1. science
2. mathematics
3. statistics

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FOREST-LITTER
DECOMPOSITION
RATE
AS A S I T E
FACTOR
F. Delecour and F. Weissen
Centra de Recherches et de Promotion Forestières
Section Pédologie Forestière
(I.R.S.I.A.)
GEMBLOUX (Belgium)
Keywords
Acid brown soils, Beechwood, Organic matter turn-over,
Productivity.
1 . INTRODUCTION
An organic matter decomposition rate coefficient has been introduced by
Jenny e t a t . (1949) . It can be calculated following an equation of the type
K
100 A
A + L
where A is the annual fall of plants residues, more specifically the autum­
nal leaf fall, and L is the total existing litter or holorganic horizons, 0,
before leaf fall. The value of K can be expressed on a dry matter, organic
matter, or any nutrient basis. This coefficient represents the proportion of
fresh decomposable matter at the beginning of the annual cycle, after leaf
fall (Delecour, 1969). It is a partial expression of the intensity of the
nutrient turn-over, indicating to which extent these tend to accumulate in
the O horizons, whenever the biogeochemical cycles are slowing down.
First, this coefficient was looked at as a climatic index, decreasing
from equatorial to temperate regions, as well as from lowlands to highlands
(Jenny e t a t . , 1949). However, Maldague (1967) found a sharp increase of K
from mor- to mull-maplestands in Canada.
So, from the few data available in the litterature, it appears that the
litter decomposition rate varies under the influence, among other factors, of
tree species, of climatic factors, and of humus form.
Some investigation has been carried on in the beechwoods, and, to a les­
ser extent, in the sprucewoods of Belgian Ardennes, in order to see if it
was possible to share the part of regional and of local factors in the va­
riations of the K coefficient. The technical specifications of the sampling
have been discussed elsewhere (Delecour e t a t . , 1967).Since then, ithasbeen
found that the relative standard error is of the same order of magnitude if
the sampling area is reduced to 0.25 m 2, provided that at least 15 samples
are collected in each site.
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2. STUDIED STANDS
The present discussion is restricted to natural beechforest.
The studied stands are situated in the Belgian Ardennes, the mean coor­
dinates being 5°30' E longitude, and 50° N latitude. The elevation varies
from 350 to 600 m.
The soils are acid brown soils (F.A.O.
dystric Cambisols
U.S.D.A.
Dystrochrepts) on schist or sandstone substrata of the Lower Devonian. The
pH of the Ah horizon is about 4.0 to 4.5, and the base saturation is very
low, less than 20 % in the mineral horizons (Delecour and Weissen, 1977) .The
beechwoods belong to the L u z u t o - F a g io n Lohm and Tx, and represent subgroups
of the L u z u Z o -F a g e turn bo ve a tZ a n t'Lcu m (Noirfalise and Vanesse, 1977) .
In "normal" stands corresponding to 180 stems/ha and 80 % covering at
the age of 150 years (Dagnelie, 1956), the autumnal leaf fall amounts to an
average of 3.4 t/ha, on a dry matter basis, with little variation from one
stand to the other. The amount of litter varies greatly, from less than 2 t/ha
in mull stands to more than 30 t/ha in dysnoder stands (*) , before leaf fall.
3. OBSERVATIONS
The interpretation of the values of the litter decomposition rate coef­
ficient can be made from different points of view. First, we shall locate the
beechwoods of Belgian Ardennes in comparison with other stands in the World.
Then, we shall consider it as an expression of the dynamics of the nutrients
during the decomposition. Finally, we shall consider its relationships with
the forest productivity.
3.1.
World values
of the K c o e f f i c i e n t
Table 1 shows intermediate values for the Belgian beechwoods. Although
the interpretation must be careful and take into account that we are compa­
ring very different ecosystems, the influence of the general climate is clear­
ly evident.
(*) The definition of humus forms is given in Delecour (1980) .
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Table 1
World values of K coefficient in different forest types (dry mat­
ter basis)
Country
Forest type
Columbia
Rain forest
48
Q u e rcu s k e l l o g i i
elev. 1200 m
elev. 1500 m
12
6
Belgium
Beechwood
15
Canada
Maplewood
mull
mor
35
5
USA, California
3.2.
Dynam ic s
Jenny e t a l .
63
Musanga fallow
Zaire
Source
K,
Jenny e t a l .
Maldague
of the d e c o m p o s i t i o n
Table 2 shows the average values as well as the standard variation of
the K coefficient, expressed on different bases.
Table 2
Average values of K coefficient (different bases)
Element
K, %
V, %
14.5
15.8
33
N
P
S
Mg
9.4
10.4
9.0
10.8
40
35
39
39
CA
22.0
20
K
27.5
25
Dry matter
C
The analysis of the data shows that they are distributed into four
groups significantly different from each other. Following decreasing evolu­
tion speedness, the elements can be arranged as follows
K > Ca > C = dry matter > N = S = P = M g .
Although K- and Ca-liberation depend to some extent on the organic mat­
ter decomposition, it is not quite parallel to the transformation of the
organic compounds. Both elements are situated in the vacuole solutions or
are adsorbed on the colloids of the cell components. They are more readily
set free, namely as a result of physical leaching, than other nutrients in­
timately integrated with the organic matter such as N, P, and S, and so,
they seem to be much more dependent upon the general climatic conditions.
