CONSERVATION OF PERIPHERAL PLANT POPULATIONS IN CALIFORNIA

2006·10.1 MB·English

by  Gordon Leppig

Madrono, Vol. 53, No. 3, pp. 264-274, 2006
CONSERVATION OF PERIPHERAL PLANT POPULATIONS IN CALIFORNIA
Gordon Leppig
California Department of Fish and Game, Northern California-North Coast Region,
CA
Habitat Conservation Program, 619 Second St., Eureka, 95501
[email protected]
Jeffrey W. White
Department of Biological Sciences, Humboldt State University, Areata, CA 95521
WW [email protected]
j 1
Abstract
Theconservation ofperipheral plant populations isparadoxical. Populationsoccurringon theedge
ofa species' range tend to be smaller, more isolated, and more genetically and ecologically divergent
than central populations. The combination of these characteristics can impart novel evolutionary
potential and local ecological significance, thus heightening their conservation value, while also
makingthemlessviableandmorepronetolocalextinction. Publicpolicysupportstheconservationof
peripheral populations, despite the commonness ofthe species elsewhere. However, the conservation
of significant peripheral populations of nonlisted plants has been arbitrary and ineffective. The
absence ofexplicit criteria to determine the conservation value ofperipheral plant populations, the
lack offiner-scaledata on plantdistributions, and ageneral unawarenessoftheirvaluehavehindered
efforts toconserve them. We review theconservationvalueofperipheral plant populationsand, using
Californiaasanexample,describeregulatorymethodstoimprovetheirconservation.Wealsopropose
a scheme to assess a population's conservation value.
Key Words: California flora, CEQA, HCP, local rarity, NCCP, peripheral populations, rare plants.
Peripheral populations occur on the geograph- occupy suboptimal or different habitats than
ic edge of a species' range. Depending on the more-central conspecifics (Soule 1973; Hoffmann
scale used to define them, peripheral populations and Blows 1994; Lesica and Allendorf 1995).
can be completely isolated from conspecifics, and Morphological or ecological divergence in pe-
therefore considered disjunct, or can occur in ripheral populations resulting from differing
closer proximity to other marginal populations. geographic selection regimes is one form ofclinal
While the evolutionary significance ofperipheral variation and can be a precursor to speciation
populations has long been recognized, other than (Mayr 1970; Garcia-Ramos and Kirkpatrick
for rare, threatened, or endangered species, their 1997). Due to the greater influence ofpopulation
conservation value typically receives little atten- bottlenecks, founder effect, and genetic drift,
tion. peripheral populations can be genetically distinct
In this paper, we review the conservation value from central populations. These differences in
ofperipheral plant populations. Using California genetic structure can result in distinct genotypes
as an example, we highlight how regulatory and phenotypes and impart enhanced evolution-
policy can and should be utilized to conserve ary potential for adaptation and speciation
biologically and culturally significant peripheral (Levin 1993; Garcia-Ramos and Kirkpatrick
populations of otherwise-common species. We 1997; Lammi et al. 1999). Thus, the combination
also propose a scheme to assess the potential of geographic isolation and genetic divergence
conservation value of peripheral populations. driven by directional selection can give peripheral
Due to their geographically marginal location, populations novel evolutionary trajectories, in
peripheral populations tend to exhibit lower and comparison to central populations (Lesica and
more-variable densities and are more fragmented Allendorf 1995; Nielsenet al. 2001; Gaston 2003).
than central populations in a species' range The isolation and decreased population size or
(Fig. 1) (Mayr 1970; Lawton 1993; Channell abundance of peripheral populations, for in-
and Lomolino 2000; Gaston 2003). For plants, stance, strongly favors the evolution of self-
peripheral populations are more likely to be compatible breeding systems in otherwise self-
influenced by different selective factors than incompatible species (Busch 2005).
