1

Native planting diversity and introduced plant litter influence the development of an urban 1

coastal scrub ecosystem 2

Theresa Sinicrope Talley1,4 Kim Chi Nguyen1, Drew M. Talley2, Erick Ruiz3, Paul K. Dayton1 3

1Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA 92093-4

0227 5

2 Dept of Marine Science and Environmental Studies, University of San Diego, San Diego, CA 6

92110 7

3Ocean Discovery Institute, 2211 Pacific Beach Dr., Suite A, San Diego, CA 92109 8

4 Current address: California Sea Grant Extension Program, Scripps Institution of Oceanography, 9

La Jolla, CA 92093-0232 10

11

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ABSTRACT 13

Invasive plants often alter the biotic and abiotic environments that they invade, making 14

conditions more conducive to further invasion and less so for native establishment. Restoration 15

in the presence of invaders, in particular after removal efforts, may therefore lead to alternative 16

and, often, undesirable states. Further inhibiting successful restoration are limited resources—17

while weed removal efforts gain momentum, the time, person-power and costs associated with 18

post-removal restoration are harder to come by. Needed are scientifically based yet simple and 19

inexpensive methods for encouraging post-removal ecosystem restoration. Using a field 20

experiment, we tested our hypothesis that the addition of organic litter and higher planting 21

diversity, characteristics of a mature system, would lead to faster development of most aspects of 22

the ecosystem (soils, communities of plants and animals) than no litter addition and a 23

2

monoculture. While we observed this general trend with the addition of plant litter, planting 24

diversity had relatively weak effects. The presence of live native plantings, regardless of 25

diversity level and often in association with litter presence, had associations with faster and/or 26

greater resemblance of experimental plots to the reference site. Resemblance occurred with 27

respect to environmental conditions, decomposition rates, plant abundance and community 28

composition, total abundance of fauna, and faunal diversity, and often within the first year. From 29

these results, we recommend 1) the use of a thick layer of organic litter as a gardening mulch and 30

carbon source for soil microbes, 2) the planting of often dispersal limited native perennials to 31

assuage harsh physical conditions and provide habitat and other functions, and 3) the planting of 32

a diversity of native species. While organic litter had the primary effect on early ecosystem 33

development, it is likely that the effects of plant diversity will increase as the restoration site 34

matures. These simple, inexpensive approaches should increase the rate of development of a 35

broadly functioning ecosystem, which will provide immediate benefits, and jump-start functions 36

that take longer to develop. 37

38

INTRODUCTION 39

Ecosystem development is complex and often unpredictable (Zedler and Callaway 1999). 40

Development trajectories are contingent upon the species present (or nearby) and their direct and 41

indirect interactions with each other and the abiotic environment. The presence of introduced 42

invasive species in particular may change the course of ecosystem development because they are 43

novel to the system, often altering the availability of resources (Zavaleta et al. 2001) and the 44

quantity, quality and form of productivity (Liao et al. 2008). Introduced invaders also often 45

engineer the abiotic environment to novel states that favor the invader and often disfavor natives 46

3

(Zavaleta et al. 2001, Byers et al. 2007). The presence of these species, therefore, adds 47

uncertainty to restoration trajectories and end points. 48

49

In Southern California coastal ecosystems, plant species such as date palm (Phoenix 50

canariensis), tamarisk or salt cedar (Tamarix spp.) and ice plant (Carpobrotus spp. and 51

Mesembryanthemum spp.) alter abiotic and biotic properties of coastal transition ecosystems 52

through alterations of disturbance regimes, native plant architecture and biomass, sediment 53

and/or litter accretion rates, and substrate light attenuation, moisture and salinity, resulting in the 54

displacement of native perennials (palm: Talley et al. 2012, Holmquist et al. 2011; ice plant: 55

D’Antonio 1990, Bossard et al. 2000; tamarisk: Whitcraft et al. 2007). Restoration in the 56

presence of invaders such as these, in particular after removal efforts, may lead to alternative 57

and, often, undesirable states (e.g., Zavaleta et al. 2001, Byers et al. 2007). 58

59

Post-removal invasive plant debris. The goal of restoration is to reestablish processes and this 60

sometimes involves speeding up or bypassing processes. Organic soil amendments are often used 61

to add organic matter to otherwise depauperate soils (Levin and Talley 2001, Sutton-Grier et al. 62

2009). The amendments mimic plant litter accumulations by mitigating physically stressful 63

conditions (e.g., shading, moisture trapping) and by replenishing soil nutrients, such as nitrogen, 64

through decomposition. Plant litter also provides a carbon source for soil microbes, which are 65

efficient at decomposition and nitrogen uptake. The microbial community creates low-nitrogen 66

conditions that favor native plant species, which evolved with these conditions and that disfavor 67

nutrient hungry invaders (e.g., Alpert and Maron 2000). Litter may also encourage the 68

development of detritally-based food webs by offering food source and structural habitat 69

4

(Gratton and Denno 2005, Kappes et al. 2007). Use of litter may be practical since off-site 70

disposal alternatives are often too expensive to pursue, on-site mulching and disposal leaves sites 71

carpeted with dead plant debris. Development may be inhibited, however, if the litter contains 72

seeds and encourages conditions favorable to the invaders. In this case, declines in grazer 73

diversity and abundance would be expected since grazers are likely more selective about food 74

plants than detritivores (Ernst and Cappuccino 2005, Gratton and Denno 2005). 75

76

Native plantings. Yet another barrier to desired developmental trajectories arises because most 77

native marsh and upland-transition plant species are recruitment limited, while several pervasive 78

invaders are not (Morzaria-Luna and Zedler 2007). The seeds of several particularly aggressive 79

invasive plants, including ice plant (Carpobrotus edulis, Mesymbryanthumum nodiflorum, M. 80

crystallinum) and sickle grasses (Parapholis incurva, P. pratensis), were virtually ubiquitous in 81

Tijuana Estuary-- found in the seed bank, rabbit pellets (ice plant only) and wrack carried into 82

newly created marshes by the tides (Morzaria-Luna and Zedler 2007). Native plant recruitment 83

limitation and prevalence of invader seeds may encourage both new and re-invasions and inhibit 84

native plant community recovery and the subsequent recovery of associated communities. 85

