COMPOSITION, INVASIBILITY, AND DIVERSITY IN COASTAL CALIFORNIA GRASSLANDS

17 Pages·2001·13.1 MB·English

by  Mark R Stromberg

Madrono, Vol. 48, No. 4, pp. 236-252, 2001
COMPOSITION, INVASIBILITY, AND DIVERSITY IN COASTAL
CALIFORNIA GRASSLANDS
Mark R. Stromberg
Hastings Natural History Reservation, 38601 E. Carmel Valley Road,
Carmel Valley, CA 93924-9141, Museum of Vertebrate Zoology,
University of California, Berkeley, and Natural Reserve System,
University of California
Paul Kephart
Rana Creek Habitat Restoration, 35351 E. Carmel Valley Rd.,
Carmel Valley, CA 93924-9141
Vern Yadon
Director Emeritus, Pacific Grove Museum of Natural History, 1119 Buena Vista,
Pacific Grove, CA 93950
Abstract
We present a detailed floristic study of coastal terrace prairies in central California that are poorly
described in California's ecological literature. Definitive native grasses include Danthonia californica
Bolander, Nassellapiilchra (A. Hitchc.) Barkworth, and Festiica rubra L. Definitive native forbs include
BaccharispiliilarisDC, Viola, Sidalcea, Cammisonia, andAcaena. Species richnessinthecoastalprairies
(1 m-) averaged 22.6, nearly twice that of relatively diverse serpentine California grasslands, and other
North American grasslands. We sampled 33 coastal prairies and found 340 plant species including 258
forbs. Nearby plant communities (Monterey Pine, Coastal Scrub) had much lower species diversity at all
spatial scales studied. Three distinct coastal grasslands, each associated with a land form, can be defined
by distinct species composition; coastal terraces, uplifted "bald hills," and inland ridges. We compared
29 coastal terrace prairies (those without tree or shrubs) to 80 inland Nassella prairies with regard to 27
floristic variables (cover, number of natives/exotics, perennials/annuals, grasses/forbs) along a gradient
from interior-coastal valley and from north to south along the coast. Coastal terrace prairies wereinvaded
by exotics, but far less so than inland Nassella prairies. Species diversity (0.1 ha) and total cover were
positively correlated. Relative cover of exotic species was negatively correlated with total cover, based
on all sites. Number ofexotic species was positively correlated with species richness in inland Nassella
prairies but not in coastal terrace prairies. Canonical correspondence analysis indicatedthatcoastalterrace
prairies with highercoverofnon-native species hadreduced total coverand/orreduced diversity ofnative
perennial species ofgrasses and forbs. Native perennial grasslands, including coastal terrace prairies, are
rare and have been eliminated by development along the narrow corridor of land between the sea and
the inland ridges ofcentral, coastal California. Ifprotection ofbiodiversity is a management goal in land
use plans, coastal grasslands should be protected as biodiversity "hotspots".
Introduction 1995). Cover of exotics is often over 80% in this
annual grassland vegetation type (Biswell 1956).
Native perennial grasslands in California are Yet, small, isolated stands ofnative perennial grass-
among the most endangered ecosystems in the lands still occur and these stands have been used to
United States (Peters and Noss 1995). An area of define "valley grassland" (White 1966b, 1967;
approximately 7,000,000 ha (about 25% ofthe area Robinson 1971), presumably once dominated by
of California) formerly in native grassland or foot- Nassella (Heady et al. 1988). Extensive fragmen-
hill savanna, is now dominated by exotic grass spe- tation of relict grasslands continues (Barry 1972)
cies primarily of Mediterranean origin (Huenneke and even within protected natural areas (Hastings,
1989). Typical annual grassland species include San Bruno Mountain, Jepson Prairie, Santa Rosa
Bromus diandrus Roth, B. mollis, B. riibens L., Av- Plateau), relatively "pure" stands of native grasses
ena barbata Link, A. fatua L., Erodium cicutarium occur in smaller, interior patches. Few studies have
(L.) UHer., E. botrys (Cav.) Bertol, and Vulpia been published to describe the original grassland
myuros (L.) C. Gmelin (Heady et al. 1988). Con- composition or that of presumed remnants. The
version to exotic annual vegetation was so fast, ex- widely held view that interior annual grasslands of
tensive, and complete that the original extent and California were originally dominated by perennial
species composition ofmost native perennial grass- grasses (primarily Nassella) is based on limited ev-
lands is unknown (Burcham 1957; Barry 1972; idence (Hamilton 1998). The view that succession
Keeley 1989; Heady et al. 1992; Holland and Keil proceeds in these interior grasslands to dominance
2001 STROMBERG ET AL.: COASTAL CALIFORNIA GRASSLANDS 237
San Francisco
Monterey Bay California
Morro Bay
H 0 95 190 380
J KLm
Fig. 1. Map of study sites on coastal California.
