Biogeomorphology and biological soil crusts: A symbiotic research relationship

Abstract

Consisting of various cyanobacteria, algae, lichens, and mosses, biological soil crusts (BSC) represent microbial ecosystems essential for many arid and semi-arid regions. Their structure and function have been researched intensely with little attention to spatial characteristics. Because it studies biota-landform interactions, biogeomorphology as a discipline stands poised to significantly narrow this apparent BSC research gap. While specific in scope, this article nonetheless outlines several key points and possible research agendas centered on the discipline of biogeomorphology that could enhance BSC research agendas. It first introduces readers to basic BSC concepts and how they have been traditionally studied with an ecological focus, noting how the discipline of biogeomorphology might influence this traditional research agenda. Then, after offering an analysis of BSC research related to remote sensing, the article then turns to how biogeomorphology stands at the forefront to conduct important BSC research through incorporation of weathering science.

Full text

Géomorphologie : relief,
processus, environnement
4/2010 (2010)
Varia
................................................................................................................................................................................................................................................................................................
Casey DuaneAllen
Biogeomorphology and biological
soil crusts: a symbiotic research
relationship
................................................................................................................................................................................................................................................................................................
Avertissement
Le contenu de ce site relève de la législation française sur la propriété intellectuelle et est la propriété exclusive de
l'éditeur.
Les œuvres figurant sur ce site peuvent être consultées et reproduites sur un support papier ou numérique sous
réserve qu'elles soient strictement réservées à un usage soit personnel, soit scientifique ou pédagogique excluant
toute exploitation commerciale. La reproduction devra obligatoirement mentionner l'éditeur, le nom de la revue,
l'auteur et la référence du document.
Toute autre reproduction est interdite sauf accord préalable de l'éditeur, en dehors des cas prévus par la législation
en vigueur en France.
Revues.org est un portail de revues en sciences humaines et sociales développé par le Cléo, Centre pour l'édition
électronique ouverte (CNRS, EHESS, UP, UAPV).
................................................................................................................................................................................................................................................................................................
Référence électronique
Casey DuaneAllen, «Biogeomorphology and biological soil crusts: a symbiotic research relationship»,
Géomorphologie : relief, processus, environnement [En ligne], 4/2010|2010, mis en ligne le 01 décembre 2012,
consulté le 02 décembre 2012. URL: http://geomorphologie.revues.org/8071; DOI: 10.4000/geomorphologie.8071
Éditeur : Groupe français de géomorphologie
http://geomorphologie.revues.org
http://www.revues.org
Document accessible en ligne sur : http://geomorphologie.revues.org/8071
Ce document est le fac-similé de l'édition papier.
© Groupe français de géomorphologie

Version abrégée en français
A partir d’une recension de la bibliographie, cet article
dresse le bilan des connexions entre la biogéomorphologie et
l’étude des croûtes cryptogamiques (CC). Constituées de
nombreux lichens, mousses, algues ou cyanobactéries, les
croûtes cryptogamiques constituent un écosystème microbien
essentiel dans les régions arides et semi-arides et, dans de
nombreux cas, y couvrent le sol de façon dominante (Belnap
et Lange 2003 ; fig. 1). Les CC jouent également un rôle clé
dans l’analyse des changements écologiques à long terme, et
plus spécifiquement dans le registre du stockage du gaz car-
bonique (fig. 2). Leur structure et leur fonction ont fait l’ob-
jet de nombreuses recherches et une classification morpho-
logique a même été proposée (fig. 3 et fig. 4) mais peu de tra-
vaux ont pris en compte leurs caractéristiques spatiales. La
biogéomorphologie, en tant que discipline étudiant les inter-
actions entre les formes de terrain et le vivant, permet de pal-
lier sensiblement cette carence apparente. En retour, cela
permettrait de réduire les insuffisances de la discipline sou-
lignées par L.A. Naylor et al. (2002), parce que les CC per-
mettent de tester le modèle holistique bioérosion / bioprotec-
tion / bioconstruction proposé par ces auteurs.
Bien que l’objectif principal de cet article soit d’examiner
le rôle important que la biogéomorphologie joue en termes
de recherches spécifiques sur les CC, cet exposé synoptique
se concentre plus spécifiquement sur les techniques biogéo-
morphologiques qui pourraient être employées pour étudier
non seulement les CCmais aussi la biogéomorphologie des
CC elle-même (un aspect totalement inédit à ce jour). L’ar-
Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Biogeomorphology and biological soil crusts:
a symbiotic research relationship
Biogéomorphologie et croûtes cryptogamiques :
relations symbiotiques de la recherche
Casey Duane Allen*
*University of Colorado Denver – PO Box 173364 – CB 172 – Denver – CO 80217-3364. E-mail: casey.allen@ucdenver.edu
Abstract
Consisting of various cyanobacteria, algae, lichens, and mosses, biological soil crusts (BSC) represent microbial ecosystems essential
for many arid and semi-arid regions. Their structure and function have been researched intensely with little attention to spatial charac-
teristics. Because it studies biota-landform interactions, biogeomorphology as a discipline stands poised to significantly narrow this
apparent BSC research gap. While specific in scope, this article nonetheless outlines several key points and possible research agendas
centered on the discipline of biogeomorphology that could enhance BSC research agendas. It first introduces readers to basic BSC con-
cepts and how they have been traditionally studied with an ecological focus, noting how the discipline of biogeomorphology might
influence this traditional research agenda. Then, after offering an analysis of BSC research related to remote sensing, the article then
turns to how biogeomorphology stands at the forefront to conduct important BSC research through incorporation of weathering science.
Key words: biological soil crusts, biogeomorphology, remote sensing, weathering.
Résumé
Constituées de nombreux lichens, mousses, algues ou cyanobactéries, les croûtes cryptogamiques (CC) constituent un écosystème
microbien essentiel dans les régions arides et semi-arides. Leur structure et leur fonction ont fait l’objet de nombreuses recherches mais
peu ont pris en compte leurs caractéristiques spatiales. La biogéomorphologie, en tant que discipline étudiant les interactions entre les
formes de terrain et le vivant, permet de pallier sensiblement ce manque. Cet article se propose de souligner les apports cruciaux de
la biogéomorphologie dans le domaine des CC et les pistes restant à explorer. Pour ce faire, sont rappelés les concepts de base des CC,
la méthodologie d’étude habituelle issue des recherches écologiques et la manière dont la biogéomorphologie pourrait faire évoluer
cette approche traditionnelle. Ensuite, après avoir rappelé l’apport de la télédétection pour la connaissance des CC, l’article montre
comment la biogéomorphologie via sa contribution à la connaissance de la météorisation peut devenir une discipline fondamentale
dans l’amélioration de la connaissance des CC.
Mots clés : croûtes cryptogamiques, biogéomorphologie, télédétection, météorisation.

