem change are complex, especially in riparian zones. To date, few models are available to project the influence of alternative landuse practices, natural disturbance and plant succession on the likely future conditions of riparian zones and aquatic habitats across large spatial extents. A state and transition approach was used to model the effects of various management and restoration practices on conditions of riparian forests, channel morphology, and salmonid habitat. We present results of model analyses for the Wilson River in the Oregon Coast Range. We focus on critical habitat for spawning and rearing salmon and how habitat quality might be influenced by alternative land-use practices over the next 50 years, especially contrasting the outcomes of passive vs. active habitat restoration strategies. Results of our simulations suggest that active restoration of large wood in streams may accelerate habitat improvement relative to recovery projections under a passive restoration strategy. Active restoration seems to be a more viable approach for species such as coho salmon in the Wilson River watershed, which has limited potential spatial distribution in the drainage network, and where a significant proportion of the available habitat is in poor condition. In contrast, using active restoration techniques to improve habitat for a widely distributed species such as steelhead seems less feasible. Steelhead habitat is abundant throughout the basin and at least some of it is currently in good or excellent condition. Thus, large portions of the Wilson River would need to be restored to substantially increase the proportion of the stream network that is in good or excellent condition for steelhead.

Very little data are available with which to validate models at this scale. Results of our model simulations appeared reasonable wherever field and lidar data were available for comparison, however we caution that these comparisons do not validate all the factors simulated in our models. Consequently, the results of the model simulations should be interpreted as hypotheses of likely outcomes from management strategies at the scale of a large watershed (one or several 5^th-field hydrologic units or HUC5s) or a large portion of a USFS ranger district. Nevertheless, the approach holds promise for simulating physical and biological responses of aquatic organisms and their habitats to alternative restoration approaches.

Parent Publication

• Proceedings of the First Landscape State-and-Transition Simulation Modeling Conference, June 14–16, 2011, Portland, Oregon

Citation

Wondzell, Steven M.; Przeszlowska, Agnieszka; Pflugmacher, Dirk; Hemstrom, Miles A.; Bisson, Peter A. 2012. Modeling the dynamic responses of riparian vegetation and salmon habitat in the Oregon Coast Range with state-and-transition models. In: Kerns, Becky K.; Shlisky, Ayn J.; Daniel, Colin J., tech. eds. Proceedings of the First Landscape State-and-Transition Simulation Modeling Conference, June 14–16, 2011, Portland, Oregon. Gen. Tech. Rep. PNW-GTR-869. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 173-196.