by Nassella (Heady et al. 1988) is not supported by and Danthonia californica; they used the term
long-term studies (Stromberg and Griffin 1996) or "coastal terrace prairie" to describe this commu-
a critical review of evidence (Hamilton 1998). nity. "Northern coastal grassland community" with
Large areas of the interior "valley grassland" the same dominant grasses, as well as Calama-
(Heady et al. 1988) may have been dominated by grostis nutkaensis (C. Presl) Steudel and Des-
native, annual forbs (Schiffman 1994; Schiffman champsia cespitosa (L.) Beauv., has been described
2000). Identification ofthese rare, scattered patches as extending from San Francisco northward to the
ofhigh biodiversity continues to be a critical activ- Klamath Mountains and in patches south to San
ity for conservation (Myers et al. 2000). GAP anal- Luis Obispo (Holland and Keil 1995). Finally, a
ysis and remote sensing serve as useful tools, but "tufted hairgrass community—" has been defined
to identify the most important habitats at a finer where Danthonia is dominant this series is part of
geographic scale, we need intensive field surveys the "coastal prairie, which extends inland from ter-
using classical methods, as presented here. races to bald hills" (Sawyer and Keeler-Wolf
The purpose of this study is to demonstrate that 1995). Such "bald hills" are a common feature
California's coastal grasslands are previously un- along the coast and arise abruptly inland from the
recognized biodiversity hotspots. We will do this coastal terraces. Coastal prairies occur on poorly
by presenting patterns of diversity, describing ma- drained soils, often clays derived from serpentine
jor gradients in diversity within habitats and com- outcrops, and often occur on a series of former
pare the coastal grasslands with other nearby hab- coastal terraces that through geological action have
itats and other United States grasslands. been moved inland and uplifted. As one moves in-
California's coastal grasslands are poorly de- land, "ecological staircases" grade into drier, high-
scribed in the literature. "Coastal terrace prairie" er interior ridges (Westman 1975; Cylinder 1995).
has had widely varying interpretations. (Kuchler Most ofthese interior ridges are forested, but many
1964) described "coastal grasslands" in a general sustain open grasslands. Further inland, conifer for-
way. Others have defined "north coast prairies" by ests are replaced by oaks and typical "annual grass-
listing dominant species that extend from the Men- land" oak savanna (Barbour and Major 1995, Hol-
docino coast south to Point Lobos (Heady et al. land and Keil 1995). Monterey pine forests are of-
1988). They described north coast prairies as being ten adjacent to coastal terrace prairies in the central
dominated by Festuca idahoensis Elmer, F. rubra coast of California. Shrubs (e.g., Baccharis)
238 MADRONO [Vol. 48
a 50.0
^
Coastal Terrace Prairie
45.0-
-e- Inland Nassella Prairie f
40.0-
Monterey Pine Forest
S 35.0-
T /
g,30.0- ?=
iT
O
25.0-
^ 7
20.0
i
Z=5 /
_L
15.0-
/
10.0-
r +- 4-4-
5.0-
0.0-
0.10 0.30 0.50 0.70 0.90 1.10 1.30 1.50 1.70 1.90 1000
Area Sampled m)
(sq.
Fig. 2. a) Average number of species present as sampling areas are added in three coastal California plant commu-
nities, ±1 standard error.
(McBride and Heady 1968) or trees (e.g., Pimis ra- general discussion of patterns in species diversity
diata D. Don) (Callaway and Davis 1993) invade (Tilman et al. 1997, Huston et al. 2000, Kaiser
these coastal grasslands without fire or grazing. 2000) and the relationship between species diver-
Pre-settlement fires in coastal grasslands were fre- sity and invasive species (Symstad 2000) in land-
quent, with 2-10 year return intervals (Greenlee scape studies (Stohlgren et al. 1997).
and Langenheim 1990). Post-settlement distur-
bances have included year-round grazing by do- Study Areas
mestic livestock (Mack 1989). In most descriptions
ofcoastal grasslands, Nassellapulchra is aco-dom- Thirty-three stands ofcoastal terrace prairie were
inant. sampled, from Avila Beach, north along the Big
Native perennial grasslands persist along a con- Sur coast to Pebble Beach and then north from
tinuum ranging from dominance by non-native spe- Santa Cruz to San Bruno Mountain near San Fran-
cies to being relatively free from exotics (Harrison cisco (Fig. 1). Stands were selected based on pre-
et al. 2001). In this case, we examined species com- vious extensive botanical surveys ofcentral coastal
position, invasibility, and diversity change along a California grasslands (Kephart 1993; Yadon 1995;
gradient from central coast terraces inland to Cali- Stromberg and Griffin 1996). Stands were not re-
fornia's central coastal mountain ranges (here, the cently grazed or cultivated and were initially se-
Sierra de Salinas). Our previous studies of the in- lected based on co-dominance of Deschampsia or
land Nassella prairies investigated the role of go- Danthonia.
