THE LARCH AND ITS IMPORTAÅNCE IN SWEDISH FOREST ECONOMY. LXTIX 
be directly measured, however, owing to lack of material for comparison. 
We thus find that pine woods on grounds of the quality of 1— 90.6, and probably 
even o.4, can advantageously be mixed with larch. A mixture of 20 2 seems 
to the present writer not to involve any danger of the spread of larch diseases, 
nor any disturbing effect on the growth of the pine, specially if the better 
races of larch are employed. By this means an increased output of 20 2 is 
attained in many cases; and this greatly increases the output value, especi 
ally owing to the greater yield of thinnings. 
The mixture of birch and larch does not bring about any greater produc 
tivity; and so far as the improvement of the ground is concerned either tree 
by itself is sufficient. 
The mixture of larch and beech is illustrated in several fine examples (see 
too (Figs. 55 and 56). 
The mixture of larch and spruce is also common in Sweden. Of special 
interest in this respect is a 32 year old stand in alternate rows at Omberg 
in Östergötland (see Plate 8). The detailed investigation on p. 650 has shown 
that the value of the stand per hectare would be 3,109 kr. if it consisted 
solely of spruce: with a mixture of 20 & of larch its value is 4,981 kr. per 
hectare. Thus this mixture has raised the value of the stand by: 20 &. 
This form of mixture — spruce and larceh — may however involve diffi- 
culties. One risk that seems to be incurred by it is that the spruce might 
give the larch too much side shade, and thereby hinder its development and 
predispose it to canker. "The present writer observed examples of this in 
Halland at the close of the nineties. From this point of view connected rows 
of larch, as at Omberg, might be expedient. As a rule, however, the larch 
gets a good start after being planted. — Another trouble may be caused by 
the appearance of canker. As canker is probably spread most frequently in 
the wounds caused by Chermes Abietis, and as that insect requires both larch 
and spruce to develop its two stages, it seems natural to suppose that it 
thrives best in mixed woods of larch and spruce, and can there make it 
possible for the canker to spread extensively. 
On these grounds the present writer has much hesitation in recommending 
the mixture of larch and spruce: 
The last subject treated in this chapter is thinning. 
As has already been mentioned in the section dealing with the require- 
ments of the larch in growing, space and climate, the larch is markedly fond 
of light. A specimen of this can be seen in the tabular appendices, where 
the valuation results from the pure larch stands have been divided into 'tree- 
strata'. 1 The bulk of the larches are of course con- 
centrated in the first tree-stratum, and a number of trees 
are also found in the second tree-stratum, but the third 
and the fourth tree-strata are strikingly little represented. 
On the whole, however, we may say that all four tree- 
! The present writer divides the stands, according to the re- 
lative heights of the trees, into four different tree-strata. The fourth 
or lowest stratum barely attains half the height of the dominant 
trees. The upper half of the height of the dominant trees is 
then thought of as divided into three equal parts. The distribu- ÅA skeleton-drawingshow- 
tion of the trees into strata in this way is shown in detail in the ing the distribution of 
adjoining figure. i the trees in tree-strata. 
