Introduction to the Freshwater Tidal Forested Wetlands of the Columbia River Estuary

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Ecology and natural history of the freshwater tidal forested wetlands of the Columbia River estuary

Laura K. Johnson

A thesis submitted in partial fulfillment of the requirements for the degree of

Master of Science

University of Washington

2010

Program Authorized to Offer Degree: School of Aquatic and Fishery Sciences University of Washington Graduate School

This is to certify that I have examined this copy of a master’s thesis by

Laura K. Johnson

and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made.

Committee Members:

______Charles A. Simenstad

______Jennifer Burke

______Kern Ewing

______Julian D. Olden

Date: ______

In presenting this thesis in partial fulfillment of the requirements for a master’s degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes, consistent with ―fair use‖ as prescribed in the U.S. Copyright Law. Any other reproduction for any purposes or by any means shall not be allowed without my written permission.

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TABLE OF CONTENTS

Chapter 1: Introduction to the freshwater tidal forested wetlands of the Columbia River estuary ...... 1 1.1 Thesis Description ...... 1

1.2 The Columbia River estuary ...... 2

1.2.1 Location and physical characteristics ...... 2

1.2.2 Natural History ...... 3

1.2.3 Estuarine Vegetation Communities ...... 7

1.2.4 Scientific and Technical Background ...... 9

Chapter 2: Ecology of the Freshwater Tidal Forested Wetlands of the Columbia River Estuary ...... 13 2.1 Introduction ...... 13

2.1.1 Study Description ...... 13

2.1.2 Background ...... 13

2.1.3 Study Objectives ...... 17

2.1.4 Hypotheses...... 17

2.2 Methods ...... 19

2.2.1 Site Selection: Rationale and Criteria ...... 19

2.2.2 Site Descriptions ...... 20

2.2.3 Site Sampling Design ...... 22

2.2.4 Timing of Sampling ...... 24

2.2.5 Sampling Variables and Methods ...... 25

2.2.6 Scales of Variability in the Columbia River Estuary and the Study Design ...... 28

2.2.7 Data Analysis ...... 30

2.3 Results ...... 34

2.3.1 Forested Wetland Vegetation Assemblages ...... 34

2.3.2 Avifauna ...... 45

2.3.3 Insects ...... 45

2.3.4 Benthic Macroinvertebrates ...... 48

2.3.5 Amphibians ...... 49

2.3.6 Mammals ...... 49

2.3.7 Summary of Floristic and Faunal Assemblages ...... 50

2.3.8 Environmental Factors ...... 53

2.4 Discussion ...... 58

2.4.1 Vegetation Assemblages ...... 58

2.4.2 Faunal Assemblages ...... 61

2.4.3 Comparison of Study Results to U.S. Army Corps of Engineers Riparian Habitat Inventory ...... 63

2.4.4 Community Ecology Summary of Freshwater Tidal Forested Wetlands ...... 65

2.4.5 The Natural Flow Regime and Environmental Factors ...... 66

2.4.6 Implications and Recommendations for Future Research and Monitoring ...... 68

Chapter 3: Effects of hydroregulation on the freshwater tidal forested wetland communities of the Columbia River estuary ...... 70 3.1 Introduction ...... 70

3.1.1 Study Description ...... 70

3.1.2 Background ...... 70

3.1.3 Study Objectives ...... 73

3.1.4 Hypotheses...... 74

3.1.5 Approach for Testing Hypotheses ...... 74

3.2 Methods ...... 75

3.2.1 Mean Flood Stage Height Calculations ...... 75

3.2.2 GIS Analysis ...... 77

3.3 Results ...... 82

3.3.1 Mean Flood Stage Height Calculations ...... 82

3.3.2 Vegetation Assemblage Change ...... 82

3.4 Discussion ...... 93

3.4.1 Issues of Scale and Potential Sources of Error ...... 93

3.4.2 Physical Disturbance at Individual Sites ...... 94

3.4.3 Alteration to the Natural Flow Regime along the Estuarine Gradient ...... 97

3.4.4 Response of Forested Wetland Vegetation Assemblages to Alteration of the Natural Flow Regime...... 97

3.4.5 Climate Change and Predicted Alterations to the Columbia River Hydrograph in the Future ...... 99

3.4.6 Major Uncertainties and Future Research Recommendations ...... 100

Chapter 4: Synthesis ...... 102 5.0 References ...... 104 Appendix A: Forested wetland study site photographs ...... 111 Appendix B: Forested wetlands study site plant species list ...... 116 Appendix C: Forested wetlands study site avifauna species list...... 119 Appendix D: Forested wetlands study site insect taxa list ...... 122 Appendix E: Forested wetlands study site benthic macroinvertebrate taxa list...... 125

iii

LIST OF FIGURES Figure Number Page 1. Location of the Columbia River basin……………………………………...... 2 2. Changes in the Columbia River hydrograph as a result of flow regulation...... 7 3. Location of freshwater tidal forested wetland study sites in the Columbia River estuary……………………………………………………………………………….20 4. Schematic drawing of sampling layout ……………………………….…………….23 5. Annual discharge of the Columbia River at The Dalles from 1998 to 2008………...24 6. Mean species richness by vegetation zone …………………………….….………...35 7. Total number of trees present in survey plots ………………………..……………..36 8. Diameters at breast height (DBH) of tree species…………………………………...37 9. Contributions of individual species to canopy cover ……………………………….39 10. NMDS ordination of vegetation presence/absence survey data …………...………..40 11. NMDS ordination plot of vegetation assemblages by site and zone ………………..41 12. NMDS ordination plot of avifauna assemblage composition……...…….………...... 45 13. NMDS ordination plot of insect assemblage composition …………………….…....46 14. Vegetation and insect species richness……………………………………….……...47 15. NMDS ordination plot of benthic invertebrate assemblage composition …………..49 16. Mean percent organic content, sand, silt, and clay………………...………………..56 17. Mean elevation of vegetation zones ………………………………………………...57 18. Hydrogeomorphic reaches of the Columbia River estuary………………………….60 19. Location of forested wetland study sites and NOAA tide gauges used in study……76 20. Example of a U.S. Coast & Geodetic Survey topographic sheet …………………...78 21. Vegetation of Rooster Rock State Park based on GLO survey notes …………….....80 22. Bankfull elevation and mean flood stage heights during recent spring freshets ……82 23. Change in vegetation classes at lower estuarine study sites ………………………...84 24. Historic vegetation at Big Creek.……………………………………………………85 25. Current vegetation at Big Creek ………………………………………………….....85 26. Historic vegetation at Julia Butler Hansen ………………………………………….86

27. Current vegetation at Julia Butler Hansen ………………………………….……….86 28. Historic vegetation at Robert W. Little ………………………………………...... …87 29. Current vegetation at Robert W. Little …………………………………...…………87 30. Change in vegetation classes at mid- and upper estuarine sites ……………….……89 31. Historic vegetation at Willow Grove………………………………………….…...... 90 32. Current vegetation at Willow Grove……………………………………………...…90 33. Historic vegetation at Willow Bar …………………………………………………..91 34. Current vegetation at Willow Bar …………...………………………………………91 35. Historic vegetation at Mirror Lake ………………………………………………….92 36. Current vegetation at Mirror Lake …………………………………………………..92 37. Historic photograph of Rooster Rock State Park/Mirror Lake wetlands …………....96 38. Columbia River annual flow at the Dalles, Oregon …………………..…………....100

LIST OF TABLES

Table Number Page 1. Mean density of trees in plots……….……………………………………...... 36 2. Average percent similarity of forested wetland study sites ……………...... 41 3. Composition of lower and upper estuarine vegetation zones based on SIMPER analysis………...…………………………………………………………………….43 4. Insects composing the majority of the insect assemblages at study sites based on SIMPER analysis……………………..……………………………….…………….48 5. Amphibian species observed at forested wetland study sites …………….………...49 6. Mammalian species observed at forested wetland study sites...……….….………...50 7. Summary of floristic and faunal assemblages.………………………..……………..51 8. Results of ANOVA test on environmental characteristics of zones within sites……55 9. P-values of ANOVA with post-hoc Bonferroni test for mean sand content of soils at study sites …………………………………………..……………………………….55 10. P-values of ANOVA with post-hoc Bonferroni test for mean silt content of soils at study sites……………………………………………………...…………...………..56 11. Location of forested wetland study sites and NOAA tidal gauges used in the study.75 12. Habitat classes attributed to digitized U.S. Coast & Geodetic Survey t-sheets……...79 13. Translation used to convert GLO survey vegetation classes to t-sheet vegetation classes for the Mirror Lake study site ……………………………………...….…....80 14. Change in area of vegetation classes at study sites over time………….…….……...83

Chapter 1: Introduction to the freshwater tidal forested wetlands of the Columbia River estuary

1.1 Thesis Description

The purpose of this thesis is to describe the ecology and natural history of a dynamic but largely unstudied community: the freshwater tidal forested wetlands present throughout the Columbia River estuary. Hydroregulation and development of the Columbia River and its estuarine floodplain have substantially reduced the extent of this community over the past century, and restoration of this habitat type is now becoming a priority in the region. The forested wetlands vary in composition along the estuarine gradient, and provide habitat for a plethora of faunal groups. However, detailed quantitative and qualitative studies of the ecological structure and community composition of forested wetlands are lacking in the scientific literature, both for the Columbia River system and in other systems throughout the world. This thesis aims to fill that gap for the Columbia River system and contribute to the body of worldwide literature on the subject. Finally, the study provides a better understanding of how human alteration of natural flow regimes has affected the freshwater tidal forested wetlands in this estuarine ecosystem.

This thesis will consist of two subsequent chapters, each of which will explore a different aspect of the ecology and natural history of the freshwater tidal forested wetlands of the Columbia River estuary. The first chapter will describe overall community structure including vegetation and faunal assemblages and variation in freshwater tidal forested wetland communities along the estuarine gradient. The second chapter will examine the effects of changes in the river hydrograph due to hydroregulation on the freshwater tidal forested wetland vegetation assemblages.

1.2 The Columbia River estuary

1.2.1 Location and physical characteristics

The Columbia River is the second largest river in the United States in terms of mean water discharge, and its watershed covers an area of 667,000 km2 (Simenstad et al. 1992). The Columbia River basin includes portions of seven states and one Canadian province (Figure 1). The estuarine portion of the Columbia River is exceptionally large and extends from the Pacific Ocean to the head of tide at Bonneville Dam, located at River Kilometer (RKm) 235.

Figure 1. Location of the Columbia River basin. Map courtesy of Jennifer Burke, University of Washington, School of Aquatic and Fishery Sciences. Base layer is ESRI world physical map, December 2009. Strong ocean tides mix with riverflow in the Columbia River estuary and produce turbulent currents and energetic water circulation (Fox et al. 1984). Saline oceanwater moves into the estuary as a result of ocean tides to the point where strong river flow restricts

3 its movement into the upper, freshwater portion of the estuary. The amount of salinity intrusion in the Columbia River estuary is affected by both tidal and riverflow conditions. Salinity intrusion is generally lowest during periods of high riverflow combined with neap tides and highest during periods of low riverflow combined with spring tides. Relative to other estuaries, the Columbia River estuary is characterized by having higher riverflow, lower salinity, and larger tidal fluctuation.

Tides affecting the lower Columbia River are mixed diurnal and semidiurnal, meaning two high and two low tides of unequal heights daily (Simenstad et al. In revision). The combination of twice-daily tidal fluctuations and the annual river discharge cycle creates dynamic conditions within the estuary (Jay and Smith 1990). Tidal amplitude in the lower estuary ranges from 1.7 to 4.0 m depending on location; maximum tidal amplitude occurs near Astoria, OR and decreases progressively upriver to the head of tide at Bonneville Dam (RKm 235) (Simenstad et al. In revision). Near Longview, WA, in the mid-estuary, mean daily tidal range is slightly over 1 m. In the upper estuary, tides are still present but minimal with a mean daily tidal range of less than 0.2 m. Thus, in the lower estuary (to 21 to 56 km depending on flow), river conditions including stage are dominated by tides. In contrast, in the mid- and upper estuary, river conditions are dominated by river flow, while tides have little effect.

Large quantities of sediment are transported through the estuary along the river bottom and in suspension (Sherwood et al. 1990). Sediment transport along the river bottom is known as bedload transport, and the movement of fine sediment in the water column is known as suspended transport. Most of the river bottom is composed of sandy sediment, while finer, silty sediment is more common in shallow, protected embayments within the estuary. As a result of the sedimentation processes within the estuary, naturally occurring soils tend to be fine in texture, while soils in the estuarine floodplain that are coarse or sandy in texture tend to be a result of dredge material deposits from maintenance of the river’s navigation channel.

1.2.2 Natural History

1.2.2.1 Geologic history of the Columbia River basin

The present physical characteristics of the Columbia River estuary are attributable to a long geologic history, dating back the formation of the North American continent in the Mesozoic period 200 million years ago or megaannum (Ma) (Simenstad et al. In revision). From about 50 to 35 Ma, the present location of the Cascade mountain range was formed and the subducting oceanic plates migrated to their present location. At that time, uplift of the Rocky Mountains combined with subduction of the oceanic plates of the Pacific Ocean provided an elevated source area for the river and a pathway to the Pacific Ocean.

Later, periodic glaciation of the Columbia River basin from 2.8 Ma to 12 thousand years ago or kiloannum (ka) restructured much of the basin, increasing runoff, erosion, and extent of the drainage basin (Simenstad et al. In revision). The Columbia River estuary was never directly affected by glaciation, but sequestration of large volumes of water into glaciers and ice sheets lowered sea level substantially (by about 120 m) and resulted in incision of the river from the Pacific Ocean to The Dalles at RKm 309.

From 17 to 14 ka, near the end of the last glacial period, the Missoula Floods had a tremendous impact on the physical landscape of the Columbia River basin (Simenstad et al. In revision). The floods are the largest known freshwater floods to ever occur on the planet, and stemmed from a repeated draining of Glacial Lake Missoula in northwestern Montana. Flow velocity from these floods was as great as 35 ms-1, and they transported and deposited huge volumes of silt, sand, and gravel that now form much of the landscape in the Columbia River basin.

Volcanism and resulting eruptions, lava flows, and lahars have affected the lower Columbia River and estuary during the last 500 ka (Simenstad et al. In revision). The modern bedload of the Columbia River is composed largely of volcanic materials that originated during this period. Mount Hood, Mount Jefferson, and Mount St. Helens all experienced volcanic events that contributed debris or sediment to the Columbia River during this period.

The geologic events in the Holocene period, which includes the last 15 to 10 kiloannum (ka), are responsible for the formation of much of the Columbia River estuary, including the floodplain and channel features present today (Simenstad et al. In revision). During the Holocene period, eruptions from the Cascade Range stratovolcanoes have

5 contributed large volumes of sediment to the river and resulted in the formation of large deltas at the confluence of the Columbia River and its tributaries within the estuary. These sediment pulses provided a major source of sediment for the lower portion of the Columbia River, created landforms that comprise the floodplain, and produced ash plumes that periodically covered portions of the floodplain with volcanic material or tephra. Additionally, large earthquakes occurred every 300 to 700 years during the Holocene, causing subsidence, tsunamis, and liquefaction, all of which have affected the landforms in the lower Columbia River. Finally, sea level rose to modern levels from about 16.5 to 11 ka, and at the end of this time, modern estuarine conditions in the Columbia River developed.

1.2.2.2 Euro-American Settlement of the Region

Euro-American development of the Columbia River estuary likely had tremendous impacts on the structure and composition of the floodplain vegetation communities. Although humans have occupied the Columbia River region since approximately 10 ka, it was the settlement of the region by Euro-Americans in the 1800s that brought major changes to the landscape and natural resource utilization (Lichatowich 1999). Although not the first Euro-Americans to explore the region, the Lewis and Clark expedition in the early 1800s set the stage for development of the region, and by the 1820s, grazing and farming activities had begun in the estuary (Christy and Putera 1992). Use of the estuarine floodplain for agricultural purposes increased dramatically after that time, peaking between 1900 and 1940. Diking of low-lying areas to prevent flooding was associated with agricultural use of the landscape, and resulted in the severing of large portions of the floodplain from the river.

At the same time, the Euro-American settlers in the region realized the potential value of salmon fisheries in the Columbia River, and began to develop commercial fishing efforts (Lichatowich 1999). The first shipment of Pacific salmon to the east coast of the United States occurred in 1829, and by the 1860s salmon canning grew into a major industry in the region. The boom in the salmon canning industry led to not only depletion of Columbia River salmon runs, but also construction of vast numbers of canneries, warehouses, fish traps, and other similar structures along the shores of the river. The construction of these structures and placement of associated pilings altered the landscape along the shores of the

6 lower Columbia River, and the remains of some structures are still present today (Christy and Putera 1992, Lichatowich 1999).

In addition to the grazing, farming, and fishing activities, logging of the tree species in the Columbia River estuary floodplain had a major impact on the landscape (Christy and Putera 1992). The history of the logging of the region is poorly documented, but research suggests that nearly all stands of riparian trees were logged at least once for lumber, fuel, and paper pulp. Prior to the 1890s, wood was the primary source of energy for heating homes and powering steamboats and locomotives.

1.2.2.3 Hydroregulation of the Columbia River

Construction of dams on the Columbia River for power generation, flood control, irrigation water diversion, industrial- and municipal-use water diversion, and recreation began in the 1930s (Simenstad et al. 1992). After World War II, construction of dams along the Columbia River and its tributaries increased, and now 28 major dams regulate flow along the mainstem of the Columbia. Although construction of dams began in the 1930s, significant alteration of river flow in the estuary did not begin until 1969 when Bonneville Dam was in full operation. Thus, the period from 1969 to the present is considered the modern period of hydroregulation.

Hydroregulation has resulted in numerous changes to the flow regime of the Columbia River (Simenstad et al. 1992). One of the most obvious impacts to the flow regime has been the dramatic reduction of peak river flow in the late spring, known as the spring freshet. Between 1969 and 1982, peak river flow was reduced 40% from flow prior to regulation (Figure 2). Flow in most other months has increased following regulation, since water from peak flow periods is stored in upstream reservoirs and released throughout the year. Additionally, river flow is now typically lower on weekends and holidays as a result of lower needs for power generation during these times.

Figure 2. Changes in the Columbia River hydrograph as a result of flow regulation. Source: Volkman (1997). Significant reductions in river flow during the spring freshet have resulted in less inundation of the estuarine floodplain compared to historical times (Kukulka and Jay 2003). Seasonal flooding of the Columbia River as part of the natural flow regime is responsible for physical restructuring of the estuarine floodplain, transfer of nutrients from the terrestrial to aquatic environment, and influencing successional trajectories of riparian vegetation communities (Naiman and Décamps 1997). Thus, the substantial alteration of the Columbia River hydrograph over time has likely had an effect on the dynamics of vegetation succession and community composition in its estuarine floodplain.

1.2.3 Estuarine Vegetation Communities

Freshwater tidal wetlands exist where tidal influences extend beyond the reach of saline water in river systems throughout the world. However, these ecosystems are highly impacted by human development centered around the world’s river systems, and those that remain today are relatively understudied (Lugo et al. 1988). Tropical mangrove forests and bottomland hardwood swamps of the southeastern United States have received the most attention in scientific studies. However, these systems and the species present in them have

8 little in common with the Columbia River estuary and its tidal freshwater forested wetlands due to climatic and geomorphological differences. Thus, limited information on ecosystems similar to the Columbia River estuary is available, and the following description of estuarine vegetation communities will focus on those of the Columbia River estuary.

Although the amount of salinity intrusion into the estuary varies based on river flow and tidal conditions, generally the area from RKm 0 to 40 is considered to be the saltwater portion of the estuary, while the area above RKm 40 is considered to be the freshwater portion of the estuary (Jay and Smith 1990). Vegetation assemblages characterizing the saline and freshwater tidal regimes of the estuary differ drastically, since the presence of salinity requires plants to have functional mechanisms to cope with salt stress (Mitsch and Gosselink 2000).

The vegetation in the saline portion of the estuarine floodplain is characterized by comparably simple plant assemblages consisting mainly of sedges and grasses such as Scirpus americanus, Carex lyngbyei, and Agrostis alba (Macdonald 1984). Above RKm 40, in the tidal freshwater portion of the estuarine floodplain, much more complex vegetation assemblages are present (Christy and Putera 1992). In addition to freshwater tidal wetlands like in the lower estuary, from RKm 40 to 63, Sitka spruce (Picea sitchensis) stands and dense scrub-shrub swamps consisting of red osier dogwood (Cornus sericea) and willow (Salix sp.) dominate the more common wetland assemblages. Above RKm 63, Sitka spruce is no longer present in the estuarine floodplain, and forested assemblages are dominated by deciduous species such as Pacific willow (Salix lucida ssp. lasiandra), Oregon ash (Fraxinus latifolia) and black cottonwood (Populus balsamifera ssp. trichocarpa). Scrub-shrub swamps of composition similar to those in the lower estuary persist throughout the mid- and upper estuary, and freshwater tidal marshes consisting of wapato (Sagittaria latifolia), creeping spikerush (Elocharis palustris), common rush (Juncus effusus), and reed canary grass (Phalaris arundinacea) are common as well.

Freshwater tidal forested wetlands are known to support high species diversity and provide essential habitat for a variety of wildlife, including mammals, birds, and amphibians (U.S. Army Corps of Engineers 1976a). Thomas (1983) calculated that 77% of the freshwater tidal forested wetland habitats have been lost since Euro-American settlement of

9 the region. Likewise, many of the animals that rely on these wetlands have experienced serious declines during this time period, and remaining wetlands provide animals with necessary habitat to maintain their populations (Christy and Putera 1992). Additionally, freshwater tidal wetlands have been shown to be important for sustaining aquatic organisms (Bottom et al. 2005). Freshwater tidal wetlands provide shade for water temperature control, high organic matter input into aquatic ecosystems, and protective habitat as a result of large woody debris contributions to associated wetlands and riparian habitat.