phers, grazing, and historic cultivation (Stromberg Data from other studies were discovered and
and Griffin 1996). Here, we extend our studies to- used. In 1965 and 1966, 46 homogenous stands of
wards the coast to include grasslands that can be Monterey pine {Finns radiata) forests were sam-
recognized as coastal terrace prairies by the con- pled from Cambria to Ano Nuevo (White 1966a,
stant presence of Danthonia califoniica and Nas- VogI et al. 1988). In 1993, 141 homogenous stands
sella. We provide a background ofdata on the more of coastal scrub were sampled from San Simeon to
2001] STROMBERG ET AL.: COASTAL CALIFORNIA GRASSLANDS 239
^ o
^ ^ o^o O^N o
Area Sampled m)
(sq.
Poppy Hills Animas RSC
PebbleFor Barker2
Pt. Lobos Flat BirdRock I
Pt. Lobos Mima BirdRock2
--
SanBruno 1 Danthonia RSC
SanBruno2 Diablo SLH
SodaSpring Olson Hill
-H- Spruance FishRanch
1
Work Ranch Fish Ranch 2
-N- Laureles Burn -B- Ft. Ord Torro
-O-
Canada 3 JadeFlat
CW
PineTree Molera
-h- CW LowPine Piedras LH
-M- CW Garage Piedras 1
CW
BigPool Piedras2
-e- Swale4 Plaskett Ridge
Fig. 2. Continued, b) Species/area curves for individual sampling localities.
MADRONO
240 [Vol. 48
Point Lobos (Heuer 1994). In 1991, 80 inland Nas- lems (Tausch et al. 1995) have been addressed, and
sella prairies in the Sierra de Salinas were sampled the method we used is inherently robust (Leps and
(Stromberg and Griffin 1996). Species richness de- Hadincova 1992).
pends on the scale of sampling (Gross et al. 2000) Species composition of the herb layer was ob-
so comparisons to other studies were made at sim- served using similar methods in 46 stands ofMon-
ilar scales (1 sq. m). terey pine forests. Discovery ofarchival records (K.
White, unpublished data, Hastings archives) al-
Methods lowed us to include observations from 40 to 80
quadrats (20 cm X 50 cm; 0.1 m-) that were read
Sampling was done at the peak of the flowering as above for plant cover. A larger area of 0.1-1 ha
season, from mid-April through May in 1996 and was then searched for additional species present
1997. At each grassland stand (Fig. 1), we chose a and each was recorded (K. White, unpublished
homogenous area and flagged a 50 m X 20 m plot data; Hastings archives).
(0.1 ha) with the long axis parallel to topographic Discovery ofadditional comparable data allowed
contours. We recorded presence ofall plant species us to include comparisons to coastal shrub com-
we could discover on the larger plots. Starting from munities (Heuer 1994). Coastal shrub communities,
the midpoint of the short axis, we placed steel often adjacent to coastal terrace prairies, were sam-
quadrats (20 cm X 50cm; 0.1 m^) at 2.5 m intervals pled with 16 sq. m quadrats at 141 locations, again
along the 50 m midline ofthe 0.1 ha plot (20 quad- at the peak of the flowering season, in 1993. No
rats/plot). For each quadrat, we recorded a cover larger sampling areas were surveyed for additional
class for canopy cover of all plant species we ob- species (Heuer 1994) and only the larger (16 sq. m)
served (Daubenmire 1959). Quadrats were painted quadrats were used.
to facilitate recognition ofDaubenmire cover class- Inland Nassella prairies were described in detail
es. A cover value of 0.01 was assigned to each previously (Stromberg and Griffin 1996). We in-
species seen only in the larger plot and not seen in cluded inland prairies in this study to examine the
any smaller quadrat. Cover for each species at each larger scale differences across the landscape as in-
stand (site) was calculated by averaging midpoints land Nassella prairies share Nassella and other spe-
of the cover classes assigned to each of species in cies with coastal terrace prairies, but occur at a dri-
m
the 20 quadrats. Stands were at least 200 apart, er, inland part of an environmental continuum oc-
and more often, many kilometers apart. For each cupied by native grasslands in coastal California.
stand, we recorded aspect, elevation, distance in- Data sets from this study will be made available
land from the coast, latitude and longitude (UTM), (ESA Ecological Archives or NRS archives).
total number of plant species (Hickman 1993), soil
type, land form, number of grasses and forbs, and Results
numbers of perennials and annuals, native and ex-
otic. Species were counted based on scores in suc- Average species richness varies with the area
cessive quadrats on original field sheets; one coastal sampled (Fig. 2). For individual sites, most reach
terrace data sheet was inadvertently lost after tran- an asymptote by about 2 m (Fig. 2a). No definitive
scribing summary numbers so the species tally by asymptote is reached for the average coastal terrace
area for one coastal terrace is missing. Nine soil prairie/Monterey pine forest (CTP) or (MPF). Spe-
series were included (Cook 1978; Ernstrom 1984). cies counts at 0.1 ha represents the best estimates
Land forms of coastal terrace prairies include: 1) for total species richness. Mean species numbers
coastal terraces immediately adjacent to the ocean between all pairs are significantly different (paired
that are almost level; 2) grasslands on the sides of t-tests, P < 0.001) for comparisons at 1 sq. m. and
isolated bald hills arising inland and up at least 10 at 0.1 ha (Table 1).