central populations, including climate and soils, Small, isolated populations, as often occur on
plant community assemblages, and disturbance the periphery of a species' range, also tend to
regimes (e.g., fire intensity and interval). Ecolog- have lower levels of heterozygosity and allehc
ically distinct peripheral populations also can variation than larger, more-central populations
occur when geographically marginal populations (Lesica and Allendorf 1992, 1995; Lawton 1993;
2006] LEPPIG AND WHITE: CONSERVATION OF PERIPHERAL PLANT POPULATIONS 265
Contrary to Peterson (2001), under certain
Incomparisontocorepopulations,peripheral circumstances, geographic isolation actually pre-
populationstendto: disposes peripheral populations to a greater
survivorship than larger, more-central popula-
tions. In analyzing range contractions of 245
•be smaller, plant and animal species, Channel! and
•havemore-variabledensities, Lomolino (2000) found that when species un-
•beecologicallydistinctive, dergo catastrophic range contractions (>75%),
•occurinmarginalhabitats, populations on the edge of the range have
•experiencedifferentselectiveregimes, significantly greater survivorship than core pop-
•haverestrictedgeneflow, ulations. This enhanced survivorship is the
•undergogreaterrates ofgeneticdrift, result of localized extinction events being
•havelessgenetic variation, primarily both anthropogenic and spatially auto-
•haveincreasedpopulation-level correlated. In other words, populations that
differentiation, persist the longest and act as refugia for a species
•havegreaterextirpationrisk, tend to be those least (or last) affected by the
and spread ofextinction forces (Channel] and Lomo-
•bemorphologically similar lino 2000).
Thus, the conservation value of peripheral
populations is paradoxical. On the one hand,
Fig. 1. Peripheral populations compared to core peripheral populations can have enhanced eco-
populations. logical and evolutionary significance. On the
other hand, this significance can be both a
cause and a consequence of their isolation and
Lammi et al. 1999; Busch 2005) and thus may small size and therefore correlated with reduced
have decreased fitness and an increased risk of viability and increased extinction risk. While
extirpation (Gaston 2003; Reed 2004). For this expert opinion is not unanimous about the
reason, the conservation of peripheral popula-
conservation value of peripheral populations,
tions is controversial, because they tend to be less the biological and intrinsic values of these
stable and are viewed by some as sink popula- populations are well documented and summa-
tions likely to be extirpated anyway, despite
rized as follows:
conservation efforts (Peterson 2001). By this
rationale, the inclusion on state and federal 1) Their high potential for genetic distinctive-
endangered species lists ofperipheral populations ness and divergence can impart novel
of species that are otherwise common and evolutionary pathways for future migration
demonstrable secure elsewhere dilutes limited and speciation events (Levin 1993; Noss
conservation resources that could be better 1994; Lesica and Allendorf 1995; Garcia-
focused on species with narrowly-restricted dis- Ramos and Kirkpatrick 1997; Nielsen et al.
tributions or species of greater risk throughout 2001; Gaston 2003).
their range (Peterson 2001). 2) The maintenance ofgenetic variation in the
However, the genetic diversity and structure form ofsmall, isolated populations contrib-
and viability of a population is determined by utes to long-term species survival and
many factors, including its degree of isolation preservation of local genetic diversity
and spatial pattern, gene flow, varyingdirectional (Millar and Libby 1991; Lesica and Allen-
selection, and the species' reproductive strategies. dorf 1992; Fiedler 1995; Lesica and Allen-
Therefore, a population's viability can depend dorf 1995; Lammi et al. 1999; Channell and
more on demographic structure and population Lomolino 2000; Caballos and Ehrlich 2002;
dynamics (Bevill and Louda 1999) (e.g., whether Gapare and Aitken 2005; Gapare et al.
the species is formerly common or historically 2005).
rare [Brigham 2003]) than on its genetic structure. 3) Even very widespread taxa (e.g., bison, sea
As well, lower levels of genetic diversity are not otter, passenger pigeon, American elm,
always associated with lower levels offitness. For American chestnut) have been regionally
example, in a comparative study of central and extirpated or brought to the brink of
peripheral populations of a rare European herb, extinction in a short time span (Nielsen et
Lychnis viscaria L. (Caryophyllaceae), Lammi et al. 2001).
al. (1999) found that while genetic diversity was 4) Peripheral populations can have impor-
positively correlated with population size, no tant local human values, (e.g., cultural,
correlation was found between lower genetic economic, and historical) regardless of
diversity ofperipheral populations and measured how common the species may be elsewhere
fitness characters such as seed set, seed germina- (Hunter and Hutchinson 1994; Gaston
tion, and seedling mass. 2003).
MADRONO
266 [Vol. 53
Despite their conservation value, there are, at drawn after the onset ofthe Age of Reason and
present, no explicit criteria to determine the are more likely Cartesian or the results of
conservation priority of peripheral populations. formulistic procedures. As a result, political
Lesica and Allendorf (1995) provide a useful boundaries as a rule do not correspond with
theoretical framework for evaluating a popula- landscape discontinuities, with floristic provinces
tion's conservation value that emphasizes the and districts, or with the conservation relevance
combination ofgeographic isolation and ecologi- ofa population (Rodrigues and Gaston 2002).
cal distinctiveness as principal criteria. We agree Toward the periphery ofmany species' ranges,
that the degree ofspatial isolation and ecological some populations are found to a lesser extent in
distinctiveness are the best criteria for assessing the next political unit and are thus rare in that
a population's conservation significance, espe- unit (Abbitt et al. 2000; Gaston 2003). A good
cially in the absence ofpopulation genetics data. example is Sequoia sempervirens (D. Don) Endl.
