An Introduction to Lichens
and their Conservation
Eric B. Peterson, Ph. D. Diane Ikeda, Regional Botanist
California Academy of Sciences U.S. Forest Service
December 20, 2017
Title: An introduction to lichens and their conservation in California
Eric B. Peterson, Ph.D., Botany Department, California Academy of Sciences, San Francisco,
Diane Ikeda, Regional Botanist, Pacific Southwest Region, U.S. Forest Service, Vallejo, California.
This report was funded by the U.S. Department of Agriculture, Forest Service.
The views and opinions expressed in this report are those of the authors.
Text and images are © Eric B. Peterson, provided under the Creative Commons license “Attribution-
Erratum: The final version of this document released in November of 2017 was missing data from Table 2.
The missing data is replaced for this December 2017 version.
Peterson, E. B. and D. Ikeda. 2017. An introduction to lichens and their conservation in California.
California Academy of Sciences, San Francisco, California. DOI: 10.13140/RG.2.2.32222.13128
Cover Photo: Brightly colored lichens on a rocky ridgeline in the Trinity Alps Wilderness (Klamath Montane
There are between 15,000 and 20,000 species of lichens worldwide.
Most of these have very broad ranges compared to vascular plants,
and approximately 10% of these are known to exist within California.
Many are specialized to very specific habitats that recur infrequently over the
landscape, rendering some species rare despite their relatively large total range.
Conservation of lichens and their habitats is not only important to biodiversity of
lichens, but also for the yet-untold numbers of arthropods they support,
as well as birds, mammals, and thus the functionality of ecosystems.
Defining a Lichen
Lichens are... bizarre! Though they are usually
overlooked, those who stop to get close to a
branch or a rock often find something akin to a
tropical reef. Lichens branching like coral, or
polka-dotted with fruiting structures, and often
with many shades and colors... sometimes even
brilliant yellows and oranges
[cover photo]. This paper
introduces lichens to land
managers and natural resource
technicians who may not be
very familiar with them, and
provides a technical foundation
for taking action on lichen
So what are lichens, really?
They are fungi that have
discovered agriculture! Fungi
themselves are heterotrophs,
obtaining energetic sugars from
other organisms. Many fungi do
this by decomposing other
organisms. Others form
mutually beneficial symbiotic relationships with
autotrophs to obtain sugars. Mycorrhizal fungi
It is intended that this paper will be followed with
others that go into detail on particular topics.
work with vascular plants, through their roots,
receiving sugar in exchange for nutrients. Lichens
cultivate one or more autotrophs, often within
their own body, or thallus, to obtain sugars in
exchange for a comfortable place to live [A]. The
fungal partner is known as the mycobiont, while
the autotroph is known as the
photobiont. Lichen photobionts
are primarily green algae, but
cyanobacteria are common too
(some lichens incorporate both),
and some mycobionts associate
with brown algae
(Phaeophyceae) or golden algae
(Chrysophyceae). Lichens with
green-algal photobionts alone are
often referred to as
chlorolichens, while those that
include cyanobacteria are known
as cyanolichens. Adding further
to the complexity, fungal yeasts
have recently been discovered to
be a component of many lichens
and can affect the form and color of the lichen
(Spribille et al. 2016).
Lichens take many forms, but the majority can be
squeezed into 3 general groups [B]. Fruticose
lichens are the most 3-dimensional, with no
[A] Cross section of a lichen thallus
showing a layer of green algae.
distinction between an upper and lower surface.
Fruticose lichens can be long and stringy or
compact and shrubby. Foliose lichens have
somewhat flat lobes such that an upper and lower
surface can be distinguished. The lobes of a
foliose lichen can be broad and leaf-like, or long
and narrow, some adhere close to their substrate,
making them difficult to distinguish from the next
group. Crustose lichens are nearly 2-
dimensional to the human eye, growing on the
surface of their substrate almost as if they were
painted on, and have no lower surface that can
be separated from the substrate.
Hand-in-hand with the variety of colors that
lichens display, comes a vast array of chemicals,
often referred to as lichen acids. Many functions
have been demonstrated for these secondary
metabolites including microbial defense (many
have antibiotic properties; Zambare &
Christopher 2012), resistance to herbivory
(Lawrey 1980), and protection from damage by
UV radiation - an aspect that is particularly
important because lichens are poikilohydric and
must survive long periods of desiccation
(Rikkinen 1995; Nguyen et al. 2013).
Within the tree of life
What’s in a name? That which we call a lichen
by any other name would be valued as much
With new perspectives from genetic studies, this
paraphrase of Shakespeare is more relevant now
than ever before. The concept of cryptic species
(those that cannot be easily distinguished by the
human eye) has been around for quite some time
(Mayr 1942), and lichen species have often been
defined solely by variations in their lichen acids
as detected by chemical spot tests (Brodo et al.
2001). Many lichens that had been thought to
represent a single species morphologically, have
proven to have multiple genetic lineages worthy
of the status of separate species (Kroken &
Taylor 2001; Leavitt et al. 2011a). Yet some that
were thought to be morphologically distinct
species have proven to be not so distinct. The
genus Xanthoparmelia seems particularly tangled
(Leavitt et al. 2011b; Lumbsch & Leavitt 2011;
Leavitt et al. 2015) with single morphologies
[B] Top: fruticose growth form of Alectoria lata, a species
deserving sponsorship under the California Lichen Society’s
process. Middle: foliose growth form of Umbilicaria phaea f.
coccinea, a rare but distinct phenotype. Bottom: crustose
growth form of the common Lecidea tessellata (gray) and
Rhizocarpon geographicum (yellow).
drawing from multiple lineages (as in cryptic
speciation) and multiple morphologies arising
within a single lineage (phenotypic variation).
There are about 100,000 species of fungi
presently described, with about 16,000 of them
forming the lichen symbiosis (Kirk et al. 2008).
