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Floristics and Distribution Patterns of Lichens and Bryophytes in
Microbiotic Crusts of British Columbia’s Ponderosa Pine Forests
Patrick Williston
Department of Botany, University of British Columbia
3529 - 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
[email protected]
ABSTRACT
Microbiotic crusts are an important though often overlooked component of the biodiversity and ecology of arid and
semiarid ecosystems. This study lists 51 terricolous lichens and 39 terricolous bryophytes of microbiotic crusts in
British Columbia’s semiarid ponderosa pine (Pinus ponderosa) forests. The list is the first to document the
terricolous lichens of these forests, and adds 14 species to previous reports of the bryophytes. This study also
describes successional patterns, following grazing disturbance, of invasive nonnative vascular plants, 3 native
grasses, and 3 microbiotic crust species. An understanding of successional patterns is essential for managing the
biodiversity of British Columbia’s ponderosa pine forests, one of the most restricted ecosystems in the province.
Key words: bryophyte, lichen, microbiotic crust, Pinus ponderosa, ponderosa pine.
BACKGROUND
Microbiotic crusts, also called cryptogamic, cryptobiotic, microphytic, biologic, and microfloral crusts, are an important
component of the biodiversity and ecology of arid and semiarid ecosystems. Unfortunately, they are also often overlooked in ecological studies and vegetation inventories.
Microbiotic crusts are assemblages of bryophytes, lichens,
algae, fungi, bacteria, and cyanobacteria that integrate with
the soil surface of arid and semiarid ecosystems. While earlier studies have reported the common bryophytes in ponderosa pine (Pinus ponderosa) forests of British Columbia,
little work has been conducted to date on the lichens, algae,
fungi, bacteria, and cyanobacteria occurring in this ecosystem (Schofield 1988). This study adds to existing lists of the
bryophytes of ponderosa pine forests and is the first to report the common terrestrial lichens in these ecosystems.
Inquiry into the ecological functions of microbiotic crusts derives from studies conducted in the United States and Australia
(West 1990; Eldridge 1993, 1996; Harper and Pendelton 1993;
Belnap 1994; Eldridge and Greene 1994; Eldridge and Tozer
1996; Eldridge et al. 1997). In these regions, microbiotic crusts
have been shown to influence nitrogen balance, water infiltration and retention, and water and wind erosion in grassland
ecosystems (West 1990, Eldridge 1993, Harper and Pendleton
1993). Recent research in the grasslands of the Okanagan
Valley of British Columbia determined that microbiotic crusts
have a significant effect on water retention after rain events
(Atwood 1998). Few studies have examined successional patterns in crust communities (Looman 1964). The research presented here is the first to describe patterns of succession in
British Columbia’s ponderosa pine forests.
MICROBIOTIC CRUSTS
Despite the rich diversity of bryophytes and lichens in the
semiarid interior of British Columbia, our understanding of
its flora and ecology is rudimentary. McIntosh (1986, 1997)
conducted the most complete survey of the bryophytes of
British Columbia’s grasslands in a thesis that included a key
to grassland bryophytes and reported several species new to
the province. While his study did not include ponderosa pine
ecosystems, several of the species overlap from the grasslands to the ponderosa pine forests. Schofield (1988) reported species belonging to ponderosa pine forests in a general
survey of the biogeoclimatic zones of British Columbia. The
present study adds 14 species to the existing list and provides insights into the ecology of 1 dominant bryophyte.
Lichens have been the focus of intensive investigation in 4
regions of the province: the coastal Douglas-fir zone (Noble
1982), the Queen Charlotte Islands (Brodo 1995), and wet
coastal and interior ecosystems (Goward and Thor 1992,
Goward et al. 1994, 1996). This research lists the terrestrial
lichens from 19 ponderosa pine study sites and discusses
successional patterns of 2 common lichens, Cladonia pyxidata and C. chlorophaea. Efforts to describe crust communities have been more thorough in the Great Basin region of
the United States (St. Clair et al. 1993). While several
species from the Great Basin are shared with the British
Columbia flora, genera such as Cladonia appear to increase
L. M. Darling, editor. 2000. Proceedings of a Conference on the Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15 - 19 Feb.,1999. Volume Two.
B.C. Ministry of Environment, Lands and Parks, Victoria, B.C. and University College of the Cariboo, Kamloops, B.C. 520pp.
