Multiscale Patterns of Riparian Plant Diversity and Implications for Restoration

RESEARCH ARTICLE Multiscale Patterns of Riparian Plant Diversity and Implications for Restoration

Joshua H. Viers,1,2 Alexander K. Fremier,3 Rachel A. Hutchinson,1 James F. Quinn,1 James H. Thorne,1 and Mehrey G. Vaghti4

Abstract herbaceous species, whereas woody species were largely 2 Planning riparian restoration to resemble historic refer- cosmopolitan across the nearly 38,000 km study area. At ence conditions requires an understanding of both local the floodplain scale, riparian floras reflected species rich- and regional patterns of plant species diversity. Thus, ness and dissimilarity patterns related to hydrological and understanding species distributions at multiple spatial disturbance-driven successional sequences. These findings scales is essential to improve restoration planting success, reinforce the importance of concurrently evaluating both to enhance long-term ecosystem functioning, and to match local and regional processes that promote species diver- restoration planting designs with historic biogeographic sity and distribution of native riparian flora. Furthermore, distributions. To inform restoration planning, we exam- as restoration activities become more prevalent across the ined the biogeographic patterns of riparian plant diver- landscape, strategies for restoration outcomes should emu- sity at local and regional scales within a major western late the patterns of species diversity and biogeographic U.S.A. drainage, California’s Sacramento—San Joaquin distributions found at regional scales. Valley. We analyzed patterns of species richness and complementarity (β-diversity) across two scales: the watershed scale and the floodplain scale. At the watershed scale, spa- Key words: biodiversity, biogeography, multiscale analysis, tial patterns of native riparian richness were driven by restoration, riparian, Sacramento, San Joaquin.

Introduction are often intended to revegetate degraded and disturbed natural Conservation of biodiversity is a critical component of ecolog- areas with native plant species, are conducted on a site-by-site ical restoration worldwide (Gann & Lamb 2006) and is artic- basis without strategic planning aimed at promoting ecosys- ulated as a unifying principle for riparian restoration (Ward tem complexity or enhancing biodiversity. Thus, horticultural &Tockner2001).Incertainregions,andespeciallyincer- restoration is often reactive to local conditions and opportuni- tain ecosystems, restoration efforts are common and cover ties rather than regional strategies, in part because of a desire sufficiently large areas such that large-scale biogeographic to promote ecosystem functioning and biophysical processes. patterns of species diversity should be described and repre- Short of defining and implementing regional restoration strate- sented in restoration planning. For example, large coordinated gies to meet multiscale objectives (Hobbs & Norton 1996), we ecosystem restoration efforts, which are intended to restore suggest that a basic understanding of local and regional pat- ecosystem functions and processes, are ongoing for the Chesa- terns of plant diversity has the potential to improve how prac- peake Bay (Hassett et al. 2005), the Florida Everglades (Sklar titioners conduct horticultural restoration, specifically species et al. 2005), the Colorado River (Patten & Stevens 2001), selection during the design phase and evaluation of restoration and the San Francisco Bay-Delta (Kondolf et al. 2008). Over success. large areas such as these, it is clear that no single restoration Riparian plant restoration efforts typically focus on a small design can emulate the inherent complexity of these ecosys- number of large, overstory species rather than explicitly tar- tems. However, many horticultural restoration efforts, which geting overall species diversity (Sweeney & Czapka 2004). It is assumed that certain species have a large impact on the

1 Department of Environmental Science & Policy, University of California, Davis, ecosystem function (e.g. bank stability, nutrient processing, One Shields Avenue, Davis, CA 95616, U.S.A. wildlife habitat, etc.) and that, if present, a host of other species 2 Address correspondence to J. H. Viers, email [email protected] will colonize after initial targeted species are established. This 3 Department of Fish and Wildlife Resources, College of Natural Resources, University of Idaho, Moscow, ID 83844-1136, U.S.A. horticultural approach often achieves initial aims of targeted 4 Placer Land Trust, 11661 Blocker Drive, Suite 110, Auburn, CA 95603, U.S.A. species establishment, yet it is unclear if a native herbaceous understory component can subsequently equal remnant ripar-  2011 Society for Ecological Restoration International doi: 10.1111/j.1526-100X.2011.00787.x ian forests in native species richness (Holl & Crone 2004).

