Factors of Pedogenesis - Major Soil Groups of the World - page 64

Above all, fires destroy not only the trees but also their roots and humus.
Rains laterally carry away the ash, that is, the basic cation reserves.
The possibility of regeneration becomes very remote. A fire, even if
not followed by cropping by man can scar the forest landscape for
centuries.

AMPHI-
MULL
TANGEL

Granular A
horizon

Presence
of an OH
horizon (in
addition to
OL and
OF
horizons)

OH >1 cm MOR

Abrupt boundary
with a mineral
horizon
(or diffused OM)

Non-granular A
horizon (or A
horizon absent)

OH >1 cm DYSMODER

Gradual boundary
with A (juxtaposed
A horizon)

OH < 1 cm,
sometimes
discontinuous

MODER

Non-granular A
horizon

HEMI-
MODER

More or less thick,
continuous OF

Granular or
microgranular
A horizon

OF horizon
present (in
addition to OL)

DYSMULL

Sporadic OF

Current year's
leaves (OLn) and
old bleached
leaves (OLv)

OLIGOMUL OH

horizon
absent

Very thick,
continuous OLv

Sporadic OLv

OF horizon
absent (MULL)

Current year's
leaves only (OLn)

Continuous OLn; A
with fine granular
structure
Sporadic OLn; A
with medium
granular structure

MESOMULL

EUMULL

Fig. 2.22 Key for identifi cation of the principal forms of humus (RP, 1995). With n = new and
v = modifi ed.

Litter is a biomass that varies with time. This was shown in a land
parcel of the Observatory of Quality of Soils (OQS) located in the
Donon pass in the Vosges and planted to spruce around 95 years ago
(Bonneau 2000). The L, F and H horizons, which together represented
104 tonnes of organic matter per hectare in 1986, had diminished to 77
t ha -1 in 1996. This change is favourable, paradoxically. The droughts
of 1971-1976 had caused wilting of the trees, resulting in fall of needles
and hence augmented the additions of litter in the early 1980s. Later, the

Dynamics