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WILLISTON
in diversity and cover with latitude, making British
Columbia’s flora unique (Goward and Ahti 1997).
PONDEROSA PINE FORESTS
British Columbia’s ponderosa pine forests are restricted to
the lowlands and low slopes of the driest valleys in the southcentral and southeastern regions of the province. The mean
annual rainfall is 280–500 mm (Meidinger and Pojar 1991).
These forests are characterized by hot, dry summers and
cool winters with little snowfall (Meidinger and Pojar 1991).
The canopy is comprised of broadly spaced ponderosa pine,
with Douglas-fir (Pseudotsuga menziesii) appearing in draws
and wetter areas. The understory vegetation is dominated by
the perennial bunchgrasses Festuca campestris and Elymus
spicata, and includes a diverse array of forbs and shrubs.
Historically, these forests were subject to natural periodic
fires; however, grazing has since replaced fire as the primary
source of disturbance, resulting in an increase in the dominance of early-successional vegetation. Turf-forming Poa
pratensis and the annual Bromus tectorum, both of which
are aggressive, nonnative graminoids, have replaced native
perennial bunchgrasses in areas of heavy disturbance
(Daubenmire 1968, 1970). Indeed, ponderosa pine forests in
a natural condition are rare in British Columbia—a conservation issue worthy of concern.
METHODS
STUDY AREA
The study was conducted along a glacial lake-bed terrace east
of Kamloops, B.C. The sites were oriented along an 18-kmlong east/west transect on the south side of the South
Thompson River. The elevation ranged between 500 and
600 m, and slopes remained between 2 and 15%, with a north
aspect. Sites represented early (E), mid (F), late (L), and natural (P) seral stages and were restricted to a zonal position in
the Ponderosa Pine biogeoclimatic zone (Lloyd et al. 1990).
Site history and the condition and composition of the dominant vegetation were used to determine seral stages. Five sites
were sampled at each seral stage except the mid-seral stage,
which was sampled at 4 sites. In total there were 19 sites.
SAMPLING
Fieldwork was conducted using a frame with 10 precise sampling points. The frame was positioned at random intervals
along 5 50-m transects on a 40-m baseline. Each transect
was sampled with 10 placements of the sampling frame to
yield 100 points per transect. These points were used to determine the percent cover of vascular plants and microbiotic crust species. Crust specimens were curated as described
by Rosentreter et al. (1988).
770
RESULTS AND DISCUSSION
BRYOPHYTE AND LICHEN SURVEY
Table 1 lists the terricolous bryophytes and lichens observed
while conducting this research, including 14 species of terrestrial bryophytes not previously reported for the ponderosa pine forests of British Columbia (Schofield 1988).
This list includes those species observed in the study area
and does not constitute a complete survey of the ponderosa
pine forest ecosystem. Voucher specimens of these species
are located at the University of British Columbia herbarium
and the British Columbia Ministry of Forests, Range Branch
in Victoria. Williston (1999) provides an illustrated key to
the common bryophytes and lichens of the ponderosa pine
forests and associated grasslands of British Columbia.
VASCULAR PLANTS
The successional transition of forested grassland ecosystems
from nonnative annual grasses to native bunchgrasses in the
British Columbia Interior has been previously described
(McLean and Marchand 1968). This study builds upon existing knowledge by examining some of the ecological effects of
these species’ distributions and vegetation structure changes.
Early successional vegetation is comprised of native and nonnative annual grasses with a high cover of the native perennial Stipa comata (Figs. 1 and 2). Over time, the cover of S.
comata and nonnative grasses decreases and the cover of
large native perennial bunchgrasses such as Festuca
campestris and Elymus spicata increases (Figs. 3 and 4). The
shrub Artemesia tridentata, a species known to be unpalatable to cattle (the primary nonnative agent of disturbance in
this ecosystem), increases in cover under intensive grazing
management strategies (Daubenmire 1970). A. tridentata provides shade in early seral sites; however, the chemistry of its
litter differs from that of the bunchgrasses. This is reflected in
the distribution patterns of microbiotic crust species, which
suggest that some late successional species, such as
Brachythecium albicans, are able to colonize under the cover
of A. tridentata, while others are not (Fig. 7).
