Landslide Disturbance 1 – Landslides, also called debris flows, can rapidly change the landscape of riparian zones. 2 – The sudden movement of debris and water can scour the upper slope of all its soil, forming a heterogeneous deposit of organic debris, rocks, and sediment (Swanson et al., 1987). 3 – These debris flows can be incredibly destructive, altering and shifting stream channels, changing a streams gradient and destroying roads, bridges and homes (Benda, 1990). Benefits of Debris Flow in the Local Ecosystem l Allows for transport of seeds and rhizomes downstream. l Sediment and woody debris in stream channels affect aquatic habitat. l They create an array of new surfaces for future plant colonization. l The developing plants affect stream and riparian ecosystems by providing shade, increasing nutrient retention and input of organic material into streams. Conclusions (1)Debris flows are a normal part of the landscape in the Oregon Coast range. (2)While sometimes destructive, debris flows help to create beneficial terrestrial and aquatic environments. (3) Newly exposed substrates provide open light areas and exposed soils that allow for increased plant diversity (Pabst and Spies, 2001). (4) Initial colonizers and their perseverance were key in plant community development. (5)Invasive species in this study only became dominant if established before native species. The largest benefit was to invasives with early growing seasons which could become established before native plants. References Cited Benda, L., 1990, The Influence of Debris Flows on Channels and Valley Floors in the Oregon Coast Range, U.S.A. Earth Surface Processes and Landforms, v. 15, p “ODA Plant Division, Noxious Weed Control”, Oregon.gov. 11 Feb May Pabst, R. J., T. A., Spies, 2001, Ten Years of Vegetation Succession on A Debris-Flow Deposit in Oregon: Journalof the American Water Resources Association, v. 37, No 6, p Swanson, F. J., L.E. Benda, S.H. Duncan, G.E. Grant W. F. Megahan, L. M. Reid, and R. R. Zeimer, Mass Failures and Other Processes of Sediment Production in the Pacific Northwest Forest Landscapes. Streamside management: Forestry-Fishery Interactions, University of Washington, Seattle, Washington, p 9-38 "Tree Damage, Timber Blowdown, and Forest Debris from Winter Storm 2007." Oregon.gov. 14 Apr Oregon dept. of Forestry. 27 May Vegetative Response to Landscape Disturbance: Is There a Correlation Between Debris- Flow Type Disturbances and Invasive Species in the Oregon Coast Range? Prepared by: Shawn Coreson Figure 3 Percent cover of plants by (A) life form and (B) origin, in the five areas of a debris flow deposit (Pabst and Spies, 2001). Abstract The Willamette Basin of western Oregon is associated with a wide variety of geomorphic and anthropogenic disturbances in riparian zones. These processes include timber harvest, cultivation, flooding, and mass wasting (landslides and debris flows). Riparian areas are particularly vulnerable to habitat disturbance. Because debris-flows cause transfer of large amounts of soil, rock and organic material, extensive scour and deposit zones are formed in the disturbed zone. These stream channels and riparian areas are well suited for vegetative colonization from both native and invasive species. Investigation of invasive plants suggests that while plant communities vary in their susceptibility, invasion may be dependent on the type of soil disturbance, or at least increase the likelihood that an invasive plant might occupy an area. The migration and distribution of both native and invasive plant species have important ecological implications for river restoration and regional land management strategies. Figure 1 A) A small debris flow downslope from a disturbed area in the Oregon coast range. B) Mean percent of ground cover 5 years after a debris flow deposit. Error bars show standard error. Soil in this figure are particles 2mm or less (Pabst, R. Spies,T., 2001). Figure 2 A) An open exposed area with a variety of species, both native and invasive. B) Number of species increased and decreased on a per-year basis on the debris flow deposit. Annual rate of turnover, using beta turnover (Wilson and Shmida, 1984), is shown as a percentage below each bar Native vs. Invasive Species Plant growth and variation was highly influenced by the composition of the deposit. Early colonizers also had a profound effect on local plant progression. Substrate variability created by debris flows increases plant diversity. Colonization can occur quickly. In the debris flow deposit over 80% of the flora had been documented by the second year. Furthermore, over two thirds of those found in year two were still present at 7 years later. Native species did well at colonization and competing as long as invasives were not able to colonize before natives could become established (Pabst and Spies, 2001). B A A B ES 473 Environmental Geology