ticle présente tout d’abord les concepts de base définissant
les CC, la méthodologie d’étude habituelle issue des re-
cherches écologiques et de quelles manières la biogéomor-
phologie pourrait faire évoluer cette approche traditionnel-
le. Ensuite, après une présentation rapide des concepts de la
télédétection appliquée aux études environnementales, une
analyse complète des recherches sur les CC par télédétection
est proposée, soulignant une fois encore de quelle manière la
biogéomorphologie pourrait contribuer à cet axe de re-
cherche sur les CC. Cette section inclut l’examen des tech-
niques de télédétection passées et présentes, ainsi que des
méthodes de télédétection «basiques » (e.g., la vision hu-
maine ; fig. 5) ou plus avancés (e.g., les algorithmes spéci-
fiques employés pour déterminer les types d’espèces par
imagerie satellitale). L’article détaille ensuite la manière
dont la biogéomorphologie qui se place en première ligne
sur le front de la recherche sur les CC pourrait contribuer au
comblement de lacunes par l’incorporation de son savoir sur
la météorisation (fig. 6). Faire appel à la météorisation pour
étudier les CC représente une voie novatrice qui n’a pas en-
core été entièrement exploitée par la biogéomorphologie ou
par la recherche sur les CC. Pourtant, cet axe de développe-
ment recèle un fort potentiel heuristique. L’article défend
l’idée que la météorisation superficielle peut être le chaînon
manquant reliant les recherches connectées aux CC avec la
biogéomorphologie, et représente l’un des domaines de la
biogéomorphologie qui, bien que fondamental, est souvent
négligé en tant que sujet principal de recherches (ce qui n’est
d’ailleurs pas spécifique aux recherches sur les CC). Ce rôle
fondamental dévolue à la météorisation est justifié par sa ca-
pacité à faire des sauts scalaires, un manque commun à la
recherche sur les CC (Belnap et Lange, 2003) et à la bio-
géomorphologie (Naylor et al., 2002).
De plus, parce que la biogéomorphologie est une discipli-
ne concernée par les propriétés spatiales telles que la géo-
métrie du relief, le climat et les modalités de la météorisation
(avec la capacité de les relier à travers de grands espaces),
elle représente un «champ» naturel pour les recherches sur
les CC. Au moyen d’une analyse approfondie de la littératu-
re, cet article suggère que la biogéomorphologie peut offrir à
la recherche sur les CC de nouveaux modèles, méthodes, ap-
proches, et techniques qui développeront davantage le do-
maine de recherche, tout en contribuant simultanément à l’ex-
tension de l’espace d’étude de la biogéomorphologie. Par
exemple, puisque les régions urbaines continuent à s’étendre
au détriment des terres non cultivées, les modèles dynamiques
spatiaux des CC élaborés par la biogéomorphologie peuvent
avoir une influence sur les politiques environnementales. En
fin de compte, indépendamment des résultats potentiels des
recherches consacrées aux CC, la biogéomorphologie, en in-
tégrant la spatialisation des processus et la météorisation, de-
meure un moteur puissant de la recherche environnementale,
dont les CC ne sont qu’un aspect.
Introduction
For much of Earth’s early history, the terrestrial surface
hosted little more than the primitive plant life of algae,
fungi, cyanobacteria (blue-green algae), and perhaps lichens
(Budyko and Ronov, 1979; Berner, 1994; Berner and Ko-
thavala, 2001). Found predominantly in arid and semi-arid
regions, today’s analog of biological soil crusts (BSCs)
contain various species of these same organisms. Interac-
tions between BSC organisms and calcium-containing mi-
nerals were key to the habitability of Earth, as they led to the
draw-down of carbon dioxide (Brady and Caroll, 1994; Ber-
ner, 1995). Mesozoic development of higher order land
plants led to further reduction in carbon dioxide (Drever,
1994), and Miocene development of the Himalaya Moun-
tains and the further evolution of plant life with C4photo-
synthetic pathways reduced carbon dioxide enough to let
earth cross over into the Pleistocene glacial condition (Mol-
nar et al., 1993). Given their potential importance to early
Earth and relatively unknown importance to global cycling
related to today’s Earth – and while more studies related to
cause and effect between landform and plants are being
conducted (Bornyasz et al., 2005) – it is perhaps surprising
that little research exists to answer a fundamental question of
exactly how BSCs respond to disturbance in different geo-
graphic (spatial) contexts. BSCs are known to exist in nearly
every arid and semiarid ecosystem in the world, and even in
microclimates of some temperate regions; only evergreen
rainforests climatic region lacks BSCs (Büdel, 2003). Yet
BSC research, as an interdisciplinary field of study, is unable
to articulate clear connections between spatial controls - spe-
cifically landform type and effects of BSC components on
weathering rates - and initial responses to disturbance.
This problem could be addressed at an infrastructural
level in the field of biogeomorphology. In a 2002 special
issue of Geomorphology, a review of biogeomorphology by
L.A. Naylor et al. (2002) identified key research needs si-
milar to those deficiencies facing BSC-related research des-
cribed by J. Belnap and O.L. Lange (2003). These include:
(i) expanding research to variable spatial and temporal
scales; (ii) creating new approaches for modeling and devi-
sing assessment techniques that will link bioprocesses
across the system; (iii) implementing a more holistic ap-
proach to studying biota-landform relationships; (iv) explo-
ring the effects of multiple processes in shaping landforms;
(v) bridging the disparity between short time scale biotic
processes and longer scale landform processes and develop-
ment; (vi) utilising new theoretical advances in geosciences.
To help satisfy these deficiencies, L.A. Naylor et al. (2002)
proposed an interactive and dynamic three-fold spectrum of
how biota and geomorphology interact. This spectrum
consists of ‘bioconstruction’, how biota construct or de-
construct landforms; ‘bioerosion’, how biota help or hinder
landform erosion; and ‘bioprotection’, how biota protect
and/or fail to protect landforms. One significant way to
connect this biogeomorphological research triumvirate rests
in the oft-overlooked, but extremely important science of
weathering. While weathering studies abound in geomor-
phological research, few studies apply weathering science to
BSC-related research. The overarching framework of this re-
view takes guidance from this three-fold conceptual structu-
re of identifying potential linkages of spatial aspects across
348 Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Casey Duane Allen

landforms, while also taking into account the broader role of
soil crusts in general (both biological and chemical) as noted
by H.A. Viles (2008), and addressing identified gaps in the
BSC literature related to spatial dynamics (Belnap and Lange,
2003). Indeed, as discussed in this article, perhaps weathering
science is the missing piece – the ‘glue’ – that connects bio-
geomorphology to BSC and BSC-related research agendas.
Though it seeks to examine the overall important role bio-
geomorphology can play in regards to BSC research, this re-
view paper supports a more specifically-focused agenda, ar-
guing not only for using biogeomorphological techniques to
study BSCs, but also advocating for studying the biogeo-
morphology of BSCs themselves. To that end, the first sec-
tion focuses on how BSCs are studied from the traditional
ecological point of view, and how the discipline of biogeo-
morphology stands ready to engage in and expand the usual
techniques used in BSC research (i.e., those research endea-
vors with an inherent ecological focus). Next, after a brief
overview of remote sensing (RS) as an assessment method,
insight is offered into past and current RS-BSC research ef-
forts, and how RS can be used to gain a better understanding
of BSC biogeomorphology. Then, before concluding, the ar-
ticle offers a brief overview (because there is so little related
research) of the anticipated significance BSC research can
have on narrowing the present gap in BSC-related research
agendas through the disciplines of biogeomorphology and
weathering, including it potential for carbon sequestration.
Soil crusts studied with an ecological
focus
Found in every major arid/semi-arid biome in the world,
biological soil crusts (BSCs) can account for up to 70% of
the ground cover in some of these areas (fig. 1). Despite
their inherent presence in desert biomes, BSC research tends
to focus on three research questions: (i) Composition, i.e.
what kinds of creatures live in the BSC; (ii) Nitrogen fixa-
tion, i.e. how BSCs fix atmospheric nitrogen in the soil to
promote higher plant growth; and (iii) Disturbance recove-
ry, i.e. how BSCs recover from disturbance, prima-
rily focusing on recovery from grazing. This section
demonstrates that the literature on BSCs is remar-
kably rich with ecological insights, focusing on pro-
cesses and nutrient cycling (particularly nitrogen),
creating an ecologically-important symbiotic soil-
plant-atmosphere relationship (Rychert and Sku-
jins, 1974; Harper and Pendleton, 1993; Brady and
Weil, 2008). Some of this literature also focuses on
BSCs’ roll in reducing soil erosion by binding
‘loose’ soils together and aiding in water retention and dis-
persion (MacGregor and Johnson, 1971). Meant as no criti-
cism to the researchers focusing first on an understanding of
these processes, the relationships of BSCs with respect to
landform distribution, (micro)climate, and weathering have
not been aggressively pursued (Belnap and Lange, 2003).
The discipline of biogeomorphology can fill two specific
gaps in BSC-related literature. First, BSC-related studies in-
clude a lack of comparative landform-climate studies ‘spe-
cifically’ over large areas, ‘without’ using ground cover
and/or soil texture as surrogates (e.g., expanding study areas
to larger than single landform-sizes, such as a dune field or
catchment basin). Second, studies that relate BSCs to wea-
thering rates, mechanisms, forms, and processes are few and
far between.
A fundamental ecological function of BSCs in the land-
scape rests in stabilizing desert surfaces (Belnap and Gillet-
te, 1998; Yair, 2003), yet BSC integrity is compromised by
even the smallest disturbance (e.g., a human footprint) and
devastated even more by larger events (e.g., off-road ve-
hicle). J. Belnap and D.A. Gillette (1998), for example, dis-
covered that BSCs have significantly higher threshold fric-
tion velocities than bare soil and disturbed BSCs. Indeed,
not only do BSCs hold fragile desert soil together, but they
also play a key role in preventing deflation of fine particu-
lates into the atmosphere. In valleys dominated by an urban
heat island that traps fine particulates and decreases air qua-
lity, understanding BSCs through a biogeomorphological
lens can play an integral role in the management of arid and
semi-arid region cities.
Important human impact studies on soil crusts (Cole,
1990; Belnap, 1993, 1995, 1996) note that valuable fiber
connections were easily broken during dry seasons. These
studies also found that recovery time for disturbed soil
crusts takes anywhere from six weeks for initial cyanobac-
terial growth to 20 years or more for larger ecosystem-es-
sential lichen and moss growth, putting to rest the previous-
ly-accepted view of soil crust communities taking centuries
to recover. Yet while most human disturbances do not kill
349
Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Biogeomorphology and biological soil crusts
Fig. 1 – Biological soil crusts as dominant ground
cover in an arid, badlands-topography biome, Grand
Staircase-Escalante National Monument, UT (USA).
Photo by author.
Fig. 1 – Les croûtes cryptogamiques comme couver-
ture dominante des sols au sein d’un biome aride et
à topographie ravinée, Grand Staircase-Escalante
National Monument, Utah (Etats-Unis). Photographie
de l’auteur.

