This document discusses methods for measuring and calculating the mean diameter and mean height of trees in uneven-aged forests. It provides an example calculation of mean diameter using basal area measurements from different diameter classes. It also defines mean height as the height that, when multiplied by the mean form factor and basal area, gives the mean volume of an average tree in the stand. Two methods are described for calculating mean height: averaging the heights of each diameter class, and using Lorey's formula which weights the height of each class by its basal area.

2. Attaullah
FWM – 6th

3. CROP DIAMETER & CROP HEIGHT

4. Measurement of diameter and height
of the crop in the even aged and
regular crops are comparatively easy
because the difference in individuals
are not very pronounced. In uneven
age crops because of the variations,
these attributes are reckoned by
their mean values which may be
defines as:

5. MEAN DIAMETER
It is the diameter corresponding to
mean basal area of a group of tree or
stands. Sometimes used for arithmetic
mean of the summated diameters.

6. Dia . class
inches
No. of trees Basal area/
tree(sq. ft.)
Basal area of
each class (sq.
ft.)
6
7
25
28
0.1963
0.2673
4.9075
7.4844
9
10
17
19
0.4418
0.5454
7.5106
10.3626
13
15
16
11
0.9218
1.2272
14.7488
13.4992
18
21
10
8
1.7671
2.4053
17.6710
19.2424
22
25
5
4
2.6398
3.4088
13.1990
13.6352
Total 143 122.2607

7. Mean Basal area = 122.2607 / 143 =
0.8550
Pi D square / 4 = 0.8550 D square =
0.855 x 4 / pi = 1.0886
D = square root 1.0886 = 1.043 ft =
12.5 inch.

8. MEAN HEIGHT
It is the height which when
multiplied by the mean form factor
and the mean basal area of a crop
gives the arithmetic mean volume of
the mean tree in the stand. In form
of formula it can be written as:

9. Mean volume = h x f x s = volume of
stand / No. of trees in the stand
Or h = volume/No. of trees / f x s
h 1 f and s stand for mean height,
mean form factor and mean basal
area respectively.

10. There is no method of determining the
mean height which can be considered
to comply with this definition but the
following method particularly the
Lorey`s formula is likely to be least
inaccurate.
In the first method, mean height of
each diameter class may be obtained by
measuring the heights of a number of
trees in the class and calculating the
mean height arithmetically or
graphically from height-diameter curve.

11. Then the crop mean height is
determined by:
H = mh1 + mh2 + mh3 + … / N
Where mh1, mh2, mh3 etc. are the
mean heights of individual classes
and N is the number of the classes.

12. The second method is based on the principle
that volume should be the basis of
calculation, a more convenient step is to
weigh the mean height with respect to basal
area. Therefore:
H = s1h1 + s2h2 + s3h3 + … (Lorey`s
Formula)
S1, S2, S3 etc and h1, h2, h3, stand for basal
areas and mean heights respectively of
various classes and S is the sum of all basal
areas.

13. THANK YOU