Restoration Ecology 1 Patterns of Riparian Diversity for Restoration

Further, there is little evidence that the cumulative result of knowledge rather than conducting wide-ranging studies (Wohl many localized restoration projects captures the inherent pat- et al. 2005; Young et al. 2005). Although many practition- terns of biodiversity found over large areas (Bedford 1999) ers likely possess an intuitive sense of how local actions fit nor that the current spatial distribution of restoration projects into broader ecosystem restoration efforts, there are too few across large areas is strategically sound if overall ecosystem examples of how baseline assessments can be utilized to ben- function or watershed-scale patterns of historic species distri- efit their projects, such as analyzing biogeographic maps of bution is a desired outcome (Kershner 1997; Teal & Peterson species diversity to determine if local projects are comple- 2005). With the recent profusion of horticultural restoration mentary in their scope or expected outcome, or alternately efforts (Bernhardt et al. 2007; Kondolf et al. 2007; Palmer evaluating field-based measures of species complementarity to et al. 2007), it is increasingly likely that uncoordinated activ- determine if a restoration project planting list is too homo- ities—coupled with narrowly defined objectives and limited geneous in its representation. Not only could the adoption implementation budgets—will influence the overall composi- of these principles early in the objective setting phase of tion and future trajectory of biodiversity in riparian ecosystems restoration help improve broader ecosystem outcomes, but also at a regional scale. provide practitioners with scientifically supported benchmarks For example, many riparian and floodplain restoration from which to objectively evaluate restoration outcomes. efforts in California’s San Francisco Bay-Delta and Central Our objective was to provide some context to the premise Valley are large in size, widely distributed, and could clearly that understanding biogeographical patterns of riparian plant impact the regional character of plant diversity (Alpert et al. diversity at local and regional scales is critical to developing 1999) and associated wildlife (Gardali et al. 2006; Golet contemporary restoration objectives. We performed a multi- et al. 2009). The widely implemented horticultural approach scale study on species distributional patterns within a riparian in this region is to establish native woody species with the restoration context, and provided critical analyses of diver- expectation that native understory species will colonize in sity patterns found in a large geographic region undergoing time (Palmer et al. 1997; Hilderbrand et al. 2005). The long- multiple, and largely uncoordinated, restoration projects as a term successes, and failures, of these projects have been well framework for restoration planning and evaluation. We cata- studied (Holl & Crone 2004) and ultimately shown to not logued multiple scale-specific studies of plant species presence adequately restore native species richness and composition to assess the patterns of species richness and turnover across when compared to remnant forest stands (McClain et al. 2011). ahydrologicallyandclimaticallycomplexregionofCalifor- Although the current approach is likely to improve certain nia. We used these data to understand patterns of diversity ecosystem functions on a localized basis (Dufour & Piegay in relation to watershed position and floodplain structure. We 2009), it is also likely to influence longer-term successional asked, over large areas, what is the number of native riparian trends and composition of regional floras. species and how variable is species richness? And, what is We believe that a regional understanding of species dis- the expected dissimilarity of herbaceous and woody species tributions is necessary if local efforts are to complement in a watershed and floodplain context (e.g. the dissimilarity in larger watershed-scale strategies aimed at ecosystem restora- species composition that would result from species represen- tion. Biogeographic patterns can help define regional restora- tation along environmental gradients or regionally from one tion objectives while also improving restoration evaluation and watershed to another)? At the watershed scale, we expected identifying gaps in habitat type representation. Although many native species richness to be uniformly distributed through- restoration projects value the concept of biodiversity (Mayer out the Central Valley due to its physical geography (i.e. 2006) from the perspective of providing localized genotypic it is a large alluvial basin with homogeneous soils and cli- source material and supporting ecosystem services from sur- mate). At the landscape scale, we were particularly interested rounding habitat (Handel et al. 1994), the actual features of in the geographic patterns of species diversity in relation biodiversity, specifically elements of biogeography and species to floodplain position and comparisons between two large diversity, such as patterns of richness and underlying environ- watersheds with distinct environmental gradients, where we mental gradients, are rarely explicitly included in the design expected native species richness to vary by disturbance regime phase (Parker 1997). Reasons for this are most likely related to and successional gradients to drive heterogeneity in species project constraints, with narrowly defined objectives and a lim- complementarity. ited planting list to choose from in the design phase. However, the lack of multiscale biogeographic assessments likely con- tributes to the constrained nature of restoration designs too. Methods Biogeographic assessments could inform a broader range of restoration practices with regard to appropriate location and Site Description diversity targets (Bornette et al. 2001). This is not to imply California’s Central Valley was created by alluvial deposi- that restoration practitioners and ecologists do not recognize tion from the surrounding Sierra Nevada and Coast Range, the importance of landscape scale patterns and processes in culminating in the low gradient, alluvial valley draining into restoration (Holl et al. 2003). However, in practice, restora- the San Francisco Bay-Delta (Fig. 1). Prior to the mas- tion efforts are often constrained by time, money, and man- sive influx of humans due to the California Gold Rush, the date, and, therefore, are forced to make decisions on available Central Valley had extensive wetlands and riparian forests.