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The mineralization of N and of S, in our beechforests has been descri­
bed by Van Praag (1972), and Van Praag and Weissen (1977)• As N-, S-, and
P-mineralization rates are smaller than C-mineralization, the former accu­
mulate relatively in the litter. That is the reason why, for instance, the
C/N-ratio decreases from mull to dysmoder in the holorganic 0 horizons (Delecour, 1975).
It is noteworthy that Mg behaves like the integrated elements and so
differs from Ca, other earth-alkali. Mg is much more intimately associated
to the organic matter, e.g. in the chlorophyll molecule where it can repre­
sent up to 30 % of the plant magnesium (Mengel, 1968). In spruce litters,
Van Praag (oral communication) has identified high proportions of apparent­
ly little degraded chlorophyll, by means of chromatography. This behaviour
difference between Ca and Mg was also observed in a detailed study of their
distribution in the L, F, and H litter layers, as well as by means of frac­
tionation in the organic and mineral horizons (Delecour e t a l . , 1977).
3.3.
R e l a t i o n s h i p with
forest p r o d u c t i v i t y
Table 3 gives the variation of the values of litter decomposition coef­
ficient and of forest productivity, in relation to different beechwood types
and humus forms.
Table 3
Litter decomposition coefficient, K, and forest productivity,
Iv7b*
Beechwood
types
Humus forms
Blueberry
(V a c c in iu m m y r t ï l l u s )
Woodrush
( L u z u la a l b i d a )
dysmoder
moder
Nb of
sites
K
^v7b
5
7-10
4.2-4.5
8
9-18
4.5-6.4
18
6.5-7.0
Wood Fescue
(F e stu ca a lt is s im a )
mullike moder
2
id
acid mull
2
Woodruff
( A s p e r u la o d o r a t a )
acid mull
1
19-21
20
7.4-7.5
6.7
As a site index, we have made use of the mean annual increment of tree
volume over 7 cm diameter at 150 years, expressed in cubic meters per hec­
tare. K coefficient is given on a dry matter basis.
The correlation coefficient between these factors equals 0.958 (Dele­
cour, 1978) , and is not significantly different with the other
"organic"
expressions of K (C, N, P, or S basis). The relation is least with the coef­
ficient expressed on the base of potassium (0.254).
So, this litter decomposition coefficient appears to be a very inte­
resting site factor in the studied beechwoods. The productivity could be
estimated from the K coefficient by means of the equation
Prod. = 0.227 (K coeff) + 2.566.
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However, this site effect is likely to interfere with a more general,
or regional effect whose causes can be very diverse
climatic differences,
forestry management, historical factors, etc... The superimposition of the
local and regional effects could possibly make understandable the rather
large range of K and I
in the woodrush beechwoods, with moder humus form.
4. DISCUSSION
The use of a litter decomposition rate coefficient taking into account
the autumnal leaf fall (A) and the litter (L) allows one to show up diffe­
rences in the rate of evolution of the nutrients during the decomposition,
and, on the other hand, to put to evidence a very good relationship with
forest productivity.
This coefficient is an approximate expression of the speedness of the
nutrient turn-over, and the results obtained in the Belgian beechwoods tend
to corroborate the hypothesis of Hartmann (1959) following which the inten­
sity of the biogeochemical cycles explains the productivity in poor soils
better than does the chemical fertility of the soil itself.
From calculations of data of Heilmann and Gessel (1963), it appears
that the K coefficient could be used to follow soil and stand responses to
fertilization
a N-input in a Douglas fir stand increased the flow of N
throughout the ecosystem and, at the same time, increased the value of the
K coefficient.
In "normal" beechwoods, as they were defined by Dagnelie (1956), the A
value is rather constant, so that a rough estimation of the K factor can be
made by means of the sole determination of the L value.
However, there are some limitations to the possibility of using this
K coefficient. Comparisons may be made only in well defined ecological con­
ditions as regards the regional climate, the tree species, and the substra­
ta which must lie in a rather narrow range of chemical fertility. Besides,
its determination is valid only for stands which have reached a steady sta­
te, i.e., stands where leaf fall equals the fraction of litter decomposed
annually. This is not yet the case in most of the articifial sprucewoods of
Southern Belgium.
On the other hand, the spatial variation of the L value being rather
large (Delecour et at., 1967) , it is hardly possible to use the K coefficient
as an indicator of seasonal evolution, unless a very large number of samples
are collected, which would make this kind of research most tedious and ti­
me-consuming .
REFERENCES
Dagnelie, P., 1956
Recherches sur la productivité des hêtraies d'Ardenne
en relation avec les types phytosociologiques et les facteurs écologi-
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ques. 2e partie. Bull. Inst. Agron. Stat. Rech. Gembloux, vol. 24,
n° 4, 249-284.
Delecour, F., 1969
Problems of forest fertilization. The importance of
the nutrient cycle. Agri-Digest, n° 17, 3-9.
