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Active versus passive restoration on restored tidal hummocks: does planting make a difference?

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  Applied Ecological Restorat ion Page 1 Humboldt State University 2013 Active Versus Passive Revegetation on Recently Restored Tidal Marsh Hummocks: Does Planting Make a Difference? By: Corinne Kennah, Katie White, Zachary Silber-Coats  Abstract The Wood Creek property in Humboldt County, California is the site of a recent tidal marsh restoration project. The property is owned b y the Northcoast Regional Land Trust (NRLT), and in 2010 the land trust conducted a restoration project that reestablished historic tidal influence to the Wood Creek property, which had been used as pastureland for decades. This study compared and analyzed the effectiveness of two revegetation techniques on eight constructed tidal marsh hummocks, six of which were actively seeded and planted with native species while the remaining two were left as-to to allow vegetation to passively establish over time. We found that three years after the restoration there was no significant difference in total colonization by exotic vegetation on actively seeded and planted hummocks compared to hummocks that were allowed to passively revegetate over time. The dominant species on both hummock types was the non- native pasture grass, Agrostis stolonifera. Planted and seeded native varieties did not flourish. Some success of active revegetation efforts were seen by the decreased presence of  A. stolonifera on actively revegetated hummocks in relation to passively revegetated hummocks, and also by a greater abundance of  Deschampsia cespitosa subs. cespitosa (an actively planted and seeded native species) on actively revegetated versus passively revegetated hummocks. However, although these differences were visible in the field as well as in our data, an alysis did not find that these differences were significant.
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Active Versus Passive Revegetation on Recently

Restored Tidal Marsh Hummocks: Does Planting

Make a Difference?

By: Corinne Kennah, Katie White, Zachary Silber-Coats 

 Abstract

The Wood Creek property in Humboldt County, California is the site of a recent tidal marsh

restoration project. The property is owned by the Northcoast Regional Land Trust (NRLT), and

in 2010 the land trust conducted a restoration project that reestablished historic tidal influence to

the Wood Creek property, which had been used as pastureland for decades. This study compared

and analyzed the effectiveness of two revegetation techniques on eight constructed tidal marsh

hummocks, six of which were actively seeded and planted with native species while the

remaining two were left as-to to allow vegetation to passively establish over time. We found that

three years after the restoration there was no significant difference in total colonization by exotic

vegetation on actively seeded and planted hummocks compared to hummocks that were allowed

to passively revegetate over time. The dominant species on both hummock types was the non-

native pasture grass, Agrostis stolonifera. Planted and seeded native varieties did not flourish.

Some success of active revegetation efforts were seen by the decreased presence of A. stolonifera

on actively revegetated hummocks in relation to passively revegetated hummocks, and also by a

greater abundance of Deschampsia cespitosa subs. cespitosa (an actively planted and seeded

native species) on actively revegetated versus passively revegetated hummocks. However,

although these differences were visible in the field as well as in our data, analysis did not find

that these differences were significant.

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Introduction

According to the U.S. Fish and Wildlife Service, wetlands can be characterized by a water

regime intermediate between those of terrestrial and aquatic systems (Zedler and Kercher, 2005).

Estuarine systems are characterized as aquatic systems located at the interface between

freshwater and oceanic environments (Schlosser and Eicher, 2012). Brackish and salt marsh

habitats, as estuarine wetlands, thus form valuable edge habitats with respect to both salinity and

hydric influence.

Coastal wetland habitats are crucial to global biodiversity (Zedler and Kercher, 2005). Important

ecological services of coastal wetlands include water purification via nutrient uptake,

amelioration of the effects of severe storms and floods, and groundwater recharge (Zedler and

Kercher, 2005). Prominent biodiversity services provided by coastal wetlands include habitat for

 juvenile fish and invertebrates of economic importance, alongside the crucial role that these

habitats play in both breeding and wintering habitat for migratory waterfowl (Zedler and

Kercher, 2005). 