However, without some means to quantify or (coast redwood) (Taxodiaceae), primarily a Cah-
otherwise characterize spatial isolation or ecolog- fornia species whose range extends into the state
ical distinctiveness, the conservation of these ofOregon, where it is rare. Other species exhibit
populations cannot be substantially improved the same pattern because the CaHfornia Floristic
during regional planning or the review ofprojects Province extends into southwestern Oregon.
that may affect them. Furthermore, with the Because conservation efforts, both public and
notable exception ofMillar and Libby (1991), we private, are primarily organized and managed
find little guidance for conservation biologists on within political units, conservation classification
strategies to protect significant populations of schemes routinely take differing geographic units
widespread plants. into account in orderto capture regional rarity as
In this paper, we focus our discussion of well as global rarity. Examples include the
conservation and land use planning strategies California Native Plant Society's (CNPS) In-
on California for the following reasons. First, ventory of Rare and Endangered Plants, which
California occupies a central biogeographic includes List 2 (plants rare, threatened, or
location and zone ofecological transition on the endangered in California, but more common
Pacific Coast of North America, so its floristic elsewhere) and a RED code combination (i.e.,
diversity includes many widespread taxa on the rarity, endangerment, and distribution) that
edge of their range. Second, California has the includes D = 1 (distribution is more or less
largest state flora in the nation and extraordinary widespread outside of California) (California
topographic, geologic, and climatic habitat het- Native Plant Society 2001). State heritage pro-
erogeneity. Third, California has some of the grams with ranks such as G5S1 (globally
strongest environmental regulations in the hemi- common and widespread, extremely rare and
sphere, e.g., the California Environmental Qual- restricted in California) portray a similar geo-
ity Act (California Environmental Quality Act graphic distribution (CaHfornia Natural Diversi-
2005) (CEQA), and the California Endangered ty Database 2005). In these cases, the range of
Species Act; see Morey and Ikeda (2001) for an taxa extendsinto California to a sufficiently small
overview ofstate and federal laws and regulatory degree that they are considered rare here.
programs used to conserve California plants. Conservationists have typically accorded less
Fourth, many of California's ecosystems and concern to taxa in these circumstances than they
plant communities are highly threatened (Hobbs have given to globally rare species. We agree with
and Mooney 1998). California, for example, has this general approach. Nevertheless, we contend
a higher percentage ofwetlands loss (an estimat- that it is precisely those "state rare but globally
ed 91 percent loss between the 1780's and 1980's) widespread" species that provide the opportunity
than any other state (Dahl 1990). to reexamine peripheral populations for their
conservation significance. Furthermore, a G5S1
Reasons why Public Policy has been RED code status illustrates an important consid-
Arbitrary and Ineffective eration regardingtheco—nservation ofpopulations
in these circumstances namely, that they may
Pohtical Boundaries: a Conservation Tool warrant heightened conservation status, not
and Impediment because they happen to fall within a political
boundary that makes them rare, but rather
Political boundaries, although not always because they are much more likely to be
arbitrary in their location, generally do not peripheral populations having the attributes de-
correspond with significant range boundaries scribed earlier (Abbitt et al. 2000). Thus, con-
for organisms. Interestingly, this lack of corre- servationists seeking to preserve the unique and
spondence is less pronounced in the Old World, rare plants within their political boundaries also
where political dynamics have more often co- may be helping to conserve widespread species
incided with constraints imposed by local terrain. by focusing on their peripheral populations (see
In the New World, political boundaries were Hunter and Hutchinson 1994).
2006] LEPPIG AND WHITE: CONSERVATION OF PERIPHERAL PLANT POPULATIONS 267
Conservation ofTaxonomic Units Emphasizes tical methods for evaluating their conservation
Morphological Distinctiveness value are compromised by the difficulty of
collecting data, or by the fact that existing data
Among the many important traits that allow are not organized specifically for this purpose.
plants to persist, morphological variation is Nevertheless, a number ofauthors have proposed
crucial and is recognized for its importance. useful criteria for assessingtheconservation value
Coarse-level morphological variation is the pre- of peripheral or other special plant populations;
ferred class of attributes used for plant identifi- these include isolation and distance, as well as
cation and, before the advent of formal taxono- genetic, environmental, evolutionary, life history,
my, served as the basis for the so-called folk threat, and utilitarian attributes (Millar and
taxonomies. Moreover, morphological variation, Libby 1991; Holsinger 1992; Hunter and Hutch-
in circumscribable and repeated patterns of inson 1994; Schemske et al. 1994; Lesica and
distinctiveness, continues to be the primary basis Allendorf 1995; Nielson et al. 2001).