86

Planting diversity. Recovery of plant diversity is especially important in dispersal-limited 87

systems, such as these coastal systems, where newly created or open areas tend to be species-88

poor (Talley and Levin 1999, Levin and Talley 2001, Morzaria-Luna and Zedler 2007). 89

Although the causes of relationships between diversity and ecosystem function are debated and 90

vary with system (e.g., Tilman et al. 1997, Huston 1997), there is general agreement that 91

ecosystems are more stable and ecologically valuable when diversity is maximized compared to 92

5

minimized (e.g., Tilman et al. 1997). Recent studies (many performed in Tijuana Estuary) 93

revealed positive relationships between plant diversity and ecosystem properties and functions, 94

such as plant recruitment, canopy architecture, cover, biomass and quality (higher N) (Keer and 95

Zedler 2002, Lindig-Cisneros and Zedler 2002, Callaway et al. 2003, Sullivan et al. 2007). 96

Diversity has similar effects in other ecosystems, in addition to decreasing invasibility through 97

more efficient utilization of space and other resources (e.g., Tilman et al. 1997, Naeem 2006). 98

99

The effects of diversity on invasiveness may, however, vary with spatial scales or location. For 100

example, Levine (2000) found overlap of native riparian and introduced species over large scales 101

(100’s meters) where plant recruitment patterns (dispersal of floating propagules) and suitable 102

abiotic conditions were driven by river hydrology. Over small-scales (cm-meters), however, 103

higher diversity native assemblages monopolized space, fending off invaders (Levine 2000). 104

Similarly, relationships among species and environment may vary with location, especially 105

location along a physical gradient (e.g., Callaway 1995) where increased stress may change the 106

major relationship from competition to facilitation (Bertness and Hacker 1994). 107

108

Restoration goal. The restoration goal of this project is to convert an area recently cleared of 109

dominant invasive annuals to an ecosystem that resembles the remnant native patches of coastal 110

sage and high marsh transition. Assessing ecosystem development using ecosystem processes is 111

the ideal, but is also complex, relatively expensive, and often beyond the scope of time allowed 112

for site assessments. For these reasons, we assessed development using a comprehensive list of 113

physical, soil, plant and faunal variables that reflect ecosystem and community processes, that 114

were then compared between the experimental and reference areas. The experimental site was an 115

6

encroached upon 1 acre parcel which had previously been a road waste dump site that was filled 116

and, in the year before this project, had been dominated by and cleared of standing 117

Chrysanthemum coronarium, Mesembryanthemum nodiflorum, and M. crystallanum. The soils 118

contained chunks of asphalt, concrete, and metal pipe; and an invasives-dominated seedbank (as 119

evidenced by regrowth of annuals outside of our experimental area). As with most restoration 120

sites, conversion of this site to a state that existed historically is not an option. The reference site 121

was an adjacent area of remnant but disturbed coastal sage and high salt marsh transition 122

ecotypes, dominated by perennial natives. The reference site had been bisected by a small paved 123

road that was later removed so contained some road debris and disturbed patches (cleared and /or 124

invaded) as in the experimental site. Despite the disturbance, the native dominated reference site 125

functions in desirable ways, such as supporting a diversity of wildlife and plants, including 126

species of concern such as the Federally endangered salt marsh bird’s beak (Cordylanthus 127

maritimus maritimus), the San Diego coastal horned lizard (Phrynosoma coronatum blainvillii), 128

the State of California endangered Belding’s savannah sparrow (Passerculus sandwichensis 129

beldingi), and the State and Federal Endangered light-footed clapper rail (Rallus longirostris 130

levipes). This disturbed but functional state makes the reference site an ideal development goal, 131

at least in the near term, for the experimental site. 132

133

GOAL AND SPECIFIC OBECTIVES 134

Our overarching research goal was to determine how the use of scientifically-based, yet 135

simple and inexpensive techniques-- varying planting diversity and adding introduced plant 136

litter-- influenced the early (first 2 yrs) development of an urban coastal scrub ecosystem. Our 137

7

specific objectives were to assess the development of soil properties, native plant communities, 138

and ground-dwelling invertebrate communities compared to a nearby reference site. 139

We expected that plant litter presence and high planting diversity, characteristics of more 140

mature ecosystems, would expedite maturation of the restored ecosystem as reflected by 141

measured variables being most similar between the reference site and the litter and high diversity 142

treatments and most different from the lower diversity, unlittered treatments. We expected that 143

higher plant diversity and litter presence would reduce substrate physical stresses, increase 144

shading and limit germination of annuals, provide more organic material for decomposition and 145

soil amendment, provide a carbon source for microbes which would favor natives, and provide 146

greater abundance and diversity of food and habitat structure for invertebrates. 147

148

149

METHODS 150

This project was conducted at two elevations in a coastal scrub ecosystem at the north end of the 151

Tijuana River Estuary: coastal sage scrub (high elevation) and high salt marsh-upland transition 152

(low elevation) The study area consisted of a restored, experimental site and a reference site as 153

described above. 154

Ten replicate blocks containing treatment plots (80 cm diameter) were established in 155

January 2009 in the experimental site at each of the two elevations. Experimental treatments 156

were combinations of a litter treatment (introduced plant mulch was added or not added) and a 157

planting diversity treatment (0, 1, 3 or 6 species where 3-species was added in 2010). Plants 158

used in the planting diversity treatments were chosen based on common occurrence in the 159

reference site and surrounding area (Table plantlist). Extra plants from each species were kept in 160

8

a nursery so that they were of similar size to those planted when used to replant mortalities. 161

Plants used to establish the 3-species plots were of larger size than the plants used in the previous 162

year in the 1- and 6-species plots in order minimize the time lag between plantings. The 163

experimental area was fenced in to avoid confounding effects of herbivores and plots were 164

watered as needed (at least two to three times per week during summer and fall, once per week 165

during the rest of the year when no rain fell). Reference site plots consisted of 18 replicate plots 166

(1m2) per elevation that captured the variability in plant diversity and composition used in the 167

experimental site. Due to the large size of the shrubs, the plot size used in the reference site was 168

larger than that used in the experimental site where plantings needed to be a bit more clustered to 169

improve survival. 170

Sampling and replanting of planting mortalities occurred biweekly throughout the first 171

season (from February through Septebember 2009). Replanting of dead plants continued 172

throughout the study but dramatically decreased after the first season so was not recorded. 173

