Classification of forest humus forms: a French proposal

article
Original

Classificationofforesthumusforms:
aFrench
proposal

ABrethes

JJ Brun

BJabiol

J Ponge

FToutain

citéadministrative
1
desrecherchestechniques,Coligny,
ONF,département
ruedu45042Orléanscedex;
131,Faubourg-Bannier,
2
CEMAGREF,
la
domaineuniversitaire,2,ruedePapeterie,
BP76,38402Saint-Martin-d’Hèrescedex;
3
54042
ENGREF,
14,rueGirardet,Nancycedex;
4
labor
Muséumnaturelld’écologiegénéra
nationald’histoiree,atoirele,
1800
4,avenueduPetit-Château,9Brunoy;
5
ru
centredeue,BP5,1 7,eNotre-Dame-des-Pauvres,
CNRS,pédologiebiologiq
France
54501Vandceuvrecedex,

218March
1994;
(ReceivedJanuaryaccepted1995)

forFrenchforest
classificationandanomenclaturearehumusforms
Summary —A2-waygridproposed
stakesinto

butwhichcouldn,tropical
includemountaiMediterraneanandformsaswell.Thiproposal
inlitter
thattake
accountourofmechanismsplant
presentknowledgebiologicalplacedecomposi-
sformationofsoilmatteofthelattertomineralandofthe
tion,tranorganicr,linkageparticlesbuilding
horifreehumusform

structureintheAzon.Bassbedefinedby
ically,byadjoiningqualifiers,may
alsofortheirchemicaland
es.
accountingphysicalparticulariti

humusform/ forest/ classification/ nomenclaturebiology
/ soil

Résumé —Laclassificationdes formesd’humusforestières :Unegrille
propositionfrançaise.
tréesetnomntleshumusrs
forestie
declassificationà2enuneenclaturesoproposéespourdeFrance,

maisaussiauxformesd’altitudproposi-
e,etméditerranéennes.Cette
pouvants’appliquertropicales
intervenant
tionenlesconnaissancesactuellesconcernantlesogiques
prendcomptephénomènesbiol
dansdécomdelalitière,latransformationdelamatièresesliensavecles
la
positionorganique,par-
etlastructurationl’horizonA.Parsonà
sminéralesdeprincipemême,grâcel’adjonctde
ticuleion
lesformesd’humusêtreàleurscaractères
dontlechoixestlibre,peuventpréciséesquant
qualificatifs
chimiquesouspa
physiquerticuliers.

dusol
formed’humus/forêt/ classification/ nomenclature / biologie

*
author
Corresponding

INTRODUCTION

Thehumus
isofdifferent
profilecomprised
scaleswhichbe
mayintegrated:regional
soil
climate,k,
parentrocvegetation,organ-
ismsb;Bemier and
(Toutain,1987a,Ponge,
for
disHumusmsareu
1993).nevenly
the
tributedoverwoforclimaticandhis-
rld,
toricalreasons.Asavarious
consequence,
classificationshavebeeninuseuntil
now,
eachfocusedon
regionalaspects.
Indescribed
Kubiëna
Europe,(1953)
numerousawide
humusforms,covering
ofrocksand
rangeclimates,parentvege-
tationHiscriteriawerederived
types.mainly
fromhisownobservations.
morphological
DuchaufourandBabellater
(1956)(1971)
differentchemicaland
investigated
microstructuralascientific
aspects,giving
basisformorerefinedclassifications.Dele-
courthenanidentification
(1980)proposed
formosthumusformswest-
in
keypresent
ern
Europe.
InNorththeneedforanother
America,
ofclassificationwas
typeemphasizedby
Wildeadetailed
(1954,1971).Morerecently,
ofhumusformswasachieved
taxonomyby
KlinkaandGreen1993).
et al (1981)et al (
Inoftheothers
otheregionsworld,
r
endeavouredtodescribeand
tropical
Mediterraneansoilsonthesamebasis

(Marin1985;Ferry,1992;Leroy
et al,et al,
1993).
inthescientificof
Progressknowledge
theinchemicaland
soil,both
its
biological
nowallowsustoafunc-
aspects,propose
tionalclassificationofforesthumusforms.A
worldwidetoolneededtoenablesoilsci-
is
entistsandforesterstodescribekind
every
ofhumusForthat
existingprofile.purpose,
weaclassificationwhichisnottax-
propose
onomical.Rather,aimsanswerthe
to
it
ofwtosee
questionho when
processes
thesoilwiththenakedand
observingeye
usethistohumusforms
knowledgeidentify
withmore
certainty.
Theclassificationisbasedon
proposed
thesameastheFrenchPedo-
principles
logicalReferenceBasefors
oil
types(AFES,
Thisisareferenceandnota
1992).system
hierarchicalandexhaustiveclassification.
Humusformsaredescribedbylinkingthem
tosomewell-definedreferenceformsand
asas
freelyadjoiningmanyqualifiers
needed.Aneffortwasmadetomakethis
classificationscientificand
pragmatic,pre-
flexible.
cise,but,nevertheless,

soilsand
Waterlogged(gleypseudo-gley)
andtheirhumusforms
will
(AFES,1992)
notbediscussedhere,asabetterknowl-
of
edgebiologicalmechanismspoor
in
ly
aeratedhorizonsisneeded.