The lichen relationship has evolved several times
(Gargas et al. 1995), and not exclusively within
the ascomycetous fungi. Several basidiomycetes
including the mushroom genus Omphalina [C]
have taken on a lichen symbiosis.
Reproduction and Dispersal
The lichen symbiosis - sometimes referred to as
a ‘dual organism’ would seem to present
challenges for reproduction. Indeed, there is a
strong tendency for lichens to reproduce
asexually, using vegetative propagules that carry
both fungal hyphae and algal cells: soredia and
Yet sexual reproduction remains common in
lichens and even species that are mostly asexual
[C] Mushroom (Basidiomycete) lichen, Omphalina. The green
covering over the substrate is algae associated with the
[D] Asexual reproductive propagules. Left: soredia that burst or erode from within; right: isidia, formed as
projections of the thallus.
[E] Sexual reproductive structures of the fungus. Left: disk shaped apothecia on thallus (body); right: cross section of
an apothecium showing spores.
may occasionally be found with sexual
reproductive structures. Sexual reproduction of
the fungus results in spores, produced in most
lichens by disk-like apothecia [E]. Spores, upon
germinating on a new substrate, must quickly find
an appropriate photobiont to associate with. Most
photobionts that form lichens are rarely found in
nature without a fungal host. Little is known about
how the two organisms find each other again.
Adding to the mystery, desert lichens, where one
might expect the reunion to be the most difficult,
are predominantly sexual reproducers.
Lichens tend to be very effective at long-distance
dispersal. Some habitats such as forests on
scattered peaks of desert mountains can be
quickly colonized by lichens from far away. Only a
few lichens with relatively large vegetative
propagules, such as Lobaria oregana, seem to
have much difficulty with dispersing large
distances (Sillett et al. 2000). It was long thought
that such long distance dispersal happened by
releasing propagules into the wind, but
increasingly it appears that lichens use animals
as vectors of dispersal. Birds, insects, and
spiders that frequent lichen habitats could act like
guided missiles taking spores or vegetative
propagules directly to just the right spot far away.
Substrate and Habitat
Lichens inhabit virtually all terrestrial habitats and
have a foothold in aquatic habitats as well. They
can grow on almost any stable surface and some
tumbleweed, or vagrant, lichens grow
unattached, drifting over soils in arid regions.
Those growing on bark or wood (including natural
fencing materials) are epiphytic. Lichens
growing on rock are referred to as saxicolous,
which can then be split into those that inhabit
acidic rock (siliceous), or growing on calcium
rich basic rocks (calcareous) such as limestone
or cement... even sidewalks! Lichens also grow
directly on soil (terricolous). Together with moss
and free living cyanobacteria, terricolous lichens
[F] form biological soil crusts, or simply
biocrusts, and are important soil enhancers and
stabilizers in desert ecosystems.
Lichens are found from some of the most
southerly rocks in Antarctica, to tropical rain
forests, to deserts that receive no reliable annual
rainfall. Lichens also inhabit semi-aquatic areas
of marine tidal zones, freshwater lakes, and
mountain streams. Peltigera gowardii [G],
previously known as the western populations of
Peltigera hydrothyria (or Hydrothyria venosa),
Biological soil crusts (or biocrusts), are important parts of desert ecosystems that have been largely lost. These
photos come from what most people regard as ‘barren’ gypsum soils in the Mojave east of Las Vegas, Nevada. After a
little rain, they can be vibrant and show their biodiversity!
even thrives permanently submerged in spring-
fed mountain streams (Davis 1999; Peterson
Within many terrestrial habitats, lichens and
mosses form a gradient, from mosses dominating
areas that stay wettest (though with some lichens
present), to lichens dominating areas that stay
driest. Gradients are often clear among the
lichens themselves. In the Pacific Northwest and
California’s north-coastal mountains, conifer
forests are initially inhabited by common
chlorolichen species with a somewhat mossy
zone close to the ground; as they mature, long
fruticose lichens known as alectorioid lichens
(primarily Alectoria and
Bryoria) colonize the
mid-canopy; then as old-
colonize a zone in the
lower canopy, just above
a mossy understory
(McCune 1993; McCune
et al. 1997).
Some lichens specialize
into even smaller
microhabitats. Gradients can be found going
around a tree trunk: mosses may dominate the
wettest areas that receive canopy drip, with larger
fruticose and foliose lichens next in the gradient,
transitioning to sheltered areas that receive no
direct liquid water [H], where one may find a
variety of powdery crustose leprarioid lichens [I]
and minute pin-lichens with tiny stalked fruiting
bodies [J]. Such sheltered microhabitats are best
developed in old-growth forests.
While conifer forest gradients may be among the
best described in the literature, similar gradients
can often be found elsewhere, even across the
face of a single large rock.
The comparison between lichen communities and
coral reefs doesn’t stop at intricacy and colors.
Like reefs, lichens form diverse habitats for other
organisms and increase productivity of
ecosystems ranging from forests to deserts.
Primary Productivity (Carbon Fixation). As
fungi harboring a photosynthetic partner, lichens
use solar energy to fix carbon and add organic
materials to ecosystems. Although lichens are
often assumed to grow slowly, epiphytic lichens in
moist forests are reported
to frequently grow in
biomass by 10-30% per
year and in some cases
upwards of 100% per
year (Keon & Muir 2002).
Where air is still clean
and humidity levels high,
California’s oak forests
are revealed in winter to
have high lichen biomass,
particularly of Usnea spp.
and Ramalina menziesii
[G] A fully aquatic lichen, Peltigera gowardii, is ranked S3,
placed on list 4 (watch), and is on the sensitive list within
Region 5 for 12 National Forests and the Lake Tahoe Basin
[H] Moisture gradient around a trunk. As trunks become large
enough to shelter areas from direct wetting by rain, mosses
and larger lichens inhabit the wet side while leprarioid lichens
and pin-lichens colonize the protected dry side - a
microhabitat that is best developed in old-growth stands and
is pointed to by the stick figure.