Sampling of physical conditions, soils, plants and invertebrates in the plots occurred in May 174

2009, three months after the start of the experiment, and in April-May of 2010 and 2011. 175

Physical properties. Substrate temperature, humidity and light attenuation were measured 176

as relative to conditions above the canopy. Photosynthetic-light was measured using an Apogee 177

Quantum handheld light meter, and both humidity and temperature using an Extech 178

humidity/temperature pen. Measurements were made during mid-day (10 am- 2 pm) over two 179

consecutive days. Three measures were taken in each plot, averaged, and then standardized to 180

above canopy conditions (e.g., substrate light [µmol photons m-2 s-1] / full sunlight [µmol photons 181

m-2 s-1]). 182

183

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Soil and litter properties. Porewater salinity, soil moisture, soil organic matter content, texture, 184

and concentrations of nitrate and ammonium were made in each plot. Three soil cores (1.5 cm 185

diam X 10 cm depth) were collected from each plot and homogenized before analysis. A portion 186

of the soil was analyzed using the texture by feel method, and then the salinity of moistened soil 187

was taken by extracting water using a 10cc syringe with a filter paper inside, and reading the 188

salinity with a salinity refractometer (Zedler METHOD). Another portion of the soil was placed 189

in a pre-weighed crucible, weighed wet, dried at 55 degrees C until no weight loss, and then 190

weighed again to calculate percent moisture content. The soil was then combusted at 500 degrees 191

C overnight, and weighed again once cooled in a desiccator to calculate percent organic matter 192

content. A final portion of the soil was dried, ground and submitted to the U.C. Davis DANR 193

facility for nitrate and ammonium analysis. 194

The C:N content of litter, both added litter and what, if any, naturally accumulated, was 195

measured by collecting litter samples. Litter was rinsed in distilled water, dried, ground with a 196

coffee grinder and analyzed for C:N content at the DANR facility at U.C. Davis. 197

198

Decomposition rates were measured using litter bags containing known and similar weight 199

samples of clean, dry, chopped (2.5-5cm long segments) Chrysanthemum litter. One bag per plot 200

was deployed for 1 year, after which bags were brought to the lab and the contents were carefully 201

rinsed with distilled water, picked of living organisms, dried (45 degrees C until no weight loss) 202

and weighed. The loss in dry weight was divided by the initial weight to calculate proportion of 203

biomass lost through the year. The abundance and diversity living organisms within the bags 204

were not correlated with decomposition rates so are not presented further. 205

206

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Plant composition and biomass were assessed using non-destructive measures of plant maximum 207

height, longest diameter and perpendicular diameter for each individual of each species. Plant 208

volume was calculated from these measures (height X longest diameter X perpendicular 209

diameter) and used as a proxy for biomass. 210

211

Ground-dwelling invertebrate community. Invertebrates were sampled each spring using pitfall 212

traps, 250 ml plastic beakers set in the center of each plot at ground level, each with a funnel 213

sitting flush in the opening with a square piece of hardware cloth over the top. A few pieces of 214

litter were placed inside each trap to provide refuge to potential prey species. Plant litter was 215

placed over the top of trap (over the mesh) if in a litter treatment plot, or a small rock if in an 216

unlittered plot, to help camoflauge and secure the trap. Traps were left out for 5-6 days when 217

they were retrieved and the contents emptied into labeled zip top bags and returned in the lab 218

where they were frozen until processing. Animals were sorted from the debris in the sample 219

using a dissecting microscope and organisms were identified to the lowest taxonomic level 220

possible and enumerated. Unknowns were photographed and were brought or sent to specialists 221

for assistance. 222

223

Statistics. Edit with new analyses- restoration site only. 224

All data were log (x+1) transformed or arcsin square root transformed (proportion data) before 225

analyses (Zar 2009). Effects of treatment on first season planting mortality were tested with 2-226

way ANOVA using species level and litter/no litter treatments. No effects of date or block on 227

plant mortality were found so data were pooled. Differences in individual physical variables, soil 228

variables, as well as plant and invertebrate abundances and diversity (species richness and H’) 229

11

between plot types (treatment and reference plots) were performed using ANOVA in JMP® 10 230

Statistical Software. Since the reference site did not have corresponding planting species and 231

litter addition treatment types, a two way ANOVA could not be used so treatment combinations 232

were used for the analyses (e.g., Litter-6 species, litter-1species vs. litter and 6 species). 233

Environmental drivers of treatment effects were explored by testing for relationships between the 234

response variable and environmental variables using forward, stepwise multiple regressions with 235

the criteria of p≤0.05 and r>0.04 for inclusion in the model. 236

Multivariate analyses were carried out on the suites of environmental conditions and 237

invertebrate assemblages using Primer Software (Clarke 1993). Environmental variables were 238

normalized, while the species lists with counts were log10 (x+1) transformed, with no other 239

abundance cut-offs, standardizations, relativizations or weighting used on the data. Euclidean 240

distance (environmental variables) and Bray-Curtis similarity indices (faunal data) of the log 241

(x+1) transformed data were calculated to compare the environment and fauna communities 242

between plots, and to relate the fauna to the environmental variables. Differences in the 243

environmental conditions and the invertebrate community between treatments were tested using 244

nonmetric multidimensional scaling (MDS) on the normalized environmental data and the Bray-245

Curtis similarity indices of log(x+1) transformed faunal data. Six different random starting points 246

with up to 1,000 steps were used. The stress values from the six runs were examined for stability 247

to determine whether a global solution had been found. Only analyses with stress values of <0.2 248

were used; stress is a measure of how well the solution (in this case the two-dimensional MDS 249

plots) represents the distances between the data. Clarke (1993) suggests values <0.1 are good and 250

<0.2 are useful. 251

12

Significance testing for differences in environmental conditions and faunal composition 252

between plot types and between plant species found in each plot type was performed using an 253

analysis of similarity (ANOSIM) procedure on the Euclidean distance and Bray Curtis similarity 254

matrices. This is a randomized permutation test based on rank similarities of samples (Clark 255