It is estimated that approximately half of all wetlands present worldwide have been lost to

competing land uses since the 1800’s, and coastal wetland loss may be greater (Zedler and

Kercher, 2005). The current extent of salt marsh ecosystems in North America is only a small

fragment of what occurred historically. Loss and degradation has occurred since European

settlement from land use changes and disturbances such as farming, grazing, dredging, and

altering of natural hydrologic regimes and sediment supply (Gedan et al ., 2009). It has been

conservatively estimated that 50% of all historic salt marshes in the United States have already

 been lost (Kennish, 2001). Laws enacted in recent decades by federal and state governments

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have helped curtail large scale impacts to the nation's wetlands through direct causes. However,

non-direct impacts from exotic species invasion, eutrophication and climate change related sea

level rise are now beginning to be seen as major sources of salt marsh loss and degradation

(Gedan et al ., 2009).

In Humboldt Bay, salt marsh loss has been particularly dramatic. Since the beginning of

European settlement in the area in the 1850’s, over 90% of Humboldt Bay’s salt marsh has been

diked, drained, and converted to pasture land or developed (Pickart, 2001). Prior to European

settlement, Humboldt Bay had 9,000 acres of salt marsh habitat (Pickart, 2001). Following

settlement, the railroad, and extensive agricultural land conversions, Humboldt Bay now has less

than 900 acres of salt marsh remaining (Pickart, 2001). Salt marsh in Humboldt Bay has not only

faced direct destruction due to lack of tidal influence, but is also threatened by a highly invasive

species. Dense-flowered cordgrass (Spartina densiflora) arrived in Humboldt Bay in the late

1800’s, most likely from ship ballast carried from Chile (USFWS, 2013). As of 2001, S.

densiflora occupied 94% of the 900 acres of remaining Humboldt Bay salt marsh (Pickart, 2001).

It was first identified as an invasive species in 1984 (USFWS, 2013). Invasive species such as S.

densiflora drastically outcompete native vegetation and therefore limit salt marsh plant diversity

(USFWS, 2013). This is of particular concern in the high salt marsh habitats of Humboldt

County, which support over 20 native plant species (USFWS, 2013).The high level of salt marsh

degradation around Humboldt Bay highlights the need for restoration. Restoration projects in the

area tend to focus either on converting agricultural land back to salt marsh, or on removing

invasive species from existing salt marsh. 

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Post-project monitoring is an important aspect of every ecological restoration project.

Monitoring allows for evaluation of the project in order to assess impacts and the degree to

which restoration goals have been met. Post-project monitoring can also help identify areas that

require further treatment or a different management approach (Bash and Ryan, 2002; Thom,

2000). Post-project monitoring also has overarching importance in that the reporting of results

can help drive the success of future restoration projects and restoration knowledge (McTigue et

al ., 2005) Aquatic restoration projects are especially susceptible to failure (Thom, 2000). For this

reason, monitoring of projects in these ecosystems is of utmost importance. Unfortunately,

monitoring efforts on restoration projects are often constrained by a lack of funding. However,

large sums of money are now being spent on restoration activities. Between 2000 and 2007, over

$100 million dollars was allocated to restoration efforts in Humboldt County (Baker and Quinn-

Davidson, 2011). With so much being spent on restoration annually, it is important to increase

the success of projects so that restoration efforts are not done in vain.

The objectives of this study were to examine vegetation on tidal hummocks in the Wood Creek

Tidal Marsh Enhancement Project. The main objective was to compare current vegetation on

hummocks that were actively revegetated versus vegetation that passively colonized on

hummocks that were not actively revegetated. 

Methods

 Site Description and CharacteristicsThe Wood Creek Tidal Enhancement project site is located north of Myrtle Avenue, northeast of

Eureka, California (Figure 1). The project is located on over 35 acres on the western portion of

the Wood Creek property (McBain and Trush, 2007). 

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Figure 1. Map of the Wood Creek property, showing the project site and constructed sloughchannels.

In 2005, the Northcoast Regional Land Trust (NRLT) acquired 54 acres of former tidal salt

marsh (NRLT, 2012). In the late 1800s or early 1900s, the land was diked by European settlers in

order to turn the salt marsh into viable agricultural land for growing crops and grazing livestock

(Schlosser and Eicher, 2012). The land has been farmed in the past, and in more recent decades

has been a cattle pasture (O’Dowd A; personal communication, 2013). Prior to site purchase in

2005 by the NRLT, the site was owned by Freshwater Farms. It was used to grow many different

species of native trees to provide propagules for sale at Freshwater Farms Nursery, a local

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restoration nursery that also provided thousands of propagules for the brackish marsh

enhancement. 