(the California State Lichen), rivaling the leaf
biomass of summer [K].
Nitrogen Fixation. Nitrogen is a limiting factor for
productivity of many ecosystems. The
cyanobacteria within cyanolichens fix nitrogen,
converting atmospheric nitrogen to a form
useable by plants. Lobaria oregana is a nitrogen-
fixing lichen that is well known in the Pacific
Northwest for its contributions of nitrogen to old-
growth forest ecosystems (Pike 1978; Rhoades
1983). Nitrogen fixing rates for L. oregana, which
inhabits some forests in California’s northern
coastal ranges, have been calculated as high as
16.5kg/ha/year in the Andrews Experimental
Forest in Washington state (Antoine 2004). As a
component of biocrusts, lichens are also a
significant source of nitrogen for intact arid
ecosystems (Belnap et al. 2001). Biocrusts also
increase the availability of nutrients in the soil for
vascular plants (Harper & Belnap 2001).
Soil Stabilization. The paucity of vascular plant
cover in deserts can expose soils to wind and
rain. Biocrusts both cover the soil, and imbed
themselves within the upper soil horizon, binding
it together and making it much more resistant to
erosive forces (Belnap et al. 2001).
Seed Germination. Possibly through physical
binding of the soil as noted above, or possibly
through chemical leachates, biocrusts have been
documented as altering seed germination and
therefore influencing vascular plant community
composition (Serpe et al. 2006). Within western
arid ecosystems, biocrusts have been
documented to inhibit germination of invasive
annual grasses – a possible mechanism for a
mutually exclusive pattern between biocrusts and
annual grasses (Peterson 2013). Efforts have
begun to find ways to propagate biocrusts for
arid-land restoration (Doherty et al. 2015).
Microhabitat for Microfauna. Lichens,
particularly foliose and fruticose forms, provide
habitat for vast communities of arthropods and
other small organisms such as tardigrades
(Young & Clifton 2016). These communities have
been demonstrated to influence bird populations
that consume those arthropods (Pettersson et al.
1995). Many insects, spiders, and even lizards
have evolved to camouflage themselves among
lichens [L]. The most famous case of lichen
mimicry is the peppered moth in England, the
light form of which became uncommon when
exposed to predation during the industrial
revolution, due to air pollution eliminating lichens
from populated regions (Richardson 1974).
[I] A leprarioid lichen.
[J] A pin-lichen, Chaenotheca chrysocephala, which has survey
and manage requirements under the Northwest Forest Plan,
but is generally thought to be common in late-successional
forests of humid areas such as the Northern Coastal Ranges.
Habitat for Macrofauna.
Many birds use lichens for
nesting materials (Richardson
& Young 1977). Northern
flying squirrels are also
known to line their nests with
lichens (Rosentreter et al.
Food Source. Lichens are
food sources for animals
ranging from arthropods to
large mammals. While
secondary metabolites may
help lichens resist herbivory,
many animals evolve ways to
cope with these chemicals.
The selective forces between
lichens and their herbivores may be a source of
genetic diversity for both (Pöykkö et al. 2010).
Slugs graze lichens heavily in wet forests of
northern California and the Pacific Northwest,
and may disperse lichens by passing fragments
through their digestive tract (Boch et al. 2011).
Caribou, elk, and deer eat lichens in winter when
other foods are scarce. Bryoria fremontii [M] is a
major food source for northern flying squirrels
(Rosentreter et al. 1997; Zabel & Waters 1997).
Through these squirrels, B. fremontii may
indirectly effect the northern spotted owl,
California spotted owl, northern goshawk, pine
martin, and American fisher (Rambo 2004).
Foods. A number of lichens, such as Umbilicaria
esculenta, are considered delicacies in certain
cuisines (Xu 2011). Bryoria fremontii, the same
lichen that is eaten by flying squirrels, was eaten
by native Americans both in times of shortages,
and by some tribes as a generally appreciated
food (Turner & Davis 1993). [Caution: in
California this species sometimes contains large
amounts of a vulpinic acid derivative, so could be
Medicines. Many lichen acids have antibiotic
properties and have been used in both traditional
and modern herbal medicines. Some of these are
being investigated in current medical research
(Zambare & Christopher 2012).
Dyes. The variety of the acids in lichens are used
in traditional dyes for cloth (Minnick 2013).
Crafting. Lichens are often seen at craft fairs
adorning birdhouses and other items. Some
species of Cladonia (Reindeer lichens) are
commonly used as trees for model railroad
displays. Though likely not provable, Usnea
longissima is thought to have inspired Christmas
garlands, as it resembles the long strings of tinsel
draped over branches, sometimes over a meter
long [see inset of image Q].
Lichenometry. Lichens can be used to
approximate ages of items for studies in
[K] Ramalina menziesii drapes an oak tree in California’s North Coastal Ranges. The lichen
may not be obvious among summer leaves, but coats the branches so densely that during
winter, little of the tree can be seen through the lichen.
anthropology and geology. Growth rates need to
be determined in nearby, similar situations to the
item of interest, then that rate can be applied to
calculate the age of lichens on the item (Scuderi
& Fawcett 2013).
Environmental Indicators. Lichens can be used
for monitoring a variety of conditions for natural
resources. Lichens absorb many of the chemicals
they are exposed to, making them valuable for
studies of air pollution (e.g. Fenn et al. 2010) and
their accumulation of metals makes them useful
for minerology (Purvis & Halls 1996). Different
species show different tolerance to air pollution,
so lichen community composition can be used to
infer pollution levels (Stolte et al. 1993; Jovan &
McCune 2004). Presence, or absence, of species
can be used to infer other environmental factors
too, such as the legacy of old-growth conditions
in forests (Selva 1994).