1993). Analyses of dissimilarities in environmental conditions and faunal composition found 256

between plot types and plant species, and the particular variables or taxa contributing to the 257

dissimilarity, were carried out using SIMPER (Clarke 1993). The SIMPER results specify which 258

variables are responsible for the ANOSIM results by comparing the average environmental value 259

or abundances of each taxon between each plot type. The average dissimilarity between samples 260

from within and between each treatment (litter X species level, reference) is computed and then 261

broken down into contributions from each variable/species. Those variables or species with high 262

average terms relative to the standard deviation are important in the differentiation of 263

environmental conditions and faunal assemblages within each plot type. 264

Tests of the environmental variables that best explain faunal community differences were 265

conducted using the Bray-Curtis similarity indices with the BEST Analysis in Primer Software 266

using the BVSTEP method (criteria: rho > 0.95, delta rho < 0.001) with fixed starting variables 267

and a Euclidean distance resemblance measure. BVSTEP sequentially adds environmental 268

variables, keeping those that best explain faunal community patterns and eliminating those that 269

explain least. Several iterations of the test are run with a random selection of variables to ensure 270

that the best match is found (Clarke 1993, Clarke and Warwick 2001). 271

272

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RESULTS Add in new restoration only results- sub for whole system analyses, simplfy results 273

(restoration only: diversity and litter effets on soil, plants, faunal ab/div). rest and ref-274

multivariate analyses – enviro (soil, plant, faunal comp), compare faunal div/ab in rest and ref. 275

Environmental state of reference and treatment plots. (was Litter and diversity effects on 276

environmental state ) 277

Throughout the two years of the study, environmental conditions remained generally more 278

similar within treatments than between treatments (Table. Anosim enviro) due to similar 279

volumes of native and/or introduced plants, plant diversity and density, and similar light 280

attenuation and substrate moisture (humidity and/or soil %water) within treatments (SIMPER 281

variables). In general during the first year (2009-2010), treatments with litter and/or with 282

plantings (regardless of diversity level) had environmental conditions that were more similar to 283

the reference site than plots without litter and/or without plantings (Table ANOSIM enviro). It 284

took two years for any of the treatments to resemble the reference site or each other (Table 285

ANOsim enviro). In particular, environmental conditions in the high marsh treatments planted in 286

the first season most resembled the reference site by the 3rd season (2011). The 3-species plots, 287

which were planted in season 2, and all unplanted treatments remained the most different from 288

the reference site due to higher volumes of introduced plants and lower volumes of native plants, 289

less shading, warmer temperatures, and denser but shorter plants than in the reference site 290

(SIMPER, variables responsible for ~75% of differences; Table ANOSIM enviro). In the coastal 291

sage scrub, all treatments resembled the reference site by the 3rd season except for the unplanted, 292

no litter treatment (Table ANOsim enviro), which also had higher volumes of introduced and 293

lower volumes of native plants, denser but shorter plants (weed seedlings) and less shading than 294

the reference site (SIMPER, variables responsible for ~75% of differences). 295

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At both elevations during all three dates, plots with litter compared with no litter (within 296

the same diversity level) had lower density and volume of introduced plants, higher substrate 297

surface humidity, soil moisture, and shading; and cooler temperatures, less soil salinity, and 298

lower nitrate concentrations (i.e., more microbial activity, REF) (SIMPER variables explaining 299

~75% of differences between litter treatments). Unplanted plots with and without litter differed 300

the most each year, while the 6-species planted plots with and without litter differed the least 301

from each other and had no significant environmental differences by the 3rd season (Table 302

ANOSIM enviro). In general, the degree of differences between the litter and no litter plots 303

decreased for all diversity levels over these two years (Table ANOSim enviro). 304

Higher planting diversity (comparisons within litter and no-litter treatments) was 305

associated with more plant species, higher native plant volume, lower introduced plant volume, 306

more shading, higher substrate humidity and moister soil throughout the two years of the project 307

(SIMPER variables explaining ~75% of differences between litter treatments). Bigger 308

environmental differences occurred, however, between planted, regardless of planting diversity, 309

and unplanted plots. Only in the coastal sage during the 3rd season did an unplanted treatment 310

(with litter) resemble planted treatments. These results illustrate that plants, especially diverse 311

plantings, and litter additions may reduce environmental stress, invasion, and variability in 312

young sites. 313

314

Litter and planting diversity effects on soil development 315

Decomposition rates in the coastal sage from the 1st year were highest in plots with both litter 316

and plantings, 2nd highest in plots with litter and no planting, and lowest in plots with no litter 317

(regardless of planting presence). Rates in the reference site were intermediate and similar to the 318

15

littered, planted plots and littered unplanted plots (Table ANOVA soil). Higher decomposition 319

rates in this first year were associated with greater relative substrate humidity (Table REG 320

decomp-env), an effect of additions of litter and plantings (Table ANOVA soil). By the end of 321

the 2nd year, there were no differences in rates between and among the experimental and 322

reference plots (Table ANOVA soil), reflected by the lack of strong relationships between 323

decomposition and environmental variables (Table REG decomp-env). Soil organic matter 324

content was similar between the experimental plots but lower than in the reference site for the 325

first two seasons. By the 3rd season, there was no difference in organic matter content between 326

any of the plots (Table ANOVA soil) illustrating that decomposition of added litter and newly 327

produced plant leaf litter may have begun contributing to soil organic matter content. 328

Similar patterns were found in the high marsh, with higher decomposition rates occurring 329

in littered plots, especially with 1-species plantings, than unlittered plots. These highest rates 330

were comparable to the rates within the reference site (Table ANOVA soil). Decomposition rates 331

in the first year were associated with both lower volumes of introduced plants and more soil 332

moisture in the high marsh (Table REG decomp-env)—conditions favored by experimental 333

additions of litter and plantings (Table ANOVA soil). By the end of the 2nd year, rates were also 334

similar among all plot types. Decomposition in the 2nd year was associated with increased 335

moisture and substrate humidity, and less introduced plant volume, but these conditions began to 336

become more similar among the treatments toward the end of the project (Tables ANOVA soil, 337

plant). Soil organic matter was initially greater in the reference site than experimental plots, 338

between which there were no differences (Table ANOVA soil). Organic matter content was 339

similar across all plots in the 2nd season, and was generally greater in the experimental site than 340

16

reference site in the 3rd season (Table ANOVA soil), again likely revealing contributions of the 341

decomposition of added litter and developing plant litter to soil organic matter content. 342

