CXXIV HENRIK HESSELMAN 
there is the proper place for a thorough preparation of the ground or a 
slight burning. The most important and the most effective of the objec- 
tions which can be made against the employment of fire seem to me to be 
of a practical nature. These are the difficulty of limiting the fire, the danger 
of setting alight the neighbouring woods, and the danger that tree-plants al- 
ready existing on the clearing should be consumed, etc. The risk that is 
thought to exist of deteriorating the ground, on the other hand, is much smaller. 
The important thing, of course, is to burn in the spring, when the ground is 
still so damp that the humus covering does not take any great harm, but 
only the mosses and the berry shrubs are burnt up. The burning involves 
the loss of a great deal of nitrogen, it is true; but the loss is of less im- 
portance because the nitrogen of the raw humus covering is not readily avail- 
able. The nitrogen in the layer of humus remaining after the burning, on 
the other hand, is readily available, not least for the tree-plants. And if the 
ground has not been too severely burnt, the lost nitrogen should be soon 
enough replaced. In the ground there live organisms that assimilate nitrogen; 
and it is very possible that the activity of these, as of other bacteria, is stimul- 
ated after a fire. But there is yet another risk. If the burning is very severe, 
the ground becomes more close and compact than before and the upper crust 
somewhat changes its structure: I have not given any close study to the 
matter; but the phenomenon might possibly be explained by the effect which 
the alkalis produced by the burning exercise on the ground. The alkalis 
are wont to destroy the flocculated structure of the ground: the soda soils 
on the Hungarian steppe (Paussta) are distinguished by a very close stratifi- 
cation, and the ground is thus very compact. In another respect, on the 
other hand, fire has often a favourable influence on the ground: it favours 
the immigration of the birch and other leaftrees, and their fallen leaves 
greatly contribute to a good condition of the humus-covering. Where leaves 
of birch or aspen are mingled with fallen needles and shrubs, the humus has a 
far looser and more favourable structure than where they are lacking (see figs. 45 
and 46). It is true that aspen and birch may immigrate in such abundance as to 
hinder the development of the more valuable conifers; but by taking pains to 
secure a supply of seed-trees of pine and spruce, and by keeping the birch 
and the aspen within reasonable bounds in the immediate neighbourhood of the 
clearing, it ought to be possible to overcome this difficuity. Denshiring or 
burning, in any case, is of such a great importance and is such a compar- 
atively cheap means of promoting regrowth on lands difficult of re- 
generation, and covered with strong raw humus, that its applic- 
ability must be discussed and investigated without preconceived 
opinions. On the lands with which we are here concerned, if we wish to 
secure a dense and strong regrowth, wherein self-sowing also can take its 
part, we have only two things to choose between—either burning 
or else systematic and thorough preparation of the soil, which 
brings about a real transformation in the tough raw humus 
covering. 
Finally it may be expedient to make a quite brief summary of the most 
important results of these studies: here I shall limit myself to our coniferous 
forests. 
In the humus-covering which is formed in our mossy coniferous 