m from the terraces, sometimes locally known as This comparison of species richness with area
"potreros"; and 3) drier, inland ridges well over leads to an interesting observation on the effects of
100 m above the coastal terraces and bases of the a major human-directed use of the ecosystem. In a
inland mountain ranges. Staview 5.0 (SAS) was previous analysis of inland Nassella prairie stands
used for statistical comparisons. Bonferroni/Dunn with and without active grazing by domestic cattle,
post-hoc tests were included to show individual dif- significantly fewer plant species were observed in
ferences in pairwise comparisons (P = 0.05). We grazed stands (Stromberg and Griffin 1996) based
used several methods to order stands based on spe- on areas of 0.1 ha. In this analysis of species num-
cies composition and with regard to measures of ber at a smaller sampling scale (1 sq. m), this pat-
diversity, including CCA, DCA and Bray-Curtis or- tern in species richness was reversed and is clearly
dinations (PC-ORD ver 4) (ter Braak 1987a, b; dependent on scale (Fig. 2).
McCune and Mefford 1999). Stand coordinates in Coastal grasslands have much greater species
our ordination were based on species data. We richness in comparison to inland Nassella grass-
dropped species that occurred in only one stand lands, coastal pine, or coastal scrub plant commu-
with a cover value less than 5% in order to reach nities. A total of 82 species of grasses or sedges
a numerical solution forCCA. Computational prob- and 258 species of forbs (340 total) were found in
2001] STROMBERG ET AL.: COASTAL CALIFORNIA GRASSLANDS 241
Table L Comparisons of Species Diversity Between Coastal Terrace Prairies (CTP), Inland Nassella Prairies
(INP) AND Monterey Pine Forests (MPF) Based on First Ten 0.1 sq. m Observations (1 sq. m) in Each Sample.
Coastal scrub species density was derived from 16 sq. m. quadrats at each stand, expressed here as species/sq. meter
using S cA' where z = 0.25.
Number of species
per square meter Count Mean Std. err.
Coastal Terrace Prairies 32 22.6 1.58
Inland Nassella Prairies 80 14.7 0.78
Monterey Pine Forests 46 6.2 0.58
Coastal Scrub 141 5.5 0.20
Comparison of means
(INR CTR MPF) DF Mean square F value P-value
Category 2 2615.2 62.9 <0.00()1
Residual 155 41.6
33 coastal terrace prairie stands. In 80 inland Nas- and North America (Table 2) when each is pre-
sella prairie stands, a total of 194 species were sented at a comparable scale (1 sq. m).
found; 136 plant species were found in 48 coastal Preliminary Bray-Curtis ordinations of the 33
Monterey pine stands (Vogl et al. 1988). Many few- stands revealed that both stands at Bird Rock and
er plant species (65 total) were found in 141 coastal both forest stands in Pebble Beach (Poppy Hills, 24
scrub stands. Species richness (species/sq. m) in Padre Lane-Table 4) were outliers. Although elim-
coastal prairies is about 3.5 times greater than in inated, they offer insights to dynamics of coastal
adjacent Monterey pine forests (Table 1) and nearly prairies. Samples at Bird Rock had unusually high
4 times greater than in adjacent coastal scrub. cover of Carex pansa L. Bailey (68% and 18%,
Coastal prairies also have a much greater species respectively). Carex pansa was only found in two
richness compared to other grasslands in California other stands, and there it was not abundant (cover
35
M M M
0
1 I I I I I I I I I I I I I I I
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 1000
Area m)
(sq.
Fig. 3. Average number of species present as sampling areas are added in 43 ungrazed (1937-1991) inland Nassella
prairies and 37 grazed (1880-1991) inland Nassella prairies (Stromberg and Griffin 1996).
MADRONO
242 [Vol. 48
Table 2. Comparison of Species Richness (Species/sq. m, ± SD or ± SE) in California Grasslands and Other
Arid Western Plant Communities. Species codes: Agr spi, Agropyron spicatum; Agr smi, Agropyron smithii; Amo
can, Amorpha canescens; Art tri, Artemesia tridentata; Fes ida, Festuca idahoensis Elmer\ Sti let, Stipa lettermanii;
Poa pra, Poa pratensis.
Community name Species density Reference
Coastal Terrace Prairies 22.62, +- 8.9 This study.