BSC microorganisms directly, water must be available for
repair mechanisms to function, something lacking in the
arid and semi-arid BSC habitats (Belnap, 1993; Belnap and
Lange, 2003). In order to obtain recovery data, these studies,
and subsequent later studies (Belnap and Gillette, 1998;
Belnap et al., 2004), focused specifically on recovery rates
for soil crusts over longer temporal scales (e.g., more than
one year) and further, only focused on microorganism reco-
very, paying no attention to the type of landform where re-
covery was measured, nor to the effects of BSC microcli-
mate or seasonal precipitation regimes (key components of
biogeomorphological research).
BSCs can also assist in monitoring long-term ecological
research. Because most mature crusts contain not only cya-
nobacteria and algae but also mosses and lichens, BSCs
represent natural long-term storage systems of carbon in
arid/semi-arid regions. Yet if left undisturbed, BSCs main-
tain extremely long life spans lasting centuries (Belnap and
Lange, 2003) and have been found to, since early environ-
ments, contribute greatly to the ecosystem (Chacon-Baca et
al., 2002; Beraldi-Campesi et al., 2004; Beraldi-Campesi
and Cevallos-Ferriz, 2005). Understanding BSC resilience
and recovery among landforms near desert cities, and the
affect BSCs have on local arid and semi-arid ecosystems,
may also lead to effective models for carbon sequestration
in these settings. Soil organic carbon (SOC) plays a consi-
derable role in the global carbon cycle, containing more than
triple the amount of organic C found in living biomass and
atmospheric CO2(Lal, 2004b). Increasing SOC storage by a
mere 5% could decrease atmospheric CO2as much as 16%
(Baldock, 2007). While C sequestration in soil remains a
slow process, it may represent an efficient natural strategy to
offset increased atmospheric CO2brought on by fossil fuel
emissions (Baldock, 2007). Some estimates suggest seques-
tration rates of up to 150 Pg CO2-C over the next century are
possible if predictive accuracy can be increased (Houghton,
1995; Lal et al., 1998; Lal, 2004a). Representing ‘natural’
long-term storage facilities for carbon in arid regions – espe-
cially relative to their mass – most mature BSCs contain not
only basic carbon producers such as cyanobacteria and algae,
but also carbon-rich producers such as mosses and lichens
(fig. 2). The avenue of BSCs as carbon sequestration sites
has been only explored slightly (Beymer and Klopatek,
1991; Evans and Belnap, 1999; Evans and Lange, 2001), and
research into carbon sequestration ‘specifically’ could prove
beneficial, as BSCs are suspected to have a significant C
draw-down potential, especially relative to their mass and
composition, and specifically in conjunction with potential
soil organic carbon drawdown from soil in general (Jeffries
et al., 1989; Beymer and Klopatek, 1991; Jeffries et al., 1993
a and b; Palmqvist et al., 1994; Palmqvist, 1995; Ziegler and
Lüttge, 1998; Lange, 2000; Palmqvist, 2000; Belnap et al.,
2003a; Evans and Lange, 2003; Baldock, 2007).
Besides the enormous amounts of BSC studies relating to
human disturbances and nitrogen fixation capabilities of soil
crusts and the limited studies relating specifically to BSC-
related carbon cycling and sequestration, a great deal of re-
search also focuses on soil crust composition and taxonomy
(Cameron et al., 1965; Follmann, 1965; Cameron et al.,
1966; Forest and Weston, 1966; Soriano, 1983; Belnap and
Gardner, 1993; Bouza and Del Valle, 1993; Flechtner et al.,
1998; Maya et al., 2002; Redfield et al., 2002). Researchers
recognize four types of crusts based on visual morphology
and potential evapotranspiration (PET): smooth, rugose
(fig. 3), pinnacled (fig. 4), and rolling. Per J. Belnap and
O.L. Lange (2003, p. 180) ‘smooth crusts occur in hyper-
arid and arid hot deserts with the highest PET; rugose
crusts… in hot, arid deserts with slightly lower PET… oc-
curring where soil freezing does not occur’. Pinnacled
crusts, however, occur in arid and semi arid cold deserts
where soil freezing does occur, and ‘lower PET supports a
higher biomass of mosses and lichens than hot deserts’.
Found in ‘even colder semiarid and cool and cold deserts,
where soils freeze…’ rolling crusts have an even lower PET
that ‘…supports a larger biomass of lichens, mosses, and
vascular plants than found in less moist deserts’ (ibid.).
While taxonomic endeavors give researchers a common
vernacular, the specific morphological names were genera-
ted from, mainly, climatic characteristics, regimes,
and/or biomes. This climate-based morphological
classification lends itself well to on-the-ground
classification over small areas, but may not be ap-
350 Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Casey Duane Allen
Fig. 2 – Lichen- and moss-dominated BSC, near Zion
National Park, UT (USA). It is thought that these types of
BSCs may play an important role in the global carbon cycle
– especially relative to their mass and relationship with po-
tential SOC drawdown in conjunction with soils – including
perhaps unidentified carbon sequestration sites. Photo by
author.
Fig. 2 – Croûtes cryptogamiques à lichens et mousses,
à proximité du Parc national de Zion, Utah (Etats-Unis).
Il est pensable que ce type de CC puisse jouer un rôle
important dans le cycle global du carbone – en regard
de leur masse et de leurs liens avec la chute du carbo-
ne organique des sols – incluant peut-être des sites de
séquestration du carbone encore inconnus. Photogra-
phie de l’auteur.

plicable to larger-area studies, as most BSC climate-related
studies focus ‘specifically’ on microclimate and influences
on smaller, local ecosystems, rather than generating an ex-
panded, more holistic view or model (cf. the many local-
based climate studies such as: L.C. Pearson and D.B. La-
wrence, 1965; A. Goudie, 1972; G.J. Kidron, 1992; G.J. Ki-
dron et al., 1995 a and b; G.J. Kidron and A. Yair, 1997;
B. Sundberg et al., 1999; G.J. Kidron et al., 2000; M. Veste
et al., 2001 a and b; C.D. Allen, 2005; S.L. Ustin et al.,
2009). Large spatial area BSC assessments would be a va-
luable addition to potential BSC-related research agendas
such as assessing climate change. Lichens, as a species, re-
main very susceptible to atmospheric disturbances, and may
be able to aid researchers studying anthropogenic climate
change factors, though using lichens in this manner is only in
its infant stage and has not yet been fully investigated (Theo-
dore Crusberg, personal communication, January 2009). Ne-
vertheless, these areas of potential research represent short-
comings in BSC-related research that the discipline of bio-
geomorphology might be able to address.
Regardless of type or classification however, BSC com-
munities remain an important part of arid region sustainabi-
lity today. They are an essential first step to producing and
protecting arable soils in the fragile desert ecosystem (Bel-
nap, 1995; Belnap and Lange, 2003; Belnap et al., 2004).
The delicate microorganisms that comprise BSCs live a te-
nuous existence subject to the uncertainties of climate, dis-
persal, animals, and humans (Cole, 1990; Belnap and Lange,
2003). Disturbances of any kind increase the damage to and
destruction of BSCs (Cole, 1990; Belnap et al., 1994), espe-
cially in the unprotected and increasingly-touristed arid re-
gions of North and Latin America (Maya et al., 2002; Ro-
sentreter and Belnap, 2003). Thus, future BSC research
needs that can be addressed by biogeomorphic research tech-
niques and principles rest in the dual problems of: (i) deve-
loping better understanding of large-area spatial dynamics
of BSCs (e.g., across landforms, across biomes); and (ii) de-
veloping better understanding of biogeomorphic circum-
stances BSCs need to initiate their disturbance recovery.
Furthermore, research challenges faced in the field of bio-
geomorphology are similar to those faced in BSC-related re-
search (i.e., small area research focused on a limited set of
questions). In short, because they can be monitored, studied,
and modeled in fine detail ‘and’ across larger areas, BSCs
are uniquely positioned to address deficiencies in both BSC-
related and biogeomorphology arenas. One important BSC
assessment and monitoring technique that may make a solid
contribution to this arena – especially when studied using a
biogeomorphologic focus – is remote sensing.
Remote sensing and BSCs
At its most basic, remote sensing (RS) is used to detect or
infer the properties of a substance without being in direct
physical contact. RS tools measure the electromagnetic (EM)
energy flow from surface phenomena in and across different
regions of the wavelength spectrum. Energy can be emitted
from an object due to its temperature or reflectance from a
natural (e.g., sun) or artificial (e.g., radar) source. Energy re-
flected from surfaces varies as a function of wavelength.
When it comes to soil, the most important factor affecting re-
flectance is the soil mineralogy (e.g., iron oxides, clay mine-
rals, carbonates), though soil reflectance, soil-water content,
organic matter content, soil texture, and soil roughness are
also factors (Karnieli et al., 2003). Remotely sensed images
combine different spectra channels to create specific indices
to assess percent of ‘cover’ and accompanying biophysical
condition. The most widely used index for these purposes is
the Normalized Difference Vegetation Index (NDVI). The
NDVI values range from -1 to +1, with denser and/or heal-
thier vegetation having higher positive values. A.R. Huete et
al. (1984), however, note that in arid regions, exposed soils
have a significant effect on NDVI values. Still, vegetation in-
dices generated via satellite-borne sensors usually consist of
351
Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Biogeomorphology and biological soil crusts
Fig. 3 – Rugose biological soil crust, McDowell Mountain Re-
gional Park, Sonora Desert, AZ (USA). Photo by author.
Fig. 3 – Croûte cryptogamique rugueuse, Parc régional de la
McDowell Mountain, Désert du Sonora, Arizona (Etats-Unis).
Photographie de l’auteur.
Fig. 4 – Pinnacled BSC, near Zion National Park, UT (USA).
Photo by author.
Fig. 4 – Croûte cryptogamique à pinacles, à proximité du Parc
national de Zion, Utah (Etats-Unis). Photographie de l’auteur.