There may be more professional botanists in
California alone, than there are professional
lichenologists world-wide. Professional
lichenologists predominantly employed on lichen
topics may number only in the lower hundreds
worldwide. Yet for each of them, there may be
another 5-10 professionally trained, but otherwise
employed scientists who continue to pursue
lichenology as time allows, plus 10 or more highly
competent enthusiasts. There are currently no
universities within California with professors
dedicated to a regular research program on
lichens (though this appears ready to change).
That said, there are individuals who regularly
pursue lichenology through various avenues
including academic herbaria and several
university professors who occasionally support a
student on a lichen topic.
Lichen enthusiast and photographer Stephen
Sharnoff recently completed the beautifully
illustrated A Field Guide to California Lichens
(Sharnoff 2014). Lichen researchers from outside
of California make occasional collecting trips
resulting in taxonomic treatments including The
Lichens of California (Hale & Cole 1988), Lichens
of North America (Brodo et al. 2001), and the
Sonoran flora works (Nash et al. 2002-2007).
Recently a number of “bio-blitz” activities have
helped draw lichenologists to specific locations
within California, particularly National Parks (e.g.
Hutten et al. 2013). For a brief history of
California lichenology, see Hale & Cole (1988) or
the online work by Tucker (2014).
[L] Animals with exhibiting lichen camouflage: a
moth, a spider, and a lizard.
[M] Bryoria fremontii, a lichen eaten by many animals, and
traditionally by humans. B. fremontii is common in western North
America, but is declining in the Sierra Nevada mountains, apparently
due to air pollution.
The California Lichen Society (CALS;
lichenologically active people together to
promote “the appreciation, conservation, and
study of California lichens”. This society is
particularly active in the greater Bay Area
with frequent amateur-oriented workshops
and field trips. The society also supports a
conservation committee that works closely
with the California Native Plant Society
(CNPS) and the state’s California Natural
Diversity Database (CNDDB) to rank and list
lichens of conservation concern (Table 1).
Due to the lack of extensive surveys relative
to vascular plants in California, the CALS
committee takes an exceptionally cautious
approach and thus far has just barely scratched
the surface of species-based lichen conservation.
A list of resources is provided below to encourage
further study of lichens in California. Such study
is seriously needed to properly comprehend the
lichens within California and their contribution to
biodiversity, both locally and globally. A search of
the international Consortium of North American
Lichen Herbaria (93 contributing institutions) at
the time of this writing found 139,618 lichen
specimens reported from California, while the
Consortium of California Herbaria (35 contributing
institutions) has over 2 million vascular plant
specimens reported. This suggests that California
lichens have been explored to at most about 5%
of the level of that vascular plants have been
explored. General surveys conducted with good
taxonomic expertise are needed across the state,
but particularly along the coast (where rare
species are known to concentrate) and in less
populated regions (which are largely unexplored).
While the U.S. Forest Service conducts some
surveys toward understanding air pollution
patterns and impacts, such studies are deserved
on other federal and non-federal lands. Studies of
lichens relative to forest ecology from the Pacific
Northwest are applicable to some conifer forests
within California, but may be of limited value
southward or in other habitat types, particularly
oak forests and woodlands. The role of lichens
(and mosses) in biocrusts in California is largely
unknown, though it is likely that biocrusts were
once a major ecological component of the Central
Valley and perhaps California's oak woodlands.
Wildfire has become a huge issue in California,
yet little is known about the impacts of wildfire,
prescribed fire, or fire-fighting practices on
Lichens in Decline
Imagine California in 1750, just prior to the first
Spanish missions and ranches. Coastal forests,
shrublands, and chaparral formed nearly
continuous wooded habitats from border to
border. Forests of the mountains and north coast
included an abundance of old-growth, and
frequent wildfires maintained a mosaic of stand
ages. Oak woodlands were similarly maintained,
Table 1: Lichens of conservation concern in California, as ranked and listed by the California Lichen Society (CALS) in
collaboration with the California Native Plant Society (CNPS) and the California Natural Diversity Database (CNDDB).
Electronic versions of this document link taxa to descriptive pages on the CALS website. Three species (noted with *) were
adopted by the CALS Conservation Committee from prior listing by CNDDB and await proper ranking and listing.
Coastal Ranges - Northern
HyperCoastal - Southern
HyperCoastal - Southern
HyperCoastal - Southern
HyperCoastal - Southern
Montane - Interior and
Montane - Klamath
Coastal Ranges - Northern
Montane - Interior,-
Montane - Klamath, and
Montane - Southern
Coastal Ranges - Northern
and HyperCoastal - Northern
HyperCoastal - Southern
HyperCoastal - Northern
Mapping needed. Arid portions
of southern California.
HyperCoastal - Northern
Coastal Ranges - Northern
with perennial bunch grasses and (likely)
biocrusts dominating the ground surface. These
grasses and biocrusts also likely dominated much
of the vast Central Valley of California.
Now, the human population of California has
grown to nearly 40 million. Development is
spreading fast around cities, into neighboring hills
and valleys that once held biologically diverse
natural communities. This spread is strongest in
coastal areas. Removal of these habitats can
eliminate lichens from the landscape. While
lichens may eventually recolonize ornamental
trees and other substrates, diversity often
remains depressed due to less microhabitat
variety and impacts of unnatural moisture
regimes from landscape watering (often laden
with fertilizers, pesticides, or simply the chlorine
of community water systems). Once nearly
continuous, coastal shrublands, oak woodlands,
and other habitats are now fragmented.
Resource use continues to impact lichens in
more remote areas. While logging is greatly
reduced from a century ago, it does persist, and
with a focus on forests at an age where lichen
communities are just becoming well developed.
