REGENERATION MEASURES AND THE FORMATION OF SALTPETRE CXIX 
instance, round Björna in Ångermanland. The higher one goes and the more 
raw the climate becomes, the less rapidly is the raw humus covering trans- 
formed after cutting, and the more slowly and with greater difficulty, on the 
whole, does the regeneration of the forest take place. When, for instance, in 
northern Ångermanland, one reaches a height of about 400 m. above sea- 
level, one notices clearly a distinct deterioration in the regeneration conditions 
of the forest; and at still greater elevations one may come across great bare 
areas where the access of light seems to be quite sufficient, but where the 
regeneration clearly proceeds at an excessively slow pace (see, for instance, 
fig. 37): Here we have to deal with not only directly, but also indirectly 
disadvantageous effects of the climate, namely its influence on the quality of 
the humus-covering. To this type belong very considerable tracts about 400 
—3500 m. above sea-level in southern and central Lapland, covered with feeb- 
ly growing spruce. From this, on the whole, correct picture of the condi- 
tions of regeneration and of ground that prevail in Norrland there is an ex- 
ception in the areas rich in lime, which, even in the immediate neighourhood 
of the alpine region, can get such a rich ground-vegetation on the clearings 
as to place considerable difficulties in the way of the regeneration of the 
forest, but where, nevertheless, if the forest is treated with prudence, it is 
possible to produce a very fair degree of natural regrowth. 
On the whole, the formation of raw humus becomes worse and deeper the 
older and thinner the woods become; and if the development were allowed 
to proceed quite undisturbed, it would gradually lead in the course of time 
to extremely thin woods which it would be extremely difficult to regenerate. 
As is well-known, fire has often brought about a radical revolution in the 
whole of this course of development, and made the ground much more suscept- 
ible of forest regeneration. As a result of the effect of fire we have in many 
places extensive fine and dense young forests. As I have said above, I feel 
inclined to find the most important cause of this in the active formation of 
saltpetre that takes place after burning, and which has favoured the strong 
development of the plants in their youth. Denshiring or the burning of brush- 
wood have also been measures of regeneration employed and recommended 
by many foresters, but strongly condemned by others. 
When, in actual practice, the important question is how one is to treat the 
ground in order to favour the regeneration of the forest, then, according 
to the view which I have tried here to maintain, it is not a ques- 
tion. of burning, but the question 1s to try to bring about the con- 
version into nitric acid otithe organically bound nitrogen in the 
HuMmuS-GOVEriIn 2 IN, SUCktsrwayrasto be favourable to the conifer- 
ous tree-plants, but not too abundant. 
In the above-mentioned forests in Jönåker, Äs, Högsjö, and Alkvättern, 
which have been examined by me such a transformation takes place after 
quite slight inroads with the axe, and the forest regenerates itself with the 
greatest ease. Under such favourable circumstances for the regeneration ot 
the forest also clear cutting is employed with or without seed trees, and 
sometimes the clearings are burnt. According to the view which I here 
put forward, this last-named measure is both unnecessary and, to a cer- 
tain extent, injurious. It would certainly seem as if on these areas, too, 
the nitrogen would be more rapidly nitrified if shrub-burning were employed; 