2 Restoration Ecology Patterns of Riparian Diversity for Restoration

and the Bay-Delta are now the focus of a wide-ranging set of restoration activities to address the loss of historic lowland riparian and wetland vegetation. In terms of the area restored, the largest efforts have been at the Cosumnes River Preserve, focusing on seasonal floodplain connectivity, and on the Sacramento River between Sacramento and Red Bluff, with afocusonwildlifehabitatandriparianforestregeneration. In addition, a complex of wetland restoration sites exist in the Yolo Bypass, a large managed floodplain channel that conveys Sacramento River floodwaters into the Bay-Delta. Most recently, a massive restoration project on the San Joaquin River is now underway to re-water significant portions of the river with concomitant reestablishment of riparian forests. To better understand patterns of species diversity, we analyzed the regional distribution of riparian plant richness within the Central Valley (the watershed scale) and again at the local scale related to floodplain dynamics (the floodplain scale). We examine species richness (α-diversity) and dissimilarity (β-diversity) at these two scales using three independent datasets. We used species richness and turnover to reflect broad biogeographic patterns of vegetation community patterns and to guide riverscape scale measures of expectation that could be used as informative benchmarks for evaluating restoration trajectories (or success). However, plant diversity in its many forms should be considered, and inclusion of composition and complementarity measures would also benefit restoration design and outcomes if the desired objective Figure 1. Location of CalJep Study Units and primary riverine features includes improving and sustaining biodiversity. We chose to described in this study. Observed native riparian richness and predicted exclude non-native species from our analyses, because restora- richness are displayed within each study unit. tion objectives often focus on reestablishing or enhancing populations of native species. Here we describe the geo- Though these ecosystems were actively managed by aborigi- graphic patterns of native composition separately from rel- nal inhabitants (i.e. burned), alteration of hydrological patterns atively recently arrived non-native species. To do otherwise prior to Euro-American settlement are thought to be mini- we would be mixing gradients of native floras with patterns mal (Anderson 1999). These wetland and riparian habitats of community invasion. Most non-native species in our study were primarily associated with its two major river systems, region are fairly ubiquitous, thus equally affecting species rich- the Sacramento River and its four major tributaries draining ness and composition, which is similar to the findings of others the northern portion of the valley, and the San Joaquin River (Sabo et al. 2005). and its eight tributaries draining the southern portion. With urbanization and modern agriculture, the valley has largely been converted to human use, and only an estimated 5–12% Watershed Scale of the original riparian habitat remains, much of that highly For the largest scale of analysis, we selected the 22 “planning degraded (Hunter et al. 1999). While the total area of ripar- unit” polygons defined by the CalJep database (Viers et al. ian forest is greatly reduced from historical accounts, very 2006) within the Central Valley (Fig. 1) and limited analyses to few native species have been lost due to localized extinction native plant taxa defined as either riparian or wetland affiliates within a specific river system. While a few rare species do by the California Rivers Assessment (Viers et al. 1998; Hunter exist in these river systems (e.g. Hibiscus lasiocarpus var. et al. 1999). This scale was used to identify region-wide occidentalis), there is no evidence of widespread species loss. patterns in species composition, dissimilarity, and diversity For this reason, it is valuable to compare species richness (i.e. in relation to watershed position and geographic patterns of presence/absence) across multiple scales despite the significant climate. historical changes to species abundances. Specifically, we used the CalJep database (Viers et al. Originally, the two river systems drained into the Bay-Delta, 2006), a spatially enabled relational database of digital flo- which mainly comprised waterways and tidal freshwater ras, to generate species lists for pre-defined planning units marsh, almost all of which was leveed and converted into within the Central Valley. The Central Valley boundary and farmland in the late 19th and early 20th century. Because of planning unit boundaries are based on a combination of phys- this wholesale landscape scale change which severely altered iographic thresholds, political boundaries (counties), and two ecosystem functioning, the Central Valley, its major rivers, historic plant species data sources—The CalFlora database

Restoration Ecology 3 Patterns of Riparian Diversity for Restoration

(http://www.calflora.org/) and The Jepson Manual (Hickman and over a downstream distance gradient (i.e. longitudinal 1993). A digitized version of Jepson Manual data was provided gradient). The vegetation plots from this study were strati- by the Jepson Herbarium (http://ucjeps.berkeley.edu/). The fied over a floodplain age and relative elevation gradient, and CalJep database is a record of 7,887 plant species, subspecies, randomly placed within riparian forest delineated polygons and varieties across the state of California (410,000 km2)with (Vaghti et al. 2009). Forests were surveyed for species pres- varying levels of precision within 228 planning units that ence in 800-m2 plots and non-forested sites were surveyed for has been used in multiple studies (see Harrison et al. 2000; species presence in 200-m2 plots. In all, 91 plots were surveyed Williams et al. 2005; Schwartz et al. 2006; Thorne et al. 2009 in 2003 along 122 km of the Sacramento River floodplain. for other examples). In addition to combining range data from We calculated pairwise species dissimilarity (JD) for each CalFlora and the Jepson Manual, CalJep also has derived pair of plots, and correlated dissimilarity to differences in finer spatial designations than either, but is not being actively relative elevation using a partial Mantel (rm)test,which updated with new records or taxonomic changes. examines the simultaneous effect of geographic distance and Within the planning units, we analyzed patterns of riparian relative elevation on plot dissimilarity. We employed a Man- plant species diversity using three methods: first, we calculated tel test to correlate mean JD with pairwise geographic dis- an area-adjusted α diversity for each planning unit using tance, downstream distance (river kilometer, RKM), and flood- the probable distribution of native riparian plant taxa from plain elevation relative to the low-flow channel water sur- CalJep (Viers et al. 2006). Second, we calculated pairwise face, as developed by Greco et al. (2008), to determine if dissimilarity (1-Jaccard) for each combination of study units floodplain gradients could explain patterns in observed plant and taxonomic groups. We used the Jaccard dissimilarity index diversity. The relative elevation data were then separated as a measure of β-diversity, denoted here as JD, where values into floodplain position categories by creating low, medium, range from 0 to 1 with 1 indicating no shared species and and high groupings based on sample distributions as rela- 0showingperfectoverlapbetweenpairwisecombinationsof tive elevation has been used in the past to investigate suc- study units. We chose JD as a primary response variable cessional pathways and species occurrence (Robertson & to specifically account for differences in species occurrence. Augspurger 1999). To address successional processes on the Lastly, we correlated Jaccard dissimilarity values to the spatial floodplains of the Sacramento River, we analyzed the relation- distance between each pair of CalJep units using a Mantel ship of α-diversity and relative elevation for each taxonomic test (rm)forallspecies,woody,andherbaceoustaxonomic group. groups north and south of the Bay-Delta to account for spatial dependence between sites. We used Monte Carlo Cosumnes River Dataset. On the Cosumnes River, we randomization to account for sample size effects. examined data from remnant riparian forests and adjacent process-based restoration of seasonal floodplain (Opperman et al. 2010). The site locations are within 2 km of each other Floodplain Scale and represent a 5-km stretch of river. Tu (2000) identified four Riparian diversity patterns vary both longitudinally and later- broad sites by their composition and successional histories: (1) ally across floodplains as local hydrological conditions allow an early successional sand splay habitat, created by intentional (Vaghti 2003; Greco et al. 2007). At the floodplain scale breaching in 1997 (Florsheim & Mount 2002); (2) an inter- we analyzed two independent floristic datasets that captured mediate Populus fremontii (Fremont cottonwood)—Salix spp. species variation across floodplains rather than between dif- (willow) stand created by an accidental levee break in 1985 fering watersheds. We used data collected from the Sacra- (Trowbridge et al. 2005); (3) a mixed riparian forest; and (4) mento River, California’s largest, and the Cosumnes River, an alatesuccessionalstandcomposedoflargeValleyoak(Quer- unregulated tributary. The Sacramento River, although heav- cus lobata) (Meyer 2002). Tu (2000) conducted repeated field ily regulated, is the focus of several restoration initiatives to surveys in 1995–1998 across the four sites (1 km2), each con- improve geomorphic and riparian conditions. The Cosumnes taining three 900-m2 plots. Although extensive abundance and River sustains not only a natural flow regime, but also one structural data were collected as part of this effort (Tu 2000), of the largest intact late-seral stage riparian forests in the we used only collective presence and absence of native species Central Valley. Compared to historical estimates of riparian for our analysis to assess successional trajectories in an area forest cover, these two river systems are likely very different at or near sea level with minimal gradient and regular flood today (Hunter et al. 1999). Although species abundances and disturbance. extent are significantly altered, species extirpation has not been For both river datasets, species lists were limited to native common (Vaghti and Greco 2007). For this reason, we feel a riparian taxa, for which α-diversity and Jaccard dissimilarity comparative study of species richness on current floodplains (JD, as above) were calculated among all floodplain loca- can be used to represent historical species diversity patterns. tions, and across all native, woody, and herbaceous taxonomic groups. All geographical information system analyses were Sacramento River Dataset. On the Sacramento River flood- conducted in ArcGIS 9.3 (ESRI, Redlands, CA, U.S.A.) and plain, we analyzed a field dataset of riparian flora to quantify statistical analyses were conducted in PC ORD 5.18, JMP 8 plant diversity over two landscape gradients—an elevation (SAS Institute, Cary, NC, U.S.A.), and Ecodist package in gradient based on surface flow (i.e. hydrologic gradient) R2.9.1.