measurements in a few channels, resulting in a coarse spec-
tral resolution (referred to as broad-band, multispectral sen-
sors, e.g., Landsat TM). Yet E. Zaady et al. (2007) success-
fully used the NDVI in conjunction with the Brightness
Index (BI) to monitor BSC succession and regeneration rates
over long periods (years) and correlated findings with slope
aspect (i.e., difference of BSC spatial distribution between
north- and south-facing slopes). This technique could prove
useful in the biogeomorphological arena.
In contrast to broad-band multispectral sensors, hyper-
spectral RS measures EM reflectance in hundreds of conti-
nuous narrow-bands (e.g., the Airborne Visible and Infra-
Red Imaging Spectrometer (AVRIS) operated by NASA /
JPL; Green et al., 1998). The ability to determine and iden-
tify absorption features in a reflectance spectrum that arise
from chemical bonds present in the surface materials gives
hyperspectral RS a sizeable advantage over multispectral
RS. This has specific implications for BSC-related spatial
studies, because hyperspectral imaging can more easily dis-
criminate between shape and wavelength position of ab-
sorption features instead of merely sensing the differential
reflectance level in two channels. Yet multispectral and hy-
perspectral imaging are generally used in non-BSC research
arenas such as geologic mapping (Lillesand and Keifer,
2002), environmental studies (Swayze et al., 2000), vegeta-
tion cover identification (Martin et al., 1998; Roberts et al.,
1998), and vegetation biochemical composition (Kokaly
and Clark, 1999). For small area assessments, such as small
plots of BSCs on differing landforms however, hyperspec-
tral imaging remains relatively expensive to conduct, while
multispectral imaging offers limited coverage, although
Landsat TM has been used to successfully distinguish BSCs
from bare ground (Wessels and van Vuuren, 1986). Less ex-
pensive and more conducive to on-the-ground fieldwork, a
hand-held spectroradiometer offers coverage over most of
the EM spectrum necessary to assess BSC biogeomorpholo-
gy, but would only be feasible over smaller areas as well.
Even capturing BSC communities on differing landforms
and/or across biomes and climatic regimes using repeat di-
gital photography from the ground can prove useful (Bow-
ker et al., 2008), as BSCs are more active over short-time
scales than formerly thought (Belnap et al., 2006), but this
requires a longer timeframe. At a more general remote sen-
sing level, A. Karnieli et al. (2003) outline how differing
forms of RS, such as spacecraft versus aircraft, might be
used in conjunction with more traditional in situ and labora-
tory techniques to quantify not only BSCs, but also higher
plants and bare soils, using examples from Israel, the Colo-
rado Plateau, and the rangelands of Southeastern Idaho.
Globally speaking, BSC spectra have similar signatures
even when species composition vary, and thus can be distin-
guished from other ground components, allowing for map-
ping based solely on RS data (Karnieli et al., 2003).
Overall, RS provides an opportunity to expand in situ
BSC and BSC-related studies, cutting-down on the costs,
time, and energy used in ground truthing. Large areal as-
sessments are important to understanding spatial dynamics
of BSCs across the larger ecosystem (Belnap and Lange,
2003). Yet even though BSCs are found in nearly every en-
vironment in the world (Büdel, 2003) - and while scientific
and research endeavors related to BSCs are growing - very
few studies have been conducted on how RS can enhance
the study of BSC spatiality. Of those studies published, ac-
cording to A. Karnieli et al. (2003), D.C.J. Wessels and
D.R.J. van Vuuren (1986) were the first researchers to detect
and map BSCs using solely satellite imagery. Their work in
the Namib Desert using Landsat TM imagery led to discri-
mination between lichen covered, bare, and vegetation-co-
vered surfaces. Later, however, Y.M. Zhang et al. (2007)
discovered that using Landsat imagery to assess BSC cove-
rage is only workable when BSCs represent more than 33%
of the field of view. Aside from these two studies focused on
using Landsat TM data, relatively few publications have
specifically studied BSCs using some kind of spectral ima-
gery and/or RS - even to map them - although studies such
as J. Chen et al. (2005) developed an algorithm-based BSC-
specific index for mapping. Other notable BSC-specific RS
algorithms include E. Ben-Dor et al. (2003) who measured
BSC structure in specific wavelengths and A. Karnieli et al.
(1995, 1996, 1997) who used spectral reflectance as a dia-
gnostic tool have proved valuable, and the more advanced
BSC-specific Continuum Removal Crust Identification Al-
gorithm (CRCIA) developed by B. Weber et al. (2008) using
hyperspectral datasets.
One characteristic of BSCs that has been noticed – at a
basic ground level by C.D. Allen (2005) and on a spectral
scale by A. Karnieli and H. Tsoar (1995), A. Karnieli et al.
(1996, 1997, 2003), S.B. Fang et al. (2008), and S.L. Ustin et
al. (2009) – is that BSC spectral reflectance changes due to
precipitation (fig. 5). This change in spectral reflectance ap-
parently alters both the NDVI and the pigment absorption,
which can sometimes be misinterpreted in RS analysis (Kar-
nieli et al., 2003; Fang et al., 2008). Further, while distingui-
shing between individual BSC stands might not be possible
using satellite imagery, this apparently does not affect the abi-
lity of using high-altitude RS to monitor local or regional
changes in BSCs (Ustin et al., 2009). Thus, while high-altitu-
de RS can be used for BSC assessment, there still remains a
need for on-the-ground, small-area assessment. For example,
after using a BSC-specific algorithm to identify and poten-
tially map BSC stands over large areas, a high-resolution
image of a specific stand could be taken closer to the ground,
and then post-processed using remote sensing software (e.g.,
ERDAS Imagine) to determine which specific wave-lengths
represent BSCs versus bare ground, rock type, and higher
plant life. This type of remotely sensed data could be obtained
through the use of ‘pole cameras’, balloon (or kite) photogra-
phy, or even low-altitude (aerial) remote controlled vehicles
with a still and/or video camera mount, yielding truly rich da-
tasets from which to analyze BSC biogeomorphology.
BSC biogeomorphology and
weathering science
When it comes to BSCs, big picture linkages remain a re-
search deficit, as J. Belnap and O.L. Lange (2003) clearly
352 Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Casey Duane Allen