1.2.4 Scientific and Technical Background

Among the earliest studies of the estuary are large-scale mapping efforts by the United States government. Both the General Land Office (GLO) and U.S. Coast and Geodetic Survey (USC&GS) conducted geographic surveys in the region from approximately 1860 to 1900 that provide data useful in temporal comparisons of Columbia River estuary vegetation. GLO surveys were conducted in order to plat and transfer or sell public lands of the United States in the 19th and early 20th centuries. Vegetation species and characteristics such as size and density were recorded during the process of marking township and range corners. USC&GS undertook large-scale, high-resolution mapping of the lands bordering coasts and waterways in the United States, with the resulting maps known as topographic sheets, or t-sheets. As part of that effort, they mapped generalized characteristics of the wetland and riparian vegetation along the Columbia River estuary from the Pacific Ocean to approximately RKm 207.

A number of scientific and technical studies have described the physical processes, biota, and natural history of the Columbia River estuary. However, the freshwater tidal forested wetlands remain relatively understudied. The Columbia River Estuary Data Development Program (CREDDP) generated the largest and most comprehensive collection of scientific studies on the estuary in the late 1970s and early 1980s (Fox et al. 1984). For the purposes of their studies, the authors considered the estuary to include the area from the Pacific Ocean to RKm 75 near Puget Island. One of the most comprehensive studies generated by CREDDP is ―The Columbia River Estuary Atlas of Physical and Biological Characteristics‖, which contains a summary of plant life, estuarine food webs, and physical processes present in the Columbia River Estuary (Fox et al. 1984). Brackish scrub-shrub

10 swamp, freshwater scrub-shrub swamp, and freshwater forested swamps are all described in general terms, and a list of plant species occurring at each type of wetland is provided. The atlas is considered an overview document for the entire Columbia River estuary, and does not contain detailed ecological information about specific sites.

Other studies generated by CREDDP focus on the vegetation in the lower portion of the Columbia River estuary. Macdonald (1984) analyzed marsh vegetation types, primary production estimates, and marsh production dynamics. He did not specifically study tidal forested or scrub-shrub wetlands, but did state that brackish scrub-shrub wetlands, freshwater scrub-shrub wetlands, and freshwater forested wetlands are present in the estuary. Species found in each wetland type along with estimates of their extent are provided in the report. Thomas (1983) compares historical data for the Columbia River estuary with data current to 1983 in order to assess the changes that occurred between the two periods. His analysis shows an overall loss of 24% of the total historical area of the estuary. Thomas refers to tidal forested and scrub-shrub wetlands and tidal swamps in his study, and reports a 77% loss in this type of habitat between the late 1800s and the 1980s. The descriptive components of the CREDDP studies for the lower 74 km of the Columbia River estuary were synthesized into a dedicated issue of the journal Progress in Oceanography published in 1990 (Sherwood et al. 1990, Simenstad et al. 1990, and others). However, the broad range of studies published in the collection still provided no perspective on the role of freshwater tidal forested wetlands in the estuary.

In the 1970s, the U.S. Army Corps of Engineers (USACE) produced a detailed riparian habitat survey that included the entire lengths of both the Columbia and Snake Rivers (U.S. Army Corps of Engineers 1976a). The survey includes an inventory of vegetation assemblages, ecosystems, and wildlife found in the riparian corridors of both rivers. A series of maps in the report illustrate where dominant plant species are located. The maps show study sites in detail, overlaid onto aerial photographs. Forty-three separate maps depict the ecosystem and associated vegetation in the riparian corridor along the lower Columbia and Snake rivers. The maps are fine-scale and sufficiently detailed to provide a good comparison between habitat conditions in the mid-1970s and present time. Additionally, intensive sampling areas were established at forty-one sites in the Columbia River estuary (U.S. Army Corps of Engineers 1976b). The primary purpose of this sampling

11 effort was to identify the types of riparian habitat present along the Columbia River, and how power peaking (supply of power during peak energy demand periods by hydroelectric dams, which results in reduced water spillage over impoundments) might affect both riparian habitat and associated wildlife. Vegetation, small mammals, songbirds, reptiles, amphibians, terrestrial furbearers, and big game were surveyed in the intensive sampling areas.

A natural area inventory was conducted in 1992 between Bonneville Dam and the mouth of the Columbia River based on ecosystem features such as the presence of undisturbed habitat, large stands of native vegetation, or the presence of rare species (Christy and Putera 1992). In this study, 92 sites were classified by habitat type (ecosystems) and ranked based on the relative importance of their features. The natural area inventory represents one of the best available sources of information as to the flora and fauna present along the estuarine gradient. A later vegetation classification system used the work of Christy and Putera (1992) to describe vegetation communities in the Columbia River floodplain based on dominant vegetation species (Kunze 1994).

A University of Washington student completed a M.S. thesis project on the ecology and biogeomorphology of Russian Island in the lower Columbia River estuary (Elliot 2004). Russian Island is located within the saline tidal area of the Columbia River estuary and is dominated by emergent marsh vegetation, but the high marsh areas of the island have some scrub-shrub tidal wetlands. The primary component of the research was a vegetation community analysis that examined large-scale and small-scale variation in Russian Island’s vegetation assemblages at four representative sites. The project also included soil texture and organic matter content analysis and soil pore water salinity.

In 2006, Battelle Marine Sciences Laboratory mapped emergent marsh vegetation types and distribution at six tidal freshwater wetland sites in the Columbia River estuary. Riparian vegetation such as trees and scrub-shrub were not included in the study, but species present at the sites were noted in the report (Sobocinski 2006).

Diefenderfer (2007) described the channel morphology and restoration of Sitka spruce tidal forested wetlands in the Grays River area, a tributary of the Columbia River that joins the mainstem in the lower estuary at RKm 37. The study provides detailed morphologic measurements for the tidal channels associated with the Sitka spruce wetlands,

12 including pool and log jam spacing and channel widths. The study is aimed at supplying useful metrics for complex forested wetlands sites that can be utilized in regional restoration efforts.

Chapter 2: Ecology of the Freshwater Tidal Forested Wetlands of the Columbia River Estuary

2.1 Introduction

2.1.1 Study Description

This study was conducted due to the lack of detailed scientific studies of the freshwater tidal forested wetlands worldwide and specifically within the Columbia River estuary. These ecosystems are known to provide valuable ecosystem services and habitat for a variety of faunal groups (Lugo et al. 1990), but have experienced significant declines over the past century as a result of human development of the estuarine floodplain and regulation of the Columbia River flow (Thomas 1983). Study findings will provide a better understanding of the composition and structure of freshwater tidal forested wetland ecosystems, and their important role in estuarine ecosystems both within the Columbia River system.

The purpose of this portion of the study was to quantitatively characterize variation in the structure of freshwater tidal forested wetlands along the estuarine gradient of the Columbia River. Study sites throughout the freshwater tidal portion of the Columbia River estuary were selected to capture the variability in forested wetlands present along the estuarine gradient. I used a combination of field surveys, laboratory techniques, and multivariate statistics to evaluate patterns in biotic and abiotic characteristics of the forested wetland sites. The specific outcome of the study was designed as a ―community profile‖ that provides a more thorough understanding of the associations among plant and animal species assemblages at freshwater tidal forested wetlands in the Columbia River estuary, and the abiotic factors that determine these relationships.

2.1.2 Background

2.1.2.1 Impetus for Study

The primary tree species that constitute the freshwater tidal forested wetlands of the Columbia River estuary are Sitka spruce, Pacific willow, Oregon ash and black cottonwood

(Christy and Putera 1992). Understory species, scrub-shrub vegetation, and a variety of emergent and aquatic plant species that grow in conjunction with these tree species and contribute to a complex assemblage of vegetation at forested wetland sites. The aquatic, emergent, and scrub-shrub assemblages may represent earlier successional stages of forested wetland vegetation. Currently, freshwater tidal forested wetlands are estimated to occupy approximately 12% of the Columbia River estuary (Garono et al. 2003, U.S. Fish and Wildlife Service 1983). These vegetation assemblages support a plethora of faunal assemblages (Christy and Putera 1992, U.S. Army Corps of Engineers 1976a) and provide shallow water habitat area for juvenile salmonids, many of which are listed as threatened or endangered under the United States Endangered Species Act (Bottom et al. 2005).

Studies of wetland ecology show that physical factors, hydrology in particular, are responsible for structuring wetland vegetation (Carter 1986). Hydrology affects the soils and their physiochemical characteristics, which along with the hydrology determine the presence and location of plant species within a wetland. Plants that occur together in a wetland site form an assemblage, which then supports a variety of faunal species that utilize the wetland for habitat and food (Mitsch and Gosselink 2000). Thus, in order to thoroughly characterize wetlands, it is necessary to study both biotic assemblages that occur at a site and physical factors that may determine the presence of these assemblages.

Although the saline portion of the Columbia River estuary has been extensively studied, the freshwater tidal portion of the estuary lacks detailed investigations (LCREP 1999). Additionally, hydroregulation of the Columbia River and urbanization of its watershed have likely had a tremendous impact on this estuarine ecosystem (Bottom et al. 2005, Simenstad et al. 1992). A thorough understanding of the assemblages that populate the freshwater tidal forested wetlands and the physical factors that determine the presence and location of these forests is crucial for ongoing restoration efforts in the Columbia River estuary (LCREP 1999).

2.1.2.2 Brief History of the Columbia River Estuary Freshwater Tidal Forested Wetlands

Prior to Euro-American settlement of the Pacific Northwest, much of the Columbia River floodplain was composed of tidal forested wetlands. Surveys conducted by the United States Coast and Geodetic Survey in the mid- to late 1800s show that forested wetlands and scrub-shrub wetlands were prevalent in the floodplain. Survey notation from around the same time by the General Land Office makes note of specific species such as Sitka spruce, black cottonwood, and Pacific willow at corners of sections within the township and range system. Losses to the forested wetlands in the lower estuary have been substantial since this time; Thomas (1983) estimated a 77% loss in Sitka spruce swamps in the lower 74 km of the estuary between the time of the initial surveys and 1983.

Sitka spruce is a primary coniferous species in the coastal temperate rain forest, which is characterized by a wet, mild, and foggy climate. It is commonly referred to as ―tideland spruce‖ in historical documents due to its prominence in tideland areas of Oregon and Washington (Franklin and Dyrness 1988). Sitka spruce occurs in the lower portion of the Columbia River estuary, from near Cathlamet to the Pacific Ocean (U.S. Army Corps of Engineers 1976a). Native Americans used parts of the tree for a variety of purposes including medicinal, ceremonial, constructing clothing and blankets, and food (Pojar and MacKinnon 2004). Once Euro-American settlement of the region commenced, much of the Sitka spruce forests were logged for their valuable timber (Peattie 2007). It is not known exactly how much Sitka spruce was removed from the Columbia River estuary, but it is estimated that 77%, or 23,000 acres, of tidal swamps have been lost since the late 1800s, of which Sitka spruce is considered a major component (Thomas 1983).

Similarly, diking land in the lower estuary in the same time period caused a loss of nearly 24,000 acres of habitat in the Columbia River floodplain, including tidal swamps, tidal marshes, and non-estuarine wetlands. Diking severs the connection between the river and its floodplain, and vegetation such as scrub-shrubs and trees are typically removed from the diked land. Much of the diked land in the Columbia River estuary was used for settlement and agricultural purposes such as cattle grazing (Lichatowich 1999).

In the upper estuary, losses of forested wetland habitats are even less well documented but occurred for similar reasons during the time of Euro-American settlement. Black cottonwood is a valuable paper and pulp species, and large amounts of this species

16 were logged for this purpose (Peattie 2007). Additionally, land in the upper estuary was diked, drained, and cleared for agricultural purposes and settlement, although the amount of tidal forested wetlands removed remains unknown (Christy and Putera 1992).

2.1.2.3 Scientific Evidence for the Unique Role of Freshwater Tidal Forested Wetlands

Although few studies of freshwater tidal forested wetlands exist in the literature, several works indicate the unique and valuable role of these systems. Most relevant literature refers to freshwater forested wetlands, a small portion of which have the additional dynamic of tidal influences. Odum (1988) compared ecological attributes of tidal freshwater and salt marshes, and noted that relative to salt marshes, tidal freshwater systems generally have high species diversity of fishes, reptiles and amphibians, fur-bearing mammals, and waterfowl, but lower invertebrate species diversity. He also noted that tidal freshwater marshes often have seasonally high nutrient fluxes, high quality of detrital matter, and rapid rates of decomposition.

A review of forested wetlands worldwide demonstrates that these systems improve the quality of water runoff from their watersheds, contribute substantially to the productivity of freshwater and coastal fisheries, play important roles in global biogeochemical cycles, and provide wildlife habitat (Lugo et al. 1990). Within freshwater tidal forested wetlands, bottomland hardwood swamps of the Southeastern United States and mangrove ecosystems in tropical areas are the most thoroughly studied (Lugo et al. 1988). Studies of these systems show that forested wetlands have high primary productivity, biomass, and scrub-shrub species diversity, but also a broad range of structural and functional characteristics (Brown 1981, Schlesinger 1978). An extensive community profile of the bottomland hardwood swamps constructed by the U.S. Fish and Wildlife Service describes these systems in further detail, providing information on the flora and fauna of these systems, as well as disturbance regimes, hydrology, and physiochemical characteristics (Wharton et al. 1982).

Few studies focus on the ecological structure and function of freshwater tidal forested wetlands of the type found in the Columbia River estuary. In fact, Lugo et al.’s (1990) comprehensive review of forested wetlands worldwide neglects to mention Sitka spruce swamps, as does the main textbook on forested wetlands of North America (Trettin et al. 1997). Recently, a doctoral dissertation describing the channel morphology and restoration

17 of Sitka spruce swamps in the Columbia River floodplain was published, providing valuable information about the structure and function of Sitka spruce forested wetlands (Diefenderfer 2007). However, the deciduous-dominated forested wetlands found further up the Columbia River estuary lack scientific documentation beyond inventories of floristic and faunal species (LCREP 1999).

2.1.2.4 Importance for Ecosystem Management and Restoration Efforts

Recently, increasing efforts have been made to restore forested wetlands in the Columbia River estuary (LCREP 1999). However, one of the primary challenges facing restoration ecologists in the Columbia River estuary is a lack of unimpacted reference sites to guide restoration efforts. When reference sites are available, data describing the sites’ ecological structure and function is often lacking. Specifically, restoration ecologists need quantitative data about reference site vegetation structure and physical attributes of sites such as soil composition and site elevation (Brophy 2009). Therefore, ecological characterization of these unique tidal ecosystems could contribute valuable information to inform future restoration efforts in the Columbia River and other comparable freshwater tidal dominated estuaries.

2.1.3 Study Objectives

The objectives of this study were to describe the floral and fauna assemblages and physical characteristics representative of freshwater tidal forested wetlands in the Columbia River estuary. The information gathered about the freshwater tidal forested wetlands of the Columbia River estuary was synthesized into a comprehensive community profile. This summary describes the species assemblages present at forested wetland sites in the Columbia River estuary, as well as physical factors that may be driving the variation in community composition. The community profile is modeled after a similar document prepared by the United States Fish and Wildlife Service that describes the ecology of the bottomland hardwood swamps of the Southeastern United States (Wharton et al. 1982).

2.1.4 Hypotheses

Hypotheses were as follows:

1. Freshwater tidal forested wetlands will transition from domination by coniferous to deciduous tree species, occurring at higher relative elevations, as tidally-driven flooding duration and frequency diminishes and fluvial regulation of water level dominates.

2. Freshwater tidal forested wetland fauna and flora assemblages will show strong correspondence in changes across the tidally-dominated to the fluvially-dominated reaches of the estuary.

2.2 Methods

2.2.1 Site Selection: Rationale and Criteria

Sites for field studies were selected based upon the presence of relatively unimpacted forested wetlands, representation of different variants of forested wetlands present in the estuary, site accessibility, and the availability of historic vegetation records for comparison purposes. Also, sites that were intensively sampled by the USACE in the 1970s were preferred over others due to the availability of detailed survey data including vegetation, birds, amphibians, and mammals (U.S. Army Corps of Engineers 1976b). Candidate sites for field studies were selected by examining current satellite imagery of the Columbia River estuary available on Google Earth® and maps of forested wetland locations present in the late 1970s (U.S. Army Corps of Engineers 1976). Individual sites were then researched using the internet, personal communications with Si Simenstad, Jennifer Burke, Kathryn Sobocinski, the Lower Columbia River Estuary Partnership (LCREP), and field visits.

The selected sites span almost the entire freshwater portion of the Columbia River estuary (Figure 3). Big Creek, Willow Bar, and Mirror Lake were selected for the 2008 field season. Sampling sites at each end of the freshwater portion of the estuary during the first year allowed for preliminary analysis and strategic placing of sites during the 2009 field season to capture transitions in community structure along the estuarine gradient. Thus, Julia Butler Hansen, Robert W. Little, and Willow Grove were sampled during the 2009 field season. Photographs of sites are located in Appendix A.

Figure 3. Location of freshwater tidal forested wetland study sites in the Columbia River estuary. Image is ESRI World Imagery, December 2009. Red circles indicate sites studied in the first (2008) field season, and yellow squares indicate sites studied in the second (2009) field season. 2.2.2 Site Descriptions

2.2.2.1 Big Creek

The study site closest to the mouth of the Columbia River was located on Big Creek (BC) (near Knappa, OR), near the confluence of the creek and Knappa Slough at approximately RKm 42 of the mainstem Columbia River. The forested wetlands at Big Creek represent Sitka spruce tidal swamps that were once common in the lower Columbia River estuary. A salmon hatchery located approximately 4.8 km upstream of the confluence also depends upon the wetlands to provide habitat for their juvenile salmon releases. Abandoned railroad tracks run along the shore of the Columbia River, crossing Big Creek, and were used to access the study site. Tidal fluctuation in Big Creek is approximately 2.0- 2.6 m. The wetlands at Big Creek are dense with scrub-shrub species such as willows, red osier dogwood (Cornus sericea), and blackberry (Rubus spp.), and large trees such as Sitka

21 spruce and western red cedar (Thuja plicata) provide canopy cover. This site was included in the U.S. Army Corps of Engineers intensive sampling efforts in the 1970s, and was thus selected in part for the availability of data for comparison purposes (U.S. Army Corps of Engineers 1976b). The forested wetlands at Big Creek are owned and monitored by The Nature Conservancy (TNC), who encourages the public to enjoy bird watching, canoeing, and kayaking in the preserve.

2.2.2.2 Julia Butler Hansen Wildlife Refuge

Julia Butler Hansen Wildlife Refuge (JBH) is located at approximately RKm 53, near Cathlamet, Washington. The Refuge was established in 1972 to protect the endangered Columbian white-tailed deer (Odocoileus virginianus leucurus), and is managed by the United States Fish and Wildlife Service. The Refuge contains over 24 km2 including Sitka spruce tidal swamps. The sampling location selected for this study is situated on the mainland portion of the Refuge across from Price Island. The wetland vegetation assemblage at the Refuge is similar to that of Big Creek, consisting primarily of Sitka spruce, Sitka willow, red osier dogwood, and red alder (Alnus rubra), with the addition of black cottonwood trees. Tidal fluctuation at this location is approximately 1.9-2.3 m, based on the nearby tidal gauge at Skamokawa, Washington.

2.2.2.3 Robert W. Little Preserve

The Robert W. Little Preserve (RWL) is positioned at approximately RKm 63 on Puget Island, Washington. The Preserve is owned and managed by the Nature Conservancy, and contains about 0.12 km2 of native Sitka spruce tidal forested wetlands. Tidal fluctuation at the site is approximately 1.8-2.1 m, based on the nearby tidal station at Wauna, Oregon. The vegetation assemblage at the Preserve is dominated by Sitka spruce, red alder, black cottonwood, red osier dogwood, and Pacific willow.

2.2.2.4 Willow Grove

Willow Grove (WG), located at approximately RKm 97, was acquired by the Columbia Land Trust for conservation purposes in August 2008. Willow Grove is approximately 1.26 km2 and includes a variety of wetland habitats including tidal channels, emergent marshes, and tidal forested wetlands. The forested wetland vegetation assemblages

22 that are the focus of this study are composed primarily of black cottonwood, Pacific willow, and Oregon ash. Tidal fluctuation at the site is estimated to be 1.1-1.4 m, based on the nearby tidal station at Longview.

2.2.2.5 Willow Bar

Willow Bar (WB) is positioned at approximately RKm 153 along the mainstem Columbia River and is connected to Sauvie Island, Oregon, via a land bridge. Between Willow Bar and Sauvie Island is an inlet that contains tidal forested wetlands comprised mainly of willow, black cottonwood and Oregon ash trees. Willow Bar appears to function as a riparian floodplain as well as a wetland area, because at peak river flows in June 2008 the study site was inaccessible due to high water. During times of lower flow, shallow water (less than 0.6 m deep at low tide) is present in the inlet, and tidal fluctuation is approximately 0.3 m. Willow Bar is part of the Sauvie Island Wildlife Area and is managed by the Oregon Department of Fish and Wildlife.

2.2.2.6 Mirror Lake

Mirror Lake (ML), located at approximately RKm 208, is a wetland area about 32 km downstream of Bonneville Dam, and is connected to the Columbia River by two large culverts underneath Interstate 84. The vegetation present is very similar to that of Willow Bar. Also like Willow Bar, the wetland area functions as a riparian floodplain, and was partly inaccessible during peak river flows in June 2008. During lower flow periods, shallow water is present in the wetland, and tidal fluctuations are minimal. Mirror Lake is part of Rooster Rock State Park managed by the Oregon State Parks department. This site was also included in the U.S. Army Corps of Engineers intensive sampling efforts of riparian habitat in the 1970s (U.S. Army Corps of Engineers 1976b).

