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CONVERSION OF FOSEST
bulk of the material is converted into humus, which gradually compacts itself
into a firm layer. Heath formation on such a soil is interestmg for the reason
that it may occur without the leaching of the upper layer, and mdeed may be
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found on heavy loam or clay. Grebe describes the action of the raw humus
upon vegetation as follows :
'
(1) The raw humus cuts off the lower soil almost
completely from its air supply. (2) It hinders the circulation of water m the
soil. It prevents the evaporation of superfluous moisture in winter and sprmg,
and in summer it hinders the penetration of light rains and of dew. (3) It is
probable that the soil beneath the layer of heath-felt passes out of the stage
of oxidation into that of stagnation and reduction. (4) The upper soil layer
is relatively poor in dissolved mineral salts, the middle and lower relatively
rich. (5) While the raw humus of the heath is as rich as the humus of the
beech woods and pine woods, it is so firmly combined as a consequence of its
peaty nature that it can not be used by the trees.'
"Grebe has been correct in his assumption that the aeration of the soil is
ialmost completely prevented by the raw hmnus. According to my opinion,
this factor sufiices almost entirely alone to make the proper growth of trees
impossible and to call forth sickness, stunting, or death according to the intensity
of its action."
Conversion of forest into moor.— "It is generally recognised that the heath
moor differs from the meadow moor in that it is not level but convex. It
grows upward not only in the middle, but also, even though slowly, at the
margin. Now if such a moor arises in a shallow depression, it slowly pushes
its edges up the slopes. Thus it finally reaches a gap in the surrounding hUls,
and it then extends a tongue through the gap into further levels. Thus it
comes about that a lively movement of water is noticed, when the tongue of the
moor lies upon sloping ground. Since the tongue lies lower than the surface
of the moor and the Sphagnum holds the water so firmly that the surplus can
soak into the soil but slowly, the tongue is constantly dripping with water,
and in most cases a quantity of water flows away from it, as at Kolbermoor.
If the soil of the slope and adjacent lower areas is not especially pernutrient at
its surface, the formation of heath moor proceeds rapidly. The cushions of
Sphagnum spread more and more widely till they reach the bottom of the low
area always fed with water from above. The bottom once reached, the constant
flow furnishes abundant water for further development, unless, as is
frequently the case, a colony of Sphagnum has already occupied the bottom as
a consequence of the accumulating water, in which event the two masses unite.
Whenever the hollow or the slope and gap are covered with forest, the soil is
converted into swamp by the Sphagnum and the air is driven out as a result.
The physiological effect upon the growth of trees is the same as in the formation
of raw humus upon the forest floor. It is a peculiarly desolate picture
that is formed by the countless dead standing trunks in a young moor. One
trunk after another falls, and soon they are all buried in the moor, and nothing
visible remains to remind one of the former forest.
"In order to exhibit the entire process of the swamping of a forest, I have
purposely chosen cases in which the moor must pass over a small elevation,
since the important events in the water movement are much clearer than in
the common instances. For the most part, the formation of heath moor upon
meadow moor, or also in lowland forest, takes place completely on the level
and in the following manner. The lowlands have become filled with meadow
moors [swamps], as a result of the forlanding of ponds and lakes, and the
consequent development of swamps. The ground level of the swamp slowly
grows upward because of the annual increment of plant remains, but only to