Napa Co.-L. Berryessa, CA 12.3, -+- 2.3 (Harrison 1999)
Serpentine Meadows
Napa Co.-L. Berryessa, CA 10.3, +- 2.2 (Harrison 1999)
Non-Serpentine Meadows
Monterey Co., Sierra de Salinas, CA 14.7, -+- 0.7 (Stromberg and Griffin 1996)
Annual Calif. Grassland
WY
Bighorn Basin, C. 10.2, -+ 0.5 (Stohlgren et al. 1999a)
Agr spi/ArtNtrWi WY
Grant Teton, 8.9, 0.6 (Stohlgren et al. 1999a)
Agr spi/Art tri
Gunnison, W. CO 8.8, -+- 0.4 (Stohlgren et al. 1999a)
Sti let/Art tri
Wind Cave, W. SD 8.7, 0.5 (Stohlgren et al. 1999a)
Poa pra/Amo can
Charles Russell NWR, E. MT 4.6, + 0.5 (Stohlgren et al. 1999a)
Agr smi/Art triWY
Yellowstone, W. 9.0, 0.6 (Stohlgren et al. 1999a)
Fes ida/Art tri
Pipestone N.M., S. MN 12.2, + 0.7 (Stohlgren et al. 1999b)
Tallgrass Prairie
WY
Cheyenne, SE. 10.7, H- 0.5 (Stohlgren et al. 1999b)
Mixed-grass Prairie
Pawnee Butte, NE CO 8.5, -1- 0.4 (Stohlgren et al. 1999b)
Short-grass Prairie
<5%). Bird Rock 2 was the only stand to have ridges, as will be seen in a pattern extending to
more than 10% LoUum multiflorum Lam. with inland Nassella prairies (below) show more domi-
34.4%. Padre Lane was the only stand where we nance by annual exotic forbs (Table 3-h) and other
found Phalaris caUfornica Hook & Arn. and Hier- exotics in general (Table 3-i) than the more diverse,
ochloe occidentalis Buckley and was one of only bald hill coastal terrace prairie.
two stands with Piniis radiata (11%). Poppy Hills Both inland Nassella prairies and coastal terrace
also had some Piims radiata (2%), but was the only prairies show an increase in the number of native
stand with Rubus ursinus Cham. & Schldl. or to species with total species richness in 0.1 ha plots
have >1% Arctostaphylos hookeri G. Don (10%). (Figure 6-a, b). The number of exotic species also
Because these four stands have such exceptional increases with species richness in inland Nassella
composition, they confound analysis of the other prairies but not in coastal terrace prairies (Figure 6-
open coastal prairies and were subsequently c, d). The relative cover of exotics decreases in
dropped from more detailed analysis of coastal ter- both inland Nassella prairies and coastal terrace
race prairies. prairies with species richness (Fig. 6-e, f). One rel-
Ordinations ofspecies composition data from the ative outlier (Fig. 6-f) is instructive. This stand, Pie-
29 coastal terrace prairies showed that different dras Blancas-1, is unusually low in both relative
land forms ("inland ridges,"" "coastal terraces," cover of exotics and species richness because it is
and "bald hills" above coastal terraces) each have the only stand with 95% cover of one native, the
a relatively distinct species composition. This was perennial grass {Deschampsia cespitosa van holci-
supported by results of the analysis of variance for formis). In some cases then, relative cover of ex-
individual measures. Comparisons ofthe three land otics can be low (—1%) even with low species rich-
forms of coastal terrace prairies showed that bald ness (—34) if the total cover of the site is high.