4 Restoration Ecology Patterns of Riparian Diversity for Restoration

Results drainage pattern of the Central Valley and homogeneity of hydrologic factors at the upper extents of the river drainages. Watershed Analysis To show how species dissimilarity changes with distance At the watershed scale, native riparian species richness from the Bay-Delta, the Mantel correlation coefficient (rm) (α-diversity) within the 22 “planning units” included 154 was re-calculated and, as with the results shown in Figure 3, native riparian species per 1,000 km2 of planning unit ( 13 the herbaceous group exhibited a larger overall dissim- ± SD). Richness and species dissimilarity were driven by the ilarity between planning units over the geographic area herbaceous group, with woody species contributing only (San Joaquin: rm 0.39, p 0.02; Sacramento: rm 0.29; asmallproportiontooverallrichness(Table1;Fig.2). p 0.03). While= we observed= that woody species were= gener- Figure 3a shows how the dissimilarity between planning units ally= more cosmopolitan, they displayed a higher rate of spatial changes with geographic distance for all pairwise combina- turnover south of the Bay-Delta (rm 0.45, p 0.002) than = = tions; woody species show less overall dissimilarity than the to the north (rm 0.24, p 0.06). herbaceous group with a reduction in the Mantel correla- = = tion coefficient, with both set of matrices significant at the p<0.05 level. The correlograms in Figure 3b show how dis- Floodplain Analysis similarity changes with increasing pairwise distance. Positive Sacramento River. On the Sacramento River, we observed a correlations reflect increasing dissimilarity with distances up gain of two native riparian species per 100 km with an upriver to approximately 100–200 km where the relationship turns trend in α-diversity (α 2.55 0.02 RKM; F1,89 3.46; negative; this negative relationship presumably is due to p 0.066) for the length= of the river+ within the study= region. the increasing environmental similarity of plots at greater Herbaceous= species dissimilarity increased with increasing distances upstream from the Bay-Delta, which reflects the interplot geographic distance (i.e., “as the crow flies”). Using distance along the river, we observed that mean JD increased with greater interplot river distance, when focusing on riparian Table 1. Watershed-scale riparian plant richness and pairwise herbs; this was also observed for all species but not for woody dissimilarity. species (Table 2). In other words, dissimilarity of woody All Taxa Herbaceous Woody species was not correlated to downriver distance, indicating that these species were common throughout the study reach. Mean Richness 154 13 138 5162 ± ± ± We also correlated the interplot difference in floodplain ele- (α) Standard vation to species dissimilarity by separating plots into one Deviation± Lower 95% 148 133 15 of three classes of relative floodplain elevation (centimeter Upper 95% 161 145 17 above water surface; Table 2). We observed no relationship Mean (JD) 0.34 0.04 0.35 0.04 0.25 0.04 of pairwise herbaceous dissimilarity and floodplain elevation Maximum (JD) 0.45± 0.47± 0.36± on low-elevation surfaces, where flood-induced disturbance is Minimum (JD) 0.29 0.29 0.19 presumed to be the most common and disturbance regimes (e.g. flood inundation and scour) likely constrain establish- For the CalJep study units (n 22), we show mean richness adjusted per 1,000 km2 of study unit area at the “probable”= distribution designation and descriptive statistics ment by many species (Table 2). On mid-elevation flood- for mean JD values for different levels of taxonomic grouping. plains, herbaceous and overall JD was positively correlated

Figure 2. Species area relationship of native riparian woody, native riparian herbaceous, and all native species in California’s Central Valley.