The vast Central Valley is now almost entirely
converted to agricultural production and other
highly modified habitats; what undeveloped land
remains has mostly degraded to annual
grasslands. Grazing of the remaining open lands
can be devastating to biocrusts and often
continues today at levels that will likely preclude
redevelopment of biocrust communities (Belnap
et al. 2001a). Biocrusts are very vulnerable to
ground disturbance [N], so recreational activities
including the use of all-terrain-vehicles (ATVs)
are another impediment to biocrust recovery.
Once lost, habitat conversion to annual grasses
may make recovery very difficult (Peterson 2013).
In general, lichens are quite vulnerable to air
pollution including sulfur dioxide, nitrogen oxides,
ammonia, ozone, and heavy metals. Air pollution
[N] Biological soil crusts, or simply biocrusts, are very sensitive to disturbance and take decades to centuries to recover. These
tire tracks in Nevada were photographed in 2005, but likely date to the original installation of the power lines in the 1960s for
the Pacific DC Intertie.
can be an invisible, yet severe and widespread
threat, as it pervades habitats not otherwise
touched by humans. Whole populations can
vanish without much notice, being replaced by a
less diverse set of common, more pollution
tolerant species. Lichen communities as far into
the mountains as Lake Tahoe have been shown
to be altered by pollution (Jovan & McCune 2004;
Fenn et al. 2010). In the mountains of southern
California, the more sensitive lichen species
continue to dwindle despite less smog in the L.A.
area (Riddell et al. 2011). High frequencies of the
more tolerant lichens can be a visible sign of air
pollution impacts, particularly the bright orange
members of the Teloschistaceae [O].
Of the early reports of lichens from California,
Tucker (2014) found that 86 had not been
collected again for a century. We simply do not
know how many of these have been extirpated
from California, or have gone extinct.
Conservation of biodiversity is really about
maintaining genetic diversity. Species provide a
convenient representation of genetic diversity as
grouped by evolution. Conservation of these units
is focused on maintaining the capability of these
evolutionary groupings to persist over time. We
have long known that reduced genetic diversity
renders species vulnerable, therefore
conservation should provide for a breadth of
genetic diversity within the evolutionary groupings
we tend to call species.
Although genetic studies are currently
complicating the definitions of lichen species,
species-based conservation remains the most
direct way to conserve genetic biodiversity. It is
also the way that conservation has most clearly
been defined within the legal framework of the
United States. The federal Endangered Species
Act (ESA) and California Endangered Species
Act (CESA) provide for powerful regulation of
activities that might harm species that are
endangered. The National Environmental Policy
Act (NEPA) provides for assessment of
conservation issues, particularly ESA listed
species, prior to most federal activities that
impact habitats. The California Environmental
Quality Act (CEQA) requires similar assessments,
both for governmental and private-sector
[O] Top: a tree covered with Xanthoria and Xanthomendozae,
orange lichens within the pollution tolerant Teloschistaceae.
Bottom: Caloplaca trachylioides is also among the pollution
tolerant Teloschistaceae, but is concentrated here due to
naturally high nitrogen compound concentrations around a
activities that require government approval
(including many land developments).
Yet lichen conservation often remains ignored
despite these laws. Just two lichens have been
declared endangered under the ESA: Cladonia
perforata, the Florida perforate raindeer lichen
was listed in 1993 and Cetradonia linearis, rock
gnome lichen (previously Gymnoderma lineare)
in 1995, which occurs in the southern
Appalachian mountains. CESA has never been
invoked for a lichen. However, California does
have lichens that could well fit both CESA and
federal ESA definitions of endangered: most
notably Sulcaria isidiifera.
The California Natural Diversity Database (CDFW
2016) and the California Native Plant Society's
“Inventory” database (CNPS 2016) are generally
used as the foundations of species-based
conservation under CEQA. Since 2001, the
California Lichen Society’s Conservation
Committee has worked closely with CNDDB and
CNPS to support ranking and listing of lichens.
Together, these organizations maintain
information on 14 lichens at present (Table 1) and
oversee a cautious proposal system. Anyone may
submit a 'sponsorship' of background information
on a lichen to the CALS Conservation
Committee, which then requires a full year of
reviews before a final decision is made.
Federal land management generally follows
CNDDB lists (or NatureServe and Natural
Heritage lists in other states; see
In the case of the U.S. Forest Service, individual
National Forests have Forest-Sensitive lists for
those species known to occur on the National
Forest lands, and often those with appropriate
geography and habitat that they are likely to be
found there in the future (see
Within the area covered by the Northwest Forest
Plan (USDA and USDI 1994), the U.S. Forest
Service and U.S. Bureau of Land Management
must also follow Survey and Manage
requirements, which involve an additional set of
taxa thought to be rare or associated with old-
growth forest conditions. Survey and Manage has
undergone several shifts due to law suits; for a
fairly concise history see
/history.php. Both Forest-Sensitive and Survey-
and-Manage lichens are listed in Table 2.
Recognizing the complexities of defining species
at present, and the limited knowledge of lichen
distributions in California, habitat-based
conservation may offer an efficient strategy for
maintaining lichen diversity without requiring a
high degree of taxonomic expertise for surveys.
Habitat-based conservation for lichens in
California has yet to be clearly defined. However,
many of the habitats that contribute most to
lichen biodiversity are readily apparent to those
who regularly investigate lichens. These habitats
are also important contributors to landscape
ecology and should be maintained wherever
possible. Habitats of interest likely include old-
growth conifer forests, undisturbed oak
savannas, rock outcrops with groundwater seeps
and other habitats that are commonly of
conservation value for many organisms.
Intersecting these habitats with broader
biogeographic patterns in lichens may provide a
strategy to identify biodiversity hotspots more
specifically over the landscape and at scales
appropriate for establishing areas of preservation
such as U.S. Forest Service “Research Natural
Table 2: Lichens that occur in California (Tucker 2014) and are identified by U.S. Forest Service Region 5 “Sensitive Species” lists
(USFS 2013) or Northwest Forest Plan “Survey and Manage” lists as of the 2011 settlement (USBLM 2011). A * denotes taxa
that are also listed in Table 1. Global and State Ranks are from NatureServe, with the exception of those also listed in Table 1.
