270 
Journal of Agricultural Research 
Vol. XXXI, No. i 
of the undesirable species, and thickets of saplings and advanced 
growth. The effect of this burning had been immediate, causing 
the crowns to die and the leaves to fall off within a short time after 
the burning. The effect of heat and fire on saplings and reproduc¬ 
tion was surprisingly great, whole thickets being completely killed 
by small fires which actually came in contact with only a small 
proportion of the trees. On the other hand, the trees which had 
been girdled but not burned were just beginning to die and lose 
their leaves at the end of the second growing season after girdling, 
and after they had produced one good seed crop. The much greater 
effectiveness and value of the brush burning, compared to girdling, 
were very apparent. From this it is thought that girdling had best 
be done after brush has been burned, in order to supplement the 
burning and reduce the cost of cleaning up the area. 
For the purpose of finding a more effective way of killing the white 
fir and hemlock by girdling or other means, an experiment was later 
installed which was planned to take into account available informa¬ 
tion on the physiological functions of trees. 
In the light of present knowledge of these functions it is easy to. 
account for the fact that the two girdled hemlock trees from wnich 
seed was collected remained green throughout the summer following 
the girdling and produced heavy crops of seed. The girdling did not 
prevent the movement of water, soluble salts, and stored food from 
the roots through the sapwood to the leaves. Nourished thus with 
this water and stored food, it was possible for the foliage to continue 
photosynthetic manufacture of new food during the summer after 
girdling. Since most or ail of the surplus food could not return to 
the roots for storage, because of the girdling of the inner bark, it 
remained in the trunk and crown and was doubtless available for the 
production of a heavy crop of seed. 
There is reason to think, furthermore, that girdling does not en¬ 
tirely prevent the movement of surplus food from the foliage to the 
roots. This theory is advanced by S. B. Elliott, 2 who cites instances 
of white pines that have lived from 5 to 22 years after girdling, 
EXPERIMENTS IN GIRDLING AND POISONING 
As winter girdling had not proved entirely successful, it was de¬ 
cided to try girdling at different times during the growing season, 
when, in accordance with the theory of food movement, there would 
be a minimum of stored food in the sapwood available for the pro¬ 
duction of seed and continued growth. Accordingly, it was decided 
to test 10 trees each of white fir and hemlock on each of the following 
dates: 
May 15 (beginning of active growth). , 
June 15 (height of active growth). 
July 15 (slackening of growth). 
August 15 (height of storing of surplus food). 
September 15 (slackening of vegetative activity at end of 
growing season). 
3 Elliott, S. B. the problem of food movement in trees. Forestry Quart. 12: 550-561. 1914. 