Restoration Ecology 5 Patterns of Riparian Diversity for Restoration

(a)

(b)

Figure 3. (a) Jaccard dissimilarity (JD) for herbaceous and woody species as a function of centroid distance (woody species: 0.0578 d0.2886, R2 0.16; = herbaceous species: 0.0759 d0.3143, R2 0.34). (b) Mantel correlogram of herbaceous and woody species showing number of comparisons (n), Mantel = correlation coefficient (rm), and significance (p)againstcentroiddistance. with relative elevation; that is, species dissimilarity among all highest floodplains (i.e., highest relative elevations) showed plots increased with increasing differences in relative elevation that differences in relative elevation were positively correlated (Table 2). However, the continuity of woody species compo- with JD for woody taxonomic subsets (rm 0.26, p 0.038), = = sition between mid- and low-floodplain surfaces indicated a and marginally so for overall species dissimilarity (rm 0.28, = homogeneous floral composition across these surfaces. The p 0.055). =

Table 2. Mantel tests of Jaccard Dissimilarity for the Sacramento River.

Relative Elevation

Geographic River Position Low 249–448 cm Mid 449–518 cm High 519–628 cm Taxonomic Grouping Distance (RKM) (n 19 ) (n 42 ) (n 30 ) = = =

All rm 0.08 rm 0.09 rm 0.015 rm 0.087 rm 0.28 p =0.17 p =0.024 p =0.378 p =0.039 p =0.055 = = = = =

Herbaceous rm 0.126 rm 0.12 rm 0.02 p 0.011 rm 0.09 = = = = =− p 0.009 rm 0.11 p 0.433 p 0.034 p 0.263 = = = = = Woody rm 0.04 rm 0.04 rm 0.049 rm 0.06 rm 0.26 p =0.15 p =0.142 p=−0.44 p =0.091 p =0.038 = = = = = Jaccard dissimilarity (JD) correlations from Mantel tests of geographic distance, river position (RKM), and relative elevation of ﬂoodplain position are shown for the Sacramento River study. Mantel statistics are denoted as rm,andtheprobabilityofrandomlyachievingthesameorhighercorrelationasp.Grayboxesindicatedstatisticallysigniﬁcant tests at p<0.05.

6 Restoration Ecology Patterns of Riparian Diversity for Restoration

Cosumnes River. The richness of native riparian plants in Table 3. Cosumnes River Study dissimilarity scores. the Cosumnes River study was relatively even across sites despite their different disturbance regimes and successional Taxonomic Grouping Study Site (α)SSCFMR status. Mean richness (α 16 2spp.)wasdominatedby = ± All Species SS (15) — the herbaceous species (α 10 1spp.)(Table3).Among CF (18) 0.625 — specific sites, the sand splay= habitat± had the fewest woody MR (13) 0.727 0.368 — species (α 4), but tied with the Valley oak forest for the VO (17) 0.769 0.542 0.333 most herbaceous= species (α 11). The cottonwood forest had Riparian SS (11) — Herbaceous the most woody species (α = 8), followed by the Valley oak CF (10) 0.500 — Species MR (8) 0.643 0.364 — (α 6) and mixed riparian= forested habitats (α 5). Most = = VO (11) 0.706 0.500 0.273 striking, however, were the high levels of average dissimilarity Riparian Woody SS (4) — between the sites (JD 0.56 all species), indicating that sites Species = CF (8) 0.800 — were more dissimilar than similar in composition, especially MR (5) 0.875 0.375 — for woody species (JD 0.68). More specifically, the Valley VO (6) 0.889 0.600 0.429 oak forest, the oldest= stand at this study site, was most Four levels of taxonomic groupings are tabulated across four sites (SS, sand splay; similar in herbaceous composition to the mixed riparian forest CF, cottonwood forest; MR, mixed riparian; VO, valley oak) from Tu (2000). (JD 0.27), the next oldest site. However, the mixed riparian Dissimilarity coefficients (JD) follow study site codes; numbers of species are = indicated parenthetically (α)foreachsitebytaxonomicgrouping.Thesuccessional forest and cottonwood forests had the most woody species in gradient follows from SS CF MR VO as predicated by flood-induced common (JD 0.38). On average, the sand splay habitat was disturbance (Florsheim & Mount→ 2002).→ → most dissimilar= to the other three sites, whereas the mixed riparian forest was the least dissimilar across all taxonomic groups. turnover was correlated to floodplain elevation on high-, but not middle- or low-elevation surfaces. We found that turnover of native herbaceous species was affected as floodplain elevation increased, but the disturbance regime drove woody species Discussion turnover, which was only correlated to floodplain elevation on We expected that the Bay-Delta portion of the study area upper (low flood frequency, low disturbance) surfaces and not would have higher species richness due to the geographic on low (high flood frequency, high disturbance) or interme- overlap of fluvial and deltaic processes influencing rates of diate elevation sites. It is open to speculation whether San sedimentation and disturbance, and corresponding floristic Joaquin floodplains would exhibit lower dissimilarity with a biogeographic overlap. While area-adjusted species richness restored seasonal flood regime. showed a peak over the Bay-Delta, a stronger biogeographic Our findings and others suggest that floodplain elevation pattern existed for areas adjacent to the Sierra Nevada foothills, relative to the low-flow water surface is a good predictor especially in the northeastern portion of the Sacramento of species distribution along the Sacramento River (Fremier Valley where residual richness was consistently higher than 2003; Vaghti 2003; Greco et al. 2007, 2008). Considering expected based on area of planning unit alone. This pattern is the high correlation between FPA and RE (R 0.34, p< characterized by the rate of turnover, as measured by species 0.0001), the environmental gradient represents a= combination dissimilarity between planning units, which was much higher of time since land creation or floodplain age (FPA) and the for herbaceous than woody species and indicates that regional intensity and frequency of flooding or relative elevation (RE). patterns of species richness are driven by heterogeneity in the This most likely represents a successional gradient (Fremier riparian understory. 2003). In effect, observed patterns of species dissimilarity At the local scale, we also found that herbaceous species are shaped by distinct hydro-geomorphic processes such as drove patterns of plant diversity. However, these patterns were flooding and soil development, and biotic processes such as dictated by local features, namely terrain and sequences of resource competition and propagule dispersal. disturbance. Geomorphic conditions differ in the upper and Asimilarpatternofspeciesrichnessandturnover,likely lower portions of the Sacramento River; the northern region related to disturbance regimes, was also observed within the includes setback levees that allow for river meander and the Cosumnes River floodplain, where cottonwood and oak forests formation of large floodplains of exposed substrates, whereas display the highest overall native species richness. In this area the southern region contains levees that confine river pro- the cottonwood forest bridges the difference in composition cesses and thus promote more dynamic and heavily flood- between the heavily disturbed sand splay community and the disturbed environments. Sites in the northern region exhib- late-seral stage Valley oak forest. The mid-seral cottonwood ited high herbaceous species richness, whereas sites in the forests, in moderately disturbed habitat, also had the high- southern region had high turnover (i.e. dissimilarity) between est woody species richness, whereas herbaceous species did adjacent sites, indicating a heterogeneous floodplain environ- not follow this trend, possibly due to light exclusion created ment. Further, we found that herbaceous species turnover was by homogeneous canopy cover. These observations are sim- influenced by floodplain elevation on mid floodplain eleva- ilar to those of others investigating intermediate disturbance tions along the Sacramento River, whereas woody species as a working hypothesis for elevated riparian richness (e.g.