Delecour, F., 1975
Note sur la distribution du carbone et de l'azote dans
les fractions humiques de quelques sols forestiers. Pédologie, vol. 25,
n° 2,, 118-125.
Delecour, F. , 1978
Facteurs édaphiques et productivité forestière. Ibid.
vol. 28, n° 3, 271-284.
Delecour, F. , 1980
Essai de classification pratique des humus. Ibid., vol
30, n° 2 (to be published).
Delecour, F., Van Praag, H. and Weissen, F., 1977
Edaphologie du site fo­
restier de Mirwart. ¿n Productivité biologique en Belgique. Trav. Sect,
belge P.B.I. (P. Duvigneaud et P. Kestemont, éd.), 73-105.
Delecour, F. and Weissen, F. , 1977
Les sols bruns acides des forêts de
l'Ardenne
Définition et amélioration. Annales de Gembloux, vol. 83,
n° 1, 27-42.
Delecour, F., Weissen, F. and Nanson, A., 1967
Aspects techniques de l'é­
chantillonnage des retombées annuelles et des horizons holorganiques
des sols de forêts. Bull. Rech. Agron. Gembloux, vol. 2, n° 3, 429-449.
Hartmann, F., 1959
Dynamik und Naturgesetzlichkeit im Nährstoffhaushalt
des Waldes. Centr. Gesamt. Forstw. Bd 76, 36--64.
Heilmann, P.E. and Gessel, S.P., 1963 : Nitrogen requirements and biologi­
cal cycling of nitrogen in Douglas-fir stands in relationship to the
effect of nitrogen fertilization. Plant and Soil, vol. 18, 386-402.
Jenny, H., Gessel, S.P. and Bingham, F.T., 1949 : Comparative study of de­
composition rates of organic matter in temperate and tropical regions.
Soil Sei., vol. 68, 419-432.
Maldague, E., 1967
Aspects faunistiques de la fertilité des sols fores­
tiers et spécialement des sols forestiers équatoriaux. Thèse, Centre
Chim. Biol, et Coll, du Sol, Louvain, 265 p. (draft).
Mengel, K., 1968 : Ernährung und Stoffwechsel der Pflanze. Fisher Verlag,
Stuttgart, 436 p.
Noirfalise, A. and Vanesse, R., 1977 : La hêtraie naturelle à luzule blan­
che en Belgique (L u z u lo - F a g e t w n ) . Comm. Centre Ecol. Forest, et Rura­
le, nouv. série, n° 13, 29 p. + annexes.
Van Praag, H.J., 1972
Contribution àl'étude de la disponibilité de l'azo­
te et du soufre dans les sols forestiers oligotrophes de l'Ardenne.
Thèse, Fac. Sei. Agron. Gembloux, 278 p. (draft).
Van Praag, H.J., and Weissen, F., 1977 : Evaluation de la quantité d'azote
minéralisé par an, dans le sol de la "hêtraie nue" de Mirwart. in Pro­
ductivité biologique en Belgique. Trav. Sect, belge P.B.I. (P. duvi­
gneaud et P. Kestemont, éd.), 327-334.
SUMMARY
For natural beechwoods of Belgian Ardennes, the authors discuss a lit­
ter decomposition rate coefficient, K, giving a ratio of leaf fall, A, to
forest litter, L (K = 100.A/(A+L)). This coefficient shows up the differen­
ces of evolution of the nutrients during the humification, namely the dif­
ferences between Ca and Mg. From an other point of view, the proposed coef­
ficient exhibits a very good relationship with the forest productivity,
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which makes it an interesting site factor.
ZUSAMMENFASSUNG
Laubstreuzersetzungskoeffizient
als
S ta n d o r t s f a k t o r
Der benutzte Laubstreuzersetzungskoeffizient K wird durch das Verhält=
nis des im herbstlichen Laubfall enthaltenen (Element-)Gewichts (A) zur to­
talen (Element-)Reserve der organischen Bodenauflage nach dem Laubfall (A+L)
dargestellt (K = 100.A/(A+L)). In den naturnahen Buchenwäldern der belgi=
sehen Ardennen zeigt dieser Koeffizient in welchem Masse verschiedene Ele=
mente gleich oder unterschiedlich schnell umlaufen. Auf das ungleiche Ver=
halten der Erdalkali Ca und Mg wird hingewiesen. Zwischen mehreren Ausdrucks^
weisen des genannten Koeffizients und der Produktivität bestehen höchst si=
gnifikante Korrelationen.
RESUME
Vitesse
de d é c o m p o s i t i o n
des
litières,
facteur de
station
Pour des hêtraies naturelles de l'Ardenne belge, les auteurs discutent
d'un coefficient de décomposition des litières, K, exprimant un rapport en­
tre la retombée automnale de feuilles, A, et l'ensemble de la litière pré­
sente sur le sol, L (K = 100.A/(A+L)). Ce coefficient permet de mettre en
évidence des différences de vitesse d'évolution des éléments nutritifs au
cours de 1'humification, en particulier entre Ca et Mg. D'autre part, le
coefficient proposé montre une excellente relation avec la productivité, ce
qui en fait un intéressant facteur de station.
15.02.1980
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