The Concept of Normal Forest
NORMAL FOREST:
It is an ideal forest. It may not be present practically on the ground.
“A normal forest is a forest which has reached and maintains a practically attainable degree of perfection in all its parts for the full and continued satisfaction of the objects of mgt.”
A normal forest is a yardstick (means standard of comparison) for our actual forest and tells us shortcomings of our forest. There are certain characteristics of a normal forest. According to a German forester (1841), any forest capable of producing annually sustained yield should have the following characteristics.
- A homogeneous mixture of spp or one spp.
- All age classes occupy an equal area.
- Should have all age classes ie 1 to the rotation.
- The site is homogeneous altogether ie the growth potential is same all the time and at every place.
- It should have normal density or stocking. It means that stocking is 100% (1 density) because a normal forest will put normal increment.
However, the above ideas were rather conventional and insufficient enough to meet the ‘to-days documents’ demands. Thus a few more remarks should be virtue of an ideal forest.
- Normal forest should have normal opening up ie forest should be equal with roads etc eg Changa Manga
- Should be uniform in prices, costs, and quality. The amount on each unit each yr is the same and quality of produce ie timber and fuelwood is same.
This is done of equal increment is put each year by each age class. It tells us that how much should be the total vol. thus fig can be represented by a graph ie there is always a constant ratio for moving from ‘a’ to ‘b’, it is called ‘q’
If thinnings are made and change is ∆. In other words, the reduction is the no of trees follows a const ratio. Now let us find the vol in the same mathematical way.
| V1
1st yr |
V2
2nd yr |
V3
3rd yr |
— | — | Vn
100th yr
|
The area is disordered into equal units say one yr crop has vol V1 and 100 yrs crop has Vn. The vol is then the average of two vol measured at two intervals ie before the start of growing season Vi and after growing season. So,
Vi = Vo + V1 + V2 + . . . . . . . . . . . . . + VR-1 (vol before the start of growing season)
V2 = V1 + V2 + . . . . . . . . . . . . . + VR-1 + VR (vol at the end of growing season)
At V2 complete one class has shifted from Vo to V1. but always the center of the season will be reckoned and this vol (Vn) is the average of the two;
Vn = (V1 + V2) / 2
Or, Vn = n/R (V1 + V2 + . . . . . . . . . . . . . + VR-1 + VR/2)
(Vn = normal forest; n = no of yrs b/w two age classes given in the table or time interval in the YT; R = rotation)
The normal growing sock vol is always worked out form YT. The above-calculated vol is the standard of comparison of our actual forest.
RELATION B/W VOLUME AND INCREMENT OF A NORMAL FOREST
RELATION B/W NORMAL GROWING STOCK AND NORMAL INCREMENT:
Consider an example and suppose that all the age classes put some amount of increment ‘i’. Now the vol at rotation age is equal to the sum of increment of yrs 1, 2, 3 . . . 100 or Ri.
If a straight line is extended if passes through the center of ‘I’ throughout.
Now the vol of a triangle
Vn = R1 * R / 2 (because A = ½ ah; here a = R1, b = R)
If the normal increment is represented by I (ie Ri = I) then normal growing stock (or normal vol) ie
Vn = R I / 2
Or I = 2Vn / R
It means that if I is cut each yr, it is equal to twice the vol of growing stock during the period of growth.
NORMAL UNEVEN AGED FOREST:
In an uneven-aged normal forest, unlike the normal even-aged forest;
- Age is not known.
- All age classes are present in the same area and the area cannot be separated from all age classes
- The harvesting area cannot be separated because the mature crops are cut with other crops (immature)
- According to SA Khan, such forest never exists.
The theoretical diagram of an uneven-aged normal forest is an inverse of ‘J’ as shown below:
But this possibility is not well matured with the actual sense. It is not possible to keep ‘q’ constant throughout. It is 1.05 now, next time it may by 1.005 or less and so on. More value of ‘q’ means greater reduction and less value of ‘q’ means a smaller reduction.
In Pakistan working plans, the reduction ratio is:
8 : 5 : 3 : 2 : 1
(8” – 12”) (12” – 16”) (16” – 20”) (20” – 24”) (Greater than 24”)
Also, there is another method of finding the ratio of reduction ie
Log Y = a + bX (here; Y = no and X = dbh)
A normal uneven-aged forest should look like ‘A’ but our forest (being compared) may look like ‘B’
‘b’ means greater no of trees in greater dia class. A similar type of description is visible from ‘a’ and ‘c’.
NORMAL FOREST IN PRACTICAL SENSE
WHAT ARE ITS APPLICATIONS?
A normal forest is meant for the following purposes
- To compare the structure of the actual forest with it. It foretells the shortcomings and deficiencies within the actual forest.
- To compare the growth and yield of the actual forest with it.
- It is also applicable to selection forest and mixture of spp (what methods should be adopted because YT is for even-aged forests).
- Normal forests is an ideal forest which is unattainable (we may be confused with an ideal patch but never an ideal ‘forest’ because the forest is a biological entity and it has variations). Moreover, yield tables are prepared on small sample plots and they are fully stocked.
- A normal forest may not be an economical (profitable) forest. Because normal forest means stocking = 100% do not need grasses, wildlife, etc. but some people earn more with the w/ life. They get income from the hunting, etc
NOTE: Normally the forests given in the YT are accepted as Normal Forests and the actual forests are compared with them.
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