Where no National Forests with known occurrences are listed, then the taxon has been reported from somewhere within
California (Tucker 2014) but knowledge of specific geographic distribution needs work.
S & M
National Forests with known
(misapplied name for D.
Leptogium burnetiae var.
S & M
National Forests with known
Lake Tahoe Basin Management Unit
Usnea hesperina (= U.
Usnea longissima *
[Table 2 continued]
Areas”, U.S. Bureau of Land Management “Areas
of Critical Environmental Concern”, California
Department of Fish and Wildlife preserves, and
state or local parks. CALS is considering a
strategy of naming “important lichen areas” to
support these locations, similar to the Audubon
Society's “important bird areas”
To begin describing the biogeographic patterns in
California lichens, Figure 1 provides a rough,
first-cut look at lichen biogeographic provinces, or
biomes. These will be used to discuss habitats of
interest and the few currently-known lichen
biodiversity hot-spots in California.
Central Valley. Once open shrublands and
grasslands with riparian woodlands and wetlands,
this biome is now almost completely converted to
agriculture and invasive annual grasslands.
Some riparian woodlands remain which may be
high-priority habitats, and the Bay-Delta area may
contain biodiversity hot-spots, but these habitats
need further investigation. Any remnants of intact
biocrusts should be a very high-priority for
conservation, both for retention of the remaining
biodiversity and for possible reservoirs from
which populations may expand in the future if
invasive annual grasses and soil disturbing
activities can be reduced. One glimmer of hope
for biocrusts may actually be found in some
highway right-of-ways (blocked from grazing),
where biocrusts can occasionally be found trying
to recolonize [P].
Coastal Ranges - Northern. Thickly forested
and dominated by conifers, this is the wettest
region in the state. Areas of old-growth redwood
and Douglas-fir should be high-priority habitats.
Well known from the Pacific Northwest, Lobaria
oregana and the watch-listed species, Usnea
longissima [Q], may be indicators of the wettest
zones and a legacy of old-growth forest (or at
least nearby old-growth trees) and thus will often
indicate hotspots. Occasional oak woodlands
may also be of interest. The Six Rivers National
Forest has conducted sufficient lichen surveys
that data could begin to be analyzed for hotspots.
Significant areas of rock outcrops are infrequent
in this biome, and those with the high moisture
levels deserve attention for floristic studies.
Figure 1: A rough first-cut map to delineate lichen biomes for California.
Coastal Ranges - Southern. Although these
areas do not receive nearly the rainfall of the
Northern Coastal Ranges, they do receive a large
amount of coastal fog, which is a pivotal factor for
lichen communities. Old-growth oak woodlands
and old chaparral, especially along ridgelines that
intercept fog, may be the habitats most deserving
conservation attention. Open rocky ridges may
offer some biocrust habitats, which could be
some of the better remaining biocrust
communities in California.
Desert - Great-Basin. This cool-desert
ecosystem harbors a diversity of biocrusts,
though much of it has been so heavily grazed
that few areas of biocrust remain intact and most
of the known remaining intact biocrust
communities are in Nevada. Any that might be
found in California would certainly be locations
with conservation value and would likely indicate
biodiversity hot spots. Older juniper woodlands
(with lots of dead wood) are high in lichen
diversity and deserve investigation, though these
may be a relatively common habitat at present.
Cottonwood and Aspen stands are less frequent,
so are habitats of interest.
[Q] Usnea longissima draping riparian vegetation as it falls from parent colonies in old conifers above. U. longissima is ranked S4,
placed on list 4 (watch), and included for survey and manage under the Northwest Forest Plan.
[P] Though difficult to see at the scale of this photo, biocrusts
are recolonizing this site along I-5 where they are fenced-off
from adjacent grazed lands.
Desert - Modoc. Another cool-desert ecosystem,
the Modoc is distinguished from the Great Basin
lichenologically due to the predominance of
basalt, a weakly calcareous rock. Therefore,
lichen communities are shifted toward more
calcareous species. Certain volcanic-bomb
boulder fields form habitats of high interest, and
any intact biocrust communities that could be
found would be of great interest, likely indicating
Desert – Mojave / Sonoran. These are hot
deserts, rarely receiving snow. Soil crusts are
much slower to develop here, so even pristine
habitats may have only intermittent soil coverage.
Again, good biocrust communities are of great
interest. Mountain-tops in this area are a high-
priority for investigation regarding given that
disjunctive populations that may occur in these
areas are likely reservoirs of genetic diversity.
Foothill Oaks. This region has been heavily
impacted by housing developments near cities,
and heavily grazed
elsewhere, for the
past couple hundred
years. These habitats
may be the most
altered after the
Central Valley itself.
Yet many old oaks
remain and have the
potential to harbor a
high diversity of
attention should be given to oak woodlands on
the western side of the Central Valley, as they are
less impacted by agricultural air pollution than the
eastern side. Areas that hold fog or have other
sources of local moisture may also be of interest.
Biocrusts were probably abundant prior to
ranching, but it is unlikely that much, if any, intact
biocrust communities have endured this long.
Still, small pockets of biocrusts might be
discovered in steep rocky areas that have not
been so heavily grazed and do not support dense
cover of annual grasses. Combined with old oaks
and sources of moisture, these areas would be
good candidates for hotspots.
Hyper-Coastal – Northern. Nearly within sight of
waves, hyper-coastal areas have very unusual
lichen communities. The northern hyper-coastal
has floristic links to Pacific Northwest coastal
lichen communities and is most notable for the
relatively common Niebla cephalota, and the list
1B Sulcaria spiralifera [R]. Pockets of older pines
and spruce among dunes are known high-priority
habitats and the dune forests of the Samoa
Peninsula could readily be named as a hotspot,
or an important lichen area. Hardwood shrubs
bordering estuaries may
also be good candidates.
