50 
BULLETIN 14 
U. S. DEPARTMENT OE AGRICULTURE 
about 0.1 foot a year for all species and conditions. These rather uni- 
form minima are due usually to some cause other than site or compe- 
tition, such as cutting back by rabbits. The slow growth of several 
of the northern white pine plantations and consequently the low 
average height growth of that species on the better sandy soils under 
40 per cent or more of cover is also the result of damage by rabbits 
or other agencies. 
Table 6. — Average and maximum height at 10 years of different kinds of planted 
trees under different soil and cover conditions 
NATURAL TREE GROWTH COVERING LESS THAN 40 PER CENT OF AREA 
[Heights in feet] 
Jack pine 
Norway pine 
Northern white pine. 
Norway spruce 
European larch 
White spruce 
Average height 
Jack 
pine- 
oak 
sands 
5.6 
2.6 
2.2 
2.0 
3.0 
Better 
sands 
and 
sandy 
loams 
6.9 
3.0 
3.2 
3.7 
3.1 
1.9 
Heavy 
soils 
2.2 
5.3 
5.7 
Culti- 
vated 
soils 
7.3 
7.0 
4.3 
22.2 
1.5 
Maximum height 
Jack 
pine- 
oak 
sands 
Better 
sands 
and 
sandy 
loams 
Heavy 
soils 
10 >. 
J ! 
4 
4 I. 
3 L 
Culti- 
vated 
soils 
12 
13 
22 
7 
122 
2 
NATURAL TREE GROWTH COVERING 40 PER CENT OF AREA AND MORE 
Jack pine 
Norway pine 
Northern white pine. 
Norway spruce 
4.6 
2.3 
2.0 
2.8 
3.0 
2.9 
1 Only one plantation. 
Occasionally a plantation makes exceptionally rapid height growth. 
The two most striking examples are the plantations of European 
larch and northern white pine which grew at the rate of 2.22 and 2.16 
feet a year, respectively. Both were at Green Lake, Wis. Large 
stock was planted on good soil and cultivated before and after plant- 
ing. The favorable climate at the southern edge of the region prob- 
ably contributed also to the unusual growth. Individual trees in 
certain years grow surprisingly fast, as did the white pine shown in 
Plate 6, A. 
The average heights of jack pine 10 years after planting on the 
different sites, specified in Table 6 and Figure 7, are 9 feet on culti- 
vated soils, 7 feet on the better sandy or sandy-loam soils, and only 
5 to 6 feet on the dry jack pine-oak sands. Norway and Northern 
white pine are closely similar in their early height growth. On 
cultivated sites even when the soil is sandy and dry, they reach 
heights of 7 to 8 feet in 10 years. On the loamy soils where the com- 
peting growth covers not to exceed 40 per cent of the area, the height 
at 10 years is usually between 5 and 6 feet. On the better sandy 
soils or on the heavy soils where there is more than 40 per cent com- 
petition of natural tree growth, they will average between 3 and 4 
feet in height in 10 years. The spruce plantations are few, and most 
of them have been so damaged by rabbits that satisfactory conclu- 