The climate of the site is transitional between cool-summer Mediterranean and moist maritime

zones (McBain and Trush, 2007). Temperature variation is remarkably small; summer maximum

temperatures rarely exceed 70°F, and winter minima rarely drop below 30˚F (NWSFO-NOAA,

2013). Rainfall is approximately 40 inches per year, concentrated between October and April

(NWSFO-NOAA, 2013). 

Soil at the project site is a silty clay loam of the Occidental series (USDA-NRCS, 2013). Depth

to the aquifer is commonly one meter or less, and surface water is frequently present (USDA-

 NCCS, 2013). Current site elevation ranges between approximately 6.0 to 7.5 feet above mean

lower low water (MLLW), placing the site towards the upper limit of tidal influence (McBain

and Trush, 2007).

Overview of Study Methods

For this study we assessed post-restoration vegetation on four tidal hummocks. Two of the

hummocks were actively revegetated after restoration, while the other two hummocks were not

revegetated, and were instead left as controls to observe the passive colonization of vegetation

naturally over time. Data for actively revegetated hummocks was then compared with data from

 passively revegetated hummocks to determine whether initial planting methods had a significant

influence on hummock vegetation. This study was conducted three years after final restoration

actions were implemented, leaving a substantial amount of time for hummock vegetation to

develop.

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Restoration Project Background

The Wood Creek Estuary Revegetation Project was a subset of a larger project, the Wood Creek

Tidal Marsh Enhancement Project. According to the Wood Creek Tidal Marsh Design Report for

the Wood Creek Tidal Marsh Enhancement Project (Anderson and Associates, 2008), the goals

of this project were to reestablish historic tidal hydrology to the site by opening the tide gate

located at the confluence of Wood Creek and Freshwater Slough and reestablishing a network of

slough channels (Figure 2). Through these actions, the project area was subject to tidal influence

for the first time in almost a century. Improvement of winter rearing habitat for salmonids, such

as Coho salmon (Oncorhynchus kisutch) and steelhead trout (Oncorhynchus mykiss), was also a

central goal of the restoration project (NRLT, 2012). Winter juvenile rearing habitat was

improved by increasing the cover of native wetland plant species, and increasing access to areas

of refuge from high velocity flow events by establishing connections to floodplains, side

channels, and off-channel ponds. Off-channel ponds were also created with the objective of

increasing and improving habitat for the federally endangered tidewater goby ( Eucyclogobius

newberryi) that has been seen on the site (NRLT, 2012). Heavy equipment was used to excavate

slough channels, create off channel ponds, remove a 300 foot berm, and build eight tidal

hummocks in the wetland area using sediment excavated throughout the project site, reducing the

exepenses associated with trucking sediments off-site (NRLT, 2012). Six of the eight hummocks

were actively revegetated with seed and plugs grown at Freshwater Farms Nursery, while the

remaining two hummocks were left as-is to allow for the monitoring of passively colonized

vegetation over time.

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Figure 2. Map showing restoration design elements of the Wood Creek Tidal MarshEnhancement Project, the larger project of which the Wood Creek Estuary Revegetation Projectwas a subset to (Image source: Anderson and Associates, 2008). 

Actively revegetated hummocks were seeded and planted with a few different native brackish

habitat plant species (NRLT, 2012). The NRLT planted 37,000 plants on the actively revegetated

hummocks, including Deschampsia caespitosa (tufted hairgrass), Carex lyngbyei (Lyngbye’s

sedge), silverweed Potentilla anserina (silverweed), Distichlis spicata (saltgrass), Juncus effusus

(softstem rush), and Scirpus microcarpus (small-fruited bulrush) (NRLT, 2012). It was difficult

to find post-project information on the specific modes of planting ultimately used, but a

 biological assessment completed in 2007 reported the NRLT’s original plans (McBain and

Trush, 2007). According to the report, the NRLT intended to plant seeds and nursery stock of

 Deschampsia cespitosa ssp. cespitosa (tufted hairgrass), Carex lyngbyei (Lyngbye sedge), and

nursery stock of Potentilla anserina (silverweed), Distichlis spicata (saltgrass), and Juncus

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lescurii (salt rush; formerly J. lesueurii) (McBain and Trush, 2007). It is unclear whether or not

these species were ultimately planted in the modes specified by the 2007 assessment, but this

information may indicate the approximate forms of outplanting propagules. 