fordistinguishingamongformal taxonomic units. Many ofthese categories overlap or are highly
In otherwords, variation amongpopulations that correlated. For example, environmentally distinc-
results in morphological distinctness is more tive populations are likely to be genetically
likely to lead to unique taxonomic status distinctive, and thus may have greater evolution-
(Panchen 1992). Given that taxa (both species ary potential, depending on a number of other
and subspecific taxa) are the principal units that circumstances. Also, distantly isolated popula-
are accorded conservation priority (when certain tions are more likely to be genetically distinctive,
criteria are met), we argue that important classes or occupy habitats that differ from core popula-
of biologically significant variation are routinely tions. As satisfying as these categories are
overlooked as a basis for conservation efforts. biologically, they are not equal in terms ofsetting
The significance ofthis issue is illustrated in the and implementing criteria for conservation.
hypothetical examples shown in Figure 2. For Assessment ofgenetic distinctiveness should be
these two scenarios, we consider the identical a primary means for identifying peripheral
geographical distributions of populations: one populations of high conservation value. Indeed,
large core range of populations in proximity to because of the number of population genetic
each other with an overall widespread geographic studies ofplant populations, we have learned that
extent, and one small range of peripheral significant levels ofgenetic variation often do not
populations. In this case, the populations are correlate with the features used for taxonomic
also disjunct and largely isolated from the core. demarcation. Genetic variation among popula-
Under scenario A, disjunct populations are tions is important because it is the basis for both
morphologically similar to the core populations, environmental distinctiveness and evolutionary
and thus given equal taxonomic status, called change. We agree that studies of these kinds
Taxon 1. In scenario B, while the populations should be conducted whenever possible. Un-
also are closely related, the disjunct populations fortunately, genetic data are expensive and time
have distinctive morphological variation that consuming to retrieve and are not available for
leads to a unique taxonomic status, one for the most California plant populations, with the
core populations, Taxon 2, and one for the exception perhaps of commercially important
peripheral populations, Taxon 3. Thus, they are conifer species. Given the rate at which plant
also sister species. These two scenarios portray habitat is being lost and peripheral populations
the differing taxonomic results for two otherwise- are disappearing, a practicable approach is
equal geographic distributions of populations. needed to evaluate the conservation value of
What if the disjunct populations in scenario A a given population.
(Taxon 1) have unique substrate or temperature Here, we propose three categories of criteria
tolerances? What if their underlying genomic for evaluating the conservation significance of
variation is substantially different from the core a peripheral population: geographic isolation,
population? What if they produce unique sec- 2) environmental distincti1v)eness, and 3) intrinsic
ondary compounds that afford them herbivore or human values. The first two criteria derive from
disease resistance? All of these are possible and, Lesica and Allendorf (1995), who emphasize the
indeed, are more likely in peripheral populations. importance of genetic drift and intensity of
Yet, they would not receive conservation status selection. The third criterion derives from many
under scenario A, while they would under sources, but is well articulated by Hunter and
scenario B. Hutchinson (1994). These three attributes are the
easiest to assess among all the criteria discussed
Assessing Conservation Criteria, Values, above. Those populations that meet one or
and Priorities a combination of these criteria should be
accorded a greater conservation value. Those
Although theoretical rationales for conserving that are also threatened or endangered should be
peripheral populations are well developed, prac- given even greater value.
MADRONO
268 [Vol. 53
AA A A ^A. A . .V /A A^AA A^AA A^A^\A A.^AAm -
•A AA ^^^^r^^KAA. A\ A A^ ^ ^^A^ \
/ \ ^ A A V ''-..A A V
\ / Sistertaxa
Taxon3 /a^!*
B
Fig. 2. Geographical distributions of two hypothetical scenarios that include a peripheral population. A) The
peripheral populations are taxonomically part of Taxon 7. B) The peripheral populations, Taxon 3, are the sister
species, or a closely related congener, to Taxon 2, the core population.