2.2.3 Site Sampling Design

I used a transect and zone based sampling design as the framework for sampling faunal assemblages and corresponding environmental variables at sites. At each site, I established three transects aligned perpendicular to the water portion of the wetland area that extended to the edge of the forested area (Figure 4). The goal of the transect method was threefold: (1) to capture the full range of variation in species present and physical conditions

23 at a given site; (2) to function as replicates for statistical analysis; and, (3) to document changes in species and conditions over the gradient from the wetland area to the forested/uplands area. Transects were positioned at least 100 m apart, because the bird survey literature generally agrees that the audio portion of point count surveys covers a 50-m radius (Ralph et al. 1995). Transects varied in length as the distance between the aquatic and forested portion of the wetlands differed at each transect, but ranged from 7 to 60 meters with a mean length of 21 meters.

Within transects, major vegetation zones were identified for sampling faunal communities (Figure 4). Based on the U.S. Fish and Wildlife Service wetland classification system (Cowardin et al. 1979), the zone designations included: aquatic (A); emergent (E); scrub-shrub (S); and forest (F).. The zones were usually easily differentiated from one another by noticeable transitions in vegetation composition from the wetland to the upland portion of the site. In the case that a zone did not exist, I did not collect samples for that location. For example, the sites studied in 2009 tended to transition from the river or side channel immediately to emergent vegetation zones, resulting in no data for the aquatic zones at those sites since they were not present.

Figure 4. Schematic drawing of sampling layout at forested wetland study sites (not to scale).

2.2.4 Timing of Sampling

Sampling of tidal forested wetland sites was timed according to seasons, peak river flow, and vegetation flowering time for the Columbia River. The hydrograph of the Columbia River has changed in recent history due to hydroregulation, so the most recent ten years of river flow data collected by the United States Geological Survey (USGS) at The Dalles, OR was plotted in Microsoft Excel (Figure 5). Based on this plot, it is apparent that the peak flows, or spring freshet, for the Columbia River in recent times occur in late May and early June. Since the life cycles of river floodplain biota often correspond to seasonal and annual fluctuations in river hydrography, most sampling of biota occurred in conjunction with the spring freshet (Junk et al. 1989). Vegetation surveys occurred in July 2008 and 2009 and were timed to coincide with the period of flowering for most of the species present. The avian community, which varies according to circannual rhythms, was sampled once in each season during a single year (Gwinner 1996).

Figure 5. Annual discharge of the Columbia River at The Dalles from 10/1/1998 to 9/30/2008. Values shown are the mean for each day during the ten water years shown; blue lines indicate the timing of the present-day spring freshet.

2.2.5 Sampling Variables and Methods

Biotic and abiotic factors were sampled at each tidal forested wetland site. Faunal assemblages sampled included vegetation, avian, insects, benthic macroinvertebrates, amphibians, and small mammals. Soil samples were collected in order to determine the percent organic content and soil grain size. All sampling locations were recorded using a handheld Garmin GPSmap 60CSx Global Positioning System.

2.2.5.1 Vegetation

A combination of 2-m wide belt transects and 10-m x 10-m plots was used to document the vegetation present at the sites (Kent and Coker 1992). A 2-m wide belt transect was established at each sampling transect from well within the aquatic vegetation zone to the edge of the forested vegetation zone (Figure 4). I recorded all vegetation species present within each 1-m interval along the length of the transect. In order to adequately capture the full range of tree species and understory present at the sites, I established a 10-m x 10-m plot at the edge of the forested zone (marked by the first tree of stem diameter of 2 cm or more). Within the forested plot, all species present were recorded, the diameter at breast height (DBH) of all trees larger than 2.0 cm was measured and recorded, and the percentage of canopy cover provided by each species of tree within the plot was visually estimated. If no forested zone was present for a given transect, I confined the vegetation survey to only a 2-m belt transect that extended well into the scrub-shrub zone. If the vegetation transitioned immediately from the water to the forested zone for a given transect (this was the case with one transect), I confined the vegetation survey to only a 10-m x 10-m forested plot. Vegetation was identified to species level according to two regional field guides (Pojar and MacKinnon 2004, Spear Cooke 1997).

2.2.5.2 Avifauna

I conducted systematic bird surveys once per season at each site to determine species presence/absence. The spring and autumn surveys occurred approximately during the periods of maximum seasonal migration. Birds present at the sites were surveyed using 10- min point count methods and both visual and audio identification (Ralph et al. 1995). The surveyor stood at a point within each transect where they felt they had a good view of all portions of the wetland, which varied among sites due to topography and vegetation.

Binoculars and field identification guides were used to visually identify species during the 10 min of the field observation. Audio identifications were also permitted, and a small recording device was used to record bird calls and songs during the length of the observation. The recording was later analyzed for any bird species not already identified visually or audibly in the field. I repeated the 10-min survey at each transect for a total of three times at a site, giving a total of 90 min of bird surveys during each visit. Sampling was conducted at first light in the morning hours or shortly thereafter, when birds at the study sites were most active and vocal.

2.2.5.3 Insects

One insect fall-out trap was placed in each transect and zone for a 24-hour period. Insect fall-out traps consist of an approximately 0.24 m2 plastic tub supported on the bottom by a PVC platform and held in place on the sides by PVC pipes or bamboo poles. The tub was partially filled with water and biodegradable dish soap which acts as a surfactant and prevents insects that have fallen into the bin from escaping. At the end of the 24-hour period, each trap was sieved into a 106-µm sieve, washed, and fixed using a 70% isopropanol solution. The taxa present were later identified in the laboratory according to a taxonomic key (Triplehorn and Johnson 2005).

2.2.5.4 Benthic Macroinvertebrates

I acquired one 5-cm dia. (19.6-cm2) benthic core to 10-cm depth in each zone and along each transect. Samples were sieved and washed over 500-µm sieves. Samples were fixed using a 10% buffered formalin solution, and were later analyzed in the laboratory to identify and enumerate the benthic macroinvertebrate taxa present (Pennak 1953).

2.2.5.5 Amphibians

Systematic visual search methods were employed for individual amphibian identification (Bury and Corn 1991). In general, amphibian surveys were most successful when walking between transects or zones for other sampling purposes, rather than during specific searches. A regional field guide was used to identify amphibians present at the forested wetland sites (Jones et al. 2005).

2.2.5.6 Mammals

I surveyed mammals present at the sites using visual sightings and track and scat identification. Mammal searches were not limited to transects and zones, since animal ranges often cover the entire site, although it was noted where within the site evidence of mammals was seen (i.e., near Transect 1, or between Transects 1 and 2). Sightings of mammals or evidence of mammals often occurred while walking from the parking area to the study sites, or while walking between sampling locations at a site. Mammals and their tracks and scat were identified using an extensive field guide (Elbroch 2003).

2.2.5.7 Environmental Characteristics

Soil cores were collected using a 5-cm diameter (19.6-cm2) benthic core to 10-cm depth in each zone and along each transect. The samples were later homogenized and split for separate analysis of soil percent organic content and grain size. Soil samples were kept on ice while in the field and placed in a freezer in the laboratory to prevent breakdown of organic matter between the time of collection and analysis.

I determined the percentage of organic material in the soil in each sample by calculating loss-on-ignition. First, soils were weighed, and then placed in drying oven at approximately 30 degrees Celsius (C) for 24 hr. Samples were then weighed and placed in a muffle furnace at approximately 500ºC for six hr (Luczak et al. 1997). The post-burn sample weights were subtracted from pre-burn sample weights to determine the percentage of soil composed of organic material.

I determined the grain size of the soil samples using a Sedigraph 5100 (Bianchi et al. 1999). The Sedigraph uses x-ray beams to calculate the sizes of particles suspended in solution in phi units, which corresponds to sand, silt, and clay grain size classes in the Wentworth scale.

The elevation of each sampling location was determined from Light Detection and Ranging (LiDAR) data. The LiDAR dataset that covers the Columbia River estuary was collected in 2005 and is relatively high-resolution at 1.8 m pixel size. Coordinates from the GPS data collected for each sampling location and rasters derived from the LIDAR data were mapped using ESRI ArcMap and elevations corresponding to GPS points were recorded. Elevations were then converted from North American Vertical Datum 1988 (NAVD88) to

Columbia River Datum (CRD), a local vertical datum, in order to compare elevations without the confounding effect of the slope of the river.

2.2.5.8 Data Preparation for Statistical Analysis

Data from field surveys and laboratory analyses were entered into a Microsoft Office Access 2007 database. Data were exported from the database into a Microsoft Office Excel 2007 spreadsheet for creation of tables, graphs, and formatting for multivariate analysis. Environmental parameters from each transect within a site were averaged by zone prior to analysis, because transects were intended to function as replicates in this study.

2.2.6 Scales of Variability in the Columbia River Estuary and the Study Design

Studying ecosystems at the appropriate spatial and temporal scale in order to determine patterns and trends present in the system is a core challenge in ecology (Hobbs 2003, Levin 1992). Scales of variability were a major consideration when planning and executing the field component of the project. Multiple scales of variability exist in a large system such as the Columbia River estuary, and include variability among forested wetland sites, within sites, and temporal factors that affect the presence of species.

The freshwater tidal forested wetland vegetation assemblages in the Columbia River estuary show general trends over the length of the estuary, but wetlands are not distributed uniformly along the estuarine gradient (U.S. Army Corps of Engineers 1976a). Therefore, site selection for this project was critical to capturing the gradient of tidal forested wetland communities in the estuary. Sites were screened first using imagery available for the region and riparian habitat inventory maps, and then by site reconnaissance visits to verify that a particular site accurately represented the tidal forested wetland communities common in that portion of the estuary. Also, sites were selected from throughout the estuary in order to capture the full range of variation in forested wetland vegetation assemblages present (Figure 3). As a consequence, based on preliminary data analysis performed between the first and second field years, I did not select sites that were distributed uniformly throughout the estuary. The preliminary surveys indicated that little change in vegetation community composition and structure occurred between Willow Bar and Mirror Lake, but between Big

Creek and Willow Bar, a dramatic shift in community composition and structure occurred. Therefore, the sites studied in the second field year were all located between Big Creek and Willow Bar.

Vegetation tends to be patchy rather than uniform within tidal forested wetland sites (U.S. Army Corps of Engineers 1976a). Wetland assemblages form a mosaic across the landscape, and careful planning of sampling techniques is necessary in order to accurately capture the variability within and among sites. Spacing out transects by a minimum of 100 meters, required by the bird survey methodology, ensured that transects were placed throughout sites rather than adjacent to one another. This increased the likelihood of sampling the various vegetation assemblages present within sites. Relatively large (10-m x 10-m) survey plots in the forested zones of the transects allowed me to include all or nearly all of the vegetation species present in the complex forest assemblages at these sites. Additionally, these large forested plots enabled me to record sufficient numbers of tree species present and measure their DBH to detect trends in forested assemblage composition and structure across the estuary.

River and tidal dynamics, faunal species, and floristic species all operate on different temporal scales of variability, and the challenge in the field component of this project was to sample at appropriate times and frequencies in order to accurately characterize the biotic and abiotic components of the tidal forested wetland sites (Hobbs 2003, Wiens 1989). For example, the avian community tends to change by season; and many of the species commonly seen in the summer were completely absent from the sites in the winter. Thus, sampling the avifauna seasonally was necessary to accurately describe the assemblages utilizing the tidal forested wetlands. Conversely, floristic species in the Columbia River estuary tend to operate on an annual cycle, blooming in the summer and entering dormancy in the winter months with the exception of coniferous species. Therefore, surveying the vegetation once at each site in the summer was sufficient to characterize the vegetation assemblages.

The physical mobility of faunal species also influenced the scale of sampling in this study. Mammalian species were observed at the whole-site level, since mammals such as beavers, river otters, and muskrats probably operate on a scale of kilometers rather than on a

30 scale contained within study sites (Elbroch 2003). Smaller species, such as insects and benthic macroinvertebrates, likely function on a scale of centimeters to meters, so sampling of these faunal groups occurred within the sites, in multiple zones and repeated across transects. Avifauna, however, occurs on multiple scales. It is possible that some birds present at the forested wetland sites spend their entire lives at the site, and may even utilize one particular portion of the site heavily if it is favorable for feeding and nesting. Other birds may migrate long distances and use larger areas within the estuary while temporarily residing at a particular site (Ambuel and Temple 1983). Thus, birds were studied at the transect level, which appeared to be effective, because observations at transects demonstrated differences within sites. On many occasions, birds were seen repeatedly at one transect in a site, but not at others.

Surveying the amphibian community provided a unique challenge in terms of matching the temporal scale of the study to the spawning patterns of amphibian species, when individuals are most likely to be observed (Bury and Corn 1991). Each of the amphibian species at the forested wetland sites spawns during a different time period, depending on factors such as temperature, water levels, and short-term weather events (Buech and Egeland 2002). The regional field guide used for this study, which is the primary text on amphibians in the Pacific Northwest, lists relatively broad spawning times, such as June through August for a particular species (Jones et al. 2005). However, species typically spawn for only a brief period of time in the larger range listed depending on environmental factors (Buech and Egeland 2002). A pilot study of amphibian spawning times specific to these study sites would have been useful for targeting field survey times to likely amphibian spawning times at these forested wetland sites.

2.2.7 Data Analysis

2.2.7.1 Univariate Analysis

Descriptive statistics were used to interpret sampling variables that had either low sample size or did not meet criteria for formal statistical analysis. Simple graphical plots were used to interpret several of the variables related to the vegetation communities at tidal forested wetland sites, including average species richness by zone, DBH measurements of trees, and canopy cover by species. Trees species that contributed less than 3% to the total

31 sampled were removed from the DBH boxplot analysis, in order to visualize trends in DBH of dominant trees at sites. Graphs and plots were created using SPSS 17.0 (version 17.0.0) and Microsoft Office Excel 2007.

The sampling methods utilized for amphibians and mammals resulted in relatively low sample numbers, so no statistical analysis was performed on these faunal groups. Instead, the results of the amphibian and mammal surveys are presented in tabular form.

I used SPSS 17.0 (version 17.0.0) to conduct a one-way Analysis of Variance (ANOVA) on the environmental characteristics (site elevation and percent sand, silt, clay and organic content) of vegetation zones within sites. A post-hoc Bonferroni test was performed in order to avoid the problem of multiple comparisons in an ANOVA test (Cabin and Mitchell 2000). The values for each factor were averaged across all sampling locations within a site, for the purposes of investigating variation in physical conditions along the estuarine gradient. I considered alpha levels of 0.05 to be statistically significant for this test.

2.2.7.2 Multivariate Analysis

PRIMER 6 (version 6.1.12) was used for all multivariate analyses (Clarke and Warwick 2001). Vegetation, avifauna, and insect community data was analyzed based on species presence/absence at sampling locations. Benthic macroinvertebrate community data was analyzed based on abundance at sampling locations, because field methods were consistent with techniques used to identify abundance and the small number of taxa observed at the sites was not well suited to analysis based simply on taxa presence and absence.

First, for each community consisting of presence/absence data (vegetation, avifauna, and insect communities) a similarity matrix of sites was calculated based on the Sorensen similarity coefficient (Sorensen 1948). The Sorensen similarity coefficient is widely used by ecologists, as it is useful for species presence/absence data. The coefficient excludes double-zeros, which is particularly useful for ecological applications where the unimodal distribution of species distributions along environmental gradients may result in the absence of a species because one site is above and another is below the optimal niche for that species (Legendre and Legendre 1998).

A similarity matrix for the benthic macroinvertebrate community was calculated using the Bray-Curtis similarity coefficient after applying a log (1+x) transformation to the species abundance data (Bartlett 1947, Bray and Curtis 1957). The Bray-Curtis similarity coefficient is mathematically comparable to the Sorensen coefficient described above, but is applied to abundance data rather than presence/absence data.

After assembling the similarity matrices, I performed two-dimensional Non-Metric Multidimensional Scaling (NMDS) on each of the vegetation, avifauna, insect, and benthic macroinvertebrate similarity matrices in order to ordinate sites by similarity of biota (Kruskal 1964, Shephard 1962). The advantage of NMDS is that it produces a graphical representation of site similarity, where sampling units located closer to one another in the ordination plot are more similar to one another than those that are further away. NMDS is considered to be an excellent method for analysis of ecological data due to its conceptual simplicity, lack of assumptions about sample data, and preservation of relationships between sampling units in ordination space (Clarke and Warwick 2001). Stress values in an NMDS plot indicate the distortion between the displayed plot and the similarity rankings of sampling units. Generally, stress values should be less than 0.2 for the 2-dimensional plot to be considered ecologically interpretable (Clarke and Gorley 2006).

NMDS ordination was also used to examine vegetation assemblages by site and zone. For this analysis, vegetation survey data from all three transects at each site were combined by zone. Then, a NMDS ordination was performed to see if zones within sites were significantly different, and if the same zone at different sites within the estuary were different in terms of vegetation assemblage composition.

I used an Analysis of Similarity (ANOSIM) to test for significant differences in community composition of sites and hydrogeomorphic reaches (Clarke 1993). ANOSIM provides a p-value that is used to evaluate the significance of the results. For all analyses, a p-value of less than 0.05 was considered statistically significant. I used a one-way ANOSIM test for each community type (vegetation, avifauna, insect, and invertebrate) by site and hydrogeomorphic reach separately.

A Similarity of Percentages (SIMPER) test was performed to determine which species primarily account for differences between tidal forested wetland sites. The SIMPER

33 function in PRIMER is based on Bray-Curtis or Sorensen dissimilarity between two samples, and breaks down the dissimilarities between sample groups by species contributions. The results of the SIMPER analysis allow the ecologist to make conclusions about which species may be good discriminators of two particular sites or sampling units (Clarke and Warwick 2001).

Finally, I performed a Mantel test, which is a test of the correlation between two matrices, to evaluate the relationship between the vegetation community composition and geographic distance between study sites (Mantel 1967). For this test, a p-value of less than 0.05 was considered statistically significant.

2.3 Results

2.3.1 Forested Wetland Vegetation Assemblages

A total of 110 plant species were observed at the six tidal forested wetland study sites (see Appendix B for a complete list of plant species identified during field surveys). Wetland vegetation assemblages changed both in assemblage composition and structure along the estuarine gradient. The lower estuarine sites were composed of emergent, scrub-shrub, and forested zones, while the two upper estuarine sites, Willow Bar and Mirror Lake, contained aquatic vegetation zones in addition to the other three zones (Figure 6). Species richness was highest in the lower estuary, decreased along the estuarine gradient to Willow Grove in the mid-estuary, and then increased to the upper estuarine sites of Willow Bar and Mirror Lake. However, the number of trees present in all forested plots at sites increased from the lower to the upper estuary, as did the density of trees in forested plots (Figure 7; Table 1).

Figure 6. Mean species richness by vegetation zone at tidal forested wetland study sites. Error bars represent +/- 1 standard error of the mean. Values in parentheses along x-axis indicate site river kilometer (RKm).

30 Western red cedar Red alder Sitka spruce Western hemlock Red osier dogwood 20 Sitka willow Black cottonwood Pacific willow

Oregon ash

of trees of Total number Total 10

0 Big Julia Butler Robert W. Willow Willow Bar Mirror Lake Creek (42) Hansen (53) Little (63) Grove (97) (153) (208) Site (RKm) Figure 7. Total number of trees present at forested wetland study sites. Values in parentheses along x-axis indicate site river kilometer (RKm). Table 1. Mean density of trees in plots at forested wetland study sites. Site (RKm) Mean density of trees present in forested plots (no. trees per 100 m2 ± 1 standard error) Big Creek (42) 10.50 ± 1.50 Julia Butler Hansen (53) 5.67 ± 0.66 Robert W. Little (63) 7.33 ± 2.91 Willow Grove (97) 12.33 ± 2.60 Willow Bar (153) 17.00 ± 4.00 Mirror Lake (208) 14.33 ± 2.60

Tree diameter at breast height (DBH) measurements are allometrically related to tree biomass and are thus an indicator of forest structure and total biomass (Ketterings et al. 2001). The Columbia River estuary freshwater tidal forested wetland sites displayed a trend of larger DBH measurements at the lower estuarine sites and smaller DBH measurements at upper estuarine sites (Figure 8). The boxplots demonstrate that Western red cedar, Sitka spruce, and red alder account for the majority of trees encountered at the down-estuarine sites (Big Creek, Julia Butler Hansen, and Robert W. Little) while Pacific willow, black cottonwood, and Oregon ash were most frequently encountered in the mid- and upper estuarine sites (Willow Grove, Willow Bar, and Mirror Lake).

Figure 8. Diameters at breast height (DBH) of tree species present at tidal forested wetland study sites. Numbers on plot indicate outlier tree DBH measurements. Values in parentheses along x-axis indicate site river kilometer (RKm).

Canopy cover showed trends across the forested wetland sites (Figure 9). The percentage of open canopy varied by forested plot within a site, but the composition of tree species contributing to canopy closure in plots demonstrated distinct differences along the estuarine gradient. Lower estuarine sites, including Big Creek, Julia Butler Hansen, and Robert W. Little, had much greater diversity in tree and scrub-shrub species contributing to canopy closure. Coniferous species, including Sitka spruce, western red cedar, and western hemlock (T. heterophylla), contributed to canopy closure, but scrub-shrub species such as vine maple (A. circinatum), red osier dogwood, Sitka spruce, and European holly (I. aquifolium) also accounted for up to 50% of the canopy cover in forested plots. The canopy of mid- to upper estuarine sites (Willow Grove, Willow Bar, and Mirror Lake) consisted of three tree species (Pacific willow, black cottonwood, and Oregon ash) and one scrub-shrub species (red osier dogwood).