Field Methods

We conducted line transects to compare vegetation on actively vegetated versus passively

vegetated hummocks within the restoration site. To do this, we recorded vegetation data on two

 passively vegetated hummocks and two actively vegetated hummocks, as indicated in Figure 3.

On each hummock, we conducted at least two transects, the combined length of which totaled

200 feet per hummock (Figure 4). The number of transects and individual transect lengths on

each hummock was determined by the size and shape of each hummock. The transect locations

were determined by a stratified sampling method (Neyman, 1934). Once the first transect on a

hummock was placed, we then placed all following transects parallel to the first at a distance of

20 feet apart. The location of the first transect on each hummock was determined by first

defining the border of the hummock and then measuring 30 feet from the northwestern edge of

the hummock, to eliminate edge effects. Dominant and subdominant vegetation were identified

directly under the transect tape until we reached a distinct change in dominant vegetation. Each

change in dominant vegetation was considered a separate sampling unit within each transect. We

then calculated percent cover of dominant and subdominant vegetation on each hummock by

comparing the total length occupied by each species from each transect to the total length of all

the transects (200 feet). We then used these data to analyze the success of native vegetation

versus nonnative or invasive vegetation on the two different types of hummocks. To analyze our

data, we ran t-tests of log-normalized percent cover by species and made bar graphs to compare

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the percent cover of each dominant or subdominant species between actively revegetated and

 passively revegetated hummocks.

Figure 3. Map showing the tidal hummocks that were constructed within the project area,distinguishing between actively revegetated and passively revegetated hummocks. The map alsoshows the four hummocks that were surveyed for this study (Image source: NRLT, 2009).

Figure 4. Map showing approximate locations of transects conducted on each hummocksurveyed (Image source: NRLT, 2009).

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Results

Surveyed transects on hummocks included both native and non-native plant species. Plant

species found, and their status as native or non-native, are listed below (Table 1).

Table 1. Plant species present on transects surveyed.Latin name Common name Native status

 Agrostis stolonifera Creeping bentgrass Non-native

 Holcus lanatus Velvet grass Non-native

 Lotus corniculatus Birdsfoot trefoil Non-native

 Elymus repens Quackgrass Non-native

 Rumex sp. Dock Non-native

 Agrostis sp. Bentgrass Non-native

 Hordeum brachyantherum  Native barley Native

 Atriplex sp. Salt bush Native

 Juncus lesueurii Salt rush Native

Carex lyngbyei Lynbye Sedge Native

 Aster chilensis Chilean Aster Native

Triglochin maritima Arrow-grass Native

 Deschampsia cespitosa ssp. cespitosa Tufted hairgrass Native

 Non-native Agrostis stolonifera (creeping bentgrass), an exotic rangeland grass, was the most

common plant species observed on both actively revegetated and passively-revegetated transects,

forming approximately 40% and 80% of the total transect distances, respectively. Native

 Deschampsia cespitosa subsp. cespitosa (tufted hairgrass) was the second most common species,

forming over 15% of surveyed vegetation on passively revegetated hummocks, and

approximately 30% on actively revegetated hummocks. Non-native Holcus lanatus (velvet grass)

was a substantial component of actively revegetated hummocks, but nearly absent from passively

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revegetated hummocks. All other species occurred sporadically and as small percentages of the

total (Figure 5). Agrostis stolonifera was prominent as a dominant component of both actively

and passively revegetated hummocks. However, A. stolonifera occupied nearly twice as much of

the passively revegetated hummocks, as compared to its presence in actively-revegetated

hummocks. Conversely, Holcus lanatus, also an invasive grass, was dominant on over a quarter

of the linear feet surveyed in actively revegetated hummocks, but all but absent on passively

revegetated hummocks.