hills have more species ofgrasses and sedges over- Including all coastal terrace prairies and inland
all (Table 3-a), more native grasses and sedges (Ta- Nassella prairies, species richness (0.1 ha) and total
ble 3-b) and more native forbs at both scales of cover were positively correlated (R^adj = 0.18, F =
sampling (Table 3-c, d) and so more species of na- 24.8, P < 0.001, residual df = 107) and relative
tive plants overall (Table 3-e). Th—e cover of the cover ofexotic species is negatively correlated with
native plants show a similarpattern Bald Hills has total cover (R-,j, = 0.19, F = 25.6, P < 0.001,
more cover ofnatives (Table 3-f), particularly more residual df = 107). Native species richness (0.1 ha)
cover of native perennial forbs (Table 3-g). Inland and exotic species richness were positively corre-
I 2001] STROMBERG ET AL.: COASTAL CALIFORNIA GRASSLANDS 243
Table 3. Based on Open Coastal Grasslands, Differ- lated for inland Ncissella prairies (R-;,,,, = 0.23, F =
ences Between Mean Values From Coastal Terraces 24.6, P < 0.001 residual df = 78) but not forcoast-
AI(CnnTta,elryiNsoir=sDor1f0y),VRaCirodigaaenssctea(.lIRB.Boannlfde=rrH9oi)nlila/srDeu(nSBnHh,opwonsnt-=Bhaosc10ecdaonmon-d ralestiedruia-alcedfpra-ir2i7e,)s.(R- = 0.02, F = 0.67, P < 0.001,
parison (e.g. BH, CT) are shown only with a significance Consideringjust the 29 open coastal terrace prai-
level of 0.05. Residual df = 26 in all 2-way ANOVA. ries, grasses and forbs differ in how they vary with
Arcsin-square root transformation ofratio data were done species richness at 0.1 ha. On this scale, neither
before ANOVA; results expressed below in ratios. total vegetative cover nor cover ofnative species is
related to species richness. However, cover of all
a. SpecieFsm=oefa3G.nr61a,ssesPstadn=.de0rS.re0od4rges 0.1 ha iexnogtiscpescpieecsiersicdhencersesas(eRs-ads,ig=nif0i.c1a5n,tlyFwi=th6.i0n,crPeas<-
0.05, residual df = 27). This decrease in cover of
CBTH 1145..54 11..24 BH, IR P < 0.05 elxarogteilcys dwuiethtoatnheidneccrreeaaseseiinn cspoevceiresofreixcohtniecssgrawsass-
IR 11.0 0.8
b. SpecieFsmo=efa6Nn.a1t,ivePsGtrd=a.s0ser.er0so0ra6nd Sedges 2 sq. m teFsi.v=elCy4o.vc9oe6rr,rePolfa<teedx0o.wt0ii5tc,hrgserpsaeiscdsiueawslardsifchs=ingen2si7sf)i.(cRaN^ndet,ilty=hen0re.g1ta2h-,e
cover of exotic forbs or the number of exotic forbs
CBTH 1145..54 11..24 BH, IR P < 0.05 was correlated with species richness in coastal ter-
IR 11.0 0.8 race prairies. The degree to which the grasses are
c. Species of Native Forbs 0.1 ha native increases with species richness; the number
F = 3.92, P = 0.032 ofnative grasses is correlated with species richness
mean std. error (R-,d, = 0.14, F = 5.56, P < 0.05, residual df =
CT 17.6 2.6 27) although the cover of native grass is not cor-
BH 28.9 3.4 BH, CT P < 0.05 related. The degree to which forbs are native also
IR 20.4 3.0 increases with increasing species richness. In this
d. Species of Native Forbs 2 sq. m case both cover and number ofnative foibs (0.1 ha)
F = 3.45 P = 0.04 were significantly correlated with species richness
mean std. error (respectively, R-.j, = 0.29, F = 12.9, P < 0.001,
CT 9.7 1.9 i-esidual df = 27 and R-,,,, = 0.83, F = 136, P <
BH 17.1 2.3 BH, CT P < 0.05 0.001, residual df = 27).
IR 13.4 1.9 The summary of the 25 most frequent and dom-
e. Species of Native Plants 0.1 ha inant species of grasses and sedges in the coastal
F = 4.39 P = 0.02 prairies (Fig. 4) reveals that coastal prairies are
mean std. error heavily invaded with non-natives. The widespread
CT 25.1 2.9 fescue, Vulpia spp. is in most samples and is often
BH 36.7 3.8 BH, IR P < 0.05 very abundant. Danthonia califomica, Nassella
IR —24.6 2.9 pidchra, and Festiica rubra are the native grasses
f. Cover Native Plants that define this community. A summary of the 25
F = 7.02. P = 0.036 most frequent and dominant species of foi^bs in
mean std. error coastal prairies (Fig. 5) show a similar dominance
CT 67.7 8.8 CT. IR P < 0.01 by non-natives; in this case by widespread PJan-
BH 77.7 5.3 BH, IR P < 0.01 tago, Erodiiim, and Hypochaeris, all of which ex-
IR —42.9 4.6 tend well inland. Most important natives include
g. Cover Native Perennial Forbs the very similar Plantago erecto E. Morris and
F m=ea3.n89, Pstd-. 0e.rr0o3r5 Baccharis pilitlaris. These natives, along with Vi-
ola, SidaJcea, Caminisoiiia, and Acaena are the na-
CBTH 2112..42 42..77 BH, IR P < 0.05 ctiovaestaflorpbrsairtiheast. Icnomtphilsetceointmhuenidteyf,initthieondoomfintahnecsee
IR 8.6 1.6
— ofgrasses drops offrapidly (Fig. 4), while the cover
h. CoverF =An6n.u8a4,l ExPot-ic0.Fo0r0b4s and frequency of the forbs is far greater for more
mean std. error species (Fig. 5).
CT 9.7 2.3 CT, IR P < 0.05 Dominance ofexotic grasses and forbs in coastal
BH 6.9 1.7 BH, IR P < 0.05 terrace prairie increases inland coastal terraces, to
IR 20.6 3.9 bald hills, and further to the drier ridges (Table 3).
i. Ratio of Exotic Species/Total Forb Cover For coastal prairies, the average ratio ofthe number
F = 4.86, P = 0.016 of exotic grass or sedge species to total species
mean std. error present is 0.44, and the average ratio ofexotic forb
CT 0.48 0.069 species is 0.33 (n = 33). Corresponding average
BH 0.37 0.048 BH, IR P < 0.05 ratios of exotic species in inland Nassella prairies
IR 0.63 0.025 are 0.79 and 0.19 (n = 80).