MICROBIOTIC CRUST SPECIES
Cladonia pyxidata is 1 of the most common crust species in
the ponderosa pine forests of British Columbia. This species
increases in cover in the mid-seral stage and then decreases
with succession (Fig. 5). C. pyxidata is a soil colonizer and is
able to utilize soil substrata created by natural and humancaused disturbances. An increase in substratum availability
in the mid-seral stage probably accounts for the greater
cover of C. pyxidata.
Cladonia chlorophaea is most commonly found beneath
the grass litter of native perennial bunchgrasses such as
Festuca campestris and Elymus spicata. It is not surprising
that this species increases in cover in later seral stages where
bunchgrasses dominate the understory (Fig. 6).
Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15–19 Feb. 1999.
Microbiotic Crusts of Ponderosa Pine Forests
Table 1. A list of the terricolous bryophytes and lichens from the study area in the ponderosa pine forests of the southern interior of
British Columbia.
Liverworts
Barbilophozia hatcheri (Evans) Loeske*
Cephaloziella divaricata (Sm.) Schiffn.
Lophozia excisa (Dicks.) Dum.*
Ptilidium ciliare (L.) Hampe*
Ptilidium pulcherrimum (G. Web.) Hampe*
Mosses
Aloina brevirostris (Hook & Grev.) Kindb.
Barbula convoluta Hedw.
Brachythecium albicans (Hedw.) Shimp. in B.S.G.
Brachythecium collinum (Schleich. ex C. Mull.) Shimp. in
B.S.G.
Bryum argenteum Hedw.
Bryum caespiticium Hedw.
Buxbaumia aphylla Hedw.*
Ceratodon purpureus (Hedw.) Brid.
Desmatodon convolutus (Brid.) Grout
Dicranum polysetum Sw.*
Dicranum scoparium Hedw.
Didymodon vinealis (Brid.) Zander
Ditrichum flexicaule (Swaegr.) Hampe*
Encalypta rhaptocarpa Schwaegr.*
Encalypta vulgaris Hedw.*
Fissidens bryoides Hedw.*
Funaria hygrometrica Hedw.
Homalothecium aeneum (Mitt.) Lawt.
Hylocomium splendens (Hedw.) B.S.G.
Hypnum revolutum (Mitt.) Lindb.
Hypnum vaucheri Lesq.
Mnium spinulosum B.S.G.*
Phascum cuspidatum Hedw.
Pohlia nutans (Hedw.) Lindb.
Polytrichum juniperinum Hedw.
Polytrichum piliferum Hedw.
Pseudoleskeella tectorum (Brid.) Broth.
Pterygoneurum subsessile (Brid.) Jur.
Pterygoneurum ovatum (Hedw.) Dix.
Rhytidiadelphus triquetrus (Hedw.) Warnst.
Rhytidiopsis robusta (Hedw.) Broth.*
Sanionia uncinatus Loeske*
Tortula ruralis (Hedw.) Gaertn. et al.
Weissia hedwigii Crum*
Lichens
Acarospora schleircheri (Ach.) A. Massal.
Amandinea punctata (Hoffm.) Coppins & Scheid
Arthonia glebosa Tuck.
Bryonora castanea (Hepp) Poelt
Buellia geophilla (Florke ex Sommerf.) Lynge
Caloplaca jungermanniae (Vahl) Th. Fr.
Caloplaca tominii Savicz
Candelariella terrigena Rasanen
Catapyrenium squamulosum (Ach.) Bruess
Cetraria ericetorum Opi
Cladina arbuscula (Wallr.) Hale & Culb.
Cladina mitis (Sandst.) Hustich
Cladina rangiferina (L.) Nyl.
Cladonia borealis S. Stenroos
Cladonia botrytes (K. Hagen) Willd.
Cladonia cenotea (Ach.) Schraerer
Cladonia cervicornis (Ach.) Flot.
Cladonia chlorophaea (Florke ex Sommerf.) Spreng.
Cladonia cornuta (L.) Hoffm.
Cladonia ecmocyna Leighton
Cladonia fimbriata (L.) Fr.
Cladonia gracilis (L.) Willd.
Cladonia mulitformis G. Merr.
Cladonia phyllophora Hoffm.
Cladonia pocillum (Ach.) Grognot
Cladonia pyxidata (L.) Hoffm.
Cladonia rei Schraerer
Cladonia subulata (L.) F. H. Wigg.
Cladonia sulphurina (Michaux) Fr.
