BEN # 251

Adolf Ceska aceska at
Sat Jun 10 03:03:28 EST 2000

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No. 251                              June 10, 2000

aceska at                Victoria, B.C.
 Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2

From: Patrick Williston [ Pwilliston at ]

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.

Study Area

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.

Positive feedback

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;
Atwood 1998).

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.

From: Dirk Albach [ albach at ]

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!

   Dirk Albach, 
   Botanisches Institut der Universitaet Wien, 
   Rennweg 14, A-1030 Vienna, Austria; e-mail: albach at

From: Adolf Ceska [ aceska at ]

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: at
   Web site:


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.

Available from:

   Koeltz Scientific Books
   P.O.Box 1360
   D-61453 Koenigstein / Germany
   Fax: (+49) 6174 937240
   Phone: (+49) 6174 93720
   E-mail: koeltz at

Please note: 
        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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