Geographic isolation criterion. Populations that Environmental distinctiveness criterion. Popula-
are distant from core populations are, by tions that occupy unusual or unique habitats are
definition, more likely to be on the periphery likely to have unique genetic traits, when
and thus be considered peripheral or, in some compared to populations occupying core areas
cases, disjunct populations. Also, the greater the of the range (e.g., peripheral populations associ-
distance from core populations, the more likely ated with community types, vegetation stands, or
peripheral populations are to be genetically habitats that differ significantly from core popu-
isolated and have distinctive traits with evolu- lations). Populations in environmentally distinct
tionary importance. This criterion thus formal- locations are also more likely to have evolution-
izes focusing on peripheral populations and has ary significance. Thus, we consider environmen-
a significant biological rationale for inclusion. tal distinctiveness another critical category.
This criterion should reflect distances that To more exp—licitly assess both environmental
correspond to an evolutionarily significant degree distinctiveness and, to some degree, the func-
of genetic isolation between peripheral and core tiona—l spatial isolation of a peripheral popula-
populations. In some cases, nearest neighbor tion we propose using the geographic subdivi-
population distances will provide suitable com- sions of Hickman (1993). Hickman utilizes
parativedistances. However,considerationshould a nested, four-tiered system ofprovinces, regions,
be given to the overall geographic structure ofthe subregions, and districts to divide California into
species' range and the specific methods used to meaningful biogeographic units. These subdivi-
characterize them (Gaston 2003; White 2004). sions are, to the greatest extent possible, based on
The application ofthis criterion should also take three main biologically relevant criteria: topog-
into account life history attributes (e.g., mode of raphy, climate, and vegetation type (Hickman
pollination, seed dispersal, life span). Because life 1993). For example, if a population is unique to
histories vary greatly, no standard measure of a given subdivision or is isolated from conspe-
geographic isolation can be utilized to assess the cifics by one or more differing subdivisions, then
conservation significance of populations among this population would have, by definition, greater
diverse taxa. environmental and geographic distinctiveness
2006] LEPPIG AND WHITE: CONSERVATION OF PERIPHERAL PLANT POPULATIONS 269
and isolation than would a peripheral population (2005) found strong spatial genetic structure in
occurring in the same subdivision as the rest ofits peripheral populations, but not in core popula-
distribution. This approach benefits from being tions. This striking difference in the distribution
easily replicated outside ofCalifornia by utilizing of genetic variation among Sitka spruce popula-
similar biogeographic subdivisions (e.g., those of tion classes has important implications for size
Cronquist et al. 1972; Takhtajan 1986; Ricketts et and location of in situ reserves and sampling
al. 1999; Oregon Natural Heritage Program strategies for ex situ conservation and research
2001). collections (Gapare and Aitken 2005).
Thus, this disjunct Fort Bragg Sitka spruce
Intrinsic human values criterion. Finally, con- population has regional ecological, evolutionary,
mpseeatrnivyan,tgioohnfutmebnaionildoivgoayslyuneicssr,athieictgh,hilcays,ndvaansldouemeptrlieadmdieelnse.cctiToohmn-es glaoencndaeltiefccorogenesotomgcirocamphmsiuicgnniivtfaiyrciaasnttcrieuocntbuearcena.dusdeomoifnaitnscerarien
play an important role in the conservation
Pinus contorta Dougl. ex Loud, (lodgepole
decision-making process (Noss 1994). There is pine) (Pinaceae) is a conifer widely distributed
general agreement that a population's cultural, from the Yukon south to California and the
eenchoannocmeisc,itshicsotonrsiecr,vaatinodn evvaleune.aeLsotchaeltichuvmaalnuse RBaojcakyCaMloiufnotraniian.s,Iwtitihs aexdtisrjeumnecltypoepcuollaotgiicoanlliyn
often assign important intrinsic values to local variable, with four named geographic subspecies
hspaevciinesg,tihfemforonntoheiorthlearndrsecaaspoe.n Ltehoapnoltdhe(y19l4i9k)e s(Cpreicticehsfiienldma1n9y57,mon19t8a0n).e Iatndiscoaasdtoamlirneagnitonstroeef
chtoeaapAvtelunra;esdkoatnheiissmsaaebynotuintmeevlneitrkewgeelrtle:lteh"geRareteli.ne"ggaThthaiepnrpgeifgnoreriesz,zsliatelosl wtaensttebronthNoecrotlhogiAcmaelrliycaa,ndaencdonaosmiscuaclhl,y.isAlilmpfooru-r
subspecies of lodgepole pine are represented in
things being equal, peripheral populations that California, with northern California havingmuch
have important human values would have greater
conservation value than those that do not (see vheirgshietry, lceovemlpsaroefdhteotemroozryegonsoirttyhearnndanaldlelRioccdkiy-
also Holsinger 1992). It is important to note that Mountain populations (Oliphant 1992).
societal values change through time and that
In the Klamath Region ofnorthern California,
through education and effective public relations,
the conservation community affects this change. an undescribed lodgepole pine race, or ecotype,
occurs on ultramafic substrates (serpentine soils).