Restoration Ecology 7 Patterns of Riparian Diversity for Restoration

Lite et al. 2005). However, at the Cosumnes site, both the sand splay complex and Valley oak forests had the highest Implications for Practice native herbaceous richness. Thus, even in this highly modified When setting restoration objectives, multiscale assess- • system, mosaics of disturbance and successional gradients pro- ments of species diversity can provide managers with mote diverse riparian communities within and across river site-specific targets that complement broader biogeo- systems. Yet, data show stronger evidence that floodplain graphic trends and utilize region-specific source mate- species richness is highest at the ecotone between riparian rials. and oak woodland, and not at intermediate levels of distur- Although woody species are often cosmopolitan at • bance as suggested by a proximal intermediate disturbance broader scales, their distribution is dependent on local- hypothesis. These two hypotheses merit further study, partic- ized environmental variables, which can affect over- ularly given the modified nature of much of our study system all restoration success. Restoration projects intended to and that we used relative elevation as a surrogate for distur- restore biodiversity features, such as β-diversity or com- bance. plementarity across sites, should instead focus on herba- Consistent patterns of floristic richness and dissimilarity ceous species establishment. emerged across both scales of analysis, consistent with the Incorporating herbaceous species into restoration efforts • findings of other studies in different regions (Nilsson et al. may facilitate attaining diversity-driven restoration objec- 1994; Pollock et al. 1998; Mouw & Alaback 2003). We tives, as restoration sites might more closely resemble found that species richness in riparian flora at both regional reference sites. This approach will also likely benefit and local scales was driven by differences in the composi- rarer species. tion of herbaceous species layer. Woody species were gener- Restoration efforts must encompass a variety of physi- • ally more cosmopolitan within the floodplain and over the cal habitats, such as gradients in terrain, if high levels entire valley, with some exceptions toward the Bay-Delta of β-diversity and increased overall diversity are to be Region. Thus, restoration objectives and designs that only achieved. To help facilitate complexity in physical habi- target woody species are likely to detract from features of tats and initiate disturbance-driven succession, dynamic plant diversity for three important reasons. One, projects that ecosystem processes such as episodic flooding should be assume that a native herbaceous component will reestablish encouraged. after overstory restoration are not likely to succeed, mean- If projects are too spatially confined to encompass a • ing that the largest portion of richness, as we showed with variety of terrains or limited in their ability to incorporate the herbaceous component at the watershed and floodplain disturbance regimes and multiple successional states, scales, will be missing. Two, as we showed at the flood- efforts should be made to embed the project within a plain scale, disturbance regimes and physical settings alter larger regional restoration framework. woody species composition, meaning that restoration that does not capture the range of underlying processes is not likely to represent a full complement of species, woody or herbaceous. Three, woody species have a lower rate of Acknowledgments geographic dissimilarity compared to herbaceous species at the watershed scale, meaning that restoration efforts target- The authors would like to thank S. Cepello, M. Schwartz, ing only woody species may actually result in a homoge- R. Naiman, and J. Stella. Research was supported by CBDA nization of the regional flora as the understory component Ecological Restoration Program (Award # ERP-01-NO1 and # may only reflect ubiquitous herbs. This argument is not ERP-01-P66) and the PIER climate change program. We also intended to suggest that woody species are unimportant, but thank S. Yates, M. Briggs, and an anonymous reviewer for rather that restored natural habitats should be biologically their thoughtful comments. diverse. We used richness (α diversity) and turnover incorporating complementarity (β diversity), as metrics at mul- LITERATURE CITED tiple scales, to provide a priori measures of expectation that could be used as informative benchmarks for evalu- Alpert, P., F. T. Griggs, and D. R. Peterson. 1999. Riparian forest restoration along large rivers: initial results from the Sacramento River Project. ating restoration trajectories (or success). While this anal- Restoration Ecology 7:360–368. ysis is only a snapshot in time, we were able to identify Anderson, M. 1999. The fire, pruning, and coppice management of temperate important patterns that could be incorporated into develop- ecosystems for basketry material by California Indian tribes. Human ing sound restoration objectives and more integrated restora- Ecology 27:79–113. tion designs. Given anticipated bioclimatic shifts with cli- Bedford, B. L. 1999. Cumulative effects on wetland landscapes: links to mate warming, and as suggested by Seavy et al. (2009), it wetland restoration in the United States and Southern Canada. Wetlands is increasingly important to develop a placed-based under- 19:775–788. standing of riparian biodiversity patterns and the underlying Bernhardt, E. S., E. B. Sudduth, M. A. Palmer, J. D. Allan, J. L. Meyer, G. Alexander, et al. 2007. Restoring rivers one reach at a time: results processes if restoration is to be a workable adaptation strat- from a survey of US River Restoration Practitioners. Restoration Ecology egy. 15:482–493.