Figure 5. Dominant nonnative (exotic) and native plant species by percentage of total transectlength, in actively and passively restored hummocks.

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 Agrostis stolonifera was also prominent as a subdominant component of vegetation on both

hummock types (Figure 6). In general, subdominant vegetation along transects was more broadly

divided among species than was the dominant vegetation, in the case of both actively and

 passively revegetated hummocks.

Figure 6. Subdominant exotic and native plant species by percentage of total transect length, inactively and passively restored hummocks.We conducted paired t-tests of log-normalized vegetation percentages for the three most

common plant species to evaluate the null hypothesis that mean measured length of dominant

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 plant species did not differ between actively and passively revegetated hummocks. Results of

this test were insignificant, suggesting that transects on active and passive hummocks did not

differ conclusively in the three most common dominant plant species (t = 0.9319, df = 2.019, p =

0.449). Results of a similar t-test on subdominant vegetation were similarly insignificant

(t=1.1626, df = 2.869, p = 0.3325).

We then calculated a Spearman’s rank-correlation coefficient (rho) to determine the extent to

which percentages of plant species on passively revegetated hummocks correlate with species

 percentages on actively-revegetated hummocks. Spearman coefficients for exotic and native

species are reported below (Table 2).

Table 2. Spearman’s correlation coefficient (Rho) for subdivisions of plants surveyed.

Plant type Vegetation Component Spearman’s Rho 

 Non-native Dominant 0.169

 Non-native Subdominant 0.514

 Native Dominant 0.368

 Native Subdominant 0.419

The low Spearman correlation coefficient for exotic dominant plant species indicates that

dominant exotic plant composition differs between actively and passively revegetated

hummocks. Higher Spearman correlation coefficients for dominant native vegetation, and for

subdominant vegetation both native and exotic, indicate that vegetation is more similar by

hummock type for these vegetation categories, as compared to the dominant exotic vegetation.

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Discussion

Before delving into the potential implications of our findings, there are a few factors which are

important to take into consideration. Our transect results may have been affected by the seasonal

timing of our survey. We observed large areas of dead thatch underneath much of the vegetation

we surveyed. While this could in many cases have belonged to the same species as the actively

growing vegetation, much of this thatch was in an advanced state of decomposition, rendering

moot any attempts at identification. In addition, we observed evidence that several species in the

larger marsh habitat had already fully senesced. In particular, dead leaves of dormant Potentilla

anserina were conspicuous in several areas outside the hummocks. 

Of the native species sown and planted on the actively revegetated hummocks, only D. cespitosa 

ssp. cespitosa was particularly successful. At 30% dominance, D. cespitosa ssp. cespitosa had

twice the percent dominance on actively revegetated hummocks, as compared to 15 % on

 passively revegetated hummocks. Neither C. lyngbyei nor J. lescurii achieved a dominant

 presence on actively revegetated hummocks, though they were 5% and 4% dominant on

 passively revegetated hummocks, respectively. While the planting of D. cespitosa ssp. cespitosa

appears to have had an impact on the species’ success, planting of other native species appears to

have had no impact. The lack of success among native species other than D. cespitosa ssp.

cespitosa on actively revegetated hummocks suggests that the revegetation strategy employed

could have been more economically efficient. Specifically, restoration practitioners might have

had more success by planting native species better able to compete with invasive grasses. Based

on the results of coastal prairie plots in more southerly areas of California, inclusion of faster-

growing native prairie plants such as Calamagrostis nutkaensis (Pacific reedgrass), and Festuca

rubra (red fescue), would likely have improved exclusion of invasive grass species (Corbin et

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al ., 2004). Differences in seed germination, growth, and seed bank may each have had a role in

the lack of success of the planted native species at this site. The low success rate of native seeds

and plugs may also be due to the significant presence of the invasive species, A. stolonifera. It is

likely that much of the native seed and plants were outcompeted by A. stolonifera, which was

found to have the highest percent cover of all species on both actively and passively revegetated

hummocks (80% and 40% respectively).

