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PESeARCH NOTE Uso) 
| PAK SrA So vwrORE ST EXPERIMEN, STATION: <0. .S DEPARTMENT OF AGRICULTURE 
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? Diameters and Numbers of Trees in Red Pine Stands 
Are Greatly Affected by Density, Age, and Site , 
Tree diameter and number of trees per 
acre greatly influence the value and kind of 
products produced from red pine stands. Un- 
til recently, predictions of diameters and 
numbers of trees per acre have not been 
available for intensively managed red pine 
stands. They have now been computed for 
a range of management alternatives. These 
computations show that diameters and num- 
bers of trees produced are affected by site, 
and can be controlled through the choice of 
initial spacing in new plantations and thinning 
intensity in existing stands. 
In this Research Note, the diameter of 
the tree of average basal area is used as the 
average stand diameter. This can be com- 
puted from the following formula if the basal 
area and number of trees per acre are known: 
D2 = (BA/N) (4/7) (144) 
where D = average stand diameter 
BA = basal area in sq. ft. per acre 
N = number of trees per acre 
A current study by the junior author has 
estimated basal areas for red pine plantations 
with given numbers of trees per acre at age 
390 over a range of sites. A recent study has 
provided basal area growth and yield esti- 
mates by basal area density, age, and site for 
stands over 35 years of age.’ These basal area 
estimates were used in a method developed 
by the senior author to predict the number of 
trees per acre left after thinning to an assign- 
ed basal area at age 35 and every 10 years 
1 Buckman, Robert E. Growth and yield of red 
pine in Minnesota. U.S. Dept. Agr. Bul. 1272, 50 
pp., illus. 1962. 
thereafter. It was assumed that the stand is 
cut from above and below so that the propor- 
tion of trees cut per acre at each thinning is 
the same as the proportion of basal area cut. 
This assures that the diameter of the tree of 
average basal area is not changed by the 
thinning. It was further assumed that no 
trees die between thinnings. 
From these estimated number of trees 
and known basal areas after thinning every 
10 years, the diameter of the tree of average 
basal area was computed. For want of better 
information, the growth and yield data from 
regularly thinned stands of a natural origin 
are assumed to apply to regularly thinned 
plantations as well. 
To illustrate how much diameters and 
numbers of trees per acre can vary in per- 
iodically thinned red pine stands, three stand 
densities and two sites have been selected as 
examples (table 1). 
' Many other combinations of initial stock- 
ing (the number of trees per acre before 
thinning at age 35) and basal area density 
after thinning could be used. However, it was 
not possible to consider separately the effect 
of initial stocking and basal area density in 
this Note. Instead, the two measures of stand 
density are presented jointly. The examples 
were deliberately chosen to show how density 
extremes can affect future diameters and 
numbers of trees: low initial stocking thinned 
to a low basal area density; medium initial 
stecking thinned to a medium basal area 
MAINTAINED AT ST. PAUL % MINNESOTA, IN COOPERATION WITH THE UNIVERSITY OF MINNESOTA 