0
244 MADRONO [Vol. 48
Table 4. Stand Names and Locations (UTM) Included in Sampling of California Coastal Grasslands.
No. Stand name Abbreviation East North Soil type
Rarkpr Ranph T fiiirplp>; RiHcrp 614.291 4041710 oCa.nc^iy TLoam
2. Barker Ranch Laureles Ridse Rarkpr 2 613.835 4041 Sa.ndy Loa.m
3. Bird Rock Inland terrace Bird Rock 1 593.202 4050 157 Sand
4. Bird Rock Inland terrace Bird Rock 2 593.177
5. Canada Woods Site No. 4 CW No. 4 603.776
76.. CCaannaaddaa WWooooddss,, GLaorwaegrePSiintee Tree CCCWWW GLaorwagPeine 660043..150000 44004487.520000 fv_^-li^ciiyv TL/Wc'iAimii
98.. CCaannaaddaa WW^ooooddss, PSiwnaeleTree CCWW PSiwnaeleTree 660036686000 44004469910000 rv~^^ild^i.\y/ JT-^rU\dc\-ri\i~\i
10. Canada Woods, Big Pool Big Pool 604085 4046295
11. Fish Ranch above Entrance Rd. Fish Ranch 1 597.300 4042.694 ^ilt\/ T c\'Am
12. Fish Ranch, above Entrance Rd. Fish Ranch 2 597.313 4042.692 Silt T opim
13. Fort Ord, opposite Toro Park Ft OrH Torn 615.941 4052 1 1 oVcQinl/lHU\.y/ TJ_-o<UQcTiTllil
14. Jade Flat Central Terrace Jade Flat 638 283 3975.370 OCljJCllLiilC V^ldy
15. Laureles Grade, Laureles Ridge Laureles 611.870 4043.319 Sandy Loam
16. Molera State Park N. Terrance Mnlpra 602.546 4016610 ^IqiiH T C\C\X\~\
17. Olson Hill, Diablo Canyon Ov_lyisoowini H1Xi1l1l1 698.859 3896.149
18. Pebble Beach, 24 Padre Lane Pebble For 592 366 4048055 L^KJCLVVVy OdllU.
19. Plaskett Ridge, Above Camp Plaskett Rdg 638.277 3975.359 OCljJCllLlllC XVCdV
20. Point Lobos, Escobar Flat Pt. Lobos Flat 597.250 4042.194
21. Point Lobos, Mima Mounds Pt. Lobos Mima 584.700 4041 300
22. Poppy Hills, Opposite GolfClub Poppy Hills 595.225 4048 980 SiinHv T o^im
23. Pt. Piedras Blancas Light House Piedras LH 646.262 3948.422 Sand
24. Pt. Piedras Blancas Terrace 1 Piedras 1 654.425 3951.349 Loam
25. Pt. Piedras Blancas Terrace 2 Piedras 2 654.347 3951.341 Loam
26. Rancho San tarlos, Animas Entr. Danthonia RSC 600.086 4040.213 Clay Loam
27. Rancho San Carlos, Animas Rdg. Animas RSC 600.071 4041.197 Clay Loam
28. San Bruno Mtn., Great Meadow San Bruno 1 548.059 4171.974 Loamy Sand
29. San Bruno Mtn., Great Meadow San Bruno 2 549.274 4171.733 Loamy Sand
30. San Louis Hill, Diablo Canyon San Luis Hill 703.599 3893.915 Clay Loam
31. Soda Springs, BluffW. ofHwy 1 Soda Spring 646.266 3965.330 Serpentine Rock
32. Spruance Meadow, Spruance Dr. Spruance 595.662 4047.953 Loamy Sand
33. Work Ranch, Hwy 68 Work Ranch 603.586 4048.821 Sandy Loam
We used CCA to sort out which individual com- tinguishes between coastal terrace prairies into
parisons ofcommunity characteristics (measures of those with relatively more dominance by exotic
diversity and the degree of invasion by exotic spe- species (Piedras Blancas Light House, Fish Ranch,
cies) are most closely associated with vegetation etc.) and those with relatively high cover ofnative,
composition across the landscape gradient from in- perennial forbs (San Bruno, Soda Springs, Piedras
—
land Nassella prairies to coastal terrace prairies. Blancas 1, etc.) (Fig. 7 joint plot).
