Carex nudata, a native sedge, as facilitator of restoration goals following passive restoration

Transcription

1 Carex nudata, a native sedge, as facilitator of restoration goals following passive restoration Middle Fork John Day River, Oxbow Conservation Area Confederated Tribes of the Warm Springs Matthew Goslin Phd Candidate Dr. Pat McDowell University of Oregon

2 Middle Fork John Day River (MFJDR) Confederated Tribes of the Warm Springs (CTWS) Oxbow Conservation Area acres 4 river miles + tribs Forrest Conservation Area 2002 MFJDR 786 acres 3.9 river miles + tribs mainstem John Day 3446 acres

3 Historic Impacts: Dredging for gold Timber harvest/ Floodplain tree removal Cattle grazing Dredge tailings

4 Key Restoration Activities Cattle grazing removed from banks (2000) Tree planting (> 2006) starting w 75,000 plantings Engineered log structures (> 2008) Channel reconstruction (> 2012) focused on dredged channels

5 C. nudata (torrent sedge) suppressed by cattle grazing. After grazing withdrawn from river banks Rapid expansion of C. nudata

6 C. nudata Key point: Native species

7 C. nudata in the river landscape Edges of gravel bars

8 C. nudata in the river landscape Mid channel islands

9 C. nudata in the river landscape In gravels at the base of eroding banks C. nudata fringe fronting eroded bank

10 C. nudata characteristics Tussock forming (not rhizomatous) mature tussocks: cm diameter, leaf lengths up to 1m Strong, dense root system erosion resistant Traps fine sediment Disturbance adapted species propagates primarily by seed & dispersed by water establishes in coarser substrate where it may have competitive advantage Organic boulders

11 Middle Fork John Day River Characteristics Stream bed: gravel cobble Banks: cohesive (silty clay loam) w lower layers of coarse material Bank retreat: undercutting by fluvial erosion followed by cantilever failure

12 How does C. nudata alter channel morphology & planform? River cross section without C. nudata Cut bank High flow Low flow Gravel Bar River cross section with C. nudata Cut bank??? C. nudata fringe High flow Low flow Gravel bar

13 How does C. nudata affect channel morphology and planform? Q 1. Do banks with C. nudata fringes retreat slower or faster than banks without C. nudata? Q 2. What patterns of stream bed erosion and aggradation are associated with the pattern of C. nudata? Q 3. What is the primary pathway for C. nudata island genesis?

14 How does C. nudata affect channel morphology and planform? Questions and Methods Repeated surveys Erosion pins Aerial imagery analysis Q1: Bank retreat rate w C. nudata? x X X Q2: Bed erosion/aggradation w C. nudata? x Q3: C. nudata island genesis? X

15 Q 1. Do banks with C. nudata fringes retreat slower or faster than banks without C. nudata? 7 sites w C. nudata fringe 250 m length total 8 sites w no C. nudata 170 m length total

16 Bank Recession Rates bank area lost (m2) / bank length (m) sites 2sites C. nudata fringe + Median.093 m/yr no C. nudata + Median.040 m/yr

17 bank area lost (m2) / bank length (m) Bank Recession Rates 2sites 2sites 3 sites C. nudata fringe + Median.057 m/yr no C. nudata + Median.097 m/yr

18 Bank Recession Rates bank area lost (m2) / bank length (m) sites 2sites C. nudata fringe + Median.074 m/yr no C. nudata + Median.077 m/yr

19 Q2: Are patterns of stream bed erosion and aggradation associated with pattern of C. nudata? Site: BEBU_F01 Repeat surveys at 5 C. nudata Fringe sites Surveyed summers 2012, 2014 DEM (Digital Elevation Model) differencing

20 Flow

21 Small pools (scour) above C. nudata islands

22 Flow

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24 Scour along C. nudata edges

25 Scour along C. nudata edges Growth/aggradation of C. nudata tussocks

26 Scour along C. nudata edges Growth/aggradation of C. nudata tussocks Currently minimal bed change but significant bank retreat

27 Q3: What is the primary pathway for C. nudata island genesis?

28 C. nudata island genesis: aerial imagery chronosequence

29 Alternative pathways of development with C. nudata 1. bank stabilization and channel narrowing Cut bank C. nudata Gravel bar High flow Low flow 2. compound channel with side channel activated at high flow Cut bank C. nudata Gravel bar High flow Low flow 3. island formation Cut bank C. nudata High flow Gravel bar Complexity Low flow

30 Lessons learned C. nudata induces complexity at multiple scales micro topographic features potential for alternative pathways of development, a patchwork of different channel forms and habitats Recognize habitat impacts of passive restoration independently of active restoration Letting the river landscape teach us how to do restoration C. nudata explosion was an unintended, unexpected consequence experimental, adaptive management critical

31 Acknowledgements Thank you Adviser: Pat McDowell Also: Andrew, Marcus, Mark Fonstad, Dan Gavin (UO Geography), Michael Hughes (OIT), Desiree Tullos (OSU) Confederated Tribes of the Warm Springs CTWS Staff: Brian Cochran, Emily Davis, Steph Charette Middle Fork John Day River Intensively Monitored Watershed (IMW) group Funding Support National Science Foundation OWEB MJFDR IMW Geological Society of America Northwest Science Association Association of American Geographers UO Geography Department

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33 C. nudata distribution: extensive but highly variable among & patchy within river basins

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36 Scour along C. nudata edges

37 Scour along C. nudata edges Growth/aggradation around C. nudata tussocks

38 Scour along C. nudata edges Growth/aggradation around C. nudata tussocks Currently minimal bed change but significant bank retreat

39 Fish cover comparison: C. nudata vs. log structures High resolution aerial imagery (Dietrich 2013) Digitize C. nudata canopy area Digitize water surface area Intersect to calculate area of overhang Correct for tussock area Similar process for log structure cover

40 Fish cover comparison: C. nudata vs. log structures C. nudata: more cover Log structures may have vertically layered cover Larger volume pools under log structures Reach C. nudata % cover Log structures % cover RABE BEBU BUTI