40 BULLETIN" 149 7, U. S. DEPARTMENT OF AGRICULTURE 
planted trees of the demands of other closely adjacent trees, brush, or 
sod for the same space, light, soil moisture, and soil nutrients. Al- 
though soil moisture is probably the most important of the elements 
in the competition, no attempt will be made in this discussion to 
distinguish between the elements. 
It is evident in all the plantations that trees planted under the 
crowns of larger trees already established grow slowly. Many trees 
so planted died or were in poor condition and seemed likely to die. 
Outside the ground area covered by their crowns the effect of the 
larger trees on the growth of the planted trees was slight. Jack pine 
is least able to survive this competition. Norway pine survives better 
than jack pine but usually not satisfactorily for more than about 10 
years after planting. Northern white pine, white spruce, and Norway 
spruce survive well in competition with trees which shade them, but 
their growth is comparatively slow. 
The only plantation studied in which northern white pine exceeded 
Norway pine in height growth where the two species were planted 
under identical conditions was one in which the natural tree growth 
covered 50 per cent of the area. The average annual growth of the 
white pine was 0.18 foot and of the Norway pine 0.14 foot. If the 
average annual height growth of all the trees in the plantations of 
the northern white pine be taken as 1, that of the pines planted under 
larger competing natural growth will be represented by 0.90. For 
Norway spruce, the relation is 1 to 0.76 : for Norway pine 1 to 0.58 ; 
and for jack pine 1 to 0.56. In other words, jack pine is most retarded 
(its early height growth being reduced almost one-half) by the 
competition of other trees, and northern white pine is least affected 
and then only to the extent of one-tenth. (Fig. 5.) 
The effect of competition on the percentage survival is more com- 
plicated than its effect in retarding growth, because conflicting influ- 
ences are involved. During the first few years the competing vege- 
tation protects the planted trees from excessive heating and thus 
may save many of them from death at critical times. On the other 
hand, competition deprives them of light, moisture, and nutrients and 
in this way causes losses which tend to become heavier as the trees 
grow larger and the struggle for life becomes keener. 
Other elements in the effect of competition include the kind and 
density of the competing natural tree growth. Of the common trees 
occurring naturally on planting areas, the competition of jack pine is 
more serious than that of aspen, which in turn is more injurious than 
that of the oaks. Even a stand of jack pine may not always be pro- 
hibitive, however, for in an experiment at CloOjiiet such a stand did 
not prevent a northern white pine underplanting from having at 12 
3^ears a 90 per cent survival. The influence of density of the natural 
tree growth is indicated by experimental plantings by the Cloquet 
Forest Experiment Station in Minnesota (89), in which northern 
white, Norway, and Scotch pines were planted under jack pine 
stands of three different densities. Survivals after five years were 
highest in the 70-year open stand, next in the 35-year dense stand, 
and poorest in the 15-year dense stand. The northern white pine had 
the largest proportion living, with successively smaller percentages of 
Scotch pine and Norway pine. 