This race is referred to by Griffin and Critchfield
ExamplesofPopulationsthat MeritConservation (1972) as "an unnamed closed-cone race in the
low mountains of Del Norte County" and by
Here, we give three examples of taxa (Sitka Critchfield (1980) as the "Del Norte race."
spruce, lodgepole pine, and various orchid Oliphant (1992) found that Del Norte race
species) with relatively widespread California populations have low levels of expected hetero-
distributions possessing regionally significant zygosity and possess a suite of rare alleles;
populations with conservation value. Nomencla- however, none are unique to the race. Krucke-
ture follows Hickman (1993). berg (1967) demonstrated a differential growth
Picea sitchensis (Bong.) Carr. (Sitka spruce) response, with plants from non-ultramafic soils
(Pinaceae) is a Pacific Northwest coastal conifer growing slower than plants from ultramafic
and economically important timber tree, occur- soils when grown on an ultramafic substrate.
ring from Alaska to northern California. Sitka Populations of the Del Norte race probably
spruce has a continuous distribution that termi- represent a distinct serpentine ecotype (Oliphant
nates just south of Humboldt Bay in Humboldt 1992). Though lodgepole pine is a common
County; however, a disjunct population occurs species in California and western North
near Fort Bragg, Mendocino County, approxi- America, these Del Norte race populations
mately 100 km to the south (Smith and Wheeler occupy edaphically extreme sites and represent
1992; Lanner 1999). environmentally peripheral occurrences with un-
In a comparative study ofthe genetic diversity usual genotypes.
of Sitka spruce throughout its range, Gapare et Coleman (1995) presents the county-wide and
al. (2005) determined that peripheral and core regional distribution and conservation implica-
populations have similar measures of heterozy- tions of California's native orchid flora (Orchi-
gosity; however, the only allele they classified as daceae). Although many of California's orchid
rare and localized was limited to disjunct and species arewidely distributed, Coleman elucidates
peripheral populations, including the Fort Bragg why marginal populations in southern California
population. Gapareet al. (2005) demonstrate that and the Santa Cruz Mountains are sufficiently
peripheral and disjunct populations of this isolated and threatened to warrant conservation
species have value for in situ conservation ofrare efforts. These taxa all have geographic ranges
alleles. In a related analysis, Gapare and Aitken that extend at least as far north as Washington.
MADRONO
270 [Vol. 53
According to Coleman (1995), orchid popula- alternatives or mitigations that will avoid or
tions on the edge of their range in southern substantially lessen significant effects, when such j
California are threatened for the following feasible alternatives or mitigations exist (Califor-
reasons: 1) populations are extremely rare in nia Environmental QualityAct 2005). Article9 of
San Bernardino and San Diego Counties and CEQA, Contents of Environmental Impact Re-
large populations in San Luis Obispo and Santa ports [section 15125 (c)], states "Knowledge of
Cruz Counties have been lost to urbanization the regional setting is critical to the assessment of
{Spircmthes romanzoffiana Cham.); 2) recent environmental impacts. Special emphasis should
attempts to locate southern California popula- be placed on environmental resources that are
tions have been unsuccessful {Spiranthes porrifo- rare or unique to that region and would be |
lia Lindley); 3) populations are so few and tiny affected by the project." 'j
that the species could be eliminated from an CEQA is of fundamental importance to plant '
entire county by a single stochastic event or conservation, because it addresses potential im-
timber harvest {Piperia leptopetala Rydb.); and pacts to any species that can be shown to meet
4) species apparently have been extirpated from the criteria for state or federal listing (section
the Santa Cruz Mountains by habitat destruction 15380[d]) (CaUfornia Environmental Quality Act
{Cypripedium fasciculatum S. Watson and C. 2005), as well as to CESA and FESA listed
montanum Lindley). species. Yet, to our knowledge, CEQA rarely has
Unlike the two previous examples, we have no been utilized to protect peripheral or otherwise
data that indicates these orchid populations are locally significant populations of widespread
genetically or environmentally distinct. Orchids plant species if the species could not be consid- j
I
are however one ofthe most charismatic compo- ered endangered, rare, or threatened pursuant to
nents of the California flora and are revered by CEQA (section 15380[d]). Despite this, a fair j
lay naturalists and biologists alike for their argument can be made by public agencies and !