343

Litter and planting diversity effects on early planting mortality 344

There was no effect of date on planting mortality so data from the first season (8 months) were 345

pooled. Total planting mortality of high marsh plants was not affected by the treatments (Talbe 346

ANOVA morts-hm). Both Salicornia subterminalis and Frankenia salina, however, had 5-12 347

times higher mortality rates when grown in monoculture with relatively little effect of litter 348

presence (Table ANOVA morts-hm). Total planting mortality was highest in unlittered coastal 349

sage scrub plots and/or in mixed (6) species plantings (Table ANOVA morts-cs). Mortality of 350

Artemisia californica, had no strong associations with the treatments, while mortality of 351

Eriogonum fasciculatum was highest in plots without litter and, as with the common high marsh 352

species, when planted alone (Table ANOVA morts-cs). 353

354

Litter and planting diversity effects on plant community development 355

At both elevations in the first season, the plant communities within all but the planted, litter 356

treatments differed from the reference site (Table ANOSIM PLT) because there were greater 357

volumes of natives in the reference site (in particular, the dominant natives such as Frankenia 358

and Salicornia in the high marsh, and Artemisia and Eriogonmum in the coastal sage; SIMPER 359

variables explaining ~90% of differences between sites). The planted plots with litter did not 360

initially differ from the reference site because introduced species growth was minimal and 361

plantings grew well (SIMPER variables accounting for <1% of differences). By the second and 362

into the third season, the plant communities of all treatments differed from the reference site 363

17

although plots with plantings (regardless of litter presence) were less different from the reference 364

communities (coastal sage: 64-86% dissimilarity, high marsh: 82-98%) than those that did not 365

receive plantings (both coastal sage and high marsh: 99-100% dissimilarity) (Table ANOSIM 366

PLT). In these 2nd and 3rd seasons, the planted treatments had greater volumes of native plants 367

(especially the less dominant species such as Malacothamnus, Lotus, Atriplex in the coastal sage 368

and Isocoma and Distichlis in the high marsh), while the unplanted treatments had smaller 369

volumes of natives and greater volumes of introduced plants, in particular Bassia, 370

Chrysanthemum, Mesymbryanthemum nodiflorum, than in the reference site (SIMPER variables 371

explaining ~ 75% of differences between treatments). 372

By the 2nd season for the coastal sage and the 3rd season for the high marsh, litter presence 373

did not influence plant communities, which were similar between treatments that received 374

similar plantings (same diversity levels of litter vs no litter) (Table ANOSIMplant). The plant 375

communities among the diversity levels remained different (Table ANOSIMplant), however, 376

because of the survival and predominance of the species originally planted. The plant 377

communities in the unplanted plots remained significantly different than the planted treatments 378

throughout the study (Table ANSOMplant) due to dominance by introduced species and a lack of 379

recruitment of native plants in the unplanted plots (SIMPER variables explaining ~90% of 380

differences between treatments). Further, by the 3rd season in both elevations, the plant 381

communities within the unplanted treatments were about as dissimilar to each other (90-97% 382

dissimilarity within treatments) as they were to the planted plots (92-100% dissimilarity between 383

treatments; Table ANOSIM plant) due to the different compositions of common weeds (SIMPER 384

variables explaining ~75% of dissimilarity within unplanted treatments). 385

386

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The ground-dwelling invertebrate community 387

Composition. In the first season, 46 species were found across the whole study area, consisting of 388

predominantly coleopterans (43%), hymenopterans (21%), collembolans (21%), thysanurans 389

(18%) and arachnids (5%). The reference plots hosted 17 species unique to the reference site, 390

including carabid and tenebrionid beetles, tussock moth larvae, a millipede, collembolans, a 391

native ant, wasps, hemipterans, psycosids, pseudoscorpion and spiders. The experimental site 392

hosted 5 species, all of which were spiders. By the 2nd season, there were 61 species found across 393

the study area including 41% coleopterans, 15% dermapterans, 13% hymenoptera, 10% 394

collembolans, and 7% arachnids. There were 15 species unique to the reference site, similar to 395

the list from the 1st season, and 14 species unique to the experimental site. In this year, the 396

unique species included carabid beetles, hemipterans, a lepidopteran, a dermapteran, 397

orthopterans, Theba paisana (Italian garden snail), and a lycosid spider. In the 3rd season there 398

were 56 species found, with 41% isopods, 25% collemolans, 8% coleopterans, 7% dermapterans, 399

7% arachnids and 4% hymenopterans. Each site had about 12 species that were unique, both 400

comprised of different representatives of coleopterans, hemipterans, lepidopterans, arachnids, 401

hymentopteras. Native ants, tussock moth, and pseudoscorpions were still only found in the 402

reference site. 403

404

Litter and planting diversity effects on faunal diversity and total abundance. 405

Total abundances of both high marsh and coastal sage faunas in the first season were similar in 406

the experimental litter plots and reference sites, and tended to be lower in the unlittered plots 407

(Table ANOVA invert). In the high marsh, abundance was negatively associated with the 408

volume of introduced plants (Table invert-env reg), which was lowest in the littered and 409

19

reference plots (Table ANOVA plant). In the coastal sage, abundance was positively associated 410

with soil moisture (Table invert-env reg), which was highest in the littered plots (Table ANOVA 411

soil). 412

In the high marsh during the 2nd season, abundance was similar within and between the 413

sites (Table ANOVA invert) and was not correlated with any of the environmental variables 414

(Table invert-env reg). Abundance, however, differed again in the 3rd season with no clear trend 415

across the treatments (Table ANOVA invert). The lowest abundance was in the littered 6-416

species plots, the highest was in the unlittered, unplanted plots, and intermediate abundances 417

occurred in the other treatments and reference site (Table ANOVA invert). In this last year, 418

abundance was weakly but negatively associated with soil moisture (Table invert-env reg), 419

which tended to be highest in the presence of litter and/or 6-species plantings and lower in the 420

unlittered and reference plots (Table ANOVA soil). 421

In the 2nd and 3rd season within the coastal sage, the differences in fauna had no clear 422

trend across treatments except that plots with litter and either no plantings or 3-species plantings 423

maintained higher abundances than in the reference site (Table ANOVA invert). Abundances 424

increased with both increased soil moisture and decreased plant heights in the 2nd season, and 425

increased with plant density in the 3rd season (Table reg invert-env), both indications of a 426

dominance of annual weeds, such as iceplant. 427

Diversity (H’ and ricnhness) in the high marsh during the first season was highest in the 428

reference site, and did not differ from the experimental 1-species littered plots. Diversity tended 429

to be lowest in plots with no litter (Table ANOVA invert). Both measures of diversity were 430

negatively associated with volume of introduced plants (Table REG invert-env), which was 431

highest in the unlittered plots (Table ANOVA plant). By the 2nd season, high marsh diversity was 432