100

90 Vine maple

Red alder 80 Red osier dogwood 70 Oregon ash

European holly 60

Sitka spruce

50 Black cottonwood

40 Pacific willow Percentage of Canopy of Cover Canopy Percentage

Sitka willow 30

Western red cedar 20 Western hemlock

Forested Plot (Site-Transect)

Figure 9. Contributions of individual species to canopy cover in tidal forested wetland survey plots. Note that the percentage of sky visible in plots accounts for the remainder of each column to equal 100%. Site abbreviations are as follows: BC = Big Creek; JBH = Julia Butler Hansen; RWL = Robert W. Little, WG = Willow Grove; WB = Willow Bar; ML = Mirror Lake. Numerals 1, 2, and 3 following site abbreviations indicate the transect number. The NMDS ordination plot of vegetation presence/absence survey data indicates that transects within sites were similar to one another, because they are located closer together in the plot (Figure 10); thus, among-site variation was consistently higher than within-site

40 variation in vegetation assemblage structure. Forested wetland sites are located farther away from one another, signifying that sites differed from one another based on vegetation species present. The NMDS ordination plot also reveals a trend in sites along the estuarine gradient, with upper estuarine sites located toward the left side of the plot and sites progressively down estuary located along the right side of the plot. Two-dimensional stress in the NMDS ordination plot is 0.12, which is considered ecologically interpretable. The ANOSIM test revealed that the vegetation community composition of sites is significantly different from one another (global R = 0.891, p = 0.001). Resemblance: S17 Bray Curtis similarity WG-2 RWL-1 2D Stress: 0.12 Site WG-1 Big Creek WG-3 RWL-2 Julia Butler Hansen RWL-3 Robert W. Little Willow Grove Willow Bar ML-3 Mirror Lake ML-1 JBH-2JBH-1 ML-2 JBH-3 WB-1 BC-1 BC-3

WB-3 BC-2 WB-2

Figure 10. NMDS ordination plot of vegetation presence/absence survey data. SIMPER analysis of the Sorensen site similarity matrix provided both an average percent similarity of sites studied and the contribution of individual species to site similarities (Table 2). All sites were less than 50% similar to one another in terms of species composition. Generally, sites that are located closer to one another within the estuary are more similar to one another than sites located farther from one another. This finding was confirmed by the use of a Mantel test, which showed a significant correlation between the geographic location of study sites and their vegetation community (p = 0.001).

Table 2. Average percent similarity of forested wetland study sites. Julia Butler Robert W. Willow Willow Mirror Big Creek Hansen Little Grove Bar Lake Big Creek Julia Butler Hansen 41.08 Robert W. Little 31.79 38.24 Willow Grove 9.46 24.90 30.06 Willow Bar 10.73 22.17 16.56 26.60 Mirror Lake 18.15 27.22 28.36 41.87 42.54

Vegetation assemblages were also examined by site and zone, and the resulting ordination plot had a two-dimensional stress of 0.14 (Figure 11). The NMDS ordination plot indicates that lower estuarine sites grouped together (Big Creek, Julia Butler Hansen, and Robert W. Little) while mid- and upper estuarine sites (Willow Grove, Willow Bar, and Mirror Lake) also grouped together. Additionally, within the lower-estuarine sites, the forest zones, scrub-shrub zones, and emergent zones plotted close to one another in ordination space. Similarly, zones within the mid- and upper estuarine group of sites were located near each other in the ordination plot. An ANOSIM test of the vegetation data by site and zone showed that there were significant differences between vegetation assemblages in sites and zones (global R = 0.446, p = 0.003). Resemblance: S17 Bray Curtis similarity RWL-E 2D Stress: 0.14 Site JBH-E Big Creek Julia Butler Hansen BC-F Robert W. Little Willow Grove ML-A Willow Bar RWL-F JBH-F RWL-S Mirror Lake WG-E BC-S WB-A WG-S ML-E WG-F ML-F ML-S WB-E

WB-F WB-S

Figure 11. NMDS ordination plot of vegetation assemblages by site and zone and tidal forested wetland sites. Zones are designated as follows: F = Forest; S = Scrub-shrub; E = Emergent; A = Aquatic.

The SIMPER analysis of vegetation assemblages by zone and estuary location (lower estuarine versus upper estuarine) was performed in order to identify the species that contribute the most in each group. Based on the NMDS ordination results and plots of tree composition at sites (Figures 7, 8, 9, and 10), the Lower Estuary group included sites Big Creek, Julia Butler Hansen, and Robert W. Little, while the Upper Estuary Group included Willow Grove, Willow Bar, and Mirror Lake. Zones were as follows: Lower Emergent, Lower Scrub-shrub, Lower Forest, Upper Aquatic, Upper Emergent, Upper Scrub-shrub, and Upper Forest (Table 3).

Table 3. Composition of lower and upper estuarine vegetation zones based on SIMPER analysis. Non-native species are denoted with an asterisk (*) after the common name.

Group (Estuarine Percent Location and Species Contribution Vegetation Zone) Lower Emergent Carex obnupta (slough sedge) 28.36 Phalaris arundinacea (reed canary grass)* 28.36 Solanum dulcamara (European bittersweet) 11.36 Sagittaria latifolia (wapato) 9.54 Impatiens noli-tangere (yellow touch-me-not) 7.46 Juncus effusus (common rush) 7.46 Lower Scrub- Shrub Cornus sericea (red osier dogwood) 14.36 Phalaris arundinacea (reed canary grass)* 14.36 Rubus ursinus (dewberry) 14.36 Athyrium filix-femina (lady fern) 6.04 Galium trifidum (small bedstraw) 6.04 Salix lucida ssp. Lasiandra (Pacific willow) 6.04 Spiraea douglasii ssp. Douglasii (hardhack) 6.04 Carex obnupta (slough sedge) 3.64 Climacium dendroides (tree moss) 3.64 Equisetum fluviatale (swamp horsetail) 3.64 Impatiens noli-tangere (yellow touch-me-not) 3.64 Polystichum munitum (sword fern) 3.64 Rosa nutkana (Nootka rose) 3.64 Rubus discolor (Himalyan blackberry)* 3.64 Lower Forest Athyrium filix-femina (lady fern) 7.45 Carex obnupta (slough sedge) 7.45 Climacium dendroides (tree moss) 7.45 Cornus sericea (red osier dogwood) 7.45 Rubus discolor (Himalyan blackberry)* 7.45 Rubus ursinus (dewberry) 7.45 Ribes lacustre (black swamp gooseberry) 3.92 Galium trifidum (Small bedstraw) 3.80 Phalaris arundinacea (reed canary grass)* 3.80 Adiantum pedatum (maidenhair fern) 3.32 Alnus rubra (red alder) 3.32

Table 3 (continued). Lythrum salicaria (purple loosestrife)* 3.32 Physocarpus capitatus (pacific ninebark) 3.32 Picea sitchensis (Sitka spruce) 3.32 Polystichum munitum (sword fern) 3.32 Vaccinum parvifolium (red huckleberry) 3.32 Iris pseudacorus (yellow-flag iris)* 1.38 Rosa pisocarpa (peafruit rose) 1.38 Angelica genuflexa (kneeling angelica) 1.33 Heracleum lanatum (cow parsnip) 1.33 Populus balsamifera ssp. Trichocarpa (black 1.33 cottonwood)Salix lucida ssp. Lasiandra (Pacific willow) 1.33 Spiraea douglasii ssp. Douglasii (hardhack) 1.33 Alectoria sarmentosa (common witch’s hair) 1.13 Upper Aquatic Eleocharis palustris (creeping spikerush) 25.00 Ludwigia palustris (water purslane) 25.00 Polygonum hydropiper (waterpepper) 25.00 Sagittaria latifolia (wapato) 25.00 Upper Emergent Hippurus vulgaris (common marestail) 25.00 Phalaris arundinacea (reed canary grass)* 25.00 Polygonum hydropiper (waterpepper) 25.00 Sagittaria latifolia (wapato) 25.00 Upper Scrub- Amelanchier alnifolia (serviceberry) 16.67 Shrub Cornus sericea (red osier dogwood) 16.67 Equisetum fluviatale (swamp horsetail) 16.67 Phalaris arundinacea (reed canary grass)* 16.67 Populus balsamifera ssp. Trichocarpa (black 16.67 cottonwood)Rubus discolor (Himalyan blackberry)* 16.67 Upper Forest Cornus sericea (red osier dogwood) 14.29 Fraxinus latifolia (Oregon ash) 14.29 Phalaris arundinacea (reed canary grass)* 14.29 Populus balsamifera ssp. Trichocarpa (black 14.29 cottonwood)Rosa nutkana (Nootka rose) 14.29 Rubus discolor (Himalyan blackberry)* 14.29 Salix lucida ssp. Lasiandra (Pacific willow) 14.29

All vegetation species present at sites were classified as to native or non-native, according to regional field guides (Pojar and MacKinnon 2004, Spear Cooke 1997). Non- native vegetation species within the Columbia River estuary comprised 18% of the documented 110 total vegetation species (Table 3).

2.3.2 Avifauna

A total of 88 avian species were observed at the study sites during all seasonal observations (see Appendix C for a complete list of avian species identified during field surveys). NMDS ordination of the avian presence/absence survey data showed that avifauna occurrence in transects within sites tended to be similar to one another, while avian assemblages differed among sites (Figure 12). The ordination plot also revealed that the lower to mid-estuarine sites of Julia Butler Hansen, Robert W. Little, and Willow Grove tended to be similar to one another. The two upper estuarine sites, Willow Bar and Mirror Lake, plot close to one another in ordination space. Finally, the lowest estuarine site, Big Creek, appears to be distinct from the all other sites. The ANOSIM test of the avian data showed that there were significant differences in species present among forested wetland sites (global R = 0.895, p = 0.001). Resemblance: S17 Bray Curtis similarity 2D Stress: 0.16 Site JBH-2 WG-1 Big Creek JBH-3 ML-2 Julia Butler Hansen ML-1 Robert W Little Willow Grove RWL-1 WG-2 JBH-1 ML-3 Willow Bar WB-2 Mirror Lake WG-3 WB-1 RWL-3 WB-3

RWL-2 BC-2 BC-1

BC-3

Figure 12. NMDS ordination plot of avifauna assemblage composition at tidal forested wetland sites. 2.3.3 Insects

A total of 87 insect taxa were observed at the forested wetland sites (see Appendix D for a complete list of insect species identified during field surveys). NMDS ordination of the insect presence/absence survey data indicated that insect composition and abundance in transects within sites was generally similar to one another (Figure 13). Sites were somewhat distinct from one another, with a slight trend along the estuarine gradient. The trend is most visible over the lower to mid-estuarine sites, including Big Creek, Julia Butler Hansen, Robert W. Little, and Willow Grove. The two upper estuarine sites, Willow Bar and Mirror Lake, were similar to one another but also appear to be similar to the mid- and lower estuarine sites and transects. The two-dimensional stress for the NMDS ordination plot is 0.19, which is relatively high. A 3-dimensional ordination plot had lower stress at 0.13, but is not shown here due to difficulties in displaying 3-dimensional data. Further testing using the ANOSIM technique revealed that the insect assemblage composition of sites is statistically significant (global R = 0.592, p = 0.001). Resemblance: S17 Bray Curtis similarity RWL-2 2D Stress: 0.19 Site Big Creek JBH-1 RWL-3 Julia Butler Hansen Robert W. Little WG-2 JBH-2JBH-3 Willow Grove WG-1 Willow Bar BC-3 Mirror Lake RWL-1 BC-2 WG-3

WB-2 WB-3 ML-2 BC-1

ML-1 ML-3 WB-1

Figure 13. NMDS ordination plot of insect assemblage composition at tidal forested wetland sites.

SIMPER analysis revealed which insect groups constituted the majority (at least 4%) of the assemblages at tidal forested wetland study sites. The diversity of insect assemblage composition by order increased along the estuarine gradient (Table 4). At Big Creek, the majority of the insect assemblage was composed of only two insect orders, while the majority of the insect assemblage contained 10 separate orders of insects at Willow Bar in

47 the upper estuary. Similarly, insect species richness increased along the estuarine gradient (Figure 14). Insect species richness appears to be correlated with habitat complexity, or the presence of additional vegetation zones as seen in the upper estuary (Figure 6, Figure 14).

30 Vegetation Taxa

Species RichnessSpecies 20 Insect Taxa

0 Big Creek Julia Butler Robert W. Willow Willow Bar Mirror Lake (42) Hansen Little (63) Grove (97) (153) (208) (53)

Figure 14. Vegetation and insect species richness at tidal forested wetland sites. Values in parentheses along the x-axis indicate site RKm.

Table 4. Insects composing the majority of the insect assemblages at tidal forested wetland study sites based on SIMPER analysis.

Insect Order and Big Julia Butler Robert W. Willow Willow Mirror Family Creek Hansen Little Grove Bar Lake Acari X X X X X Araneae X X X Coleoptera Carabidae X Coleoptera Tenebrionidae X Collembola Entomobryiidae X X X Collembola Isotomidae X X X X X Collembola Sminthuridae X X X X X X Diptera Cecidomyiidae X X Diptera Ceratopogonidae X X X X X Diptera Chironomidae X X X X X Diptera Culicade X X Diptera Dolichopodidae X X X Diptera Ephydridae X X X Diptera Ptychopteridae X Diptera Sciaridae X Diptera Sphaeroceridae X Diptera Tipulidae X X X Hemiptera Miridae X Homoptera Cicadellidae X X X X Hymenoptera Chalcidoidea X Hymenoptera Formicidae X X Hymenoptera Tenthredinoidea X Psocoptera X X Thysanoptera Thripidae X X X X Zoroptera X

2.3.4 Benthic Macroinvertebrates

Ten benthic macroinvertebrate taxa were found at the tidal forested wetland study sites (see Appendix E for a complete list of benthic macroinvertebrate species identified during field surveys). Of these, two taxa, Oligochaeta and Nematoda, composed the vast majority of all benthic macroinvertebrates collected (96%). An NMDS ordination plot of the benthic macroinvertebrate abundance data indicates that transects within sites tended to be relatively similar to one another, but site similarity did not follow a consistent trend along the estuarine gradient (Figure 15). The two-dimensional stress of the ordination plot was moderate (0.14). An ANOSIM test showed that benthic macroinvertebrate assemblage was

49 significantly different among sites (global R = 0.31, p = 0.011). However, due to the low number of taxa found at the tidal forested wetland sites and the lack of statistical significance in the ANOSIM test, a SIMPER test was not performedTransform: Log(X+1) on this dataset. Resemblance: S17 Bray Curtis similarity WG-2 2D Stress: 0.14 Site WG-3 Big Creek Julia Butler Hansen WB-3 Robert W Little WB-1 Willow Grove WB-2 RWL-1 Willow Bar Mirror Lake WG-1 ML-1 JBH-3 RWL-2

RWL-3 ML-3 ML-2 BC-2 JBH-1 JBH-2 BC-1

BC-3

Figure 15. NMDS ordination plot of benthic invertebrate assemblage composition at forested wetland study sites. 2.3.5 Amphibians

A variety of amphibian species were observed at the tidal forested wetland sites, although sample numbers were not sufficient to perform statistical analysis on the dataset. As a result, the taxa observed at the study sites are presented in tabular format in Table 5.

Table 5. Amphibian species observed at forested wetland study sites. Amphibian species Big Julia Willow Willow Mirror scientific name(common name) Creek Butler Grove Bar Lake Hansen Taricha granulosa (rough-skinned newt) X Rana aurora (Northern red-legged frog) X Pseudacris regilla (Pacific tree frog) X X X Rana luteiventris (Columbia spotted frog) X X Amybstoma gracile (Northwestern salamander) X X Rana catesbeiana (American bullfrog) X

2.3.6 Mammals

Similar to the amphibian survey, the mammalian survey resulted in too low of sample numbers to perform statistical analysis on the dataset. As a result, the mammalian taxa observed at the study sites are presented in tabular form in Table 6. The Northern raccoon, Procyon lotor, was the most commonly detected species at the tidal forested wetland sites. The Columbian white-tailed deer, which is listed as endangered in the U.S. Endangered Species Act, was seen at two sites in the lower estuary (U.S. Fish and Wildlife Service 1983). One of the two sites, the Julia Butler Hansen Wildlife Refuge, was established specifically to conserve this species.

Table 6. Mammalian species observed at tidal forested wetland study sites. Mammalian species Big Julia Robert Willow Willow Mirror scientific name (common name) Creek Butler W. Little Grove Bar Lake Hansen Ondatra zibethicus (Muskrat) X Procyon lotor (Northern raccoon) X X X X Lontra canadensis (River otter) X X Odocoileus virginianus leucurus (Columbian white-tailed deer) X X Castor canadensis (Beaver) X X X Sylvilagus sp. (Rabbit) X Canis latrans (Coyote) X Odocoileus hemionus columbianus (Black-tailed deer) X X Cervus canadensis (Elk) X

2.3.7 Summary of Floristic and Faunal Assemblages

The results of SIMPER analyses, which indicate the species that constitute the majority of an assemblage at each site, were compiled into a table to summarize floristic and faunal species assemblages (Table 7). Amphibian and mammalian species reported in the summary table are all observed species at study sites, since sample numbers were low for those faunal groups.

Table 7. Summary of floristic and faunal assemblages. Plant, avian, and insect species listed are the result of SIMPER analyses. Amphibian and mammalian species are all species observed in the field. Big Julia Butler Robert W. Willow Willow Mirror Creek Hansen Little Grove Bar Lake Vegetation Trees Alnus rubra (red alder) X X X Fraxinus latifolia (Oregon ash) X X X Picea sitchensis (Sitka spruce) X X Populus balsamifera ssp. Trichocarpa (black cottonwood) X X Scrub-Shrub Acer circinatum (vine maple) X Amelanchier alnifolia (serviceberry) X Cornus sericea (red osier dogwood) X X X X Physocarpus capitatus (Pacific ninebark) X X Ribes lacustre (black swamp gooseberry) Rosa eglanteria (sweetbrier rose) X Rosa nutkana (Nootka rose) X X Rosa pisocarpa (peafruit rose) X X Rubus discolor (Himalyan blackberry) X X Rubus parviflorus (thimbleberry) X Rubus spectabilis (salmonberry) X Rubus ursinus (dewberry) X Salix lucida ssp. Lasiandra (Pacific willow) X X Salix sitchensis (Sitka willow) X Spiraea douglasii ssp. Douglasii (hardhack) X Vaccinum parvifolium (red huckleberry) X Emergent and Aquatic Plants Adiantum pedatum (maidenhair fern) X X Alectoria sarmentosa (common witch's hair) X X Angelica genuflexa (kneeling angelica) X Aruncus dioicus (goatsbeard) X Athyrium filix-femina (lady fern) X X X Callitriche heterophylla (different leaved water-starwort) X Carex obnupta (slough sedge) X X X X X Climacium dendroides (tree moss) X X X Elocharis palustris (creeping spikerush) X X Equisetum fluviatale (swamp horsetail) X X Equisetum telmatiea (giant horsetail) X Eriophorum angustifolium (narrow-leaved cotton grass) X Galium aparine (cleavers bedstraw) X Galium trifidum (small bedstraw) X Gaultheria shallon (salal) X X Hedera helix (English ivy) X Heracleum lanatum (cow-parsnip) X Hippurus vulgaris (common marestail) Impatiens noli-tangere (yellow touch-me- not) X X Iris pseudacorus (yellow-flag iris) X X

Table 7 (continued). Juncus effusus (common rush) Lilaeopsis occidentalis (Western lilaeopsis) X Ludwigia palustris (water purslane) X Lysichiton americanum (skunk cabbage) X X X Lysimachia nummularia (creeping jenny) X X Lythrum salicaria (purple loosestrife) X Medicago lupulina (black medic) X Oenanthe sarmentosa (Pacific water parsley) X Phalaris arundinacea (reed canary grass) X X X X X Polygonum hydropiper (waterpepper) X X X Polystichum munitum (sword fern) X X Pteridium aquilinum (bracken fern) X Sagittaria latifolia (wapato) X X X X Senecio jacobaea (tansy ragwort) X Senecio sylvaticus (wood groundsel) X Solanum dulcamara (European bittersweet)

Birds Agelaius phoeniceus (red-winged blackbird) X Anas platyrhynchos (mallard duck) X X X Ardea herodias (great blue heron) X X X X X Bombycilla cedrorum (cedar waxwing) X Branta canadensis (Canada goose) X X X X X X Carduelis tristis (American goldfinch) X X X Catharus ustulatus (Swainson's thrush) X X Corvus brachyrhynchos (American crow) X X X X X X Cyanocitta stelleri (Steller's jay) X X X Dendroica coronata (yellow-rumped warbler) X X Dendroica petechia (yellow warbler) X Eilsonia pusilla (Wilson's warbler) X Empidonax traillii (willow flycatcher) X X Geothlypis trichas (common yellowthroat) X Grus canadensis (sandhill crane) X Haliaeetus leucocephalus (bald eagle) X Ixoreus naevius (varied thrush) X Junco hyemalis (dark-eyed junco) X Larus sp. (gull) X Melospiza melodia (song sparrow) X X X X X X Molothrus ater (brown-headed cowbird) X Pandion haliaetus (osprey) X Pheucticul melanocephalus (black-headed grosbeak) X X Picoides pubescens (downy woodpecker) X X X X Pipilo maculatus (spotted towhee) X Poecile atricapilla (black-capped chickadee) X X X X X X Regulus satrapa (golden-crowned kinglet) X X X X Selasphorus rufus (rufus hummingbird) X X X Sterna sp. (tern) X Thryomanes bewickii (Bewick's wren) X X X X Troglodytes aedon (house wren) X Troglodytes troglodytes (winter wren) X Turdus migratorius (American robin) X X X X X X Vermivora celata (orange-crowned warbler) X X Zenaida macroura (mourning dove) X X

Table 7 (continued). Insects Acari X X X X X Araneae X X X Coleoptera Carabidae X Coleoptera Tenebrionidae X Collembola Entomobryiidae X X X Collembola Isotomidae X X X X X Collembola Sminthuridae X X X X X X Diptera Cecidomyiidae X X Diptera Ceratopogonidae X X X X X Diptera Chironomidae X X X X X Diptera Culicade X X Diptera Dolichopodidae X X X Diptera Ephydridae X X X Diptera Ptychopteridae X Diptera Sciaridae X Diptera Sphaeroceridae X Diptera Tipulidae X X X Hemiptera Miridae X Homoptera Cicadellidae X X X X Hymenoptera Chalcidoidea X Hymenoptera Formicidae X X Hymenoptera Tenthredinoidea X Psocoptera X X Thysanoptera Thripidae X X X X Zoroptera X

Amphibians Taricha granulosa (Rough-skinned newt) X Rana aurora (Northern red-legged frog)) X Rana catesbeiana (American bullfrog) X Rana luteiventris (Columbia spotted frog) X X Ambystoma gracile (Northwestern salamander) X X X Pseudacris regilla (Pacific tree frog) X X

Mammals Ondatra zibethicus (muskrat) X X Castor canadensis (beaver) X X Odocoileus hemionus columbianus (black- tailed deer) X X Odocoileus virginianus leucurus (Columbian white-tailed deer) X X Canis latrans (coyote) X Cervus canadensis (elk) X Procyon lotor (Northern raccoon) X X X X X Sylvilagus sp. (rabbit) Lontra canadensis (river otter) X X

2.3.8 Environmental Factors

Based on ANOVA, sites and zones were significantly different in the mean percent sand, silt, and organic content of soils (Table 8). The mean percent clay and mean elevation

54 of zones were not significantly different from one another. A post-hoc Bonferroni pairwise test indicated significant differences in mean sand and mean silt content of soils among some sites (Tables 9 and 10). Although the ANOVA showed percent organic content to be statistically significant, the post-hoc Bonferroni pairwise test did not show any significant differences among specific sites. Significant differences in the mean sand content were present among Willow Bar and Julia Butler Hansen, Robert W. Little, and Willow Grove. The mean sand content at Willow Grove and Mirror Lake was also statistically different from one another. Significant differences in mean silt content were present when comparing Julia Butler Hansen to Willow and Mirror Lake, and when comparing Willow Grove to Willow Bar.