Many of the broader, flat
areas of terrain within this
biome (e.g. the Crescent
City area) likely deserve
attention as hotspots, yet
are focal points for human
development. Less at-risk,
sea stacks are likely
valuable lichen habitats
Southern. The southern
hyper-coastal biome also harbors unusual lichen
communities, though with floristic links to Baja
California. A number of Niebla species are
frequent in this zone. Possibly the rarest lichen in
[R] Sulcaria spiralifera (mixed with Ramalina menziesii,
another long fruticose species) on spruce among dunes in the
Northern HyperCoastal biome.
California is endemic to this biome: Sulcaria
isidiifera (list 1B). The only known western
hemisphere population of Cladonia firma (list 2B)
also occurs here.
Both inhabit coastal
dune scrub at
Montaña de Oro
State Park – a clear
Islands are also
expected to contain
lichen hotspots. Much
of this biome is highly
estate and all
significant areas of
intact shrublands, woodlands, or vegetated dune
systems probably deserve conservation.
Montane - Interior. This biome represents the
Sierra-Nevada and southern Cascade mountains.
Known habitats of conservation priority include
streams that are not
which often harbor
Leptogium rivale, and
forests at lower
harbor a high
diversity of lichens
and are good candidates for hotspots, particularly
any within deep canyons in the relatively rainy
Plumas National Forest. Old-growth giant
sequoia are also of conservation importance for
lichens. Despite the remoteness of many of these
mountains, air pollution from cities and agriculture
of the central valley is impacting this biome and a
growing body of evidence suggests that Bryoria
species are declining
within the biome (McCune
et al. 2007), including B.
fremontii, an important
food for the Northern
(Rosentreter et al. 1997;
Zabel & Waters 1997).
Montane - Klamath. The
abundance of Douglas fir,
and floristic links to the
distinguish this biome from the Montane - Interior
biome. Yet again, lower elevation old-growth
conifer forests are infrequent, but harbor a high
diversity of lichens and are good candidates for
hotspots. This region also has many diverse oak
woodlands [S] which are poorly known
deserve research and
especially those that still
have sporadic biocrusts.
Small patches of biocrusts
can also be found in the
decomposing granite [T],
and need floristic
Montane - Southern.
These may be closely allied to the Montane –
Interior biome for lichen floristics. However, their
southern reach and discontinuities with other
ranges renders them likely to have a large
[S] Oak woodlands in the Klamath Montane biome, a diverse
lichen habitat that is poorly surveyed.
[T] Patches of decomposing granite (foreground) provide a
habitat for biocrusts in the subalpine of the Klamath Montane
proportion of disjunct populations, which often
have population-level genetic variety (Printzen et
al. 2003) and could be important for species
adapting to changing climates. Higher-elevation
sites with sources for moisture may deserve the
most attention, and recently a population of
Solorina spongiosa (list 2B) was discovered in
just such a situation (Knudsen & Crawford 2014).
Urban / Sub-urban Development. As humans
invade the natural environment, it would be ideal
to retain what we can, maybe even encourage
the natural environment to invade our developed
areas. Planning for open space, and simply
retaining trees and rock outcrops would be a
huge start. Another idea which can enhance
existing development is xeriscaping. Unnatural
moisture regimes from landscape watering can
be disruptive for lichens, so eliminating landscape
watering can allow lichens native to the area to
colonize and survive. A third idea is to increase
use of natural materials. For example, fencing
with untreated redwood or cedar as opposed to
plastic, metal, or treated wood [U].
Air Pollution. As already noted, most
lichens are vulnerable to air pollution,
which is known to have impoverished
lichen communities at regional scales in
Europe (Richardson 1974; Hawksworth
1990). Similar signs of air pollution
impacts are being seen in the Sierra-
Nevada Mountains, likely due to
agricultural practices in the Central
Valley (Jovan & McCune 2004, 2005;
McCune et al. 2007; Fenn et al. 2010).
We must steadfastly continue to make
progress toward cleaner air.
Invasive Exotic Plants. Plant invasions
can shift the ecology of habitats, or even
entire biomes, with unknown
repercussions for lichen communities.
Remnant open spaces in the Central
Valley are almost entirely lost to invasive
annual grasses. The desert biomes,
particularly in the Great Basin, are
undergoing similar conversion (Pellant
1996). Evidence has been reported that
soil biocrusts and annual grasses are
mutually exclusive (Belnap et al. 2001b;
Deines et al. 2007; Peterson 2013).
Therefore recovery after loss will likely
[U] Natural fencing materials provide habitat for a diversity of epiphytic
species, encouraging native lichens to invade areas of human development.
Cedar fence posts dug straight into the soil can outlast the more commonly
used pressure treated fir with cement footings. The cedar posts for this
garden have been in place for more than 40 years and remain strong.
be difficult, but where intact crusts remain, annual
grasses may be held in check. This suggests a
two-fold approach is possible: first retaining what
remains, so that biocrusts have colonization
potential, then finding a way to reduce annual
grasses so that biocrust recolonization can
Forestry Practices. Forestry has come a long
way over the past 100 years, but progress in this
field still has further to go. Old-growth stands,
both coniferous and hardwood, need further
research on the biodiversity they host (McCune
1993; Sillett 1995; Williams & Sillett 2007).
Among younger managed stands, thinning
forests, rather than clear-cutting, should be
promoted. Thinning should not be uniform, as it
results in a homogenization of forests pushing
lichen communities toward the more common
species (Peterson & McCune 2001). Variable
thinning, resulting in pockets of older trees
among young stands [V], can form mini-hotspots
of biodiversity (Peterson & McCune 2003).