Dominant invasive vegetation between actively and passively restored hummocks was found to

have a lower Spearman correlation coefficient (0.169) than other components of vegetation

sampled, suggesting high dissimilarity in invasive plant cover between hummock types. This

can be explained primarily by the predominance of H. lanatus on approximately 25% of the

transect length in actively restored hummocks. In contrast, this species was nearly absent on

 passively revegetated hummocks. If we consider the sum of  A. stolonifera and H. lanatus 

 percentages on actively revegetated hummocks, invasive grasses occupied 65% of transect length

on these hummocks, as compared to 80% of transect length on passively restored hummocks.

According to the results of the t-test of dominant vegetation, there is not a significant difference

in total cover of these two invasive species between hummock types, so we can interpret the

approximately 15% difference in invasive grass cover as insignificant.

The dominant presence of A. stolonifera on the hummocks is not surprising considering the

nature of the species. Agrostis stolonifera is a perennial pasture grass that reproduces both

sexually by seed and vegetatively through stolons (Zapioloa et al ., 2008). Unlike many perennial

grasses, A. stolonifera is able to set seed in a single growing season (Esser, 1994). This allows

for the establishment of a large bank. In addition to having a large seed bank, A. stolonifera seeds

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are very small, making them more easily dispersed by wind than many other grasses (Zapiola et

al ., 2008). Due to the ease of dispersal through both seed and stolons, A. stolonifera readily

colonizes disturbed sites. The species is also known to exhibit high levels of phenotypic

 plasticity (Zapiola et at., 2008), making it extremely tolerant to changing environmental

conditions and management actions employed to control the spread of the species. The seedbank

of A. stolonifera is viable in soil for one to four years (Esser, 1994; Zapiola et al ., 2008). The

material used to create the eight tidal hummocks on the project site came from the sediment

excavated during restoration activities. The site was formerly used as a cattle pasture for several

decades prior to the restoration project (O’Dowd, A.; personal communication, 2013), and

 because of this, the sediment was probably dominated by the seed banks of pasture grasses such

as A. stolonifera and H. lanatus. Therefore, it is likely that a viable A. stolonifera seedbank

existed in the excavated soils that were used to build the hummocks.

Since D. cespitosa spp. cespitosa was dominant on substantial proportions of both hummock

types, its success may also be due to the existing seedbank for this species. Despite the higher

success rate of D. cespitosa spp. cespitosa on actively revegetated hummocks than on passively

revegetated hummocks, passively revegetated hummock transects suggest that the species can

compete with reasonable success against A. stolonifera up to a 15% cover dominance without the

need for active outplanting.

Although revegetation efforts may have decreased the success rate of A. stolonifera, the

apparently lower success rate of A. stolonifera on actively revegetated hummocks than on

 passively revegetated hummocks might be attributed to the relative success of another invasive

grass, Holcus lanatus, or might instead reflect the relatively greater success of native

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Humboldt State University 2013

 Deschampsia cespitosa ssp cespitosa. While the active revegetation was not successful in

repopulating the hummocks with only native species, the slight difference in A. stolonifera 

success suggests that further research and management actions might yield effective strategies

for limiting A. stolonifera on the site.

The successful predominance of  Agrostis stolonifera on both hummock types, and the low

 percent dominance of planted and unplanted native species, indicate that the active revegetation

conducted by the NRLT was somewhat ineffective. However, as suggested in a grant proposal

 prepared by NRLT for the project, the revegetation effort can still benefit restoration knowledge

as a whole. By collecting data on the success of the different hummock types, the effort will

 provide background research on the effectiveness of active revegetation on excavated soils,

 particularly in historical brackish marshland impacted by former agricultural use. Future research

may lead to insight on effective strategies to decrease A. stolonifera success, to mitigate negative

impacts of revegetation (such as the increased success of H. lanatus on actively revegetated

hummocks), in addition to insight as to outplanting choices better able to establish in favor of

invasives.

Long-term monitoring at the site may also yield results in contrast to earlier data. For instance, it

is possible that planted native seed or plugs may result in the establishment of those native

species several years after this study. Given the findings of this study, similar restoration projects

conducted in the future may save resources by either foregoing active restoration or researching

and utilizing native plant species known to be competitive with invasive pasture grasses, such as

Calamagrostis nutkaensis (Pacific reedgrass), and Festuca rubra (red fescue) in their active

revegetation efforts (Corbin et al., 2004). 