articulate, and contribute to the need for a better linkage bet-
ween BSC-related research and the larger conceptual need
for a systemic conceptual biogeomorphic framework, as
L.A. Naylor et al. (2002) argue. With specific regards to bio-
geomorphology, BSC research should help fill the gap bet-
ween the biogeomorphology triumvirate (bioconstruction,
bioerosion, and bioprotection; Naylor et al., 2002) by buil-
ding strong connections through innovative environmental
models by assessing spatial effects of human disturbances of
BSCs. This in turn would lead to research regarding BSC re-
siliency, opening new possibilities for ecosystem sustainabili-
ty research, as suggested in the work of M.A. Bornyasz et al.
(2005), and important emerging fields of study related to
BSCs, such as geobiology, a field of study that combines earth
science and biology and influences environmental decision
making and the larger arena of biocomplexity (Naylor et al.,
2002; Noffke, 2005), much as BSCs could do if specific land-
form type, differing climatic regimes (even meta-analyses),
and weathering parameters were studied through a biogeo-
morphological lens. Indeed, when it comes to BSCs and wea-
thering science, few disciplines are better prepared to assess
linkages than those trained in biogeomorphology, where the
interaction between biota and landform - usually through wea-
thering - comes to the forefront.
Researchers such as C. Ollier (1974) discuss weathering
and landforms in detail and C. Ollier and C. Pain (1996) dis-
cuss weathering in the context of soils in general, yet few
studies focus specifically on weathering as related to BSCs,
though recently C. Ollier and H. Sheth (2008) discuss duri-
crusts in relation to soil formation (in India) and H. Mura-
kami and S. Ishihara (2008) studied rare earth elements in
weathered crusts of China and Japan. Because it focuses on
spatial relationships (e.g., the weathering-climate-landform-
organisms continuum) biogeomorphology, as a discipline,
should stand at the forefront of future BSC research endea-
vors, especially when it comes to weathering.
While BSCs have been studied in nearly every environ-
ment around the globe, most studies remain ecologically-
specific, only taking into account ‘specific’ landform and
climate types randomly (for locational overviews, see chap-
ters 2-11 in J. Belnap and O.L. Lange, 2003). Nevertheless,
important studies related to local scale BSC landform type
and local climate can be found, though they seem to focus
on ‘specific’ dune fields and ‘seasonal’ rainfall in the Negev
Desert (Kidron and Yair, 1997; Kidron et al., 2002, 2003,
2009), “specific” alluvial fans (Barker et al., 2005) or dunes
(Brostoff et al., 2005) in the Mojave Desert, ‘specific’ pedi-
ments in the Sonora Desert (Allen, 2005; Beraldi-Campesi
et al., 2009), and mostly basin or other ‘fill’ in the Colorado
Plateau (Belnap, 1990; Lange et al., 1997; Bowker et al.,
2002; Belnap et al., 2003b; Belnap, 2006). Other locations
that have received limited study in relation to “local” land-
form type and climate include: Namib Desert (Goudie,
1972; Lange et al., 1994; Lalley and Viles, 2008), Antarcti-
ca (Boyd et al., 1966; Wynn-Williams, 1993; Green and
Broady, 2003), and the Atacama (Rundel et al., 1991; War-
ren-Rhodes et al., 2007). While it may be possible to
conduct a meta-analysis of broader landform-climate rela-
tions from these studies, no specific model has yet been de-
veloped, though such models have been suggested in re-
gards to general biogeomorphic and ecological research
(Viles et al., 2008) and more specifically to a biogeomor-
phic approach to rock weathering (Viles, 1995). Neverthe-
less, such overarching studies would probably be constrai-
ned by comparative time-scales. That is, while studies do
exist, they have occurred at disparate timeframes, some in
the 1970s, some in the 1980s, some in the 1990s, etc., and
correlating ‘old’ data with newer data might pose a problem.
As epilithic organisms, however, BSCs play an intimate
role in weathering processes through bedrock colonization
and trapping dust that eventually filters into rock through
fissures, where their small size allows for penetration into
interstices of sands and silts, especially compared to higher
plants (Hunt, 1979). With increased weathering, more Ca-
silicates are exposed to carbonic acid, improving porosity
and permeability because rock fragments (from weathering)
eventually become sedimentary rocks (e.g., limestone and
subsequent CO2storage, sandstone with high silica content;
fig. 6). And when it comes to weathering-BSC relationships
specifically, studies are fewer, and seem to only account for
BSC-weathering related research when consequential to
other topical investigations.
One of the first such studies was performed by N.A. Kra-
sil’nikov (1949), and focused specifically on mountain
rocks, though his later study in the same area focused on
high-altitude nitrogen fixing potential of microflora (Kra-
sil’nikov, 1956), a notable and continuing research thread
still prevalent in BSC-ecological research fields today [see
F.L. Pérez (1997) for work in the Andes, and R. Türk and G.
Gärtner (2003) for research overview in the Alps]. While
353
Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Biogeomorphology and biological soil crusts
Fig. 5 – Spectral difference between wet (left) and dry (right) ru-
gose BSC, Snow Canyon State Park, UT (USA). Real-time video of
change in spectral reflectance due to precipitation available here:
http://www.youtube.com/watch?v= 1ybZM9MRjxM. Photo by author.
Fig. 5 – Différence spectrale entre des croûtes cryptogamiques
rugueuses humide (gauche) et sèche (droite), Snow Canyon
State Park, Utah (Etats-Unis). Vidéo en temps réel du changement
de la réflectance spectrale dû aux précipitations disponible ici :
http://www.youtube.com/watch?v= 1ybZM9MRjxM. Photographie de
l’auteur.

many studies continue Krasil’nikov’s nitrogen-fixing stu-
dies, BSC-weathering related research in alpine environ-
ments remains scant, usually leaving the relationship – if it
is noted at all – as a side note (Gold, 1998; Dickson, 2000;
Zielke et al., 2002). Studies relating to CO2and nitrogen
fixation in alpine environments abound, but again, these stu-
dies neglect to mention the important BSC-weathering
connection (Alexander and Schell, 1973; Forman and Dow-
den, 1977; Wojciechowski and Heimbrook, 1984; Henry and
Svoboda, 1986; Chapin, 1996; Liengen and Olsen, 1997;
Dickson, 2000; Zielke et al., 2002).
Contemporary climate-weathering studies relatable to bio-
geomorphology-BSC research agendas include P.V. Brady et
al. (1999) who centered on lichens in relation to silicate wea-
thering, J.D. Brotherson et al. (1985) focusing specifically on
plant communities, B. Büdel’s (1999) work in topical envi-
ronments, R. Chen et al. (2009) who studied mineral compo-
nents of BSCs, A. Danin’s (1983) work on cyanobacteria
weathering limestone, H. Murakami and S. Ishihara (2008)’s
study using rare earth elements, and Viles’ broad ecological
scope of rock decay (Viles, 1995). Notwithstanding the
contribution of these landform-climate and weathering-BSC
studies to biogeomorphological-BSC research, these two ove-
rarching research foci still represent areas where biogeomor-
phology can make significant contributions. In fact, H.A.
Viles (2008) strongly suggests BSCs may be the key to un-
derstanding weathering in arid and semi-arid regions. The
path seems clear then for biogeomorphology to take the lead
in – or at least pave the way for – future, and very signifi-
cant, spatially-based BSC research (i.e., broader climate-
landform-weathering-BSC relationships).
Conclusion
A first step in understanding key issues of how biogeo-
morphology can influence BSC research rests in evaluation
of BSC spatial characteristics, specifically landform, clima-
te, and weathering parameters (and, if possible link these
across large areas). This article seeks to discuss these resear-
ch topics in relation to each other generally, and how
biogeomorphology might inform them specifically. Because
a fundamental ecological function of BSCs in the landscape
rests in stabilizing desert surfaces (Belnap and Lange,
2003), it then follows that if particular landforms (at a regio-
nal scale instead of the more-studied local scale) are more
frequently ‘used’ (e.g., tourism and/or ecotourism) or ‘inva-
ded’ (e.g., urban sprawl) by humans, understanding BSC
recovery across landforms, biomes, and seasonality (clima-
te), could enhance their preservation, or at least augment
associated land management practices. As cities expand, and
begin to sprawl across the landscape, there exists an inherent
need for careful preservation and management of the sur-
rounding regions, especially in ecologically fragile biomes.
Creating new, widely-applicable spatial dynamic models of
BSCs, using the discipline of biogeomorphology as a guide,
could alter environmental decision making by, for example,
restricting recreational and/or developmental activities on
certain types of landforms and/or certain climatic regimes.
When conducted through a biogeomorphological lens, BSC
research will also open new possibilities for resiliency and
ecosystem sustainability research (e.g., geobiology). Yet
even regardless of potential research outcomes it remains
clear that, as a discipline, biogeomorphology stands poised
to offer strong contributions to BSC research agendas and
could have long-lasting impacts on the field. There exists a
fundamental need for researchers who study spatial interac-
tions between landform, biota, and climate - biogeomorpho-
logists - to become involved in and work alongside our more
ecologically-trained colleagues (Viles et al., 2008). By be-
coming more engaged in BSC research, biogeomorpholo-
gists can also help narrow already-identified research gaps
in this fundamental field of inquiry through their inherent
focus on spatiality. Indeed, it is precisely the focus on spa-
tiality that current BSC research lacks, and where biogeo-
morphology as a discipline remains strongest.
References
Alexander V.A., Schell D.M. (1973) – Seasonal and spatial varia-
tion of nitrogen fixation in the Banow Alaska tundra. Arctic
Alpine Research 5, 77-88.
Allen C.D. (2005) – Micrometeorology of a smooth and rugose
biological soil crust near Coon Bluff, Arizona. Journal of the
Arizona-Nevada Academy of Science 38, 21-28.
Baldock J.A. (2007) – Composition and Cycling of Organic Car-
bon in Soil. In Marschner P., Rengel Z. (Eds): Nutrient Cycling
in Terrestrial Ecosystems. Springer, Berlin, 1-35.
Barker D.H., Stark L.R., Zimpfer J.F., McLetchie N.D., Smith S.D.
(2005) – Evidence of drought-induced stress on biotic crust moss in
the Mojave Desert. Plant Cell and Environment 28, 939-947.
354 Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Casey Duane Allen
Fig. 6 – Rugose BSC as an epilithic organism, weathering
sandstone rock, Near Zion National Park, UT (USA). This wea-
thering-BSC interaction represents perhaps the most important
category of future biogeomorphological research. Photo by author.
Fig. 6 – Croûte cryptogamique rugueuse épilithique météori-
sant un grès, à proximité du Parc national de Zion, Utah (Etats-
Unis). Cette interaction entre la CC et la météorisation représente
probablement la plus importante des pistes de recherche biogéo-
morphologique futures. Photographie de l’auteur.