Wildfire. The impacts of wildfire on lichens are
poorly studied. Most studies are on biocrust
communities in cool deserts (Hilty et al. 2004), or
ground dwelling lichens in forests of other regions
(DeBolt et al. 2007). The few studies of wildfire
effects on epiphytic lichens are from other
systems (e.g. Mistry & Berardi 2005), or only
tangentially address wildfire (Lehmkuhl 2004;
McCune et al. 2007). These enable little more
than circumstantial speculation that the lichen
[V] A patch of older trees amidst a young stand of Douglas-fir provided a continuity of habitat for lichens through logging of the
stand and probably encouraged faster recovery of lichen biodiversity. These serve as an example for modern thinning of
flora of the west must have developed in
conjunction with wildfires. The logic follows that
while fire may burn lichens in close proximity,
natural fire regimes should not be a major
conservation problem for lichens.
Obviously, direct burning destroys lichens, but
how much heat can they tolerate? Most natural
wildfires occur in dry weather when lichens would
be dormant. Dormancy should offer some level of
protection, both from heat and smoke. However,
when lichens are moist, smoke may have similar
effects to air pollution. Note though, that lichens
are accumulators of some pollutants; a short-term
dose of heavy smoke may have effects different
from long-term air pollution.
There is a general assumption among many
lichenologists that a short dose of smoke while
lichens are dormant will have very minor effects,
but this topic certainly deserves research.
Following that assumption, naturally timed low-
intensity wildfires may have only minor local
effects on lichen except where directly burned.
However, prescribed burns performed when
moisture levels are high may cause greater
damage to lichens as the lichens may be
biologically active and thus more sensitive.
Wildfire-fighting Practices. Unfortunately,
wildfire-fighting practices may be as problematic
for lichens as the wildfires themselves. Fire
retardant (essentially a fertilizer) dropped from
aircraft appears to be toxic to lichens [W].
Retardant drops are often performed along
ridgelines, which frequently have habitats of
conservation value and biodiversity hotspots.
One subalpine ridgeline in the Klamath Montane
biome is known where lichens are generally
abundant on rocks but areas remain that are
barren and still show a reddish stain from a
retardant drop during a 1987 wildfire.
California simply needs more basic floristic work
on lichens. Species-based conservation offers
direct conservation of biodiversity, while habitat-
based conservation may add efficiency to
achieving conservation goals. Both rely on
understanding the lichen floristic patterns in
We need to solidify much of the research on
ecosystem functions and services in order to
[W] Left: Rhizoplaca melanopthalma in the Great Basin, dead after exposure to fire retardant; right: the same species alive under
better explain the need for lichen conservation.
The items described earlier demonstrate that
lichens play many important roles, but much of
the research mentioned is from just a handful of
studies, often fairly distant from California. A
broader body of more local work would improve
evidence of services in particular ecosystems,
and therefore should strengthen the case for
Perhaps of most imminent importance, our
knowledge of how lichens respond to wildfire and
fire-fighting methods is a huge black-hole. As
climate change and human population expansion
continue, wildfires in California will continue to be
problematic. Even the most basic questions
about lichens and fire need research!
Lastly, research is needed on lichen recovery and
restoration. What lichen communities could be
realistically developed within anthropocentric
landscapes? What can we do to help lichen
communities recover after fire or other
disturbances? Can we do anything to help lichens
cope with climate change? … Or to eventually
recover once we humans get our impacts under
Given the changes our environments are currently
experiencing, short-term reactionary conservation
strategies may only slow our losses.
Knowledge-based strategies with a long-term focus,
perhaps on the scale of centuries, and with a
consideration for rebuilding lost ecosystems, may
ultimately succeed best.
California Lichen Society (CALS). An
association dedicated to educating people about
lichens and their conservation, CALS is very
welcoming of novice biologists and naturalists
and has frequent field trips and workshops,
particularly in the broader Bay Area.
Northwest Lichenologists (NW). Another
association dedicated to educating people about
lichens and their conservation, NWL maintains a
certification program to promote professionalism
in lichen surveys. http://northwest-
Floristic and Ecological Works
Field Guide to California Lichens (Sharnoff
2014). A beautiful photographic guide to the
majority of foliose and fruticose lichens known
from the state, along with many crustose lichens
Lichens of North America (Brodo et al. 2001)
and updated keys (Brodo 2016). These are the
books to have for learning about and identifying
lichens in North America. Amazingly illustrated
and photographed, these have remarkably good
coverage of California lichens.
Biotic Soil Crust Lichens (McCune and
Rosentreter 2007). Although this book is written
for the Columbia Basin, it is very useful for most
biocrusts in California as well.
Biological Soil Crusts: Ecology and
Management (Belnap et al. 2001a). This online
publication provides all the necessary
foundations for understanding biocrusts.
Macrolichens of the Pacific Northwest
(McCune & Geiser 2009). Excellent keys and
descriptions for foliose and fruticose species of
Oregon, Washington. This book is quite relevant
to California forests as well.
Sonoran Desert Lichen Flora (Nash et al. 2002-
2007). These are highly technical works, but are
the only attempt to be truly comprehensive for a
large region that includes part of California (much
of the southern end of the state, including
Databases and Checklists
California Checklist (Tucker 2014). A list of the
1869 lichen taxa reported from California, and a
brief history of lichenology within the state.
Consortium of North American Lichen
Herbaria (CNALH 2017). A database of the
digitized lichen specimen data from 93 herbaria
at the time of this writing.
Inventory of Rare, Threatened, and
Endangered Plants of California (CNPS
Inventory). This online database provided by the
California Native Plant Society (CNPS) now
includes lichens as listed by the California Lichen
Society (CALS). http://www.rareplants.cnps.org/
North American Checklist (Esslinger 2015). A
list of the 5388 lichen taxa reported from North
America (north of Mexico).
Recent Literature on Lichens (Culberson et al.
2016). This online database covers more than
just recent literature; it is nearly comprehensive
with literature extending back into the 1800’s.
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