REGENERATION MEASURES AND THE FORMATION OF SALTPETRE CXVII 
not be able to explain a number of phenomena in the developmentt of our 
coniferous forests, e. g. the very gradual development of the pine on the clean 
cut pine-heaths or the immigration of the spruce into the mossy pine forests. 
But the nitrification of the humus nitrogen has such a favourable influence, 
and is of such importance, that a discussion of our methods of forest-regenera- 
tion, with this feature as the dominant one, may fitly close this treatise. 
CHaP,. xi. Discussion of our measures for forest regeneration with 
reference to their bearing on nitrification of the humus 
nitrogen and the productive capacity of the soil. 
Under certain circumstances the too active conversion of nitrogen into salt- 
petre may be an obstacle to the regeneration of coniferous forests. This 
is especially the case on very fertile areas, where even quite a little gap 
may produce a luxuriant ground vegetation which is obstructive to the tree- 
plants. Such a case is illustrated in fig. 32. In the quite insignificant gap 
there is a rich growth of raspberries, nettles, Epilobium angustifolium and dande- 
lions (Taraxacum officinale), that is, pure nitrate plants. By keeping the gaps 
quite small, we can to some extent keep back this development of vegetation. 
To remove the cause of this vegetation, namely the rich bacterial life of the 
ground and the active conversion of its supply of nitrogen, would be identical 
with trying to reduce the productive capacity of the ground. Such areas, 
however, occur in Sweden only to a very slight extent, chiefly on grounds 
rich in lime—that is to say within Swedish Silurian regions, and in the dis- 
tricts of primeval rock, where the moraine has become rich in lime owing 
to the fact that the ice has conveyed there from other quarters crushed ma- 
terial rich in lime. The areas within the hyperite regions of Värmland which 
have been made fertile by the occurrence of material rich in lime and easily 
weathered, also belong to this type (cf. fig. 1). The coniferous forests on such 
ground usually have a rather herbulent covering and a mould-like humus; and 
consequently they belong, as a rule, to the type where a weak nitrification takes 
place even beneath the shade of the trees (see HESSELMAN, 1917). The observant 
forester can thus, from the very nature of the ground-covering in the wood, 
draw his conelusions as to how the soil will behave with an increased 
access of light and can take his measures on the strength of this. Small re- 
growth-areas and rapidly taken measures for sowing or planting may lead to 
the object in view. Such areas may also, if the axe is wielded with prudence, 
be regenerated by self-.sowing. Even the northernmost parts of Sweden the 
spruce renews itself on such grounds in rather small gaps (see figs. 33 
and 28). 
In difficult cases the clump-planting of spruce may be employed. The great 
productive capacity of the ground, of course, also allows costlier measures of 
regeneration than in other types of forest. Apart from these grounds, 
which are often especially fertile, it is an important problem for Swedish 
forest economy to manage the forest in such a way that on the regenerating 
areas it may be possible to bring about a conversion of the humus nitrogen 
into saltpetre that is favourable to coniferous tree-plants. This problem is 