Belnap J. (1990) – Microbiotic crusts: their role in past and present
ecosystems. Park Science Resource Management Bulletin 10, 3-4.
Belnap J. (1993) – Recovery rates of cryptobiotic crusts: inoculant
use and assessment methods. Great Basin Naturalist 53, 89-95.
Belnap J. (1995) – Surface disturbances: their role in accelerating
desertification. Environmental Monitoring and Assessment 37,
39-57.
Belnap J. (1996) –Soil surface disturbances in cold deserts:
effects on nitrogenase activity in cyanobacterial-lichen soil
crusts. Biology and Fertility of Soils 23, 362-367.
Belnap J. (2006) –The potential roles of biological soil crusts in
dryland hydrologic cycles. Hydrological Processes 20, 3159-
3178.
Belnap J., Gardner J.S. (1993) –Soil microstructure in soils of
the Colorado Plateau: the role of the cyanobacterium Microco-
leus vaginatus. Great Basin Naturalist 53, 40-47.
Belnap J., Gillette D.A. (1998) –Vulnerability of desert biologi-
cal soil crusts to wind erosion: the influences of crust develop-
ment, soil texture, and disturbance. Journal of Arid Environ-
ments 39, 133-142.
Belnap J., Lange O.L. (2003) – Biological soil crusts: structure,
function, and management. Springer-Verlag, Berlin, 503 p.
Belnap J., Harper K.T., Warren S.D. (1994) –Surface distur-
bance of cryptobiotic soil crusts: nitrogenase activity,
chlorophyll content, and chlorophyll degradation. Arid Soil
Research and Rehabilitation 8, 1-8.
Belnap J., Büdel B., Lange O.L. (2003a) –Biological soil crusts:
characteristics and distribution. In Belnap J., Lange O.L. (Eds):
Biological Soil Crusts: Structure, Function, and Management.
Springer, Berlin, 3-30.
Belnap J., Hawkes C.V., Firestone M.K. (2003b) –Boundaries in
miniature: two examples from soil. BioScience 53, 739-749.
Belnap J., Phillips S.L., Miller M.E. (2004) –Response of desert
biological soil crusts to alterations in precipitation frequency.
Oecologia 141, 306-316.
Belnap J., Phillips S.L., Troxler T. (2006) –Soil lichen and moss
cover and species richness can be highly dynamic: The effects of
invasion by the annual exotic grass Bromus tectorum, precipita-
tion, and temperature on biological soil crusts in SE Utah.
Applied Soil Ecology 32, 63-76.
Ben-Dor E., Goldlshleger N., Benyamini Y., Agassi M., Blum-
berg D.G. (2003) –The spectral reflectance properties of soil
structural crusts in the 1.2- to 2.5-mu m spectral region. Soil
Science Society of America Journal 67, 289-299.
Beraldi-Campesi H., Cevallos-Ferriz S.R.S. (2005) –Microfos-
sil diversity in the Tarahumara Formation, Sonora. Revista
Mexicana De Ciencias Geologicas 22, 261-271.
Beraldi-Campesi H., Cevallos-Ferriz S.R.S., Chacon-Baca E.
(2004) –Microfossil algae associated with Cretaceous stromato-
lites in the Tarahumara Formation, Sonora, Mexico. Cretaceous
Research 25, 249-265.
Beraldi-Campesi H., Hartnett H.E., Anbar A., Gordon G.W., Gar-
cia-Pichel F. (2009) –Effect of biological soil crusts on soil elemental
concentrations: implications for biogeochemistry and as traceable
biosignatures of ancient life on land. Geobiology 7, 348-359.
Berner R.A. (1994) –3GEOCARB-II - A revised model of atmos-
pheric CO2over phanerozoic time. American Journal of Science
294, 56-91.
Berner R.A. (1995) –Chemical weathering and its effect on at-
mospheric CO2and climate. In White A.F., Brantly S.L. (Eds):
Chemical Weathering Rates of Silicate Minerals Chemical Wea-
thering and its Effect on Atmospheric CO2and Climate. Minera-
logical Society of America, 565-583.
Berner R.A., Kothavala Z. (2001) –GEOCARB III: A revised
model of atmospheric CO2over phanerozoic time. American
Journal of Science 301, 182-204.
Beymer R.J., Klopatek J.M. (1991) –Potential contribution of
carbon by microphytic crusts in pinyon-juniper woodlands. Arid
Soil Research and Rehabilitation 5, 187-198.
Bornyasz M.A., Graham R.C., Allen M.F. (2005) –Ectomycor-
rhizae in a soil-weathered granitic bedrock regolith: Linking
matrix resources to plants. Geoderma 126, 141-160.
Bouza P., Del Valle H.F. (1993) –Micromorphological, physical,
and chemical characteristics of soil crust types of the central
Patagonia region, Argentina. Arid Soil Research and Rehabilita-
tion 7, 355-368.
Bowker M., Reed S.C., Belnap J., Phillips S. (2002) –Tempo-
ral variation in community composition, pigmentation, and Fv
/Fm of desert cyanobacterial soil crusts. Microbial Ecology 43,
13-25.
Bowker M.A., Johnson N.C., Belnap J., Koch G.W. (2008) –
Short-term monitoring of aridland lichen cover and biomass
using photography and fatty acids. Journal of Arid Environments
72, 869-878.
Boyd W.L., Staley J.T., Boyd J.W. (1966) –Ecology of soil
microorganisms in Antarctica. In Tedrow J.C.F. (Ed.): Antarctic
Soils and Soil Forming Processes. Antarctic Research Series 8,
125-159.
Brady P.V., Caroll S.A. (1994) –Direct effects of CO2 and tem-
perature on silicate weathering: possible implication for climate
control. Journal of Geophysical Research 58, 853-1853.
Brady N.C., Weil R.R. (2008) – The nature and property of soils.
14th ed. Pearson Prentice Hall, Upper Saddle River, NJ, 960.
Brady P.V., Dorn R.I., Brazel A.J., Clark J., Moore R.B., Gli-
dewell T. (1999) –Direct measurement of the combined effects
of lichen, rainfall, and temperature on silicate weathering. Geo-
chimica et Cosmochimica Acta 63, 3293-3300.
Brostoff W.N., Sharifi M.R., Rundel P.W. (2005) –Photosynthe-
sis of cryptobiotic soil crusts in a seasonally inundated system of
pans and dunes in the western Mojave Desert, CA: Field studies.
Flora 200, 592-600.
Brotherson J.D., Evenson W.E., Rushforth S.R., Fairchild J.,
Johansen J.R. (1985) –Spatial patterns of plant communities
and differential weathering in Navajo National Monument, Ari-
zona. Great Basin Naturalist 45, 1-13.
Büdel B. (1999) –Ecology and diversity of rock-inhabiting cya-
nobacteria in tropical regions. European Journal of Phycology
34, 361-370.
Büdel B. (2003) –Synopsis: Comparative Biogeography and Eco-
logy of Soil Crust Biota. In Belnap J., Lange O.L. (Eds):
Biological Soil Crusts: Structure, Function, and Management.
Springer, Berlin, 141-152.
Budyko M.I., Ronov A.B. (1979) –Chemical evolution of the atmos-
phere in the Phanerozoic. Geochemistry International 16, 1-9.
Cameron R.E., Blank G.B., Gensel D.R., Davies R.W. (1965) –
Soil studies-desert microflora. X. Soil properties of samples
355
Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Biogeomorphology and biological soil crusts

