BEN # 251
aceska at victoria.tc.ca
Sat Jun 10 03:03:28 EST 2000
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No. 251 June 10, 2000
aceska at victoria.tc.ca Victoria, B.C.
Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2
A LUST FOR CRUST:
SUCCESSION AND MICROBIOTIC CRUSTS IN BRITISH COLUMBIA
From: Patrick Williston [ Pwilliston at bulkley.net ]
Microbiotic crusts are assemblages of lichens, bryophytes
(mosses and liverworts), algae, fungi, bacteria, and cyanobac-
teria that are important contributors to the ecology and species
diversity of terrestrial ecosystems in semiarid regions. Unfor-
tunately they are also inconspicuous and taxonomically challeng-
ing, and are often overlooked in ecological studies and vegeta-
tion inventories. In many regions, the importance of these
crusts is poorly understood and their basic floristics com-
pletely unknown. Indeed, only in the last 30 years have research
efforts focussed upon how human caused disturbances, such as
trampling by domestic livestock, affect crust diversity and
Over the past three years I have spent some time examining the
successional patterns of microbiotic crusts in ponderosa pine
forests, one of British Columbia's most restricted ecosystems.
This article summarizes some observations made along a distur-
bance gradient reflecting past grazing activity by livestock
(Williston 1999). Early successional sites were sampled in
recently heavily grazed (as evidenced by the presence of dung
and consumed forage) while later successional sites had not been
used by livestock for a period of time. The precise dates of use
were not determined.
Sites were situated in ponderosa pine forests on a silt terrace
along the South Thompson River near Kamloops. These silt ter-
races are residual lakebed sediments created by glacial lakes
that formed during the melting of the Pleistocene glaciers. They
occur in many inland valleys in southern British Columbia and
tend to support an unusually rich community of ground-dwelling
lichens and bryophytes.
While vascular plants have long been used to evaluate succes-
sional patterns and rangeland condition, microbiotic crust
species are now recognized as being equally valuable indicators
of succession. In the Kamloops area, Nuttall's pussytoes (Anten-
naria parviflora) and pasture sage (Artemisia frigida) are
associated with the crustose lichen Diploschistes muscorum, and
the mosses Bryum caespiticium and Ceratodon purpureus in areas
of recent disturbance. Stipa comata and Poa secunda are as-
sociated with the lichens Physconia muscigena, Cladonia
pyxidata, Placythium uliginosum, and the haircap moss
Polytrichum piliferum in moderately disturbed, or mid-
successional sites. Bluebunch wheatgrass (Pseudoroegneria
spicata), junegrass (Koeleria macrantha), yarrow (Achillea
millefolium), and umber pussytoes (Antennaria umbellata) are
associated with the pelt lichen Peltigera rufescens, and the cup
lichens Cladonia borealis and C. chlorophaea in late succes-
sional sites. The latest succession associates include rough
fescue (Festuca campestris), the moss Brachythecium albicans,
and the cup lichen Cladonia gracilis.
In general, disturbance-tolerant species tend to be drought-
tolerant and are often small. These include crustose and
squamulose lichen life forms, and diminutive (often < 1mm tall)
bryophytes. Late successional species tend to be larger, and
among lichens, structurally more complex. This includes
fruticose and foliose lichens, and mainly acrocarpous, or creep-
ing mosses. In late successional sites, pleurocarpous mosses
eventually replace most lichens which are poorer competitors.
Mosses have faster growth rates than lichens, and have been
shown to be more effective at retaining moisture (West 1990;
The patterns of microbiotic crust succession suggest a positive
feedback mechanism. A developed microbiotic crust absorbs and
retains a greater amount of water than does bare soil (Atwood
1998). Crust-covered microsites with greater moisture encourages
the germination of native perennial bunchgrasses (St. Clair et
al. 1984; Reitkerk and van der Koppel 1997). Shade provided by
bunchgrasses favors mosses and taller, broader lichens. These
larger, broader species further retard water loss due to
evaporation. Disruption of the crust by grazing livestock
results in a loss of moisture and a change in the species com-
position to smaller, drought-tolerant species. These observa-
tions mirror those by Reitkerk and van der Koppel (1997) who
described how positive feedback loops within a semiarid vascular
plant community were vulnerable to disruption by grazing live-
stock, causing a loss of moisture and nutrients.
The microbiotic crusts of ponderosa pine forests on silt ter-
races near Kamloops, British Columbia, support an unusually rich
assemblage of ground-dwelling lichens and bryophytes. Among them
are numerous rare or seldom collected species. The crusts in
this region form successional assemblages that change in species
composition over time. Early successional sites are often
dominated by diminutive, xerophytic bryophytes, and crustose and
squamulose lichens, while late successional sites also support
foliose lichens, fruticose lichens, and larger bryophytes. It is
hypothesized that this trend from smaller to larger species
relates to increased moisture retention, and denotes a positive
feedback mechanism. Referring to vascular plants, Rietkerk and
van de Koppel (1997, p. 74) assert that "plant-soil interactions
serve as one of the most influential positive feedback loops in
semi-arid grazing systems." My research suggests that the same
mechanism applies to the microbiotic crust community and may be
of equal importance.
Atwood, L. 1998. Ecology of the microbiotic crust of the
antelope-brush (Purshia tridentata) shrub steppe of the south
Okanagan, British Columbia. M.Sc. thesis, University of
British Columbia, Vancouver, Canada. 130p.