Some of these measures were highly correlated, so By restricting our focus to only coastal terrace
we proceeded with only 19 (Table 5). Plant species prairies, we can examine the pattern of species
with total cover of less than 0.05% and which oc- composition and floristic characteristics at a smaller
curred in 5 orfewer stands were eliminated, leaving scale. By dropping the 80 inland Nassella prairies,
192 species. With these simplifications (tolerance the number of plant species (total cover >0.5%)
set to O.lOOOOOE-12), PCord reached a CCA solu- included in the CCA dropped to 149. Correspond-
tion after fewer than 100 iterations. InlandNassella ingly, more of the floristic variables were highly
prairies were clearly grouped to the left (Fig. 7) and correlated (Table 5) and only 12 were relatively in-
coastal terrace prairies were on the right. The high- dependent. Ajoint plot (Fig. 8) shows many coastal
est "intraset correlation" (ter Braak and Smilauer terrace prairies in a group with relatively high cover
1998) with this first axis was the cover of native, of exotic species. The highest intra-set correlation
perennial grass and on the second axis, the cover with the first axis was with cover ofexotic species.
of exotic species (Fig. 7). Coastal terrace prairies The highest intra-set correlation with the second
are characterized as having both more species and axis was with the number of native forbs. Stands
higher cover of native perennial grasses than any such as San Bruno, Soda Springs, the stands near
ofthe tightly grouped (thus similar) 'm\2Lr\dNassella Avila Beach (Olson Hill, San Luis Hill) are ex-
prairies that are clearly placed to the left ofthe first emplary coastal terrace prairies with fewer exotics
axis where stands can be described as having higher and higher cover of native forbs. The Point Lobos
cover of annual, exotic forbs (for example, Ero- Mima mound prairie and Piedras Blancas 1 are
dium cicLitarium (L.) L. Her). The second axis dis- coastal terrace prairies with fewer exotics, higher
STROMBERG ET AL.: COASTAL CALIFORNIA GRASSLANDS 245
Dominant Grasses/Sedges - Coastal Grasslands
^100
Deschampsia cespitosa cespitosa
Vulpia niyuros myuros ElymUS glaUCUS
Native
Danthonia californica JunCUS bufonius Non-Native
I 1
Bromus hordeaceus
Lolium multiflorum
Nassellapulchra Avena barbata
10 Aira caryophyllea Nassella cernua
Briza minor Hordeum branchyantherum
Festuca rubra
Deschampsia cespitosa holciformis
Avenafatua Bromus carinatus
Loliumperenne Hordeum marinum
Juncuspheocephalus
Distichlis spicata
Bromus diandrus Leymus triticoides
Briza maxima
li Nassella lepida
Inn III.
0.1
Species Importance Order
Fig. 4. Importance value (frequency X average percent cover) ofthe 25 most dominant species ofgrasses and sedges,
averaged from 29 coastal terrace prairies in central, coastal California.
cover of native forbs and more native grasses (Fig. cies may occur more readily in areas oflow species
—
8 joint plot) while stands clustered on the left side diversity than in areas of high species diversity
relatively more cover of exotic species. (Darwin 1859). Plant communities with low species
Soils and locations of the various sites are de- diversity (and total cover) may use resources less
scribed in Table 4. Fourteen of the coastal terrace completely, allowing invasion by similar species
prairies (44%) occurred on soils with a hardpan (MacArthur and Wilson 1967; Pimm 1991; Tilman
from 10-20 cm beneath the surface. An additional et al. 1997). Evidence for this relationship between
three coastal terrace prairies occurred on serpentine diversity and invasions in grasslands depends on
rock or clay with limited drainage. A hardpan that scale, and at a landscape scale, may be reversed
provides standing water during the winters was of- (Stohlgren et al. 1999b). Based on the number of
ten present, but apparently not required. Coastal species, our studies do not support the theory that
terrace prairies also occurred on sands, loams and exotics are more abundant where species diversity
clays. is relatively low; inland Nassella prairies (but not
coastal terrace prairies) with the highest diversity
Discussion have more exotic species (Fig. 6c, d). But, numbers
Diversity of plant species in coastal terrace prai- of species probably do not reflect ecosystem func-
ries is among the highest in grasslands of North tion. Species occupying more space intercept more
America (Stohlgren et al. 1999b). County and wild- light, and presumably are more important in nutri-
land planners often have selected coastal terrace ent capture and storage. In both inland Nassella
prairies for development, perhaps not recognizing prairies and coastal terrace prairies, most species in
the biodiversity of coastal terrace prairies or be- our grasslands have cover <5%. Two species may
cause political support to protect forests or coastal be equally counted as present, but one may occupy
scrub has been comparatively well organized. If far more cover in the community. Based on relative
protection ofbiodiversity is a goal, then coastal ter- cover (Figs. 6e, f, 7) both diverse inland Nassella
race prairies should be protected and development prairies and coastal terrace prairies have reduced
should be focused on relatively species-poor plant exotic dominance, supporting the theory that less
communities. diverse communities are more likely to be invaded.
Invasions of natural communities by exotic spe- Ordinations of the species and stands agree with