STUDIESONFUNCTIONALASPECTS

Transformationof leaf litter

Recentstudiesthe
emphasizedimportance
ofeof
thechemicalnaturplantmacro-
moleculesinthefateofhumusIn
layers.
earlierobservations
particular,followingby
Handley(1954),Reisingeret al (1978),
and
Toutain(1981 )Françoiset al (1986)
describedthefollowedtannin-
pathwayby
foodwebs
soil
proteincomplexesthrough
indifferenthumusSeveralcritical
types.
wereatfirstthesenes-
phasesrecognized,
cenceoftreewithof
foliage,appearance
stabledarkwherewas
pigmentsnitrogen
70%
oftotalin
sequestered(egnitrogen
beechunavailablefor
foliage),rending
it
nutrition
plant(Toutain,1981).Investiga-
tionsondifferentscalesleaf
(soilslides,
trastructure,etc)showedthat
ul oafew
nly
biota,suchasearthwormsandwhite-rot
abletosuch
fungiweredisintegrate
(fig1),
recalcitrantmolecular
assemblages
these
(Toutain,1981).Whenorganisms
wereandthe
presentactive,disappearance
ofleafwasWhen
litter
rapid(mullhumus).
werelitterdis-
theyabsent,however,slowly
theofsmallani-
appearedthroughactivity
suchasand
mals,microarthropodsenchy-
traeidworms
(moderhumus).
thereisathresholdfornutrient
Thus,
thatnotbea
y
cyclesmay ormalockup,
ontheorbsenceof
a
dependingpresence
efficientTheir
organisms.presencedepends
onenvironmentalandhis-
(Toutain,1987a)
toricalconditionsthatleadtoaof
variety
functionalHereistheborderline
types(fig2).
betweenmullandmoder.moderhumus
In
iseffectivebutsoil
forms,biologicalactivity
foodchainsareTherinc
discontinuous.
p
ivisibletothenakedisthe
palactivity,eye,
transformationofalfae-
litterintoanim
plant
ceswherealotofmatterremains
organic
atleast
977;
untouched,temporarily(Webb,1
Toutain
et al,
onge,
1982;P1991 a,b).

Theborderlinebetweenmoderandmor
humusformsmoredetermine,
isdifficultto
andmoreon
knowledgebiologicalpro-
cessesisneededbeforecleartrendscan
beOurownobservationsindi-
perceived.
catedtha
twormswerepartic-
enchytraeid
abundantmorhumusforms
in
ularly(Bernier
et al,1993;thus,
Ponge,unpublisheddata);
theirdominancecouldbemorethanan
exclusionoftheotherthe
groups;however,
truemechanismsareunknown.

ofmatter
Assemblageorganic
withmineral
particles

Thechemicalnatureofmatterand
organic
intheA
itswithmineralmatter
assemblage
horizonontheaforementioned
dependpro-
cesses.We3main

aydistinguishpathm
et al,,
ways(Berthelin1994;Duchaufour
1995):
-
BiomacrostructuredAhorizon:
Clay-min-
eralbe
complexesmaycementingmacroag-
duetotheofsoil-
gregates,mixingactivity
earthwormsand
dwelling(BernierPonge,
1994);
-
"Insolubilisation"Ahorizon:Soluble
metabolicofwhite-rot
productsfungimay
on
precipitateclay-ironparticles;
-
horizon:Inherited
"Juxtaposition" Aorganic
mattermadeofcellwallsrec-
plant-fungal
transmission
in
ognizable(Toutain,1981)
oreven1991
lightmicroscopy(Ponge,a,b)
beinfaecalof
maypresentpelletsmany
smallanimals
(litter-dwellingearthworms,
sidesidewith
arthropods,enchytraeids),by
mineral
grains.

BASESFORANEWCLASSIFICATION
INTEGRATINGMORPHOLOGICAL
ANDFUNCTIONALFEATURES

Theexistenceofaclose
relationship
between and
morphologybiochemistry

hasbeenoften
(Duchaufour,1995)ques-
tioned.Thesamehumuswitha
typehigh
humusfromamor-
biologicalactivity(mull
ofwellcorre-
may
phologicalpointview)
toawideofvaluesand
spondrangepH
indicator
plantspecies(Duchaufour,1995).
different
Conversely,morphologicaltypes
havethesameorC/N.
maypH
Giventhesewiththecur-
discrepancies
rentviewthatofthehumus
morphology
isthereflectionofitschemical
profileprop-
erties,weusethelattequal-
decidedtoras
ifiersforbasedonmor-
groupsprimarily
th