Lloyd, D., Angove, K., Hope, G., and C. Thompson. 1990. A Guide
to Site Identification and Interpretation for the Kamloops
Forest Region. B.C. Ministry of Forests, Victoria, Canada.
Reitkerk, M. and J. van der Koppel. 1997. Alternate stable
states and threshold effects in semi-arid grazing systems.
Oikos 79: 69-76.
St. Clair, L.L. Webb, B.L., Johansen, J.R., and G.T. Nebeker.
1984. Cryptogamic soil crusts: enhancement of seedling estab-
lishment in disturbed and undisturbed areas. Reclamation and
Revegetation Research 3: 129-136.
West, N.E. 1990. Structure and function of microphytic soil
crusts in wildland ecosystems of arid and semi-arid regions.
Advances in Ecological Research 20: 179-223.
Williston, P. 1999. Floristics and successional patterns of
microbiotic crusts in ponderosa pine forests of southern
inland British Columbia. M.Sc. thesis, University of British
Columbia, Vancouver, Canada. 115p.
WANTED: VERONICA WORMSKJOLDII AND VERONICA CUSICKII
From: Dirk Albach [ albach at gmx.net ]
The ice age might have had different effect on alpine species in
Europe and North America. I am a Ph.D. student at the university
of Vienna studying this hypothesis using the sister taxa
Veronica alpina (Europe) and Veronica wormskjoldii and Veronica
cusickii (North America). Due to shortage of funding for travel
expenses I will not be able to collect all necessary populations
myself. Can you, please, help me collect specimens (3-5
individuals/population preferably dried over silicagel + a
voucher herbarium specimen) from various populations across the
U.S. and Canada? Thank you for your help!
Botanisches Institut der Universitaet Wien,
Rennweg 14, A-1030 Vienna, Austria; e-mail: albach at gmx.net
TWO MOUNTAIN FLORAS FROM WASHINGTON AND OREGON
From: Adolf Ceska [ aceska at victoria.tc.ca ]
The Oregon State University Press recently published two impor-
tant contributions to our knowledge of local flora of Mount
Rainier, Washington, and the Steens Mountain, Oregon. Both are
similar in format, layout and depth of taxonomical treatment.
They both cover all species of vascular plants known from the
areas and are excellent field guides. They both contain a short
introduction with geographical and historical information on the
area, followed by keys for identification and descriptions of
the species. Both use illustrations from Hitchcock et al. Vas-
cular Plants of the Pacific Northwest; those in the Flora of
Mount Rainier are pasted in the text, and in the Steens Mountain
flora are collected in plates at the end of the book. Both books
have eight centre pages filled with colour photographs. I cannot
say which format I prefer, as they are both equally excellent.
Biek, David. 2000. Flora of Mount Rainier National Park.
[Washington] Oregon State University Press, Corvallis,
Oregon. 506 p. ISBN 0-87071-470-8 [soft cover] Price:
"Flora of Mount Rainier National Park provides a complete list-
ing of the 866 species of native and introduced plants found in
the Park, with keys, line drawings, and descriptions for iden-
tification, as well as a guide to plant location."
Mansfield, Donald H. 2000. Flora of Steens Mountain. [Oregon]
Oregon State University Press, Corvallis, Oregon. 410 p. ISBN
0-87071-471-6 [soft cover] Price: US$29.95
"A significant contribution to Oregon and Great Basin flora,
this comprehensive field guide identifies plants of Steens
Mountain and surrounding areas in southeastern Oregon, including
Malheur national Wildlife Refuge, Diamond Craters, and the
Alvord Desert." Altogether 871 species.
One nice detail that I noticed in Mansfield's Flora was that the
author did not sweep the taxonomical problems of Poa secunda
s.l. under the carpet, but mentioned all the formerly recognized
species, such as "Poa ampla, P. canbyi", etc. that occur in the
area. This follows the suggestion which Dr. Kellogg (the author
of the much simplified Poa secunda treatment) gave in her 1985
paper (Kellogg, E.A. 1985. Variation and names in the Poa
secunda complex. Journal of Range Management 38: 516-521). This
will enable guide users to understand the variation within the
broad Poa secunda complex better.
Both books are available from:
Oregon State University Press, 101 Waldo Hall,
Corvallis, OR 97331-6407
Phone: (541) 737-3166 Fax: (541) 737-3170
E-mail: osu.press at orst.edu
Web site: http://osu.orst.edu/dept/press
THE BOOK YOU WILL LOVE TO HATE:
INTERNATIONAL CODE OF BOTANICAL NOMENCLATURE (ST. LOUIS CODE)
The new International Code of Botanical Nomenclature (St. Louis
Code) has been printed:
Greuter, W., J. McNeill, F.R. Barrie, H.M. Burdet, V. Demoulin,
T.S. Filgueiras, D.H. Nicolson, P.C. Silva, J.E. Skog, P.
Trehane, N.J. Turland, D.L. Hawksworth [Editors and
Compilers]. 2000. International Code of Botanical Nomencla-
ture (Saint Louis Code) adopted by the Sixteenth Interna-
tional Botanical Congress St. Louis, Missouri, July-August
1999. (Regnum Vegetabile, 138). xviii + 474 p. ISBN 3-904144-
22-7 [hard cover] Price 80.00DM or US$44.44.
Koeltz Scientific Books
D-61453 Koenigstein / Germany
Fax: (+49) 6174 937240
Phone: (+49) 6174 93720
E-mail: koeltz at t-online.de
IAPT members must indicate their membership in IAPT in
order to obtain the membership discount!
[ IAPT = International Association of Plant Taxonomists]
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