Patterns in soil composition at sites reveal some trends across the estuarine gradient (Figure 16). The soils at the upper estuarine sites (Willow Bar and Mirror Lake) had relatively high mean percent sand, while lower estuary sites tended to have higher mean percent silt and organic content. The mean percent clay at zones within forested wetland sites was relatively low (less than 24% of soil composition) at all sites but fluctuated throughout the estuary. Although the mean elevation of zones within forested wetlands sites were not significantly different from one another, the scrub-shrub and forested zones of Mirror Lake in the upper estuary are higher than all other zones within sites (Figure 17).

Table 8. Results of ANOVA test on environmental characteristics of zones within sites. Statistically significant P-Values are presented in bold text. Environmental Source of Sum of Mean Factor Variation Squares df Square F Value P Value Percent Sand Among Groups 7356.622 5 1471.324 8.203 0.001 Within Groups 2152.279 12 179.357 Total 9508.901 17 Percent Silt Among Groups 2120.188 5 424.038 9.871 0.001 Within Groups 515.482 12 42.957 Total 2635.670 17 Percent Clay Among Groups 125.789 5 25.158 0.669 0.654 Within Groups 451.196 12 37.600 Total 576.985 17 Percent Organic Content Among Groups 2562.568 5 512.514 3.185 0.046 Within Groups 1931.053 12 160.921 Total 4493.621 17 Elevation Among Groups 41.379 5 8.276 1.959 0.158 Within Groups 50.685 12 4.224 Total 92.064 17

Table 9. P-values of ANOVA with post-hoc Bonferroni test for mean sand content of soils at study sites. Values in bold text denote statistically significant values at the 95% confidence level. Julia Butler Robert W. Willow Mirror Big Creek Hansen Little Grove Willow Bar Lake Big Creek Julia Butler Hansen 1.000 Robert W. Little 1.000 1.000 Willow Grove 1.000 1.000 1.000 Willow Bar 0.237 0.018 0.039 0.002 Mirror Lake 1.000 0.232 0.717 0.031 1.000

Table 10. P-values of ANOVA with post-hoc Bonferroni test for mean silt content of soils at study sites. Values in bold text denote statistically significant values at the 95% confidence level. Julia Butler Robert W. Willow Mirror Big Creek Hansen Little Grove Willow Bar Lake Big Creek Julia Butler Hansen 0.123 Robert W. Little 1.000 0.095 Willow Grove 1.000 0.260 1.000 Willow Bar 0.199 0.000 0.068 0.021 Mirror Lake 1.000 0.006 1.000 0.667 0.960

100.00 Organic Content Sand 80.00 Silt Clay

60.00

40.00

20.00 MeanPercent Soil Composition 0.00

-20.00

Site and Zone (A=Aquatic, E=Emergent, S=Scrub-shrub, F=Forest)

Figure 16. Mean percent organic content, sand, silt, and clay at zones within forested wetland sites. Error bars represent +/- 1 standard error of the mean. Site abbreviations are as follows: BC = Big Creek; JBH = Julia Butler Hansen; RWL = Robert W. Little, WG = Willow Grove; WB = Willow Bar; ML = Mirror Lake. Letters following sites indicate vegetation zones: A=Aquatic, E=Emergent, S=Scrub-Shrub, F=Forest.

4.5 Aquatic 4 Emergent 3.5 Scrub-Shrub 3 Forest 2.5

1.5 Mean elevation CRD) elevation (m, Mean 1

0.5

0 Big Creek Julia Robert W. Willow Willow Bar Mirror (42) Butler Little (63) Grove (97) (153) Lake (208) Hansen (53)

Figure 17. Mean elevation (m relative to CRD) of zones within tidal forested wetland sites. Error bars represent +/- 1 standard error of the mean. Site abbreviations are as follows: BC = Big Creek; JBH = Julia Butler Hansen; RWL = Robert W. Little, WG = Willow Grove; WB = Willow Bar; ML = Mirror Lake. Letters following sites indicate vegetation zones: A=Aquatic, E=Emergent, S=Scrub- Shrub, F=Forest.

2.4 Discussion

2.4.1 Vegetation Assemblages

Vegetation assemblages changed dramatically over the length of the Columbia River estuary, in terms of species present, species richness, and structure. Sites in the lower estuary were characterized by having fewer vegetation zones, primarily emergent, scrub-shrub, and forest zones, and high species richness within these zones than sites in the mid- and upper estuary (Figure 6). Big Creek, Julia Butler Hansen, and Robert W. Little had complex assemblages of species within each zone, and each meter along the transect tended to have many species present. In contrast, sites in the mid- and upper estuary, including Willow Grove, Willow Bar, and Mirror Lake, had lengthy vegetation zones, particularly emergent zones that included only several species. Two non-native species, reed canary grass and yellow-flag iris, were prevalent at these sites and formed quite dense, sometimes monotypic stands when present. Reed canary grass in particular was present at every site in the estuary, and often in every zone within a site. The broad environmental tolerances of this grass species, which was introduced intentionally within the estuary for cattle grazing (Christy and Putera 1992) appears to allow it to thrive well in sunny emergent and aquatic zones and as an understory species, although less dominant, in scrub-shrub and forested zones (Hovick and Reinartz 2007). These results are similar to those of Lavoie et al. (2003), who found that freshwater tidal forested wetlands in the lower St. Lawrence River estuary had lower numbers of exotic species than wetlands further up the river (above the reach of tides). In particular, they noted that purple loosestrife and reed canary grass were extensive in the upper portions of the river, and hypothesized that regular tidal freshwater inundation makes establishment of non-native species much more difficult.

All aspects of vegetation assemblages studied, including species and types of vegetation zones present, composition of canopy cover, tree density, and tree DBH showed trends across the estuarine gradient. The major shift in the structure and composition of vegetation assemblages appears to occur between Robert W. Little and Willow Grove, or between Puget Island, WA and Longview, WA. Interestingly, this is the portion of the estuary where the dominant tree species in the forested portions of the wetlands transitions from Sitka spruce to black cottonwood. At the lower estuarine sites where Sitka spruce is the

59 dominant tree species, a greater variety of scrub-shrub and tree species contribute to the canopy cover than in the mid- and upper estuary, despite the fact that the lower estuarine sites have a greater proportion of large trees in terms of DBH (Figures 8 and 9) . However, the amount of sky visible in the forested plots did not show any discernible trends across the estuary. In the mid- and upper estuary, canopy cover is comprised of fewer species and typically only tree species rather than a mix of trees and scrub-shrubs. The sites in this portion of the river tended to have a greater density of grasses and sedges as the understory in forested plots, while the lower estuarine sites had large scrub-shrubs such as red osier dogwood and vine maple growing in the understory. The lower estuary had up to seven total species contributing to canopy cover in the forested plots, while in the mid- and upper estuary, a maximum of three species contributed to canopy cover. Tree density (number of trees per site and per forested plot) showed striking differences across the estuarine gradient (Figure 7; Table 1). The lower estuarine sites, Big Creek, Julia Butler Hansen, and Robert W. Little, had fewer trees per plot and per site than the mid- and upper estuarine sites. Values ranged from a mean of 5.67 trees per 100 m2 in the lower estuary (at Julia Butler Hansen) to as high as 17.0 trees per 100 m2 in the upper estuary (at Willow Bar). In contrast, the proportion of sky visible in forested plots ranged from 5 to 50% but did not show a consistent trend across the estuarine gradient. Therefore, since the proportion of sky visible in the canopy of forested plots did not show much variation across the estuarine gradient (Figure 9), individual trees in the forested plots in the lower estuary likely provide more canopy cover per tree than more numerous, smaller trees in the mid- and upper estuary.

The transition in vegetation communities along the estuarine gradient appears to correspond to hydrogeomorphic reaches described in the Columbia River Estuary Ecosystem Classification (CREEC) (Simenstad et al. In revision). According to the Classification, the Columbia River estuary is composed of eight hydrogeomorphic reaches that are the result of hydrologic processes and geomorphologic formation of the estuarine floodplain (Figure 18). The transition seen in vegetation community composition and structure along the estuarine gradient is evidence for the strong influence of hydrology and geomorphology on floodplain forests. I identified Willow Grove (RKm 97) as transitional within the Columbia River estuary in terms of forested wetland composition and structure. This site lies in the upper portion of Reach C (Volcanoes Current Reversal), as having a shift in tidal influence over the

60 length of the reach. The upper portion of Reach C, where Willow Grove is located, is the area of the river where tidal influence diminishes and fluvial hydrology plays a larger role in the estuarine floodplain.

Figure 18. Hydrogeomorphic reaches of the Columbia River estuary (Data courtesy of Jennifer Burke, University of Washington. Imagery is ESRI World Imagery, December 2009. In summary, the vegetation assemblages in the lower portion of the Columbia River estuary are different in both composition and structure from the assemblages in the mid- and upper portions of the estuary. Most likely, the variations are due to a suite of environmental factors, including flow velocity, site topography, frequency and duration of combined fluvial and tidal flooding inundation, and shifts in overall climate when moving away from the Pacific Ocean. The correlation between hydrogeomorphic reaches and biotic assemblages was confirmed by additional ANOSIM testing. Test results revealed significant differences in vegetation communities according to hydrogeomorphic reach (p = 0.001). Similarly, avifauna and insect assemblages are significantly different according to hydrogeomorphic reach (p = 0.004 and 0.018, respectively).

Vegetation assemblages in other river systems around the world appear to follow similar patterns of structure along environmental gradients. The Tana River floodplain in

Kenya is composed of evergreen forests (Acacia elatior) in the lower portion of the river, and the riparian forest transitions to Populus spp. in the upper portion of the basin (Hughes 1990). Flooding regimes, including frequency and duration, were found to control the location of riparian forest community types. Although all of the Tana River floodplain forests have limited tolerances to high frequency and duration of flooding, the Populus spp. forests were located in a portion of the river that experienced more flooding than the evergreen trees, since they require flooding for regeneration. The distribution of forest types in the Tana River floodplain thus parallels those of the Columbia River estuary, although the dominant species differ.

Extensive studies conducted on regulated and non-regulated rivers in northern Sweden point to shifts in vegetation that occur as a result of river regulation, including decreased species richness and cover, and shifts in composition of vegetation according to dispersal mechanism (Jansson et al. 2000a, Jansson et al. 2000b, Nilsson et al. 1997). Their finding that alteration to the natural flow regime of boreal rivers dramatically affects the associated riparian vegetation which demonstrates the importance of river hydrology as a controlling factor of vegetation community composition and structure.

Thus, studies of river floodplain vegetation communities around the world illustrate the importance of hydrology and flooding regimes in determining the location, composition, and structure of riparian floodplain forests. Therefore, although a variety of environmental factors probably play a role in shaping the estuarine floodplain forests in the Columbia River system, discharge and flooding regimes are probably the most important.

2.4.2 Faunal Assemblages

In general, faunal assemblages did not show as distinct of a trend across the estuarine gradient as vegetation assemblages did. The avian and insect assemblages appeared to differ according to the estuarine gradient more than the benthic macroinvertebrate, amphibian, and mammalian assemblages (Figures 12, 13, 15; Tables 5, 6). Interestingly, although the vegetation assemblages at Willow Grove are most similar to the upper estuarine sites Willow Bar and Mirror Lake, the avian assemblages at Willow Grove are statistically most similar to the lower estuarine sites Julia Butler Hansen and Robert W. Little. This is likely a reflection of the shift in hydrogeomorphology at this point in the estuary, as described in the CREEC

(Simenstad et al. In revision; Figure 18). Thus, the area around Willow Grove is a transitional area in the ecological community of the Columbia River estuary, with some physical and biological similarities to both the lower estuarine and upper estuarine sites.

The insect assemblages, which are often closely associated with vegetation and physical characteristics of sites (Lawton and Strong 1981), showed trends in composition across the estuarine gradient in a pattern similar to the vegetation assemblages (Figure 13). Specifically, collembolans and dipterans formed the majority of the insect assemblages at the lower estuarine sites (Table 4). These results are generally in agreement with another recent study of insect emergence in the lower Columbia River estuary (Ramirez 2008). These insects may have an association or preference for either the vegetation or physical factors present at these sites. Since the tidal range is much greater at the lower estuarine sites than those in the upper estuary, these insect groups may have life history adaptations linked with the tidal inundation of the lower estuary, as other studies have showed (Saigusa and Akiyama 1995). Diversity of insect groups increased in the upper estuary, and at Willow Bar, the insect assemblages consisted of a wide range of groups including coleopterans, hemipterans, homopterans, hymenopterans, as well as the collembolans and dipterans common in the lower estuary. This increase in insect assemblage diversity may be a result of the increase in types of vegetation zones present or a preference for the plant species at these sites (Figure 14). Additionally, physical factors such as sandy substrate, minimal tidal fluctuation, or climatic dissimilarity may play a role in the higher diversity of insect assemblages at the upper estuarine relative to lower estuarine tidal forested wetland sites.

Sampling of the benthic macroinvertebrate community revealed almost no differences in species found at study sites. This finding suggests that identification of benthic macroinvertebrates to a lower taxonomic level is necessary to detect trends across the estuary if present. The two most common groups of benthic macroinvertebrates present in samples across all sites were oligochaetes and nematodes, which is unsurprising since these two groups are common in many areas of the country (Pennak 1953).

The mammalian community showed little variation in composition across the estuary (Table 6). Small sample sizes likely prevented the detection of a trend present across the estuarine gradient; however, it may also be that the same mammalian species inhabit

63 different forested wetland sites. Similarly, the amphibian sampling effort yielded too small a sample size to make conclusions on an estuarine level (Table 5). However, since amphibian species observations were generally unique to one or two sites, this suggests that different forested wetland sites may support different amphibian species. Five amphibian species were observed at Big Creek, whereas only one or two species were seen at any other site within the estuary, which may indicate a more diverse amphibian community inhabits the lower estuary.

Thus, it appears that there are associations between vegetation assemblages of the forested wetland sites and the faunal assemblages present. The associations may be a direct result of faunal preference for particular vegetation assemblages for feeding and habitat, or the faunal and vegetation assemblages may be independently driven by the physical factors that govern the estuary.

2.4.3 Comparison of Study Results to U.S. Army Corps of Engineers Riparian Habitat Inventory

Two sites included in this study were also intensively sampled by the USACE in the 1970s as part of their riparian habitat inventory in the lower Columbia River: Big Creek and Mirror Lake (U.S. Army Corps of Engineers 1976b). Vegetation, mammal, avifauna, and amphibian survey data from the riparian habitat inventory were compared with the results of this study in order to determine if sites had changed substantially in the forty years between the two studies. In general, the USACE surveys covered a larger area more intensively than the current study due to a large group of scientists collaborating over a longer study period.

The methodology used by the USACE was the placement of vegetation transects parallel to the river or side channel, in contrast to the perpendicular orientation used in this study (U.S. Army Corps of Engineers 1976b). However, the vegetation survey results in terms of species present and DBH of trees was comparable to those in this study. They described Big Creek as a ―Sitka spruce/red alder/salmonberry/mosses‖ habitat, which corresponds well with the most common species I observed at the site. They report that Sitka spruce and red alder co-dominate the stand, which is the same as my survey results (Figure 7, Table 7). They reported a mean DBH of 55.9 cm for Sitka spruce and 22.9 cm for red alder, while my study found a mean DBH of 83.5 cm for Sitka Spruce and 19.2 cm for red alder

(Figure 8). The scrub-shrubs and understory species reported by the USACE are also comparable to those observed in my study. Thus, it does not appear that the vegetation at Big Creek has changed noticeably in the four decades separating the two studies.

The USACE vegetation survey at Mirror Lake described the site as ―Black cottonwood/Pacific willow/Oregon Ash‖ dominant with red osier dogwood and reed canary grass in the understory (U.S. Army Corps of Engineers 1976b). The dominant species identified are consistent with those in my study, with the exception of Pacific willow, which I found to be present but not dominant (Figure 7, Table 7). However, of the three dominant species, the USACE found Pacific willow composed the smallest percent canopy cover when present in the sampling area (15% relative to 34% and 95% of Oregon ash and black cottonwood, respectively). The USACE reported the mean DBH of the dominant trees as follows: 63.5 cm for black cottonwood, 17.8 cm for Oregon ash, and 38.1 cm for Pacific willow. My study results show smaller trees overall, at a mean DBH of 15.9 cm for black cottonwood, 14.7 cm for Oregon ash, and only one Pacific willow tree was encountered in my study plots, at 45.0 cm DBH (Figure 8). Similar to the USACE study, I noted that reed canary grass tended to dominate the understory and emergent areas of the site. Red osier dogwood was abundant at the time of the USACE surveys, but I did not observe this species at the site during my surveys. Therefore, it does appear that either the vegetation has transitioned at the site during the last forty years, or the slightly different sampling location (across a small channel and about 150 m from my nearest transect) yielded different results in both composition and size of species present.

Mammals, avifauna, and amphibians observed during the USACE intensive sampling efforts were summarized across segments of the lower Columbia River (U.S. Army Corps of Engineers 1976b). In their study, Segment 2 extends from RKm 19 to 127 and thus includes my lower and mid-estuarine sites, Big Creek, Julia Butler Hansen, Robert W. Little, and Willow Grove. Segment 3 in the USACE riparian habitat inventory covers from RKm 127 to Bonneville Dam (RKm 235), and thus includes both of my upper estuarine sites, Willow Bar and Mirror Lake. Comparison of my survey data, which was collected on a relatively small, site specific scale to data summarized across such large areas of the estuary is difficult and presents a problem of scale. However, many of the species that were most common in the USACE study such as beaver, northern raccoon, and many of the avifauna were also

65 observed in my field studies (Table 7). One of the notable differences between the present study and the USACE study is the relative lack of amphibians observed. The USACE study reported both greater numbers and variety of amphibian at study sites. As discussed previously, this is most likely due to the life history strategies employed by amphibian species, and the intensive efforts and dedicated team of scientists available to study this particular faunal group in the USACE study.

2.4.4 Community Ecology Summary of Freshwater Tidal Forested Wetlands

The freshwater tidal forested wetlands in the Columbia River estuary appear to fall into two main groups according to analyses of faunal and floral assemblages: lower estuarine forested wetlands, and mid- and upper estuarine forested wetlands. The lower estuarine forested wetland vegetation assemblages are dominated by coniferous species such as Sitka spruce and western red cedar and have associated scrub-shrub zones that are densely vegetated with a diverse group of large scrub-shrubs. The coniferous-dominated forested wetlands are utilized by multiple faunal assemblages. The avian assemblages includes a broad range of bird groups, including eagles, thrushes, sparrows, wrens, and warblers. Insect assemblages in the lower estuarine forested wetlands consist mainly of collembolans and dipterans, and nematodes and oligochaetes are the primary benthic macroinvertebrates present. Northern raccoons, river otters, Columbian white-tailed deer, and a variety of amphibians utilize these sites. Tides are the dominant hydrological regime affecting these sites on a daily basis, and the hydrological differences between the lower and upper estuarine sites may be a determining factor in the biota present at these sites (Fox et al. 1984).