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Works Cited

Anderson, J. and Associates. 2008. Wood Creek tidal marsh design report for the Wood Creektidal marsh enhancement project. Prepared for Northcoast Regional Land Trust.

Baker, J. M. and L. N. Quinn-Davidson. 2011. Jobs and community in HumboldtCounty, California. Human Dimensions of Ecological Restoration. Island Press/Centerfor Resource Economics.

Bash, J. S. and C. M. Ryan. 2002. Stream restoration and enhancement projects: is anyonemonitoring? Environmental Management  29(6): 877-885.

Corbin, J.D., M. Thomsen, J. Alexander, and C.M D’Antonio. 2004. Out of the frying pan:

invasion of exotic perennial grasses in coastal prairies. Proceedings of the California

 Invasive Plant Council Symposium 8:27-28.

Esser, L. L. 1994. Agrostis stolonifera. Fire Effects Information System,U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, FireSciences Laboratory. < http://www.fs.fed.us/database/feis/> Accessed October 30, 2013.

Gedan, K. B., B. R Silliman and M. D. Bertness. 2009. Centuries of human-driven change insalt marsh ecosystems. Annual Review of Marine Science 1:117-141.

Kennish, M.J. 2001. Coastal salt marsh systems in the US: a review of anthropogenic impacts. Journal of Coastal Research 17(3): 731-748.

McBain and Trush, Inc. 2007. Biological assessment: Wood Creek tidal marsh enhancement

 project. Prepared for Northcoast Regional Land Trust.

McTigue, T. A., R. J. Bellmer, F. M. Burrows, D. H. Merkey, A. D. Nickens, S. J. Lozano and P.T. Pinit. 2005. Science-based restoration monitoring of coastal habitats. Vol. 2.US Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Center forSponsored Coastal Ocean Research.

 Neyman, J.1934. On the two different aspects of the representative method: the method ofstratified sampling and the method of purposive selection. Journal of the Royal Statistical

Society 97(4): 558-625.

 National Weather Service Forecast Office (NWSFO-NOAA). 2013. The Climate of Eureka,California. National Oceanic and Atmospheric Administration.<http://www.wrh.noaa.gov/eka/climate/summary.php> Accessed October 30, 2013.

 Northcoast Regional Land Trust (NRLT). 2012. Wood Creek Tidal Marsh EnhancementProject: Year 2 Performance Monitoring Report. Northcoast Regional Land Trust,Bayside, CA.

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 Northcoast Regional Land Trust (NRLT). 2009. Wood Creek Estuary Revegetation Project.Grant proposal for TNC-NOAA Community-Based Habitat Restoration Grants.

Pickart, Andrea. 2001. The distribution of Spartina densiflora and two rare salt marsh plants

in Humboldt Bay 1998-1999. U.S. Fish and Wildlife Service, Humboldt Bay NationalWildlife Refuge.

Schlosser, S. and A. Eicher. 2012. The Humboldt Bay and Eel River Estuary Benthic HabitatProject. California Sea Grant Publication T-075. <http://www-csgc.ucsd.edu/bookstore/documents/HumboldtLR.pdf> Accessed October 22, 2013.

Thom, R.M. 2000. Adaptive management of coastal ecosystem restoration projects. Ecological

 Engineering  15: 365-372.

United States Department of Agriculture, National Cooperative Soil Survey (USDA-NCCS).

2013. Official series description: Occidental. <https://soilseries.sc.egov.usda.gov>Accessed October 30, 2013.

United States Fish and Wildlife Service (USFWS). 2013. Spartina Invasion and Management,Humboldt Bay. <www.fws.gov/refuge/Humboldt_Bay> Accessed December 14, 2013.

Zapiola, M. L., C. K. Campbell, M. D. Butler and C. A. Mallory‐Smith. 2008. Escape andestablishment of transgenic glyphosate‐resistant creeping bentgrass Agrostis stolonifera in Oregon, USA: a 4‐year study. Journal of Applied Ecology 45.2: 486-494.

Zedler, J.B., and S. Kercher. 2005. Wetland resources: Status, trends, ecosystem services, and

restorability. Annual Review of Environmental Resources 30: 39-74. 


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