8 Restoration Ecology Patterns of Riparian Diversity for Restoration

Bornette, G., H. Piegay, A. Citterio, C. Amoros, and V. Godreau. 2001. flood disturbance, San Pedro River, Arizona, USA. Journal of Arid Aquatic plant diversity in four river floodplains: a comparison at two Environments 63:785–813. hierarchical levels. Biodiversity and Conservation 10:1683–1701. Mayer, P. 2006. Biodiversity—the appreciation of different thought styles and Dufour, S., and H. Piegay. 2009. From the myth of lost paradise to targeted values helps to clarify the term. Restoration Ecology 14:105–111. river restoration: forget natural references and focus on human benefits. McClain, C. D., K. D. Holl, and D. M. Wood. 2011. Successional models as River Research and Applications 25:568–581. guides for restoration of riparian forest understory. Restoration Ecology Florsheim, J. L., and J. F. Mount. 2002. Restoration of floodplain topography 19:280–289. by sand-splay complex formation in response to intentional levee Meyer, V. C. 2002. Soil moisture availability as a factor affecting Valley oak breaches, Lower Cosumnes River, California. Geomorphology 44:67–94. (Quercus Lobata Nee)´ seedling establishment and survival in a ripar- Fremier, A. K. 2003. Floodplain age modeling techniques to analyze channel ian habitat, Cosumnes River Preserve, Sacramento County, California. migration and vegetation patch dynamics on the Sacramento River. USDA Forest Service, Albany, California. University of California, Davis. Mouw, J. E. B., and P. B. Alaback. 2003. Putting floodplain hyperdiversity in Gann, G. D., and D. Lamb. 2006. Ecological restoration: a mean of conserving aregionalcontext:anassessmentofterrestrial-floodplainconnectivityin biodiversity and sustaining livelihoods. Society for Ecological Restora- aMontaneenvironment.JournalofBiogeography30:87–103. tion International, Tucson, Arizona. Nilsson, C., A. Ekblad, M. Dynesius, S. Backe, M. Gardfjell, B. Carlberg, S. Gardali, T., A. L. Holmes, S. L. Small, N. Nur, G. R. Geupel, and G. H. Golet. Hellqvist, and R. Jansson. 1994. Comparison of species richness and 2006. Abundance patterns of landbirds in restored and remnant riparian traits of riparian plants between a main river channel and its tributaries. forests on the Sacramento River, California, U.S.A. Restoration Ecology Journal of Ecology 82:281–295. 14:391–403. Opperman, J. J., R. Luster, B. A. Mckenney, M. Roberts, and A. W. Meadows. Golet, G. H., T. Gardali, J. W. Hunt,D.A.Koenig,andN.M.Williams.2009. 2010. Ecologically functional floodplains: connectivity, flow regime, and Temporal and taxonomic variability in response of fauna to riparian scale. JAWRA Journal of the American Water Resources Association restoration. Restoration Ecology 19:126–135. 46:211–226. Greco, S. E., A. K. Fremier, R. E. Plant, and E. W. Larsen. 2007. A tool for Palmer, M. A., R. F. Ambrose, and N. L. Poff. 1997. Ecological theory and tracking floodplain age land surface patterns on a large meandering community restoration ecology. Restoration Ecology 5:291–300. river with applications for ecological planning and restoration design. Palmer, M., J. D. Allan, J. Meyer, and E. S. Bernhardt. 2007. River restoration Landscape and Urban Planning 81:354–373. in the twenty-first Century: data and experiential future efforts. Restora- Greco, S. E., E. H. Girvetz, E. W. Larsen, J. P. Mann, J. L. Tuil, and tion Ecology 15:472–481. C. Lowney. 2008. Relative elevation topographic surface modelling of Parker, V. T. 1997. The scale of successional models and restoration objectives. alargealluvialriverfloodplainandapplicationsforthestudyandman- Restoration Ecology 5:301–306. agement of riparian landscapes. Landscape Research 33:461–486. Patten, D. T., and L. E. Stevens. 2001. Restoration of the Colorado River Handel, S. N., G. R. Robinson, and A. J. Beattie. 1994. Biodiversity resources ecosystem using planned flooding. Ecological Applications 11:633–634. for restoration ecology. Restoration Ecology 2:230–241. Pollock, M. M., R. J. Naiman, and T. A. Hanley. 1998. Plant species richness Harrison, S., J. H. Viers, and J. F. Quinn. 2000. Climatic and spatial patterns of in riparian wetlands - a test of biodiversity theory. Ecology 79: diversity in the serpentine plants of California. Diversity & Distributions 94–105. 6:153–162. Robertson, J. M., and C. K. Augspurger. 1999. Geomorphic processes and Hassett, B., M. Palmer, E. Bernhardt, S. Smith, J. Carr, and D. Hart. 2005. spatial patterns of primary forest succession on the Bogue Chitto River, Restoring watersheds project by project: trends in Chesapeake Bay USA. Journal of Ecology 87:1052–1063. Tributary restoration. Frontiers in Ecology and the Environment 3: Sabo, J. L., R. Sponseller, M. Dixon, K. Gade, T. Harms, J. Heffernan, et al. 259–267. 2005. Riparian zones increase regional species richness by harboring Hickman, J. C. 1993. The Jepson manual: higher plants of California. Univer- different, not more, species. Ecology 86:56–62. sity of California Press, Berkeley. Hilderbrand, R. H., A. C. Watts, and A. M. Randle. 2005. The myths of Schwartz, M. W., J. H. Thorne, and J. H. Viers. 2006. Biotic homogenization restoration ecology. Ecology and Society 10:19. of the California flora in urban and urbanizing regions. Biological Hobbs, R. J., and D. A. Norton. 1996. Towards a conceptual framework for Conservation 127:282–291. restoration ecology. Restoration Ecology 4:93–110. Seavy, N. E., T. Gardali, G. H. Golet, F. T. Griggs, C. A. Howell, R. Kelsey, Holl, K. D., and E. E. Crone. 2004. Applicability of landscape and island S. L. Small, J. H. Viers, and J. F. Weigand. 2009. Why climate change biogeography theory to restoration of riparian understorey plants. Journal makes riparian restoration more important than ever: recommendations of Applied Ecology 41:922–933. for practice and research. Ecological Restoration 27:330–338. Holl, K. D., E. E. Crone, and C. B. Schultz. 2003. Landscape restoration: Sklar, F. H., M. J. Chimney, S. Newman, P. McCormick, D. Gawlik, moving from generalities to methodologies. Bioscience 53:491–502. S. L. Miao, et al. 2005. The ecological-societal underpinnings of ever- Hunter, J. C., K. B. Willett, M. C. Mccoy, J. F. Quinn, and K. E. Keller. glades restoration. Frontiers in Ecology and the Environment 3: 1999. Prospects for preservation and restoration of riparian forests in 161–169. the Sacramento Valley, California, USA. Environmental Management Sweeney, B. W., and S. J. Czapka. 2004. Riparian forest restoration: why each 24:65–75. site needs an ecological prescription. Forest Ecology and Management Kershner, J. L. 1997. Setting riparian/aquatic restoration objectives within a 192:361–373. watershed context. Restoration Ecology 5:15–24. Teal, J. M., and S. Peterson. 2005. Restoration benefits in a watershed context. Kondolf, G. M., S. Anderson, R. Lave, L. Pagano, A. Merenlender, and Journal of Coastal Research, Special Issue 40:132–140. E. S. Bernhardt. 2007. Two decades of river restoration in California: Thorne, J. H., J. H. Viers, J. Price, and D. M. Storns. 2009. Spatial patterns of what can we learn? Restoration Ecology 15:516–523. endemic plants in California. Natural Areas Journal 29:344–366. Kondolf, G. M., P. L. Angermeier, K. Cummins, T. Dunne, M. Healey, W. Trowbridge, W. B., S. Kalmanovitz, and M. W. Schwartz. 2005. Growth of Kimmerer, et al. 2008. Projecting cumulative benefits of multiple river Valley oak (Quercus Lobata Nee) in four floodplain environments in the restoration projects: an example from the Sacramento-San Joaquin River Central Valley of California. Plant Ecology 176:157–164. System in California. Environmental Management 42:933–945. Tu, I.-Y. M. 2000. Vegetation patterns and processes of natural regeneration in Lite, S. J., K. J. Bagstad, and J. C. Stromberg. 2005. Riparian plant species periodically flooded riparian forests in the Central Valley of California. richness along lateral and longitudinal gradients of water stress and University of California, Davis.