The mid- and upper estuarine freshwater tidal forested wetlands have more diverse vegetation zones, with the forested zone dominated by deciduous trees, primarily black cottonwood, Oregon ash, and Pacific willow. All of the vegetation zones at these sites have lower species richness than the lower estuarine zones, and in some cases zones are monotypic in composition. The groups of birds present in the upper estuary are similar to those in the lower estuary, but specific species within groups differ significantly. The insect assemblages in the upper estuary are much more varied in terms of composition compared to

66 those in the lower estuary and include members of many insect orders. Beavers, black-tailed deer, elk, coyotes, and river otters were observed at forested wetland sites in the upper estuary. Although technically within the reach of tides in the Columbia River estuary, the seasonal and annual variations in river flow are the dominant flow regime affecting these sites (Fox et al. 1984). Little if any changes in hydrology at the sites occur on a daily basis, which may determine the biota present in the mid- and upper estuarine forested wetlands.

2.4.5 The Natural Flow Regime and Environmental Factors

Hydrologic events, specifically flood pulses, are the component of the natural flow regime primarily responsible for structuring biota in riparian systems (Junk et al. 1989). In the case of the Columbia River estuary, flood pulses are dampened relative to pre-regulation times, but still occur albeit less frequently and of lower magnitude (Figure 2). The freshwater tidal forested wetlands in the Columbia River estuary are subject to flooding on an annual scale due to the spring freshet, and twice-daily inundation due to tidal cycles (Fox et al. 1984). Tides cause frequent but short duration inundation of vegetation, while high river flows cause infrequent but lengthy inundation of forested wetlands (Mitsch and Gosselink 2000). Although the natural flow regime affects all of the biota living in a tidal floodplain, vegetation is especially affected due to its generally stationary life history strategy. Each type of inundation experienced by wetland vegetation constitutes a different hydrologic regime, requiring a distinct suite of adaptations by vegetation in order to thrive at these sites. In the lower estuary, twice-daily tidal inundation is the primary hydrologic regime, while the seasonal and annual variations in the natural flow regime result in additional flooding in the estuarine floodplain. The peak annual flows in the estuary are the result of a complex combination of river flow dynamics, tidal forcing, and geomorphology of the river floodplain (Fox et al. 1984, Simenstad et al. In revision).

Although this study showed that elevations of sampling locations were not significantly different from one another, slight differences in elevation can translate to substantially different patterns of frequency and duration of inundation in this system (Kukulka and Jay 2003). At the sites in the lower estuary where tidal ranges are on the order of 1.8–2.6 m, an elevation discrepancy of a few centimeters between one sampling location and another could mean the difference between twice daily submersion of vegetation and no

67 regular inundation. The scrub-shrub and forest zones at Mirror Lake show the highest elevation of all sampling locations (Figure 16; mean of 3.40 and 4.61 m, respectively). These two zones are therefore the least likely to receive inundation, and decreases in river flow and inundation at sites will have the most effect in the upper estuarine scrub-shrub and forest zones.

Water temperature is another physical factor that may determine the presence or absence of certain species at a specific site (Hudon 2004). Temperature gauges were originally deployed at the study sites, but logistical difficulties, primarily the fact that some of the channels adjacent to forested wetland study sites in the upper estuary almost completely de-water in late summer, prevented useful measurements from being completed. However, it is likely that water temperatures differ greatly between the wetlands at sites in the upper and lower estuary. The twice daily influx of tides probably moderates temperatures in the lower estuarine wetlands, while the wetlands in the upper estuary are generally shallow and stagnant during low river flow conditions, possibly resulting in higher water temperatures. Although temperature gauges are present along the mainstem of the Columbia River, the data were not used here due to the likely differences between mainstem temperature and those in shallow wetlands or channels associated with the forested vegetation assemblages.

Patterns of sediment deposition in the Columbia River estuary are generally determined by currents, which are relatively strong and variable in this system compared to other estuaries (Sherwood et al. 1990). Fine sediment travels suspended in the water column in the Columbia River, and is generally flushed out to sea with the exception of slower moving water in side channels and peripheral bays. Due to the differences in currents and circulation patterns between the upper and lower estuary, I expected to see differences in soil grain size across the estuarine gradient. As hypothesized, there were significant differences between the compositions of soils by grain size classes. Willow Bar and Mirror Lake in the upper estuary had soils with a high percentage of sand, and relatively low percentages of silt compared to sites in the mid- and lower estuary (Figure 16). These trends are likely a result of the higher velocity currents present in the upper estuary, and the lower velocity and reversing currents that are found in side channels of the lower estuary. Also, ambiguous locations of dredge deposits resulting from maintenance of the navigation channel may play a

68 role in sand composition at the upper estuarine sites. The distribution of clay size particles did not show any trends across the estuary, and comprised less than 22% of the soil samples at all locations.

The organic content of soils at tidal forested wetland sites did not show statistically significant difference at sites, although the values do appear to peak in the mid-estuary, at Robert W. Little and Willow Grove (Figure 16). The percent organic content in soil samples was indicative of the amount of detrital matter present, dissolved organic matter including carbon, nitrogen, and phosphorus, and below-ground biomass. The combination of these three different components into one measurement may have prevented the detection of trends in any one of the three across the estuarine gradient. However, I believe the high values seen in the mid-estuarine sties, particularly the emergent zone at Willow Grove (45 to 70%), are a reflection of particularly dense stands of vegetation and subsequent root structures in the soil. Overall, values for soil organic content were high compared to soil standards and similar to other freshwater tidal forested wetlands in the region (Brophy 2009, USDA Natural Resources Conservation Service 1996). My sites had a mean organic content of 22.3%, and a range of 5.54 to 69.69%. Brophy (2009) found organic content of similar forested wetland sites in the region averaged 22.2% with a range of 9.29 to 45.14%. The higher range in organic content of my sites is most likely explained by the larger range in types of forested wetlands in my study, while Brophy’s (2009) study focused on forested wetlands most similar to my lower estuarine sites. For comparison, the USDA Natural Resources Conservation Service considers any soil with more than 5% organic matter to be high in organic content. The high soil organic content found in most of the freshwater tidal forested wetlands included in this study indicate that they are able to provide biological functions such as water purification and invertebrate habitat (Adamus 1995).

2.4.6 Implications and Recommendations for Future Research and Monitoring

Detailed information about the community ecology of the freshwater tidal forested wetlands of the Columbia River estuary from this study will likely be useful to both restoration efforts and the ecosystem classification. Recently, restoration of tidal forested wetlands has become a priority in the Columbia River estuary (LCREP 1999). In restoration

69 ecology, reference sites are often lacking but are vital to the success of restoration projects (Brophy 2009). The data gathered at these relatively unimpacted forested wetland sites in the Columbia River estuary may provide valuable information for restoration project managers during the design phase of restoration projects. In addition, a multi-faceted ecosystem classification of the Columbia River estuary is currently underway (Simenstad et al. In revision). Quantitative characterization of the vegetation along the length of the Columbia River estuarine gradient will add useful detail to the hydrogeomorphic reaches described in the classification system.

Due to hydroregulation of the Columbia River, freshwater tidal forested wetlands located in the estuary are directly affected by river management practices and the altered river flow regime (Simenstad et al. 1992). Ideally, river managers utilize available ecological data to practice adaptive management in order to manage river flow in the most sustainable method possible (Richter et al. 2003). Therefore, detailed ecological data about the ecosystems downstream from river impoundments is crucial for the implementation of adaptive management in a river system. The information provided by this study may be useful to river managers for managing the hydrologic impacts to the remaining freshwater tidal forested wetlands in the Columbia River estuary. For example, in other regulated river systems, managers have altered river flow in order to facilitate establishment and survival of riparian tree species (Rood et al. 2005). Ensuring that peak spring flows continue to occur may help flood-dependent species such as cottonwood and willow thrive in the mid- and upper estuary where fluvial hydrology dominates (Sherwood et al. 1990).

In addition, this study could potentially serve as baseline information for future research projects focusing on specific sites within the estuary, or on particular species or assemblages present at the forested wetland sites. Baseline ecological information is important in future studies for comparison and change analyses, especially given the relatively short period of time since hydroregulation of the Columbia River began (Simenstad et al. 1992). Ecological studies such as this are critical to our understanding of how alterations to ecosystems, ecosystem processes, the climate and natural flow regimes impact ecosystems.

Chapter 3: Effects of hydroregulation on the freshwater tidal forested wetland communities of the Columbia River estuary

3.1 Introduction

3.1.1 Study Description

The purpose of this portion of the study was to examine the potential effects of hydroregulation of the Columbia River on the freshwater tidal forested wetlands considered in Chapter 2. Historic flood levels (prior to the beginning of hydroregulation in 1969) were compared to recent hydrology data to determine the changes in the amount of inundation occurring at freshwater tidal forested wetland study sites during the spring freshet, or highest annual river flow period. A Geographic Information System (GIS) analysis was performed to determine the corresponding changes in vegetation assemblages present at these same sites over time. The study provides a better understanding of how alterations to the natural flow regime of the Columbia River may have affected some of its freshwater tidal forested wetland communities.

3.1.2 Background

3.1.2.1 Impetus for study

An estimated two-thirds of the world’s rivers are obstructed by dams or impoundments (man-made structures that in some way disrupt natural river flow), which result in a multitude of alterations to river ecosystems (Nilsson and Berggren 2000). Dams fragment river ecosystems, retain sediment that would normally flow downstream, alter seasonal flow magnitude and timing, and raise water temperatures. Additionally, dams often cause inundation of the riparian zone upstream of impoundments, and water table declines downstream. The mainstem and tributaries of the Columbia River contain 28 major dams constructed for power generation, flood control, recreation, and irrigation, industrial, and municipal water diversion (Simenstad et al. 1992).

The Flood Pulse Concept is one of the foundations of river ecology, and states that seasonal high river flows are the driving forces behind the existence, productivity, and

71 interaction of the diverse biota in riparian ecosystems (Junk et al. 1989). The result of flood pulses in a riparian ecosystem is that the organisms present in the ecosystem reflect the characteristics of the flood regime. Hydroregulation disrupts a river’s natural flood pulses and thus the biota present in the ecosystem experience stress and may fail to survive in their native habitat. Native plants and animals that live in the river or adjacent riparian zone have often evolved life history strategies to coincide with the natural flow regime, which are disrupted by hydroregulation (Nilsson and Berggren 2000).

The effect of hydroregulation on a river hydrograph can be illustrated using flow data from the Columbia River prior to and after construction of dams (Figure 2). As the hydrograph shows, hydroregulation drastically altered the natural flow regime of the Columbia River, and caused changes in the timing and amplitude of seasonal flows. Reductions in river discharge translate to less inundation of the estuarine floodplain, which can affect wetland vegetation communities that are accustomed to periodic inundation (Nilsson and Berggren 2000). Investigating the changes in inundation over time as a result of hydroregulation will provide a better understanding of how the forested wetland communities of the Columbia River estuary have changed during the recent period of river flow regulation.

3.1.2.2 Previous studies on changes in riparian ecosystems due to hydroregulation

Numerous studies have documented the effects of river hydroregulation on riparian vegetation. Jansson et al. (2000b) conducted a study comparing eight rivers in northern Sweden, four of which were heavily hydroregulated and four of which were free-flowing. Among their findings was a reduction in vertical zoning of vegetation along regulated rivers, while free-flowing rivers had distinct communities of forest, scrub-shrub, herbaceous, and amphibious plant species. They also reported that hydroregulation led to reduced habitat availability and decreased species richness.

North American riparian forest communities, primarily Populus spp. dominated forests, have experienced dramatic losses at least partially due to hydroregulation (Rood and Mahoney 1990). The Populus genus includes cottonwood trees, one of the most common riparian and wetland tree species in North America. They are an important early successional species and provide valuable habitat for a variety of animal species. Riparian

72 cottonwoods have evolved a life-history strategy that is closely linked to peak seasonal river flows, as they require moist, newly exposed sites for seed germination. As hydroregulation of North American rivers has increased over time, peak seasonal flows have been reduced and shifted temporally. These changes in river flow regimes have altered the ability of riparian cottonwoods to survive in their native habitat. Rood et al. (1999) cored and aged black cottonwood individuals along the Bow River in Alberta, Canada, a river that was extensively dammed between 1910 and 1954. Flow regulation on the Bow River has both decreased high flows and increased low flows, much like the alterations to the Columbia River hydrograph, which has resulted in channel stabilization and less recently exposed barren bars that are available for colonization by riparian cottonwoods. The authors found that black cottonwoods occurred in an irregular age distribution. A lack of recruitment after 1955 suggested a correlation between flood events and tree recruitment, and a linear regression analysis revealed that a highly significant positive correlation existed between peak flows and cottonwood establishment along the Bow River.

Changes in the amount of floodplain habitat are sometimes caused by alteration of the natural flow regime. In the Columbia River estuary, Kukulka and Jay (2003) studied changes in shallow water habitat area (SWHA) since hydroregulation, and found a 29% decrease in SWHA over time. SWHA in the Columbia River estuary provides valuable habitat for juvenile salmonids, which use the area for refuge and foraging. The authors found that a more than 40% reduction in peak river flows during the spring freshet corresponded to a 62% reduction in SWHA available during the same time period. In addition to the reduction in habitat available for juvenile salmonids, the decrease in the area of inundation may affect where particular plants are able to grow within the estuarine floodplain due to their specific suite of environmental tolerances (Mitsch and Gosselink 2000).

3.1.2.3 The role of the natural flow regime in riparian systems

The natural flow regime, along with soil properties and biological processes related to succession, is responsible for determining forest structure in riparian systems (Naiman and Bilby 1998). The physical forces present in a system that occur periodically such as fire, wind, and flooding result in the alteration of successional processes in riparian vegetation. Species that are able to either withstand the periodic flood pulses or establish as a result of it

73 constitute the vegetation community in the riparian floodplain. The removal of flooding as part of the natural flow regime in a riparian system often alters the community by providing an opportunity for species with alternate life history traits to establish. Often, this leads to the decline of native species populations and the establishment of non-native species, if they are able to outcompete native species due to the change in physical processes (Lockwood et al. 2007).

In the Columbia River estuary, the primary flood pulse usually occurs annually as a spring freshet in May or June (Simenstad et al. 1992). Three components of flooding influence wetland and riparian vegetation: depth, duration, and frequency (Casanova and Brock 2000). Flood events serve two primary purposes in a riparian ecosystem. First, they physically restructure landscapes and provide fresh sediment deposits for plant colonization (Walker et al. 1986). Second, they cause the transfer of nutrients from the terrestrial portion of the floodplain to the aquatic, resulting in increased primary productivity in the aquatic portion of the ecosystem (Junk et al. 1989). Thus, flooding provides important ecological connectivity between the terrestrial and aquatic zones, and altering any one component of the flooding associated with the natural flow regime (depth, duration, or frequency) may change the biotic composition of the riparian or estuarine ecosystem.

3.1.3 Study Objectives

The objectives of this study were to examine the changes in the primary annual flood pulse experienced in the Columbia River estuary and its effect on forested wetland vegetation over time: the depth of flooding occurring along the estuarine gradient. The goal of the study was to examine changes in the depth of flooding at the same forested wetland sites considered in Chapter 2, in order to place the community ecology of these sites in the context of the natural history of the system. In order to accomplish this, I compared levels of flooding typically seen along the estuarine gradient prior to hydroregulation to levels of flooding occurring during the spring freshet in recent times. Mean flood height data was used to draw general conclusions about inundation that may occur at forested wetland sites in the estuarine floodplain. In order to determine the potential effect of any changes in the amount of inundation on the vegetation assemblages at forested wetland sites, a GIS analysis of vegetation assemblages was conducted. Historic maps of the forested wetland sites based

74 on the U.S. Coast and Geodetic Survey topographic sheets (t-sheets) were compared with recent maps, satellite imagery, and field vegetation survey data to calculate changes in the proportion of cover of particular types of vegetation assemblages (forest, scrub-shrub, marsh) within a site. The field studies described in Chapter 2 document the dominant species comprising vegetation assemblages at each study site. Environmental tolerances of dominant species were integrated with the analysis of vegetation change to explain the effect of altered flow regimes on vegetation assemblages.

3.1.4 Hypotheses

Hypotheses were as follows:

1. The magnitude of flooding experienced by the freshwater tidal forested wetlands during the spring freshet has decreased along the estuarine gradient since flow regulation began in 1969.

2. Because of the interaction of fluvial and tidal hydrology in the lower portion of the estuary, less change in vegetation has occurred over time compared to the upper portion of the system, where fluvial hydrology is dominant.

3.1.5 Approach for Testing Hypotheses

The goal of this study was to examine how the alterations to the flow regime of the Columbia River and thus the depth of flooding occurring in the system may have affected the freshwater tidal forested wetlands described in Chapter 2. A variety of historical information including river flow records, maps, and land survey documents were compared with information for the modern period of hydroregulation. Field studies of vegetation at the forested wetland sites presented in Chapter 2 were utilized for ground-truthing recent maps depicting riparian habitat and imagery of the study sites (U.S. Army Corps of Engineers 1976a). The first hypothesis was tested using post-hydroregulation river flow records at various stations throughout the estuary and known levels of flooding that occurred commonly prior to hydroregulation. The second hypothesis was tested by analyzing historical and recent maps and imagery in a GIS to determine changes in the presence and extent of vegetation assemblages at study sites.

3.2 Methods

3.2.1 Mean Flood Stage Height Calculations

The water years 1999-2008 (water year = October 1 through September 30) were selected for analysis of current river flow and inundation. Studying a ten-year period dampens the effect of any extreme high or low flows during that time period. The spring freshet or peak annual flow was the time period selected for the study. Since the spring freshet has shifted temporally prior to hydroregulation, I determined the current timing of the spring freshet by plotting the river flow at The Dalles, OR for the water years 1999-2008 (Figure 5). I concluded that the spring freshet occurred between May 19 and June 19 during these years, which were the days that mean flow exceeded 250,000 cubic feet per second (cfs).

The National Oceanic and Atmospheric Administration’s (NOAA’s) Advanced Hydrologic Prediction Service operates tidal gauges throughout the Columbia River estuary. For this portion of the study, the gauges nearest to the forested wetland study sites described in Chapter Two were identified (Figure 19, Table 11). The gauges used to correspond with forested wetland study sites are as follows:

Table 11. Location of forested wetland study sites and NOAA tidal gauges used in the study. Forested Wetland Study Site (RKm) NOAA tidal gauge (RKm)

Big Creek (42) Astoria, Tongue Point (27)

Julia Butler Hansen (53) Skamokawa (53)

Robert W. Little (63) Wauna (66)

Willow Grove (97) Longview (105)

Willow Bar (153) St. Helens (137)

Mirror Lake (208) Bonneville Dam (232)

Figure 19. Location of forested wetland study sites and NOAA tide gauges used in study. Image is ESRI World Imagery, December 2009. Stage height data for each tidal gauge is archived on the internet by the USACE, Northwestern Division. Stage height data for the period May 19 through June 19, 1999-2008 was downloaded into a Microsoft Office Excel 2007 spreadsheet. The stage height data was converted from feet relative to the National Geodetic Vertical Datum of 1929 (NGVD 29) into meters relative to the North American Vertical Datum of 1988 (NAVD 88) using the National Geodetic Survey’s Vertcon conversion factor for each location. The mean and standard deviation for all stage height measurements during the study time period were calculated in the spreadsheet.

Bankfull elevations in meters relative to NAVD 88 were used as the measure of historic flooding common in the Columbia River estuary as determined by the USACE. The bankfull elevation is the elevation above which water flows onto the estuarine floodplain. This elevation represents a level of flooding regularly achieved in the Columbia River estuary prior to hydroregulation, and is well below the elevations of extreme floods that occurred prior to 1969. Bankfull elevations at the location of the existing tide gauges operated by NOAA were recorded in the spreadsheet for analysis. The bankfull elevation for each point corresponding to NOAA tide gauges was compared to the mean river stage height

77 during the spring freshet from 1999-2008 to determine the amount of change in current spring freshet inundation since hydroregulation.

3.2.2 GIS Analysis

3.2.2.1 Historic vegetation GIS analysis

The historic vegetation communities at forested wetland study sites were mapped in a GIS using U.S. Coast and Geodetic Survey topographic sheets, or t-sheets (Burke 2010). The t-sheets were originated in the late 1800s as part of an effort to map the coasts and waterways of the United States (Figure 20). The t-sheets that cover the Columbia River estuary extend from the Pacific Ocean to approximately RKm 207. ESRI ArcInfo version 9.3 was used for all GIS processing, analysis, and mapping. The digitization of the t-sheets and historic vegetation information for the Columbia River estuary is part of a larger project in process at the University of Washington (Burke 2010). For this particular project, the t-sheet GIS layers were clipped to the extent of the forested wetland study sites described in Chapter Two. The extent of study sites was determined by the location of the mainstem Columbia River or side channels running along one side of the site, and fixed boundaries running along other edges, such as roads or railroad tracks. When necessary, the extent of sites was determined somewhat arbitrarily, such as a distance from a nearby structure, or placing a site boundary where field observations ended. The U.S. Coast and Geodetic Survey t-sheets were digitized into polygons attributed with codes signifying habitat classes derived from the map symbology (Table 12).

Figure 20. Example of a U.S. Coast & Geodetic Survey topographic sheet for a portion of the Columbia River estuary.