beauty and unusual reproductive biology. For conservationists that potentially significant im-
example, southern and central California alone pacts to these populations must be disclosed and
has oversix orchid societies, and theirimportance avoided if: 1) the population is locally rare or
in the horticultural trade is manifest. Therefore, unique (pursuant to CEQA section 15125 [c]) and
we contend that given the intrinsic value placed therefore may have intraspecific variation and |
i
upon these species, their regional rarity, and potential evolutionary significance; 2) the popu- '
documented habitat loss and range contractions, lation has regionally significant ecological impor-
,
these scarce southern California and Santa Cruz tance; and 3) the population has local cultural,
Mountains orchid populations warrant protec- economic, or historic value. |
tion during regional conservation planning ef-
forts and review ofprojects potentially impacting Regional Conservation Planning
or eliminating them.
In California, land use plann—ing on nonfederal
Regulatory Process lands is done on the local scale most commonly
through municipal and county general plans, j
California Environmental Quality Act However, regional planningalso occurs underthe j
!
auspices of state Natural Community Conserva-
i
Here we review certain regulatory programs tion Plans (NCCPs) Natural Community Con-
that could be more effectively used to conserve servation Planning Act (2002) and federal Hab-
significant peripheral plant populations. In doing itat Conservation Plans (HCPs). NCCPs and
;
so, we aim to better integrate current under- HCPs in California are regional conservation
standingsaboutthebiologicalattributesofperiph- planning tools used to protect habitats ofCESA I
eral and disjunct populations with the broader and FESA listed and potentially listed species i|
aims of the California regulatory framework. across a large area. A principal objective of
I
CEQA, together with the California and NCCPs is to bring about species recovery by j
federal Endangered Species Acts (CESA and protecting natural communities on which the
FESA, respectively), is a principal tool used to species depends. The principal federal objective
conserve rare and endangered species in Califor- ofan HCP is to minimize and mitigate impacts to ,
nia. CEQA is landmark legislation that requires listed species to the maximum extent practicable.
(with someexceptions) that potentially significant Land owners often enter into HCPs because it is
environmental impacts resulting from a proposed the only means to receive an incidental take
project (e.g., a housing development, dam in- permit for a federally listed species. An incidental
stallation, or timber harvesting plan) be disclosed take permit is a permit to incidentally "take"
to the public and reviewing state agencies. (kill) a listed species during the course of an
CEQA
Furthermore, (section 21002) states that otherwise-legal activity.
(again, with exceptions) public agencies should NCCPs and HCPs both hold greater promise '
not approve projects that do not include feasible in conserving listed species and significant por-
2006] LEPPIG AND WHITE: CONSERVATION OF PERIPHERAL PLANT POPULATIONS 271
GRMUs
tions of their habitat, or even entire ecosystems, the necessity of creating to conserve
than project-by-project mitigations (Noss et al. regional genetic diversity, and we recognize that
1997; Rolfe 2001; Hopkins 2004). Regional simply by protecting large areas, NCCPs and
conservation plans are also potentially much HCPs can also protect significant peripheral
more effective in protecting habitats and species populations. However, the full potential of
from large-scale, spatially autocorrelated threats regional conservation plans and other designated
such as urbanization, climate change, sea-level conservation areas in protecting regionally sig-
rise, and invasive species, most ofwhich typically nificant peripheral populations cannot be realized
are not addressed or mitigated for effectively by until their importance is better appreciated,
smaller projects outside the HCP/NCCP realm. actual populations are identified, and most
Regional conservation planning is potentially importantly, their conservation priority is in-
more effective in addressing cumulative impacts tegrated into the management objectives ofthese
than are multiple, smaller-scale projects subjected regional plans.
to CEQA individually (Noss et al. 1997; Hopkins Currently, there are 22 NCCPs being devel-
2004). This is because cumulative impacts assess- oped in California and nine that have been
ment is essentially a large-scale and rate-de- approved and permitted. All ofthese NCCPs are
termined process not well suited to smaller, joined with an HCP and are typically 50-to 80-
multiple, ongoing, regionally concentrated proj- year agreements. Together, these 31 NCCPs
ects such as timber harvesting plans in a water- cover over seven million acres (28,328 km-),
shed or urban sprawl in the Central Valley. representing approximately seven percent of
However, as reviewed by Rolfe (2001), NCCPs California. This is, therefore, a propitious time
and HCPs have significant shortcomings and to emphasize the significance of peripheral
incongruous objectives due to their reliance on populations during regional planning.