20

similar or higher in the experimental sites than reference site with no clear trend across 433

treatments. Species richness in this 2nd season was negatively associated with soil salinity, which 434

did not differ between plots, and positively associated with soil nitrate concentration, which 435

tended to be higher in the unlittered and/or unplanted plots than in littered, planted or reference 436

plots (Table ANOVA soil). Diversity represented by H’ did not differ in the 2nd season, and no 437

high marsh faunal diversity differences were found in the last season (Table ANOVA invert). 438

Similarly, these diversity variables were not correlated with any of the environmental variables 439

for these dates (Table REG invert-env). 440

In the coastal sage during the 1st season, faunal diversity was similar across all plots and 441

between the experimental and reference sites. There were, however, positive correlations 442

between diversity (both richness and H’) and soil organic matter content (Table REG invert-env), 443

which was highest in the reference site and similar across all experimental treatments (Table 444

ANOVA soil). In the 2nd season, species richness was highest in the planted and littered plots (1-, 445

3- and 6-species), intermediate in the unplanted plots (litter and no litter) and the 3-species, 446

unlittered plots, and lowest in the other planted, unlittered plots (1- and 6-species) and the 447

reference site (Table ANOVA invert). H’ did not differ among plots. Both species richness and 448

H’ were positively associated with soil moisture, which did not differ among plots, and richness 449

was also positively associated with soil organic matter content (Table REG inv-env), which was 450

highest in the reference site and similar among all treatments (Table ANOVA soil). By the 3rd 451

season, diversity tended to be highest in plots with litter regardless of planting diversity level, 452

and similar or lower in the no litter and reference plots (Table ANOVA invert). In this last 453

season, diversity was positively associated with relative substrate temperature, which did not 454

differ among plots (Table ANOVA soil). 455

21

456

Faunal responses to litter and planting diversity treatments. 457

In the first season within the high marsh and coastal sage, the faunal communities generally 458

differed between the litter and no litter treatments, with no clear trends in similarity or 459

differences with planting diversity treatment (Table ANOSIM pitfall). In general, plots with 460

litter supported more of the Argentine ant, bristletails, silverfish and sometimes more of the 461

beetles, Harpalus herbivagus and Metoponium abnorme, while unlittered plots had higher 462

abundances of the beetle Blapstinus sp (SIMPER taxa contributing ~75% of differences between 463

treatments). Most of the factors influencing fauna at both elevations (BEST high marsh R=0.27, 464

coastal sage R=0.17) in this first season differed across these treatments, with soil nitrate 465

concentration, soil salinity, and volume of introduced plants lowest in high marsh litter compared 466

with unlittered plots (Tables ANOVA soil, plant); and soil moisture and light attenuation highest 467

in coastal sage litter compared with unlittered plots (Tables ANOVA soil, plant). 468

In the high marsh, this trend continued into the 2nd season except that the litter and no-469

litter 6-species plantings developed similar communities (Table ANOSIM pitfall hmt) with 470

dominance by Harpalus herbivagus, Forficula auricularia (European earwigs), Metoponium 471

abnorme, and Armadillid isopods in both treatments (Table taxa). The 6-species treatments did 472

not differ in many of the environmental factors that were important for fauna (based on BEST 473

R=0.23), including similar soil moisture, salinity, ammonium, and volume of plants (Table 474

ANOVA soil, plant). By the 3rd season, there was community similarity between all the litter and 475

no-litter plots within each planting diversity (ANOSIM Table pitfall hmt). Most of the remaining 476

community differences in this last season were between the unplanted plots and/or the plots 477

planted in the 2nd season (3-species plantings), and the plots planted in the first year (1- and 6-478

22

species planted plots). The unplanted and recently planted plots had higher abundances of 479

earwigs, bristletails, and the Argentine ant, while the 1- and 6-species planted plots had generally 480

higher abundances of Harpalus herbivagus and occasionally higher abundances of Metoponium 481

abnorme (SIMPER taxa explaining ~75% of differences between treatments). In the final two 482

seasons, faunal communities were responding mostly to soil salinity, soil nitrate (2010 only), 483

plant diversity (weeds and plantings), native plant volume and light attenuation (BEST R=0.23 in 484

2010, R=0.12 in 2011), which were greatest (except for soil salinity and nitrate) in the more 485

diversely planted and/or littered plots (Table ANOVA plant). 486

In the 2nd season in the coastal sage, many of the experimental communities resembled 487

each other except for no litter, planted plots (1- and 6-species) which were similar to each other, 488

but differed from most of the littered plots (ANOSIM Table pitfall css) due to generally higher 489

abundances of European earwig, Argentine ant, Metoponium abnormae and Harpalus herbivagus 490

in the unlittered plots and more Armadillid isopods, spiders and collembolan in the litter plots, 491

(SIMPER taxa contributing ~75% of differences between treatments). Faunal communities were 492

driven by the density and total area of plants (BEST R=0.15), with density greatest in these 493

planted, unlittered treatments (i.e., weed presence increased plant density). By the 3rd season, 494

none of the treatments differed significantly from each other (ANOSIM Global P=0.72) due to 495

similar occurrences of collembola, armadillid isopods, and dictynid spiders (Table taxa). Taxa 496

were responding to number and volume of plants, as well as light attenuation, variables which 497

did not vary too much among treatments in the coastal sage during this 3rd season (Tables 498

ANOVA plant, soil). 499

500

Faunal community development. 501

23

Invertebrate communities in all treatments differed from those in the reference site until 502

the 3rd season when the communities in the experimental and reference coastal sage scrub 503

became fairly similar (ANOSIM Global P=0.72); and one high marsh community (one-species, 504

litter treatment) resembled the reference site (ANOSIM pairwise p=0.135) in this 3rd season. The 505

other high marsh treatments were an average (±1SD) of 72±0.07% dissimilar from the reference 506

site in 2011, down from 90±0.01% dissimilar in 2010 and 77±0.01% dissimilarity in 2009. 507