Table 12. Habitat classes attributed to digitized U.S. Coast and Geodetic Survey t-sheets (Burke 2010). Code Description 1 riverine/estuarine 2 reef 3 sandflat 4 submerged marsh 5 marsh 6 wooded marsh 7 scrub-shrub marsh 10 sand 11 grass 12 pine 13 woodland 14 mixed forest 15 shrubs 16 stream/river 17 rocky bluff 18 eroded bank 19 depression 20 open water 21 road 22 orchard 23 cultivated fields 24 pasture 25 dwelling / structure 26 levee 27 overwater structure 30 unclassified 40 unknown The area of each type of habitat class was calculated in the GIS, and recorded in a Microsoft Excel 2007 spreadsheet. The percentage cover of each of the habitat classes was calculated and entered into the spreadsheet.

Mirror Lake, the furthest up-estuarine study site, lies just outside the extent of the t- sheet maps. However, the United States General Land Office (GLO) conducted a survey of this area in 1860 (Christy 1990). During the survey process, notes about topography, woody vegetation, and soils were recorded. Species and size (diameter at breast height) of woody vegetation was included in the survey notes. Based on the survey note transcription, John Christy of Oregon State University created a map of the likely historic vegetation of Rooster Rock State Park, part of which includes the Mirror Lake forested wetland study site (Figure 21). An electronic copy of the

80 map was georectified and the vegetation information was digitized to provide historic vegetation information for this site in lieu of the t-sheets used for the rest of the sites. The map inferred from the GLO survey notes contained different vegetation classifications from the t-sheets, and the vegetation types were re-classified to correspond with the t-sheet classification as shown in Table 13.

Figure 21. Vegetation of Rooster Rock State Park based on GLO survey notes (Christy 1990).

Table 13. Translation used to convert GLO Survey vegetation classes to t-sheet vegetation classes for the Mirror Lake Study site. GLO Survey Vegetation Classification T-sheet classification Cottonwood-Fir Woodland Wet Prairie Marsh Willow Bottom Scrub-shrub marsh Ash Bottom Wooded marsh

The area of the site covered by water, whether wetland, tidal channels, or mainstem of the Columbia River, was not included in either the current or historic calculations with the exception of at Willow Bar. At Willow Bar, the historic site was quite small compared to the present day site, and in order to compare the proportional change in vegetation type over time, similar total site areas were required. For the remainder of the sites, areas covered by water were not included since the objective was to determine change in the type of vegetation at sites over time.

3.2.2.2 Current vegetation GIS analysis

The present-day vegetation classification of forested wetland study sites was accomplished using several methods and sources of information. A 1976 Inventory of Riparian Habitats for the Columbia River provided maps of the entire estuary with vegetation classified according to the primary species and landforms occurring throughout the floodplain (U.S. Army Corps of Engineers 1976a). The maps covering the forested wetland study sites were scanned and georectified. The vegetation information was digitized into a polygon layer and attributed according to the t-sheet classification system (Table 12). Field studies described in Chapter Two revealed that although the 1976 maps were often still representative of the location of particular vegetation types in the estuary, the location of vegetation had sometimes changed during the past three decades. Observations from field studies combined with visual interpretation of recent high-resolution imagery available for the Columbia River estuary, was used to further refine the polygon layer to represent the current vegetation at the forested wetland study sites. Sources of imagery included Quickbird imagery dating from 2004 through 2007, National Agricultural Inventory Program (NAIP) from 2005 and 2006, and 2006 Aerials Express Imagery. Once completed, the area covered by each vegetation class was entered into the spreadsheet and the proportion of area covered by each class was calculated and recorded. Based on the historic and current vegetation information compiled in the spreadsheet, the change in vegetation classes over time at study sites was calculated and graphed.

3.3 Results

3.3.1 Mean Flood Stage Height Calculations

Mean flood stage height during the spring freshet in the water years 1999-2008 was lower than the bankfull elevation at all tide gauges (Figure 22). Mean flood stage height at upper estuarine sites (St. Helens and Bonneville) was further below the bankfull elevation than at lower and mid-estuarine sites (Astoria, Skamokawa, Wauna, and Longview). The largest discrepancy (2.123 m) between bankfull elevation and mean flood stage height was seen at the St. Helens gauge, while the smallest discrepancy was at Astoria (0.493 m).

10.0 9.516

8.0 7.403

6.0 5.220

4.298 Bankfull Elevation 4.0 3.322 3.110 2.997 3.097 2.767 2.547 Elevation (m; NAVD 88) NAVD (m; Elevation 2.274 2.294 Mean flood stage height 2.0 during spring freshet, 1999-2008

0.0

NOAA Tide Gauge (RKm)

Figure 22. Bankfull elevation and mean flood stage height during recent spring freshets at NOAA tide gauges in the Columbia River estuary. Error bars represent the standard deviation of the mean flood stage height. 3.3.2 Vegetation Assemblage Change

Change in vegetation classes at forested wetland study sites occurred along the estuarine gradient. Sites in the lower estuary (Big Creek, Julia Butler Hansen, and Robert W. Little) showed no change in vegetation classes over time, while sites in the mid- and upper estuary (Willow Grove, Willow Bar, and Mirror Lake) displayed changes in vegetation classes over the time period studied (Table 14).

Table 14. Change in area of vegetation classes at forested wetland study sites over time. Historic percentage Current Historic of total Current percentage Percent Site (RKm) Vegetation Class Area (ha) site Area (ha) of total site Change Big Creek (42) Wooded Marsh 31.0045 100.0% 30.2805 100% 0% Julia Butler Hansen (53) Wooded marsh 4.4116 100.0% 4.4116 100% 0% Robert W. Little (63) Wooded Marsh 7.7084 100.0% 7.7313 100% 0% Willow Grove (97) Marsh 99.6626 63.0% 60.3556 34.2% -28.8% Scrub-Shrub Marsh 0.9435 0.6% 51.5920 29.2% 28.6% Wooded Marsh 57.5100 36.4% 64.6037 36.6% 0.2% Willow Bar (153) Marsh 0.0000 0.0% 9.9104 10.8% 10.8% Sand 0.0000 0.0% 4.3669 4.8% 4.8% Sandflat 7.4863 8.2% 5.9262 6.5% -1.7% Scrub-Shrub Marsh 0.0000 0.0% 8.0424 8.8% 8.8% Shrubs 0.0000 0.0% 10.8911 11.9% 11.9% Woodland 4.6948 5.1% 52.4377 57.2% 52.1% Open water 79.5936 86.9% 0.0000 0.0% -86.9% Mirror Lake (208) Marsh 9.5936 9.3% 53.3071 49.6% 40.3% Scrub-Shrub Marsh 20.2627 19.6% 0.0000 0.0% -19.6% Shrubs 0.0000 0.0% 1.3510 1.3% 1.3% Wooded Marsh 61.0162 58.9% 21.9336 20.4% -38.6% Woodland 12.5784 12.2% 30.9843 28.8% 16.6%

3.3.2.1 Lower estuarine sites

The vegetation at all three of the lower estuarine sites (Big Creek, Julia Butler Hansen, and Robert W. Little) was classified as 100% wooded marsh based on both the t- sheets and current information, resulting in no change in vegetation classification over time (Table 14, Figures 23-29). The slight discrepancies in hectares at Big Creek and Robert W.

Little reflect shifts in the location of tidal channels over time, which were not included in the calculations and thus do not reflect an overall change in vegetation classes at those sites.

35 Historic Area

30 Current Area

Area (ha) Area 15

Wooded Marsh Wooded Wooded MarshWooded Wooded marshWooded

Big Creek Julia Butler Robert W. Little Hansen

Site and Vegetation Class

Figure 23. Change in vegetation classes at lower estuarine sites over the study period.

Figure 24. Historic vegetation at Big Creek. Image is ESRI World Imagery 2009 courtesy of i-cubed Nationwide Prime 1m imagery.

Figure 25. Current vegetation at Big Creek. Image is ESRI World Imagery 2009 courtesy of i-cubed Nationwide Prime 1m imagery.

Figure 26. Historic vegetation at Julia Butler Hansen. Image is ESRI World Imagery 2009 courtesy of i-cubed Nationwide Prime 1m imagery.

Figure 27. Current vegetation at Julia Butler Hansen. Image is ESRI World Imagery 2009 courtesy of i-cubed Nationwide Prime 1m imagery.

Figure 28. Historic vegetation at Robert W. Little. Image is ESRI World Imagery 2009 courtesy of i- cubed Nationwide Prime 1m imagery.

Figure 29. Current vegetation at Robert W. Little. Image is ESRI World Imagery 2009 courtesy of i- cubed Nationwide Prime 1m imagery. 3.3.2.2 Mid- and upper estuarine sites

In contrast to the lower estuarine sites, the mid- and upper estuarine sites including Willow Grove, Willow Bar, and Mirror Lake were found to have substantial changes in vegetation classes over the time period studied (Table 14, Figures 30–36). Gains and losses of specific vegetation classes were not consistent across these three sites. At Willow Grove, large areas of marsh vegetation transitioned to scrub-shrub marsh between the late 1800s and present time (Figures 30, 31, 32). The portion of the site covered by marsh vegetation decreased by 28.8% over time, while the portion of the site classified as scrub-shrub marsh increased by 28.6% over the same time period. Meanwhile, the area of wooded marsh showed little change over time, increasing by 0.2%. In the late 1800s, at the time of the t- sheet surveys, almost none of the site was classified as scrub-shrub marsh and what little there was existed at the edge of the site where it borders a tidal slough. Today, scrub-shrub vegetation covers large areas of the interior of the site and the entire edge areas of the site have transitioned to wooded marsh vegetation.

Of all the sites, Willow Bar showed the most change in vegetation over time (Figures 30, 33, 34). At the time of the t-sheet surveys by the U.S. Coast and Geodetic Survey in the late 1800s, the site consisted of two small sandflat islands in the mainstem of the Columbia River and a small area of woodland along the edge of nearby Sauvie Island, Oregon. At the present time, the site is a large peninsula attached to Sauvie Island. The site is now a diverse mosaic consisting of sandflats, sand, marsh, scrub-shrub marsh, shrubs, and woodland. The primary shift in habitat type was a loss of 73.5% of open water and an increase of 52.1% in woodland (Table 14). The majority of the site is now woodland, which differs from wooded marsh in the frequency of inundation received. The interior of the Willow Bar site is above mean higher high water, and is typically dry except during extreme high water due to spring flooding. Black cottonwood comprises the majority of the woodland interior of Willow Bar, as described in Chapter Two. Similarly, the shrub component of the present-day site differs from the scrub-shrub marsh due to the lack of regular tidal inundation. A large area of marsh (9.9104 ha) now exists in the interior of the channel between Willow Bar peninsula and Sauvie Island. No marsh area existed at Willow Bar historically. The present-day marsh consists of emergent species such as creeping spikerush, reed canary grass, and waterpepper lines the interior of the inlet between the Willow Bar peninsula and Sauvie Island.

Mirror Lake, the furthest upper estuarine site, also showed changes in vegetation type over time. The site was historically covered mostly by wooded marsh, which decreased by 38.6% over time (Table 14, Figures 30, 35, 36). Similarly, scrub-shrub marsh areas which were composed primarily of willow according to the GLO survey notes, decreased by 19.6% over time. The present day site is covered mostly by areas of marsh and woodland, and these two vegetation classes increased by 40.3% and 16.6%, respectively.

120 Historic Area

100 Current Area

60 Area (ha) Area

Sand

Marsh Marsh

Marsh

Shrubs Shrubs

Sandflat

Woodland Woodland

Open Water Open

Shrub Shrub Marsh Shrub Marsh Shrub Marsh

- - -

Wooded MarshWooded MarshWooded

Scrub Scrub Scrub

Willow Willow Bar Mirror Lake Grove

Site and Vegetation Class

Figure 30. Change in vegetation classes at mid- and upper estuarine sites over the study period.

Figure 31. Historic vegetation at Willow Grove. Image is ESRI World Imagery 2009 courtesy of i- cubed Nationwide Prime 1m imagery.

Figure 32. Current vegetation at Willow Grove. Image is ESRI World Imagery 2009 courtesy of i- cubed Nationwide Prime 1m imagery.

Figure 33. Historic vegetation at Willow Bar. Figure 34. Current vegetation at Willow Bar. Image is ESRI World Imagery 2009 courtesy Image is ESRI World Imagery 2009 courtesy of i-cubed Nationwide Prime 1m imagery. of i-cubed Nationwide Prime 1m imagery.

Figure 35. Historic vegetation at Mirror Lake. Image is ESRI World Imagery 2009 courtesy of i- cubed Nationwide Prime 1m imagery.

Figure 36. Current vegetation at Mirror Lake. Image is ESRI World Imagery 2009 courtesy of i- cubed Nationwide Prime 1m imagery.

3.4 Discussion

3.4.1 Issues of Scale and Potential Sources of Error

3.4.1.1 Mean flood stage height calculations

Mean flood stage height calculations serve as a surrogate for inundation at specific points along the Columbia River estuarine gradient in this study, and thus are not a direct calculation of the amount of inundation physically experienced by forested wetland vegetation. Since the high-accuracy tide gauges operated by NOAA are not located at forested wetland sites, the mean flood stage height and bankfull elevation at sites will differ slightly from those at the gauge locations. Additionally, tidal fluctuation plays a large role in the hydrological regime of the sites in the lower to mid- estuary but was not directly analyzed in this study. Thus, the mean flood stage height calculations presented here do not accurately reflect the dynamic combination of tides combined with high river flows that affect the forested wetlands in the mid- and lower estuary. However, the comparison between bankfull elevation and mean flood stage height does provide an idea of the changes in the natural flow regime along the Columbia River estuarine gradient since the beginning of hydroregulation.

3.4.1.2 GIS analysis

Due to the different methods of collecting vegetation data for historic and current vegetation surveys, several potential sources of error and issues of scale exist in the analysis. The t-sheets produced by the U.S. Coast and Geodetic Survey sometimes suffered from inconsistent symbolization among surveyors or symbology that is difficult to interpret (Shalowitz 1964). These issues may have resulted in misinterpretation of vegetation in the Columbia River estuary; however, the notes made by the GIS professional who interpreted the t-sheets for this region state that the areas covering the study sites have moderate to high certainty of correct vegetation symbology interpretation. Shalowitz (1964) also states that while Coast and Geodetic surveys all had to conform to standards for accuracy, standards for the detail required in surveys were nonexistent and often left up to the individual surveyor. In all likelihood, the present-day representations of vegetation at study sites include more detail than historic accounts, since I was focused on the mapping and description of these six

94 sites rather than the estuary as a whole. However, since there is no metric for level of detail associated with the t-sheets, it is impossible to know to what level of detail modern vegetation description should occur. As described in Chapter Two, the forested wetland sites considered in this study are a complex mosaic of forest, scrub-shrub, emergent, and aquatic vegetation, and it is difficult to accurately map the vegetation occurring within them across large scales. For these reasons, the comparison of historic vegetation to current vegetation at study sites is qualitative and statistical significance cannot be used to provide a measure of certainty to the results. Nevertheless, the overall comparison of the t-sheet survey data to present-day conditions does reveal that while some areas remain quite close to historic conditions, other areas, such as at Willow Bar, have most likely changed dramatically over time.

The correct interpretation of historic vegetation survey data at Mirror Lake is even less certain than that of the t-sheet data for other sites. Since the t-sheet surveys stopped inexplicably only a kilometer down-estuary from the Mirror Lake site, the graphical interpretation of hand-written GLO survey notes by Christy (1990) was the best available information about the historic vegetation. No other historical maps of vegetation for the Mirror Lake site are known to exist.

3.4.2 Physical Disturbance at Individual Sites

Presumably, anthropogenic physical disturbance to the vegetation communities at individual study sites between the time of the historic surveys and present-day surveys has played a role in shaping the community composition and structure. The three lower estuary sites, Big Creek, Julia Butler Hansen, and Robert W. Little are not known to have a history of disturbance, and all are currently owned by conservation-oriented organizations: The Nature Conservancy owns Big Creek and the Robert W. Little Preserve, and the United States Fish and Wildlife Service operates the Julia Butler Hansen Refuge to protect and manage the endangered Columbian white-tailed deer. Most likely, the lack of change in the overall vegetation structure at these sites reflects in part a lack of direct physical disturbance.

The three mid- and upper estuarine sites have all experienced some amount of anthropogenic disturbance, although detailed documentation of activities at these sites is generally lacking. Willow Grove was recently acquired by the Columbia Land Trust (CLT),

95 a non-profit organization that works to conserve and protect land in the Columbia River basin. Prior to acquisition by CLT in 2008, the site was privately owned. The Bonneville Power Administration (BPA) reported that the site had been used for grazing at some time in the past, although not recently (Bonneville Power Administration 2008). The site scored high for ecological functions and salmon rearing use on the Washington State Wetland Rating Form. Thus, physical disturbance at Willow Grove has occurred, but probably has not had a large impact on the site as a whole.

Willow Bar is the likely site of dredge deposit material resulting from maintenance of the Columbia River’s navigation channel, but I was unable to locate documents that either confirm or deny the use of the site for this purpose. The data presented in Chapter 2 demonstrate that the soil at Willow Bar is high in sand content, which is expected of dredge deposit material (Fox et al. 1984). Furthermore, it is unlikely that over 67 hectares of material were deposited naturally at this location since the time of the t-sheet surveys when all other sites show only minor geomorphological changes over the time period studied (Table 14, Figures 30, 33, 34). In any case, the present-day, greatly expanded site has developed into a mosaic of marsh, scrub-shrub marsh, woodland, shrubs, and sandy areas, and supports an equally diverse faunal community, as discussed in Chapter 2. It appears that black cottonwood were effective in colonizing the new sandy substrate, as well as a variety of native and non-native shrubs and emergent vegetation. Riparian cottonwoods tend to favor newly exposed sandy substrate for colonization, so it is not surprising that they are the dominant tree species in the woodland portions of the site (Rood and Mahoney 1990).

Mirror Lake also has a history of physical disturbance, which is slightly better documented than that of Willow Bar. At the time of the GLO surveys, an orchard owned by Joseph Latourell was located at the southern edge of the site, just above the present-day railroad grade (Christy 1990, Figure 21). Christy (1990) states that it is unknown if Latourell owned cows, but that if he had, he may have grazed them in the Mirror Lake wetlands when not flooded in the spring. A more definite source of physical disturbance to the landscape at Mirror Lake occurred between 1880 and 1910, when a photograph of the site taken from nearby Crown Point shows that a large area of the Oregon ash forested wetlands were removed for the development of farm fields and pasture improvements (Figure 37, Christy 2010).

Figure 37. Historic photograph of Rooster Rock State Park/Mirror Lake wetlands dating between 1880 and 1910. The two parallel lines on the photo indicate the location of present day I-84. The area outlined in white shows the portion of Mirror Lake wetlands where Oregon ash forested wetlands were removed for far and pasture development (Christy 1990, 2010). Following the removal of Oregon ash forested wetlands, the farm fields were abandoned and subsequently colonized by black cottonwood, which has the ability to reproduce vegetatively by root sprouts and thus may have a competitive advantage over Oregon ash (Christy 1990). The areas of the site that are currently marshy, which includes much of the interior of the site, were used for grazing cattle until the early 1990s (Parametrix 2009). Recently, restoration efforts have been undertaken at the eastern end of the site in order to improve fish passage and quality of rearing habitat for juvenile salmonids.

Therefore, in addition to changes in the natural flow regime on an estuary-wide scale that have most likely affected forested wetlands in the Columbia River estuary, anthropogenic disturbance at sites has likely also played a role in changing the vegetation communities over time. However, physical disturbance such as clearing specific areas for farming or grazing activities and subsequent recolonization of vegetation occurred on a small, within-site scale, and did not affect the entire extent of each site.

3.4.3 Alteration to the Natural Flow Regime along the Estuarine Gradient

Alterations to the natural flow regime of the Columbia River estuary operate on a large scale, and likely combine with the effects of small-scale anthropogenic disturbance to affect the forested wetland vegetation communities. Changes to the natural flow regime in the system as evidenced by reductions in the mean flood stage height relative to bankfull elevation occur along the estuarine gradient (Figure 22). The upper estuary appears to have substantially less flooding in present times, while in the lower and mid- Columbia River estuary, only minor changes in the peak annual floods have occurred since hydroregulation. In the upper estuary, the mean flood height is more than 2 m below bankfull elevation (2.113 m and 2.123 m at Mirror Lake and Willow Bar, respectively). In the mid-estuary, at the Longview tide gauge, the mean flood height in recent times is 1.301 m below bankfull elevation, while in the lower estuary the mean flood height is within a meter of bankfull elevation (0.493 m, 0.816 m, and 0.775 m below bankfull elevation at Astoria, Skamakowa, and Wauna, respectively).

The changing geomorphology and size of the floodplain along the estuarine gradient are primarily responsible for the differing effects of high river flows on flood stage height (Simenstad et al. In revision). The upper portion of the estuarine floodplain is much narrower than the lower, thus causing high river flows to translate to very high flood stage heights (Figure 18). In the lower estuary, a larger floodplain allows high volumes of water to have much smaller effects on the flood stage height, which may explain why reduction of river flows over time has differentially affected the upper and lower portions of the estuary.

3.4.4 Response of Forested Wetland Vegetation Assemblages to Alteration of the Natural Flow Regime

As noted previously, one of the primary effects of alteration of the natural flow regime of the Columbia River is a loss in shallow water habitat area in its estuary (Kukulka and Jay 2003). Species such as black cottonwood and willow species that have evolved life history strategies that are closely tied to the seasonal flooding historically present in the system may be affected by this loss of habitat with preferable hydrological characteristics (Amlin and Rood 2002). One potential response of vegetation species in this situation may

98 be migration of species over time into lower elevation areas at a site, if such locations are available for colonization (Cramer and Hytteborn 1987). This may be the case at Willow Grove, where large areas classified as marsh in the mid- to late 1800s are now scrub-shrub marsh (Figures 31, 32).