Cladonia symphycarpa (Florke) Fr.
Collema tenax var. crustaceum (Kremp.) Degel.
Diploschistes muscorum (Scoop) R. Scant
Endocarpon pusillum Hedw.
Leptogium sp.
Nephroma parile (Ach.) Ach.
Ochrolechia upsaliensis (L.) A. Massal.
Peltigera canina (L.) Willd.
Peltigera didactyla (With.) Laundon
Peltigera didactyla var. extenuata (Nyl.) Goffinet & Hastings
Peltigera lepidophora (Vainio) Bitter
Peltigera malacea (Ach.) Funck
Peltigera ponojensis Gyel.
Peltigera rufescens (Weis) Humb.
Physconia muscigena (Ach.) Poelt
Placynthiella uliginosa (Schrader) Coppins & P. James
Polychidium muscicola (Sw.) Gray
Psora cerebriformis W. A. Weber
Psora globifera (Ach.) A. Massal.
Psora montana Timdal
Stereocaulon sp.
Xanthoria wyomingica (Gyel.) Hale
* Denotes species added to reported lists of bryophytes of British
Columbia’s ponderosa pine forests.
Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15–19 Feb. 1999.
771
WILLISTON
Figure 1. Percent cover of invasive, nonnative vascular plants
over 4 successional stages: early (E), mid (F), late
(L), and natural (P). Cover is the mean per transect.
Figure 2. Percent cover of Stipa comata over 4 successional
stages, as described in Figure 1.
Figure 3. Percent cover of Festuca campestris over 4 successional
stages, as described in Figure 1.
Figure 4. Percent Cover of Elymus spicata over 4 successional
stages, as described in Figure 1.
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Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15–19 Feb. 1999.
Microbiotic Crusts of Ponderosa Pine Forests
Figure 5. Percent cover of Cladonia pyxidata over 4 successional
stages, as described in Figure 1.
Figure 6. Percent cover of Cladonia chlorophaea over 4 successional stages, as described in Figure 1.
Brachythecium albicans is most abundant in partially
shaded microsites. In most stages, this pleurocarpous
bryophyte is common in needle litter beneath ponderosa
pine. In early seral stages it is also under Artemesia tridentata, while in the natural condition, where its cover is greatest, it occurs under the cover of bunchgrasses (Fig. 7).
CONCLUSIONS
Figure 7. Percent cover of Brachythecium albicans over 4 successional stages.
Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15–19 Feb. 1999.
This study lists 51 terricolous lichens and 39 terricolous
bryophytes known to occur in British Columbia’s ponderosa
pine forests. This list represents the first for the lichens of
this ecosystem and adds 14 species to previous reports of the
bryophytes. Trends in the cover of vascular plants,
bryophytes, and lichens suggest the following patterns with
succession: 1) nonnative vascular plants decrease; 2) Stipa
comata and Cladonia pyxidata have the greatest cover in
the mid-seral stage and then decrease; 3) the large, native,
perennial bunchgrasses Festuca campestris and Elymus spicata, and the lichen Cladonia chlorophaea increase; and 4)
the pleurocarpous bryophyte Brachythecium albicans decreases in the mid-seral stage and has its greatest cover in
the natural condition.
Analysis suggests that the surface vegetation in ponderosa
pine ecosystems is composed of a dynamic community of
vascular and nonvascular organisms with discernible early
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WILLISTON
and late successional species. By examining the patterns of
vascular plants and microbiotic crust species it is possible to
determine which seral stage a site is in. Evaluating seral development is essential to managing rangelands for an array of
successional stages, and for protecting representative areas
that are in a natural condition. Research in progress will
elaborate on relationships between microbiotic crust species
and successional patterns in this ecosystem.
ACKNOWLEDGEMENTS
Thanks to: G. Bradfield, research design, statistics, manuscript review, and supervising; M. Fairbarns, research design
and logistics; S. Ford, logistics; G. Hayes, logistics; T.
Goward, taxonomic consultation and manuscript review; K.
Johnston, fieldwork; T. McIntosh, taxonomic consultation; T.
Redding, logistics; K. Sadler, manuscript review; R. Tucker,
research design and site selection; C. Wulff, manuscript review; and W. Zhang, statistics and manuscript review.
Financial support was provided by the British Columbia
Ministry of Forests, Range Branch.
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