recorder surveys in 1961 and 1963. The area of top killing and 
tree mortality corresponds to the area of heavy and severe de- 
foliation as defined by the survey. The undamaged area shown 
corresponds to the area of little or no spruce budworm feeding. 
Within these two areas, which represent the majority of the com- 
mercial balsam fir and white spruce type in Minnesota, other 
forest types make up roughly three-fourths of the commercial 
forest land acreage. The flight lines of the 1961 survey were ex- 
tended beyond the general infestation area to define the host type 
boundary. The nonhost forest type is shown in white. 
The heavy black line in the figure is the 1961 mortality bound- 
ary and encloses an area of 1,406,000 acres. It shows mainly the 
area of top killing and tree mortality that existed at that time; 
however, the total infested area was considerably larger. The 
1963 operation recorder data, which determined the expanded 
boundary of top killing and tree mortality, was not used in deter- 
mining volume loss. 
Data obtained from the 1963 operation recorder survey defined 
the acreages of various forest types within the 1961 mortality bound- 
ary. Standing dead spruce and fir were considered stocking for 
type determinations and were found to cover 544,000 acres. Within 
this forest type, there were 85,000 acres where mortality of the 
host species (upland spruce and balsam fir) was 10-50 percent, and 
106,000 acres where mortality exceeded 50 percent. This tree 
mortality occurred in 67 townships within the mortality survey 
boundary and accounts for a large reduction in acres of living 
spruce-fir type since the beginning of the infestation. 
An additional class of 1963 recorder survey data that was 
particularly useful in adding to the general knowledge of the 
infestation area was host type stocking. Within the 1961 mortality 
boundary, the spruce-fir type was broken into two categories: 
(1) 255,000 acres, 20-50 percent stocked, and (2) 289,000 acres, 
over 50 percent stocked. 
Aerial Photographic Survey 
Initially, the volume loss survey was limited to a photographic 
sample of 25 l-acre plots within 25 townships randomly selected 
from the 67 within the mortality survey boundary. Five of the 25 
plots were randomly selected for ground sampling in addi- 
tion to photographic sampling. On these five, the height and 
d.b.h. of each dead spruce and fir were measured. This type of 
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