As numerous other studies of regulated rivers have described, hydrology and flooding regimes are the primary determinant of the structure and composition of riparian floodplain forests (e.g. Hughes 1990, Jansson et al. 2000b, Nilsson et al. 1997, Rood and Mahoney 1990, Rood et al. 2003). In particular, riparian cottonwood forests in arid portions of the United States have experienced dramatic declines in response to hydroregulation (Fenner et al. 1985, Kranjcec et al. 1998, Rood and Mahoney 1990, Scott et al. 1997). However, the species of cottonwood (black cottonwood) prevalent in the mid- and upper Columbia River estuarine floodplain tends to favor cooler, wetter climates than the species common in arid climates (Rood et al. 2003). In arid climates where the water table is easily drawn down if river hydrology is altered, much more dramatic effects to cottonwood trees have been observed than in the generally cool, temperate climate of the Columbia River estuary. Furthermore, the reductions in flood stage height seen even in the upper Columbia River estuary following hydroregulation are not as substantial as those in arid climates (Fenner et al. 1985, Rood and Mahoney 1990, Rood et al. 2005, Scott et al. 1997). In the Columbia River estuary, it is possible that black cottonwood are more extensive than in historic times, since the placement of sandy material at certain locations in the floodplain may provide ideal habitat for riparian cottonwoods. This certainly seems to be the case at Willow Bar (Figures 30, 33, 34) where areas that were open water in the mid-1800s now have an abundance of cottonwood forest.

The amount of change in the flooding component of the natural flow regime over time at the forested wetland sites throughout the estuary corresponds well to changes in the forested wetland vegetation assemblages along the estuarine gradient (Table 14, Figure 22). At the upper estuarine sites (Mirror Lake and Willow Bar) the amount of woodland habitat present has increased over time, by 16.6% and 52.1%, respectively. Similarly, the amount of marsh habitat has increased by 40.3% and 10.8%, respectively. In the mid-estuary, at Willow Grove, moderate change in the depth of flooding over time appears to correspond to a conversion of marsh into scrub-shrub marsh, which increased by 28.6% over the study

99 period. In contrast to both the upper and mid-estuarine sites, the lower estuarine sites exhibit both less change in the depth of flooding and no change in the vegetation assemblage present. These sites, Big Creek, Julia Butler Hansen, and Robert W. Little show only slightly lower mean flood stage heights relative to bankfull elevation, and are classified as 100% wooded marsh both historically and currently. The primary coniferous tree in these forested wetlands, Sitka spruce, is moderately flood tolerant but does not require seasonal flooding for regeneration like black cottonwood (Peterson et al. 1997).

Another potential effect of the alteration of the natural flow regime in the Columbia River estuary is an increase in non-native species and consequently a loss in biodiversity over time (Lockwood et al. 2007, Olden and Poff 2003). A prime example of this is the presence of reed canary grass, a persistent non-native grass species, at every forested wetland site studied. Reed canary grass comprised a major component of forested wetland vegetation assemblages at every forested wetland site with the exception of Big Creek (Table 7). Christy and Putera (1992) report that the grass was introduced for the purposes of cattle grazing in the estuary between 1940 and 1960, and has since spread throughout the estuary. The grass is so dense at upper estuarine sites that it has likely caused decreased biodiversity at these sites. The same phenomenon, including the example of reed canary grass, has occurred in the St. Lawrence River estuary (Lavoie et al. 2003). However, it is impossible to quantify the potential increases in non-native species or losses in biodiversity in the Columbia River estuary over time since historical records and maps lack detailed descriptions of all species present at sites.

3.4.5 Climate Change and Predicted Alterations to the Columbia River Hydrograph in the Future

Hydroregulation has caused dramatic shifts in the hydrograph of the Columbia River (Figure 2), and further alterations to the hydrograph are expected in the future as a result of climate change (University of Washington Climate Impacts Group 2009). Specifically, by the 2040s, the hydrograph of the Columbia River is expected to show further dampening and temporal shifting of seasonal high flows (Figure 38). Forested wetland vegetation communities that have evolved life history strategies corresponding to seasonal high flows may be further impacted by shifts in the river hydrograph. This is an area of research that will require

100 additional research in order to make specific conclusions about how individual species or assemblages may be affected.

Figure 38. Columbia River annual flow at The Dalles, Oregon. The blue line represents the current river flow, green represents forecasted flows for the 2020s, and red represents forecasted flows for the 2040s (University of Washington Climate Impacts Group 2009). 3.4.6 Major Uncertainties and Future Research Recommendations

One of the primary uncertainties of this study is the exact change in vegetation at forested wetland sites as a result of generalized historical maps and survey documents (Christy 1990, Shalowitz 1964). The changing Columbia River hydrograph presents an opportunity for further study of the effects of alteration of the natural flow regime on forested wetlands over time. As remote sensing technology continues to improve in its ability to detect differences in habitat type at high resolution over large areas, the monitoring of vegetation in systems such as the Columbia River should become both easier and more accurate (Lefsky et al. 2002, Levin 1992). Combining large-scale remote sensing studies of the vegetation of the Columbia River estuary with small-scale field studies similar to the one

101 that I conducted will lead to a wealth of information about the effect of changing natural flow regimes on estuarine floodplain forests.

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Chapter 4: Synthesis

Estuarine ecology has traditionally focused on the saline portion of the estuarine gradient, and the freshwater portion is underrepresented in the scientific literature. In the case of the Columbia River estuary, the freshwater portion of the estuary is extremely large at nearly 200 km in length. The freshwater portion of the Columbia River estuary is dynamic and complex, as are the forested wetlands that exist along its length. Twice-daily tidal fluctuation combined with large variations in river flow annually creates unique hydrological conditions, and the absence of salinity allows a broad range of faunal and floristic species to thrive in this environment. Forested wetlands and their associated fauna are not often discussed in scientific literature, but my research as well as others indicates that they play an important role in the estuarine environment (Brophy 2009, Diefenderfer and Montgomery 2009, Wharton et al. 1982).

My study has shown that the structure and composition of the freshwater tidal forested wetlands of the Columbia River estuary varies along the estuarine gradient, with distinct communities present in the upper and lower portions of the estuary. Additionally, I have demonstrated that these wetlands support high species richness and provide habitat for myriad faunal assemblages, including avifauna, insects, amphibians, mammals, and benthic macroinvertebrates. Furthermore, I have shown that the alteration of the natural flow regime, which is integrated with the life history strategy of many estuarine and riparian species (Junk et al. 1989), has likely had an impact on the vegetation communities of the Columbia River estuary’s freshwater tidal forested wetlands.

Many of the forested wetland habitats in the Columbia River estuary have been lost as a result of Euro-American development of the region (Thomas 1983), and most of those remaining have likely been affected by flow regulation, physical disturbance, and invasion by non-native species. As humans continue to develop the riparian and estuarine environments, we must recognize the value of forested wetland habitat and work to conserve and protect remaining forested wetlands. Restoration of forested wetlands is now becoming a priority in some regions including the Columbia River estuary, and hopefully efforts will yield productive forested wetlands similar in structure and function to those that existed prior to human alteration. Finally, flow regulation in river systems such as the Columbia is typically

103 considered with respect to fish passage and numerous water use issues; however, river managers must not forget the effects of altered flow regimes on floodplain habitats that support diverse faunal groups.

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Appendix A: Forested wetland study site photographs

Figure A1. Big Creek study site.

Figure A2. Julia Butler Hansen study site (view from Columbia River).

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Figure A3. Julia Butler Hansen study site (view from site access road).

Figure A4. Robert W. Little study site.

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Figure A5. Willow Grove study site (view from across channel).

Figure A6. Willow Grove study site (interior/marsh portion of site).

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Figure A7. Willow Bar study site (looking south). Jennifer Burke and Sean Luis in photograph.

Figure A8. Willow Bar study site (looking north).

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Figure A9. Mirror Lake study site.

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Appendix B: Forested wetlands study site plant species list

Table B1. Forested wetland study site plant species list. Site (RKm) Julia Big Butler Robert Willow Willow Mirror Creek Hansen W. Little Grove Bar Lake Species (42) (53) (63) (97) (153) (208) Acer circinatum (vine maple) X Adiantum pedatum (maidenhair fern) X X X Agrostis capillaris (colonial bentgrass) X Agrostis gigantea (redtop) X Agrostis scabra (hair bentgrass) X Alectoria sarmentosa (common witch's hair) X X Alnus rubra (Red alder) X X X Amelanchier alnifolia (serviceberry) X X X Angelica genuflexa (kneeling angelica) X X Antitrichia curtipendula (hanging moss) X Aruncus dioicus (goatsbeard) X Aster subspicatus (Douglas aster) X Athyrium filix-femina (lady fern) X X X X Beckmannia syzigachne (American sloughgrass) X Bidens cernua (nodding beggarticks) X Callitriche heterophylla (different leaved water- starwort) 2 Carex comosa (bearded sedge) X Carex macrocephala var. macrocephala (big-head sedge) X Carex obnupta (slough sedge) X X X X X Cinna latifolia (wood reedgrass) X Cirisium vulgare (bull thistle) X Cirsium arvense (Canada thistle) X Climacium dendroides (tree moss) X X X X Conium maculatum (poison hemlock) X Cornus sericea (red osier dogwood) X X X X X X Crataegus douglasii (black hawthorne) X Crepis capillaris (smooth hawksbeard) X Dicentra formosa (bleeding heart) X Eleocharis palustris (creeping spikerush) X X X Epilobium angustifolium (fireweed) X Epilobium ciliatum (purple-leaved willow herb) X X X Equisetum arvense (common horsetail) X Equisetum fluviatale (water horsetail) X Equisetum fluviatile (swamp horsetail) X X X Equisetum telmatiea (giant horsetail) X Erigeron philadelphicus (Philadelphia fleabane) X Eriophorum angustifolium (narrow-leaved cotton grass) X Evernia prunastri (antlered perfume) X Fraxinus latifolia (Oregon ash) X X X

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Table B1 (continued). Galium aparine (cleavers bedstraw) X X Galium trifidum (small bedstraw) X X Galium triflorum (sweet-scented bedstraw) X Gaultheria shallon (salal) X X Geum macrophyllum (large-leaved avens) X Hedera helix (English ivy) X Heracleum lanatum (cow parsnip) X X X Hippuris vulgaris (common marestail) X X Hypericum anagalloides (bog St. John's wort) X X X Hypericum formosum (western St. John's wort) X X Hypericum perforatum (common St. John's wort) X Hypnum subimponens (curly hypnum) X Ilex aquifolium (European holly) X Impatiens noli-tangere (yellow touch-me-not) X X X X Iris pseudacorus (yellow-flag iris) X X X Juncus articulatus (jointed rush) X Juncus effusus (common rush) X X X X Juncus tenuis var. tenuis (slender rush) X Lilaeopsis occidentalis (western lilaeopsis) X Lonicera involucrata (black twinberry) X Ludwigia palustris (water purslane) X X Lysichiton americanum (skunk cabbage) X X X Lysimachia nummularia (creeping jenny) X X Lythrum salicaria (purple loosestrife) X X Medicago lupulina (black medic) X Metaneckera menziesii (Menzies' neckera) X Myosotis laxa (small water forget-me-not) X X Oemleria cerasiformis (indian plum) X Oenanthe sarmentosa (Pacific water parsley) X Oplopanax horridus (devil's club) X Phalaris arundinacea (reed canary grass) X X X X X X Physocarpus capitatus (Pacific ninebark) X X X Picea sitchensis (Sitka spruce) X X X Polygonum hydropiper (waterpepper) X X X Polystichum munitum (sword fern) X X X Populus balsamifera ssp. Trichocarpa (black cottonwood) X X X X Potentilla anserina ssp. Pacifica (Pacific silverweed) X Prunella vulgaris (self-heal) X Pteridium aquilinum (bracken fern) X Ribes lacustre (black swamp gooseberry) X X X Rosa eglanteria (sweetbrier rose) X Rosa gymnocarpa (baldhip rose) X X Rosa nutkana (Nootka rose) X X X X Rosa pisocarpa (peafruit rose) X X X Rubus discolor (Himalayan blackberry) X X X X X X Rubus laciniatus (evergreen blackberry) X Rubus parviflorus (thimbleberry) X X X Rubus spectabilis (salmonberry) X X X

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Table B1 (continued). Rubus ursinus (dewberry) X X X X X Rumex crispus (curled dock) X Sagittaria latifolia (wapato) X X X X Salix lucida ssp. Lasiandra (Pacific willow) X X X X Salix sitchensis (Sitka willow) X X X Scirpus americanus (three-square bulrush) X Senecio jacobaea (tansy ragwort) X Senecio sylvaticus (wood groundsel) X Solanum dulcamara (European bittersweet) X X Spiraea douglasii ssp. Douglasii (hardhack) X X X Stachys mexicana (Mexican hedge-nettle) X Stellaria media (chickweed) X Symphoricarpos albus (common snowberry) X X X X Taraxacum officinale (common dandelion) X Thuja plicata (western red cedar) X X Tsuga heterophylla (western hemlock) X Typha latifolia (common cattail) X X Urtica dioica (stinging nettle) X Usnea longissima (Methuselah's beard) X Vaccinum parvifolium (red huckleberry) X X X Vicia americana (American vetch) X Vicia cracca (tufted vetch) X Vicia gigantea (giant vetch) X

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Appendix C: Forested wetlands study site avifauna species list

Table C1. Forested wetland study site avifauna species list. Site (RKm) Julia Robert Big Butler W. Willow Willow Mirror Creek Hansen Little Grove Bar Lake Common name Scientific Name (42) (53) (63) (97) (153) (208) American Crow Corvus brachyrhynchos X X X X X X American Goldfinch Carduelis tristis X X X X X X American Robin Turdus migratorius X X X X X X Bald Eagle Haliaeetus leucocephalus X X X Barn Swallow Hirundo rustica X X X Belted Kingfisher Ceryle alcyon X Bewick's Wren Thryomanes bewickii X X X X X X Black-capped Chickadee Poecile atricapilla X X X X X X Black-headed Grosbeak Pheucticul melanocephalus X X X X Black-throated Gray Warbler Dendroica nigrescens X X Black-throated Sparrow Amphispiza bilineata X Blue-winged Warbler Vernivora pinus X Brewer's Blackbird Euphagus cyanocephalus X X Brown-headed Cowbird Molothrus ater X X X X Bufflehead Bucephala albeola X X Bullock's Oriole Icterus bullockii X X Bushtit Psaltriparus minimus X X X X Canada Goose Branta canadensis X X X X X X Caspian Tern Sterna caspia X X Cedar Waxwing Bombycilla cedrorum X X X X X Common Loon Gavia immer X Common Merganser Mergus merganser X X Common Raven Corvus corax X X Common Yellowthroat Geothlypis trichas X X X X Dark-eyed Junco Junco hyemalis X X Double-crested Cormorant Phalacrocorax auritus X Downy Woodpecker Picoides pubescens X X X X X X European Starling Sturnus vulgaris X Flycatcher Empidonax sp. X Fox Sparrow Passerella iliaca X Gadwall Anas strepera X Golden Eagle Aquila chrysaetos X Golden-crowned Kinglet Regulus satrapa X X X X X Golden-crowned Sparrow Zonotrichia atricapilla X Gray Jay Perisoreus canadensis X Great Blue Heron Ardea herodias X X X X X Great Egret Ardea alba X X Gull Larus sp. X X X X Hawk Buteo sp. X

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Table C1 (continued). House Sparrow Passer domesticus X House Wren Troglodytes aedon X Hummingbird Selasphorus sp. X X Killdeer Charadruis vociferus X Lesser Goldfinch Carduelis psaltria X Lesser Scaup Aythya affinis X X Mallard Duck Anas platyrhynchos X X X X X Marsh Wren Cistothorus palustris X X Mountain Chickadee Poecile gambeli X Mourning Dove Zenaida macroura X X Northern Flicker Colaptes auratus X X X X X X Orange-crowned Warbler Vermivora celata X X X X Osprey Pandion haliaetus X X X X X Pileated Woodpecker Dryocopus pileatus X Pine Siskin Carduelis pinus X Purple Finch Carpodacus purpureus X X Purple Martin Progne subis X Red-breasted Sapsucker Sphyrapicus ruber X Red-winged Blackbird Agelaius phoeniceus X X X X Ring-necked Duck Aythya collaris X Ruby-crowned Kinglet Regulus calendula X X X Rufous Hummingbird Selasphorus rufus X X X X X Sandhill Crane Grus canadensis X Song Sparrow Melospiza melodia X X X X X X Spotted Towhee Pipilo maculatus X X X Stellar's Jay Cyanocitta stelleri X X X X Swainson's Thrush Catharus ustulatus X X X X X Swallow Family Hirundinidae X X Tern Sterna sp. X Townsend's Warbler Dendroica townsendi X Tree Swallow Tachycineta bicolor X Tundra Swan Cygnus columbianus X Turkey Vulture Cathartes aura X X Varied Thrush Ixoreus naevius X X X Violet-green Swallow Tachycineta thalassina X X Western Grebe Aechmophorus occidentalis X Western Gull Larus occidentalis X Western Scrub Jay Aphelocoma californica X X X White-breasted Nuthatch Sitta carolinensis X White-crowned Sparrow Zonotrichia leucophrys X Willow Flycatcher Empidonax traillii X X Wilson's Warbler Eilsonia pusilla X X X Winter Wren Troglodytes troglodytes X X X X X Wood Duck Aix sponsa X X

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Table C1 (continued). Woodpecker Family Picidae X X X Yellow Warbler Dendroica petechia X X X X X Yellow-bellied Sapsucker Sphyrapicus varius X X Yellow-breasted Chat Icteria virens X X Yellow-rumped Warbler Dendroica coronata X X X

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Appendix D: Forested wetlands study site insect taxa list

Table D1. List of all insect taxa identified at forested wetland study sites. Site (RKm)

Taxa (Order, Family) Big Creek Julia Butler Robert W. Willow Willow Bar Mirror Lake (42) Hansen (53) Little (63) Grove (97) (153) (208) Acari (unknown) X X X X X X Araneae (unknown) X X X X X X Coleoptera (unknown) X X Coleoptera Bostrichidae X Coleoptera Cantharidae X X X X Coleoptera Carabidae X X Coleoptera Coccinellidae X Coleoptera Curculionidae X Coleoptera Dascillidae X Coleoptera Derodontidae X Coleoptera Eucinetidae X Coleoptera Eucnemidae X Coleoptera Heteroceridae X Coleoptera Hydrophilidae X Coleoptera Latriidae X X Coleoptera Monotomidae X Coleoptera Staphylinidae X X Coleoptera Tenebrionidae X X Collembola Entomobryiidae X X X X X X Collembola Hypogasturidae X Collembola Isotomidae X X X X X X Collembola Onychiuridae X Collembola Poduridae X X Collembola Sminthuridae X X X X X X Diptera Agromyzidae X Diptera Anthomyiidae X Diptera Cecidomyiidae X X X X Diptera Ceratopogonidae X X X X X X Diptera Chironomidae X X X X X X Diptera Chloropidae X X X Diptera Culicidae X X X Diptera Dolichopodidae X X X X X X Diptera Drosophilidae X Diptera Empidadae X X X X Diptera Ephydridae X X X X X Diptera Lonchopteridae X Diptera Muscidae X

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Table D1 (continued). Diptera Mycetophilidae X X X Diptera Phoridae X X X Diptera Ptychopteridae X X X Diptera Rhagionidae X Diptera Sciaridae X X X X X Diptera Sphaeroceridae X X Diptera Syrphidae X X Diptera Tipulidae X X X X Ephemerata Ephermerideae X Hemiptera Aphididae X X X X Hemiptera Corixidae X Hemiptera Delphacidae X Hemiptera Gerridae X Hemiptera Mesoveliidae X Hemiptera Miridae X X X Hemiptera Pseudococcidae X Hemiptera Psyllidae X Hemiptera Saldidae X X Hemiptera Cicadellidae X X X X X X Hymenoptera (unknown) X Hymenoptera Andrenidae X Hymenoptera Apidae X X X Hymenoptera Braconidae X Hymenoptera Chalcidoidea X X X X Hymenoptera Diapriidae X Hymenoptera Eulophidae X Hymenoptera Formicidae X X X X X X Hymenoptera Ichneumonidae X X X X Hymenoptera Mymaridae X X X Hymenoptera Tenthredinidae X X X Isopoda (unknown) X Isopoda Armadillidae X Lepidoptera (unknown) X X Lepidoptera Hepialidae X Odonata (unknown) X X Odonata Coenagrionidae X Odonata Gomphidae X Odonata Zygoptera X Orthoptera Acrididae X X Orthoptera Copiphorinae X Orthoptera Gryllidae X X Plecoptera Perlidae X Psocoptera (unknown) X X X X X X

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Table D1 (continued). Psocoptera (unknown) X X X X X X Psocoptera Caeciliusidae X X Psocoptera Trogiidae X Thysanoptera Thripidae X X X X X X Trichoptera (unknown) X X Trichoptera Brachycentridae X Trichoptera Lepidostomiatidae X X X Zoraptera (unknown) X

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Appendix E: Forested wetlands study site benthic macroinvertebrate taxa list

Table E1. List of all benthic macroinvertebrate taxa identified at forested wetland study sites. Site (RKm)

Taxa Big Julia Butler Robert W. Willow Willow Mirror Creek Hansen (53) Little (63) Grove Bar (153) Lake (42) (97) (208) Acari X

Amphipoda X X

Collembola Isotomidae X X X X X X

Diptera Chironomidae X X X X X

Hemiptera Cicadellidae X

Hymenoptera X X

Nematoda X X X X X X

Oligochaeta X X X X X X

Polychaeta X