from the Chile Atacama Desert. California Institute of Techno-
logy, National Aeronautics and Space Administration, Jet
Propulsion Laboratory, Pasadena, CA, 214-222.
Cameron R.E., Gensel D.R., Blank G.B. (1966) –Soil studies—
desert microflora. XII. Abundance of microflora in soil samples
from the Chile Atacama Desert, supportive research and advan-
ced development. National Aeronautics and Space Administra-
tion, Jet Propulsion Laboratory, Pasadena, CA, 140-147.
Chacon-Baca E., Beraldi-Campesi H., Cevallos-Ferriz S.R.S.,
Knoll A.H., Golubic S. (2002) –70 Ma nonmarine diatoms
from northern Mexico. Geology 30, 279-281.
Chapin D.M. (1996) –Nitrogen mineralization, nitrification, and
denitrification in a high arctic lowland ecosystem, Devon Island,
N.W.T., Canada. Arctic and Alpine Research 28, 85-92.
Chen J., Zhang M.Y., Wang L., Shimazaki H., Tamura M.
(2005) –A new index for mapping lichen-dominated biological
soil crusts in desert areas. Remote Sensing of Environment 96,
165-175.
Chen R., Zhang Y., Li Y., Wei W., Zhang J., Wu N. (2009) –The
variation of morphological features and mineralogical compo-
nents of biological soil crusts in the Gurbantunggut Desert of
Northwestern China. Environmental Geology 57, 1135-1143.
Cole D.N. (1990) –Trampling disturbance and recovery of crypto-
gamic soil crusts in Grand Canyon National Park. Great Basin
Naturalist 50, 321-325.
Danin A. (1983) –Weathering of limestone in Jerusalem by cya-
nobacteria. Zeitschrift für Geomorphologie 27, 413-421.
Dickson L.G. (2000) –Constraints to Nitrogen Fixation by Crypto-
gamic Crusts in a Polar Desert Ecosystem, Devon Island, N.W.T.,
Canada. Arctic, Antarctic, and Alpine Research 32, 40-45.
Drever J.I. (1994) –The effect of land plants on weathering rates
of silicate minerals. Geochimica et Cosmochimica Acta 58,
2325-2332.
Evans R.D., Belnap J. (1999) –Long-term consequences of dis-
turbance on nitrogen dynamics in an arid ecosystem. Ecology
80, 150-160.
Evans R.D., Lange O.L. (2001) –Biological soil crusts and eco-
system nitrogen and carbon dynamics. In Belnap J., Lange O.L.
(Eds): Biological Soil Crusts: Structure, Function, and Manage-
ment. Springer, Berlin, 263-279.
Evans R.D., Lange O.L. (2003) –Biological soil crusts and eco-
system nitrogen and carbon dynamics. In Belnap J., Lange O.L.
(Eds): Biological Soil Crusts: Structure, Function, and Manage-
ment. Springer, Berlin, 263-269.
Fang S.B., Liu H.J., Zhang X.S., Dong M., Liu J.D. (2008) –
Progress in spectral characteristics of biological soil crust of arid
or semiarid region. Spectroscopy and Spectral Analysis 28,
1842-1845.
Flechtner V.R., Johansen J.R., Clark W.H. (1998) –Algal com-
position of microbiotic crusts from the central desert of Baja
California, Mexico. The Great Basin Naturalist 58, 295-311.
Follmann G. (1965) –Fensterflechten in der Atacamawüste.
Naturwissenschaften 14, 434-435.
Forest H.S., Weston C.R. (1966) –Blue-green algae from the Ata-
cama desert of northern Chile. Journal of Phycology 2, 163-164.
Forman R.T.T., Dowden D.L. (1977) –Nitrogen fixing lichen
roles from desert to alpine in the Sangre de Cristo mountains,
New Mexico. The Bryologist 80, 561-570.
Gold W.G. (1998) –The influence of cryptogamic crusts on the
thermal environment and temperature relations of plants in a
high arctic polar desert, Devon Island, N.W.T., Canada. Arctic
and Alpine Research 30, 108-120.
Goudie A. (1972) –Climate, weathering, crust formation, dunes
and fluvial features of the central Namib Desert, near Gobabeb,
South West Africa. Madoqua 2-1, 15-31.
Green R.O., Eastwood M.L., Sarture C.M., Thomas G.C.,
Aronsson M., Chippendale B.J., Faust J.A., Pavri B.E., Cho-
vit C.J., Solis M., Olah M.R., Williams O. (1998) –Imaging
Spectroscopy and the Airborne Visible/Infrared Imaging Spec-
trometer (AVIRIS) - Remote Sensing of the Environment 65,
227–248.
Green T.G.A., Broady P. (2003) –Biological soil crusts of An-
tarctica. In Belnap, J., Lange, O. L., (eds): Biological Soil
Crusts: Structure, Function, and Management. Springer, Berlin,
133-139.
Harper K. T., Pendleton R.L. (1993) –Cyanobacteria and cya-
nolichens: can they enhance availability of essential minerals for
higher plants? Great Basin Naturalist 53, 59-72.
Henry G.H.R., Svoboda J. (1986) –Dinitrogen fixation (acetyle-
ne reduction) in high arctic sedge meadow communities. Arctic
and Alpine Research 18, 181-187.
Houghton R.A. (1995) –Changes in the Storage of Terrestrial
Carbon Since 1850. In Lal R., Kimble J., Levine E., Stewart
B.A. (Eds): Soils and Global Change. CRC Press, Boca Raton,
45-65.
Huete A.R., Post D.F., Jackson R.D. (1984) –Soil Spectral
Effects on 4-Space Vegetation Discrimination. Remote Sensing
of Environment 15, 155-165.
Hunt J.M. (1979) – Petroleum Geochemistry and Geology. W.H.
Freeman and Company, San Francisco, 617.
Jeffries D.L., Link S.O., Klopatek J.M. (1989) –CO2fluxes of
cryptogamic crusts in response to resaturation. Bulletin of the
Ecological Society of America 70, 156.
Jeffries D.L., Link S.O., Klopatek J.M. (1993a) –CO2fluxes of
cryptogamic crusts. I. Response to resaturation. The New Phyto-
logist 125, 163-173.
Jeffries D.L., Link S.O., Klopatek J.M. (1993b) –CO2fluxes of
cryptogamic crusts. II. Response to dehydration. The New Phy-
tologist 125, 391-396.
Karnieli A., Tsoar H. (1995) – Satellite spectral reflectance of bio-
genic crust developed on desert dune sand along the Israel-Egypt
border. International Journal of Remote Sensing 16, 369-374.
Karnieli A., Shachak M., Tsoar H., Zaady E., Kaufman Y.,
Danin A., Porter W. (1996) –The effect of microphytes on the
spectral reflectance of vegetation in semiarid regions. Remote
Sensing of Environment 57, 88-96.
Karnieli A., Kidron G.J., Glaesser C., Ben-Dor E. (1997) –
Spectral characteristics of cyanobacterial soil crust in the visible,
near infrared and short wave infrared (400-2,500 nm) in semia-
rid environments. In Twelfth International Conference and
Workshops on Applied Geologic Remote Sensing, Denver, Colo-
rado, 417-424.
Karnieli A., Kokaly R., West N.E., Clark R.N. (2003) –Remote
sensing of biological soil crusts. In Belnap J., Lange O.L. (Eds):
Biological Soil Crusts: Structure, Function, and Management.
Springer-Verlag, Berlin, 431-455.
356 Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Casey Duane Allen

Kidron G.J. (1992) –The impact of the microbial crust upon the
relationship of rainfall, runoff and sediment yield at longitudinal
dunes in an arid environment. Nizzana, Western Negev, Israel. In
The First Israel Geomorphological Conference, Beer Sheva,
Israel, 81-82.
Kidron G.J., Yair A. (1997) –Rainfall-runoff relationship over
encrusted dune surfaces, Nizzana, Western Negev, Israel. Earth
Surface Processes and Landforms 22, 1169-1184.
Kidron G.J., Vonshak A., Abeliovich A. (1995a) –Five micro-
biotic crust types in the Nizzana dune field: factors affecting
their variability and measurements of their regeneration time.
Israeli Geological Society Annual Meeting 62-94.
Kidron G.J., Yair A., Abeliovich A. (1995b) –Paleo-climatologi-
cal implications concerning runoff over encrusted dune slopes in
an arid region, Nizzana, Western Negev Desert, Israel. The Se-
cond International Symposium on the Geology of the Eastern
Mediterranean Region, Jerusalem, Israel, 10.
Kidron G. J., Barzilay E., Sachs E. (2000) –Microclimate
control upon sand microbiotic crusts, western Negev Desert,
Israel. Geomorphology 36, 1-18.
Kidron G.J., Herrnstadt I., Barzilay E. (2002) –The role of dew
as a moisture source for sand microbiotic crusts in the Negev
Desert, Israel. Journal of Arid Environments 52, 517-533.
Kidron G.J., Yair A., Vonshak A., Abeliovich A. (2003) –Micro-
biotic crust control of runoff generation on sand dunes in the
Negev Desert. Water Resources Research 39, 1108.
Kidron G.J., Vonshak A., Abeliovich A. (2009) –Microbiotic
crusts as biomarkers for surface stability and wetness duration in
the Negev Desert. Earth Surface Processes and Landforms 34,
1594-1604.
Kokaly R.F., Clark R.N. (1999) –Spectroscopic determination of
leaf biochemistry using band-depth analysis of absorption fea-
tures and stepwise multiple linear regression. Remote Sensing of
Environment 67, 267-287.
Krasil’nikov N.A. (1949) –The role of microorganisms in the
weathering of (mountain) rocks. Mikrobiologiya 18, 224-232.
Krasil’nikov N.A. (1956) –Microflora of high-altitude rocks and
nitrogen-fixing effect. Uspehi. Sovrem. Biol. 412.
Lal R. (2004a) –Soil carbon sequestration to mitigate climate
change. Geoderma 123, 1-22.
Lal R. (2004b) –Agricultural activities and the global carbon
cycle. Nutrient Cycling in Agroecosystems 70, 103-116.
Lal R., Kimble K., Follet R., Cole C. (1998) – The potential of
US cropland to sequester carbon and mitigate the greenhouse
effect. Ann Arbor Press, Chelsea, MI, 144.
Lalley J.S., Viles H.A. (2008) –Recovery of lichen-dominated
soil crusts in a hyper-arid desert. Biodiversity and Conservation,
17, 1-20.
Lange O.L. (2000) –Photosynthetic performance of a gelatinous
lichen under temperate habitat conditions: long-term monitoring
of CO2exchange of Collema cristatum. Bibliotheca Lichenolo-
gica 75, 307-332.
Lange O.L., Meyer A., Zellner H., Heber U. (1994) –Photosyn-
thesis and water relations of lichen soil-crusts: Field measure-
ments in the coastal fog zone of the Namib Desert. Functional
Ecology 8, 253-264.
Lange O.L., Belnap J., Reichenberger H., Meyer A. (1997) –
Photosynthesis of green algal soil crust lichens from arid lands
in southern Utah, USA: role of water content on light and tem-
perature responses of CO2exchange. Flora 192, 1-15.
Liengen T., Olsen R.A. (1997) –Nitrogen fixation by free-living
cyanobacteria from different coastal sites in a high arctic tundra,
Spitsbergen. Arctic and Alpine Research 29, 470-477.
Lillesand T.M., Keifer R.W. (2002) – Remote Sensing and Image
Interpretation. John Wiley and Sons, New York, 736.
MacGregor A.N., Johnson D.E. (1971) –Capacity of desert algal
crusts to fix atmospheric nitrogen. Soil Science Society of Ame-
rica Proceedings 35, 843-844.
Martin M.E., Newman S.D., Aber J.D., Congalton R.G. (1998)
–Determining forest species composition using high spectral
resolution remote sensing data. Remote Sensing of Environment
65, 249-254.
Maya Y., López-Cortés A., Soeldner A. (2002) –Cyanobacterial
microbiotic crusts in eroded soils of a tropical dry forest in the
Baja California Peninsula, Mexico. Geomicrobiology Journal
19, 505-518.
Molnar P., England P., Martinod J. (1993) –Mantle dynamics,
uplift of the Tibetan Plateau, and the Indian Monsoon. Review of
Geophysics 31, 357-396.
Murakami H., Ishihara S. (2008) –REE Mineralization of Wea-
thered Crust and Clay Sediment on Granitic Rocks in the Sanyo
Belt, SW Japan and the Southern Jiangxi Province, China.
Resource Geology 58, 373-401.
Naylor L.A., Viles H.A., Carter N.E.A. (2002) –Biogeomorpho-
logy revisited: looking towards the future. Geomorphology 47,
3-14.
Noffke N. (2005) –Geobiology - a holistic scientific discipline.
Palaeogeography Palaeoclimatology Palaeoecology 219, 1-3.
Ollier C. (1974) – Weathering and Landforms. Nelson Thornes
Ltd, Cheltenham, 64 p.
Ollier C., Pain C. (1996) – Regolith, Soils and Landforms. Wiley,
Hoboken, NJ, 326 p.
Ollier C., Sheth H. (2008) –The High Deccan duricrusts of India
and their significance for the ‘laterite’ issue. Journal of Earth
System Science 117, 537-551.
Palmqvist K. (1995) –Uptake and fixation of CO2in lichen pho-
tobionts. Symbiosis 18, 95-109.
Palmqvist K. (2000) –Carbon economy in lichens. New Phytolo-
gist 148, 11-36.
Palmqvist K., Máguas C., Badger M.R., Griffiths H. (1994) –
Assimilation, accumulation, and isotope discrimination of inor-
ganic carbon in lichens: further evidence for the operation of a
CO2concentrating mechanism in cyanobacterial lichens. Cryp-
togamic Botany 4, 218-226.
Pearson L.C., Lawrence D.B. (1965) –Lichens as microclimate
indicators in northwestern Minnesota. The American Midland
Naturalist 74, 257-268.
Pérez F.L. (1997) –Microbiotic crusts in the high equatorial
Andes, and their influence on paramo soils. Catena 31, 173-
198.
Redfield E., Barns S. M., Belnap J., Daane L.L., Kuske C.R.
(2002) –Compariative diversity and composition of cyanobac-
teria in three prominent soil crusts of the Colorado Plateau.
FEMS Microbiology Ecology 40, 55-63.
Roberts D.A., Gardner M., Church R., Ustin S., Scheer G.,
Green R.O. (1998) –Mapping chaparral in the Santa Monica
357
Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Biogeomorphology and biological soil crusts