take permits under FESA Section 10(a) and
CESA Section 2835. Simply put, the FESA and Need for more Accurate Delineation of
CESA are reactive responses to species in Local Floras
jeopardy of extinction, while regional conserva-
tion plans are ostensibly a proactive approach to Closer scrutiny of local floras and phytogeo-
prevent the decline of species in the first place graphic patterns is required to identify peripheral
(Rolfe 2001). While NCCPs aim to promote populations having significant conservation val-
multispecies and multihabitat management and ue. A principal impediment to theconservation of
the conservation ofbroad-based natural commu- locally significant peripheral populations is the
nities and species diversity, the impetus to initiate relative absence of finer-scale data on species
one is typically the conservation of listed or distributions. Presently, the general geographic
potentially listed species. distribution ofcommon species, such as those not
County general plans and ordinances are tracked by CNPS, is understood only at the
another important yet underutilized tool to county-level scale, (for example Munz 1959,
conserve peripheral populations and other locally 1968), and therefore is of limited use in conser-
significant species and habitats. Santa Cruz vation planning because the spatial scale is too
County, for instance, has a ''Sensitive Habitats coarse.
Protection Ordinance" that requires that no Recently, however, CNPS chapters and others
development activities or land disturbance that have begun compiling regional lists ofperipheral,
results in disturbance to locally unique disjunct, or what has been termed "locally rare"
. .
plants and animals or their habitats" can occur taxa, in an effort to conserve them (Lake 2004;
until a biotic review is conducted and necessary Magney 2004). Other regional and county floras
mitigation measures are developed to protect the (such as Thomas 1961; Hoover 1970; Smith and
habitat (Santa Cruz County Planning Depart- Wheeler 1992), although outdated, provide im-
ment 2005). The Ventura County, CaHfornia portant data on peripheral populations (many
General Plan specifies that "locally important now extirpated). Thomas (1961), for instance,
species/communities" are a significant biological lists 181 taxa with their southern geographic
resourceto preserve and protect (Ventura County limits and 61 taxa with theirnorthern limits in the
1988). Santa Cruz Mountains. We encourage the
Millar and Libby (1991) suggest that important continued documentation and compilation of
populations of widespread species be conserved, local floras and peripheral populations and
in part, by the creation of "genetic resource otherwise regionally significant plant lists as
management units" (GRMUs). These GRMUs a first step in understanding their conservation
can be, in essence, wilderness areas, botanical value and protecting them where appropriate.
areas, or lands covered by a NCCP/HCP, iftheir Local floras are also important tools for
management objective is the in situ conservation identifying where concentrations of regionally
of biodiversity at the regional genetic-variation and locally significant populations occur (i.e.,
level. We agree with Millar and Libby (1991) on biodiversity hotspots, potential reserve sites,
MADRONO
272 [Vol. 53
and finer-scale ecological boundaries) (Araujo tion, but many clearly are. Identifying which
2002; Leppig 2004). Heckard and Hickman populations warrant conservation efforts poses
(1984), for example, demonstrate how a detailed a continuing challenge. More genetic data,
local flora can highlight the conservation a better understanding of how metapopulation
significance of a location due to its high theory applies to these populations, and an even
concentration of peripheral plant populations. more-explicit approach than we present here for
In the absence of more-spatially explicit data assessing conservation significance will clearly
on plant species distributions, locally significant help.
peripheral plant populations will continue to be We acknowledge that conservation resources
unknowingly extirpated with no attempt to are scarce, and will likely remain so. However, in
conserve them. our view, placing greater conservation emphasis
Lastly, the v—ariation in size of county-level on certain important peripheral populations will
political unit—s both within California and not necessarily take scarce resources away from
among states hampers effective comparative species in perhaps greater need; rather, it will
analyses and uniform application ofconservation enhance current conservation efforts and large-
criteria. To ameliorate this problem, we advocate scale regional planning.
the use ofmethodologies based on 5 km X 5 km
grids for characterizing plant distributions. Al- ACKNOWLEDGMENTS
though some limitations and cautionary notes
should be considered when using these method- This paper stemmed from discussions of the Cali-
fornia Native Plant Society Locally Rare Working
ologies (White 1999, 2004), they have been used Group. We thank that group, the California De-
effectively elsewhere (lUCN 2001; Pearman and partment ofFish and Game BotanicalWorkingGroup,
Dines 2002) to accurately describe plant spatial and the members of the Biodiversity Research and
patterns. Education Center at Humboldt State University for
helpful conversations about these ideas and for pro-
Summary Considerations vidingmanyusefulcomments, information,andinsight.
John C. Hunter and two anonymous reviewers pro-
— vided numerous suggestions and careful review that
The evolutionary—significance and therefore greatly improved this manuscript.
conservation value of peripheral populations
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