The Woodlands of England. 
J 33 
obtain enough food, or by the formation below the surface of a layer 
of “Ortstein” (moor pan), i.e., a hard layer of sand bound together 
by humous compounds, which the roots of the trees cannot pene¬ 
trate, the rejuvenation of the wood is rendered impossible, the gaps 
formed by the dying of the old trees are not filled up, and the forest 
is eventually replaced by heath. 
Whether all the steps of such a natural process unassisted by 
human activity have actually occurred in this country has not yet 
been ascertained: the subject needs a great deal more investigation. 
It is certain, however, as Graebner admits, 1 that the process of re¬ 
placement of woodland by heath is at any rate much accelerated by 
extensive felling of trees; this, as was explained earlier in the 
present paper, leads to rapid deterioration of the soil through 
destruction of the mild humus by sun and wind, and, on suitable 
soils, enables certain mosses and other plants of the heath-association 
to find an entry. Not only does the felling of mature trees 
considerably diminish the supply of seed, but there can be no doubt 
that the occupation of the soil by a heath-vegetation with its accom¬ 
panying layer of acid peat checks, or altogether arrests, its re¬ 
colonisation by such a tree as the oak. This is perhaps partly due 
to unfavourable conditions for germination. The growth of seed¬ 
lings is also severely handicapped by the enormous multiplication of 
rabbits, that especially affect the light sandy soils in which they 
can easily burrow. The actual stages of degeneration of woodland 
on sandy soils through such factors as these can be readily observed 
in scores of places in the south of England ; and there is little doubt 
that many of the heaths of this region were at one time covered 
with forest. Whether they were all so covered is another question. 
Some southern heaths are certainly very old, as we know from old 
descriptions and place-names ; but if a natural process of forest 
degeneration by the leaching of the surface soil has been going on 
since the close of the Glacial Period, it may be that heath had in 
some cases replaced forest by the beginning of the historical age. 
It is also a possibility that some soils were primitively colonised by 
heath-plants, and not by trees, owing to the extreme poverty of the 
soil. Perhaps this is true of the East Anglian heaths, as it is of 
some of our fixed littoral sand-dunes; but the problem has not yet 
been investigated. 
Though the oak, from whatever cause, certainly finds a difficulty 
in recolonising our heaths, the birch is much more successful. This 
1 Graebner, loc. cit., p. 64. 