The high marsh experimental plots started out with higher abundances of the Argentine 508

ant, bristletails, and silverfish, while the reference plots had more native ants, Armadillidae 509

isopods, spiders, and several beetles (Harpalus herbivagus, Harpalus sp., Metoponium abnorme, 510

unknown Tenebrionid). The exception was that the unplanted, unlittered plots contained fewer of 511

the Argentine ant than the reference site. Differences in high marsh faunal communities in 2009 512

were associated with volume of introduced plants, litter C:N ratios, soil nitrate concentration, and 513

soil salinity (BEST R=0.27), all of which except salinity were lower in the reference site than 514

experimental site (Table ANOVA soil). In the following two seasons, compositions in the 515

experimental site remained similar except that in 2010, the Argentine ant declined and there were 516

increases in European earwigs, the beetles Harpalus herbivagus and Metoponium abnorme, and, 517

in 2011, there were additionally increases in springtails relative to the reference site (SIMPER 518

taxa contributing ~75% of the differences between sites each year). The environmental variables 519

explaining faunal differences were soil moisture, ammonia concentrations, soil salinity, and total 520

plant density and species richness (BEST R=0.23) with soil moisture and ammonium 521

concentrations being greatest in the reference site, and plant density and richness intermediate 522

(Tables ANOVA soil, plant). The community similarity between the littered, one species 523

treatment and the reference plots was due to the occurrences of isopods and collembola in both 524

24

areas (Table taxa), which also experienced similar soil moisture and ammonium concentrations 525

(Table ANOVA soil). 526

The taxa and trends in the coastal sage were similar to those of the high marsh. During 527

the first season in the coastal sage scrub, the experimental site housed higher abundances of the 528

Argentine ant, bristletails, silverfish, European earwig and the ground beetle Harpalus 529

herbivagus than the reference site, which had more native ants, spiders, earthworms and the 530

tenebrionid beetle, Metoponium abnorme (SIMPER species accounting for ~75% of dissimilarity 531

between sites). The only exception was that the unplanted, unlittered experimental plots 532

contained few Argentine ant and silverfish. These coastal sage fauna were associated with soil 533

moisture, light attenuation and litter C:N ratios (BEST R= 0.17), where soil moisture and light 534

attenuation (litter plots only) were highest in the experimental site (Table ANOVA SOIL). These 535

faunal trends extended into the 2nd season (SIMPER species accounting for ~75% of dissimilarity 536

between sites) except that in the experimental site, abundances of the Argentine ant decreased, 537

while springtails and Metoponium abnorme abundances increased. Litter C:N was the strongest 538

correlate of faunal communities in 2010 (BEST R=0.20) and was highest in the reference site 539

(Table ANOVA SOIL). In the third season, communities in all the experimental and the 540

reference plots were somewhat similar. While the trends of the first two seasons could still be 541

observed, there were ubiquitous occurrences of isopods (Armadillidae), Lycosid spiders, 542

earthworms, and Harpalus herbivagus throughout both sites. Fauna communities were associated 543

with decomposition rate, plant density, total plant volume and light attenuation (BEST R=0.20), 544

none of which differed in 2011 between the reference and experimental sites (Table ANOVA 545

soil). 546

547

25

DISCUSSION 548

We hypothesized that the addition of organic litter and higher planting diversity, characteristics 549

of a mature system (e.g., Odum 1969) would lead to faster development of most aspects of the 550

ecosystem (soils, communities of plants and animals) than no litter addition and a monoculture 551

(e.g., O’Brien and Zedler 2006, Sutton-Grier et al. 2009, Isbell et al. 2012). While we observed 552

this general trend with the addition of plant litter, planting diversity had relatively weak effects. 553

The presence of live native plantings, regardless of diversity level and often in association with 554

litter presence, had associations with faster and/or greater resemblance of experimental plots to 555

the reference site. Resemblance occurred with respect to environmental conditions, 556

decomposition rates, plant abundance and community composition, total abundance of fauna, 557

and faunal diversity, and often within the first year. This is not to say that the experimental site 558

was functionally similar to the reference site within the time frame of this study- many of the 559

measured variables still differed by the 2nd year, and the longer-term trajectories of those 560

variables that did resemble the reference site are uncertain (Zedler and Callaway 1999). Further, 561

many more variables reflecting potentially important ecosystem functions, such as direct 562

measure of microbial communities (van der Heijden et al. 2008) and vertebrate community 563

members, were not measured in this study so are also uncertain. Finally, our focus was within 564

our plots. The site as a whole (including areas between plots) was still visibly different and will 565

take time to fill in and continue to develop, as with any restoration site (REF-restoration is an 566

ongoing process). The early trajectory of increasing resemblance between the littered and/or 567

planted treatments and the reference site, however, indicates that these treatments establish 568

environments conducive to our restoration goals (Klotzi and Gootjans 2001). In particular, litter 569

26

and live plants ameliorate physical stresses, and likely enhance trophic and non-trophic resources 570

for plants, invertebrates and microbes. 571

572

The presence of plant litter contributed to development likely through both physical and 573

trophic pathways. Litter presence, especially within the first year, mitigated harsh physical 574

substrate conditions (trapped moisture, increased shade), supported the highest decomposition 575

rates (similar to the reference site) and reduced coastal sage planting mortality. Litter also 576

reduced introduced plant invasion through physical effects of shading, and encouraging 577

microbial communities and, therefore, lower nitrate levels (Alpert and Maron 2000), which can 578

favor native plants (Lowe et al. 2003). Litter, at least initially, influenced faunal abundance, 579

diversity, and community composition through its effects on physical conditions and plant 580

community characteristics. Litter hosted more invertebrate pests, such as silverfish, the European 581

earwig and the Argentine ant, than in the reference site. Since these species favor moist 582

conditions and use plant litter for nesting (Flint 1998, Johnson and Triplehorn 2004, Menke and 583

Holway 2006), it follows that higher abundances were found in plots with litter and plantings. 584

Litter hosted higher abundances of detritivores and/or microbivores such as collembolan and 585

isopods, likely due to both provision of food and moist habitat conditions (e.g., Johnson and 586