Mountains using multiple endmember spectral mixture models.
Remote Sensing of Environment 65, 267-279.
Rosentreter R., Belnap J. (2003) –Biological soil crusts of North
America. In Belnap J., Lange O.L. (Eds): Biological Soil Crusts:
Structure, Function, and Management. Springer, Berlin, 31-50.
Rundel P.W., Dillon M.O., Palma B., Mooney H.A., Gulmon
S.L., Ehleringer J.R. (1991) –The phytogeography and ecolo-
gy of the coastal Atacama and Peruvian deserts. Aliso 11, 1-50.
Rychert R.C., Skujins J. (1974) –Nitrogen fixation by blue-green
algae-lichen crusts in the Great Basin Desert. Soil Science Socie-
ty of America Proceedings 38, 768-771.
Soriano A. (1983) –Deserts and semi-deserts of Patagonia. In
Ecosystems of the World 5, Temperate Deserts and Semi-deserts.
N.E. West Amsterdam, Elsevier, 423-460.
Sundberg B., Ekblad A., Näsholm T., Palmqvist K. (1999) –
Lichen respiration in relation to active time, temperature, ni-
trogen and ergosterol concentrations. Functional Ecology 13,
119-125.
Swayze G.A., Smith K.S., Clark R.N., Sutley S.J., Pearson
R.M., Vance J.S., Hageman P.L., Briggs P.H., Meier A.L.,
Singelton M.J., Roth S. (2000) –Using imaging spectroscopy
to map acidic mine waste. Environmental Science & Technology
34, 47-54.
Türk R., Gärtner G. (2003) –Biological soil crusts of the subal-
pine, alpine and Nival areas in the Alps. In Belnap J., Lange O.L.
(Eds): Biological Soil Crusts: Structure, Function, and Manage-
ment. Springer, Berlin, 67-73.
Ustin S.L., Valko, P.G., Kefauver S.C., Santos M.J., Zimpfer
J.F., Smith S.D. (2009) –Remote sensing of biological soil
crust under simulated climate change manipulations in the Moja-
ve Desert. Remote Sensing of Environment 113, 317-328.
Veste M., Littmann T., Breckle S.W., Yair A. (2001a) –The role
of biological soil crusts on desert sand dunes in the northwestern
Negev, Israel. In Breckle S.W., Veste M., Wucherer W. (Eds):
Sustainable Land Use in Deserts. Springer, Berlin, 357-367.
Veste M., Littmann T., Friedrich H., Breckle S.W. (2001b) –
Microclimatic boundary conditions for activity of soil lichen
crusts in sand dunes of the north-western Negev desert, Israel.
Flora 196, 465-474.
Viles H. (1995) –Ecological perspectives on rock surface weathe-
ring: Towards a conceptual model. Geomorphology 13, 21-35.
Viles H.A. (2008) –Understanding dryland landscape dynamics: do
biological crusts hold the key? Geography Compass 2, 899-919.
Viles H.A., Naylor L.A., Carter N.E.A., Chaput D. (2008) –Bio-
geomorphological disturbance regimes: progress in linking eco-
logical and geomorphological systems. Earth Surface Processes
and Landforms 33, 1419-1435.
Warren-Rhodes K.A., Dungan J.L., Piatek J., Stubbs K.,
Gomez-Silva B., Chen Y., McKay C.P. (2007) –Ecology and
spatial pattern of cyanobacterial community island patches in the
Atacama Desert, Chile. Journal of Geophysical Research-Bio-
geosciences 112, G04S15.
Weber B., Olehowski C., Knerr T., Hill J., Deutschewitz K.,
Wessels D.C.J., Eitel B., Büdel B. (2008) –A new approach for
mapping of Biological Soil Crusts in semidesert areas with
hyperspectral imagery. Remote Sensing of Environment 112,
2187-2201.
Wessels D.C.J., van Vuuren D.R.J. (1986) –Landsat imagery—
its possible use in mapping the distribution of major lichen
communities in the Namib Desert, South West Africa. Madoqua
14, 369-373.
Wojciechowski M.F., Heimbrook M.E. (1984) –Dinitrogen fixa-
tion in alpine tundra, Niwot Ridge, Front Range, Colorado.
Arctic and Alpine Research 16, 1-10.
Wynn-Williams D.D. (1993) –Soil crust microbes as indicators of
environmental change in Antarctica. In Guerrero R., Pedrós Alió
C., (Eds): Trends in Microbial Ecology. Spanish Society for
Microbiology, Barcelona, 105-108.
Yair A. (2003) –Effects of Biological Soil Crusts on Water Re-
distribution in the Negev Desert, Israel: a Case Study in Longi-
tudinal Dunes. In Belnap J., Lange O.L. (Eds): Biological Soil
Crusts: Structure, Function, and Management. Springer, Berlin,
141-152.
Zaady E., Karnieli A., Shachak M. (2007) –Applying a field
spectroscopy technique for assessing successional trends of bio-
logical soil crusts in a semi-arid environment. Journal of Arid
Environments 70, 463-477.
Zhang Y.M., Chen J., Wang L., Wang X.Q., Gu Z.H. (2007) –
The spatial distribution patterns of biological soil crusts in the
Gurbantunggut Desert, Northern Xinjiang, China. Journal of
Arid Environments 68, 599-610.
Ziegler H., Lüttge U. (1998) –Carbon isotope discrimination in
cyanobacteria of rocks of inselbergs and soils of savannas in the
neotropics. Botanica Acta 111, 212-215.
Zielke M., Ekker A.S., Olsen R.A., Spjelkavik S., Solheim B.
(2002) –The influence of abiotic factors on biological nitrogen
fixation in different types of vegetation in the high Arctic, Sval-
bard. Arctic, Antarctic, and Alpine Research 34, 293-299.
Article soumis le 23 novembre 2009, accepté le 24 août 2010.
358 Géomorphologie : relief, processus, environnement, 2010, n° 4, p. 347-358
Casey Duane Allen