Restoration Ecology 9 Patterns of Riparian Diversity for Restoration

Vaghti, M. G. 2003. Riparian vegetation classiﬁcation in relation to environ- Viers, J. H., J. H. Thorne, and J. Quinn. 2006. Caljep: a spatial database mental gradients, Sacramento River, California. Master’s thesis in Ecol- of Calﬂora and Jepson. San Francisco Estuary and Watershed Science ogy. University of California, Davis. 4:1–18, http://repositories.cdlib.org/jmie/sfews/vol4/iss1/art1/. Vaghti, M. G., and S. E. Greco. 2007. Riparian vegetation of the Great Valley. Ward, J. V., and K. Tockner. 2001. Biodiversity: towards a unifying theme for Pages 425–455 in M. G. Barbour, T. Keeler-Wolf, and A. Schoenherr, river ecology. Freshwater Biology 46:807–819. editors. Terrestrial vegetation of California. 3rd edition. UC Press, Williams, J. W., E. W. Seabloom, D. Slayback, D. M. Stoms, and J. H. Viers. Berkeley. 2005. Anthropogenic impacts upon plant species richness and net primary Vaghti, M., M. Holyoak, A. Williams, T. Talley, A. Fremier, and S. Greco. productivity in California. Ecology Letters 8:127–137. 2009. Understanding the ecology of blue elderberry to inform landscape Wohl, E., P. L. Angermeier, B. Bledsoe, G. M. Kondolf, L. Macdonnell, D. M. restoration in semiarid river corridors. Environmental Management Merritt, M. A. Palmer, N. L. Poff, and D. Tarboton. 2005. River restora- 43:28–37. tion. Water Resources Research 41:W10301. DOI:10.1029/2005WR00 Viers, J. H., M. C. Mccoy, J. F. Quinn, K. Beardsley, and E. Lehmer. 1998. 3985. California rivers assessment: assembling environmental data to charac- Young, T. P., D. A. Petersen, and J. J. Clary. 2005. The ecology of restoration: terize California’s watersheds. 1998 ESRI International User Conference historical links, emerging issues and unexplored realms. Ecology Letters Proceedings. Environmental Systems Research Institute, Redlands, CA, 8:662–673. San Diego, California.

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