Triplehorn 2004). Spiders were also associated with litter, which could have been due to the litter 587

itself and/or the higher proportions of native plants acting as a cover for hunting predators, or 588

increasing associated prey species (Bultman and Uetz 1984, Talley et al. 2012). 589

590

The presence relative to absence of plantings generally had a stronger effect than planting 591

diversity level. Often in combination with litter addition, planting presence contributed to more 592

27

environmental similarity among littered plots, and greater soil moisture, shading, native plant 593

community development, and initially higher decomposition rates than unlittered plots. More of 594

the herbivorous beetles, Metaponium abnorme and Harpalus herbivagus, were observed in 595

planted plots, especially with litter present. The presence of native plants may have served as a 596

food source while the enhancement of the proportional abundance of natives offered by litter 597

may have also contributed to support of herbivores (Wolkavich 2010). 598

599

When planting diversity did have effects, different planting diversity levels conferred different 600

benefits. The higher diversity treatment compared with the lower diversity treatments was 601

associated with lower mortality rates of common-species plantings, higher overall plant 602

diversity, higher native plant volume, lower introduced plant volume, and lower variability of 603

environmental conditions and faunal communities within treatments. It may be that the higher 604

diversity mixes resulted in complementarity effects, where mixes of different species more 605

efficiently used limiting resources (e.g., light, nutrients) and resulted in less environmental and 606

faunal variability (more stability) than monocultures (e.g., Tilman and Downing 1994, Worm et 607

al. 1996). Mixes may also have resulted in sampling effects, where multiple species increase the 608

chance of inclusion of a species that is a better competitor and/or stabilizer (e.g., Naeem et al. 609

1996, Loreau 2000, Dukes 2002). 610

The monoculture plantings (1-species) were often associated with lower total planting 611

mortality rates, comparatively high substrate humidity and, in combination with litter in the high 612

marsh, high initial decomposition rates and the first resemblance to reference site faunal 613

community. This was likely due to the selection of particular species that contributed to these 614

processes and not a monoculture per se (e.g., Dukes 2002). Monoculture plantings consisted of 615

28

plants that were among the most abundant in the reference site, often forming large monocultural 616

stands. Their abundance indicated that these species are were suited for the local environment 617

with respect to their physiological tolerances and/or intra-specific facilitation (Padilla and 618

Pugnaire 2006, McIntire and Fajardo 2011). In particular in the experimental high marsh, 619

Frankenia salina formed dense patches that were uniformly low to the ground relative to the 620

varying heights of mixed plots. The dense patches were able to trap humidity, a strong correlate 621

with decomposition rates, and ameliorate harsh physical conditions such as soil salinity. In harsh 622

physical environment such as this, plant taxa that grow quickly with dense, low cover might have 623

a large effect on development. 624

The 3-species plantings did not differ from the other diversity levels for most variables. 625

When differences did occur, the differences were consistent with the younger age of these plots 626

and not intermediate diversity effects (e.g., smaller native shrubs, higher introduced plant 627

volumes, faunal abundance overshoots in the 3-species compared with reference plots.) 628

629

Recommendations 630

The biotic and abiotic differences among the experimental treatments and the reference site 631

began to decrease with the timeframe of this study, especially in the plots that received organic 632

litter and live native plants. Methods that encourage the rapid establishment of a broadly 633

functioning ecosystem provide immediate benefits, and may jump-start functions that take longer 634

to develop. 635

Organic litter. The use of a thick layer (5-8 cm) of plant litter as a gardening mulch 636

shades the soil surface limiting germination of the seedbank, which consists mostly of introduced 637

annuals. Litter also retains moisture, encouraging growth of plantings. The downside of litter, 638

29

especially in combination with irrigation is encouragement of pests like Argentine ant, earwigs 639

and silverfish. It is best to use litter from the site, so as not to spread these species, or from a 640

clean litter source. After native plants establish, allow the natural precipitation regime with 641

desiccation throughout the dry season to curb the growth of pest populations. 642

Plant native perennials after invasive annual removal. Natives in this ecosystem are 643

dispersal limited and would be slow to recruit naturally, if at all (Lindig-Cisneros and Zedler 644

2002, Morzaria-Luna and Zedler 2007). Without plantings, the introduced annuals will germinate 645

from the seedbank (Morzaria-Luna and Zedler 2007) and re-dominate after the first rains. 646

Limiting reinvasion of annuals is crucial because a shift from a perennial shrub to an annual herb 647

dominated plant community would dramatically change the physical, chemical and trophic 648

characteristics of an ecosystem, with bottom–up effects on the greater community (Cook and 649

Talley in revision). Perennial shrubs, compared with annual herbs, tend to be larger (more 650

volume), provide live woody biomass throughout the year, and live much longer allowing the 651

provision of more of the functions that are desirable for this area such as mitigating harsh 652

physical conditions and providing habitat for invertebrates (this study), providing habitat for a 653

diversity of vertebrates (e.g., Chase et al. 2002), enhanced carbon storage (Zan et al. 2001, 654

Koteen et al. 2011), upland runoff filtration, erosion control and storm surge buffering (e.g., 655

Mitsch and Gosselink 2007). The inclusion of fast growing, generally larger native shrubs such 656

as Frankenia salina, Iscoma, menziesii, Artemisia californica, Eriogonum fasciculatum and 657

Artriplex canescens, would quickly add needed biomass to immediately provide physical 658

modifications, habitat and to start accumulating litter biomass. 659

Include a diversity of native species in the plantings. While organic litter had the primary 660

effect on early ecosystem development, it is likely that the effects of plant diversity will increase 661

30

as the restoration site matures. With time, plants will fill in and come into direct contact with 662

each other leading to stronger interactions. Time also allows for the colonization of species, in 663

particular, those species that are rare or slow to colonize resulting in higher numbers of and more 664

intense interspecific interactions (Thompson 1994). Further, recent studies reveal mechanistic 665

links between diversity and function across an array of ecosystems (Isbell et al. 2011) and the 666

need for diversity to sustain multiple ecosystem functions (Zavaleta et al. 2010). For this estuary 667

in particular, plant diversity was linked with higher primary productivity (Zedler et al. 2001, 668

Callaway et al. 2003), canopy complexity (Keer and Zedler 2002), and reduced invasion (Lindig-669

Cisneros and Zeder 2002). 670

671

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