Forest surveys of Norway

By ALF LANGSAETER

Under the First National Strip Survey of Norway, carried out between 1919 and 1930, the entire forest area of the country was surveyed by a special institution "Landsskogtakseringen" (Norwegian Forest Survey). The mensuration was conducted as a strip survey, and area, number of trees, volume, increment, etc., were investigated on survey strips 10 meters wide. These survey strips were drawn parallel with a constant distance between them for each county. The distance was set so as to ensure a satisfactory degree of accuracy in the results obtained for each county.

In the survey strips the area of the different site classes of productive forest land, and the area of arable land, bog, nonproductive land, etc. were determined. Within the strips the breast-high diameter of all trees exceeding 15 cm. was measured, and the trees were divided into diameter classes of 5 cm., 15 to 20 cm., 20 to 25 cm., etc. Trees ranging from 5 to 15 cm. at breast height were measured in 5-meter-wide strips, and trees under 5 cm. at breast height were measured by means of sample plots placed at fixed distances within the strips. Tree height, bark thickness, increment in diameter and height, and injuries, if any, were investigated by studies of sample trees selected systematically within each diameter class.

In 1937 a new strip survey of the forests of Norway was begun. The second survey followed the pattern of the first in most respects, but efforts were made to make use of new developments in forest survey technique. The distance between the survey strips was reduced in order to obtain more accurate results for areas smaller than counties. Thus, more detailed forest statistics for the individual parts of the country were obtained.

The method of mensuration employed in the Second National Strip Survey differed from that of the first survey.

(1) The forest land was divided into five site classes according to a common method for the whole country.

(2) The forests were divided into six cutting classes:

Class I: Stands under regeneration.

Class II: Young stands below thinning age.

Class III: Young stands that ought to be thinned.

Class IV: Older stands not yet ripe for regeneration cutting.

Class Va: Stands ripe for regeneration cutting.

Class Vb: Stands of every age, so sparse or damaged that in future they will be unable to utilize the yield capacity of the habitat.

Cutting classes II, III, IV, and Va should be of a fairly satisfactory density.

This division into cutting classes affords highly valuable material both for estimating the present condition of the forests, and for outlining measures to be taken in the future to increase the production of the forests:

(3) On sample plots placed at fixed distances in the survey strips, the distribution of age-classes, density of the stand, ground vegetation, etc. were examined.

In both the first and second national surveys the standard error was calculated in order to determine the accuracy obtained by the method chosen¹.

¹ Comprehensive literature is available within this nerd; those who might be interested are referred to the following works, which include further documentation on this subject

A. Langsaeter, "Noiaktigheten ved injetaksering av skog I og II" (Accuracy in strip survey of forests) Meddelelser fra Det norske Skogforsoksvesen, nr. 15 (1932) og nr. 18 (1934). With a short English summary.

Manfred Näslund, "Om medelfelets härledning vid linje- och provytetaxering." (On computing the standard error in line and sample plot surveying), Meddelanden från Statens Skogsforsöksanstalt, Häfte 31 (Stockholm, 1939). With an English summary.

Bertil Matérn "Metoder att uppskatta noggrannheten vid linje- och provytetaxering" (Methods of estimating the accuracy or line and sample plot surveys) Meddelanden från Statens Skogsforsknings institut, B. 36 (Stockholm 1947). With an English summary.

Results of the first national strip survey

Each of the 16 counties shown in Figure 1 was surveyed separately, but the results of the survey have been summarized on the basis of the following groupings:

Eastern Norway (Counties 1 to 6)
Southern Norway (Counties 7 to 9)
Western Norway (Counties 10 to 13) Trøndelag (Counties 14 and 15)
Northern Norway (Counties 16 to 18)

Area

The total area and the area of productive forest land are shown in Table 1, and the percentage distribution of land classes within the individual counties is indicated in Figure 2.

TABLE 1. - TOTAL AREA AND AREA OF PRODUCTIVE FOREST LAND

Region	Productive forest land
	Total area	Area	Coniferous forest	Broadleavel forest
	1,000 ha.	1,000 ha.	Percent	percent
Eastern Norway	7,950	3,462	89	11
Southern Norway	3,178	1,011	82	18
Western Norway	5,822	536	49	51
Trøndelag	4,112	1,150	79	21
Northern Norway	11,375	1,470	20	80
All Norway	32,437	7,629	70	30

Volume

The volume and volume growth found in the first, as well as in the second national survey, are expressed in solid cubic meters, excluding bark. The figures represent gross values inasmuch as no deduction has been made for tops left in the forest, decayed wood, loss in floating, etc.

Total volumes, without bark, for all coniferous trees and for broadleaved trees of more than 5 cm. d.b.h. are shown in Table 2.

TABLE 2. - VOLUME OF CONIFEROUS AND BROADLEAVED TREES

Region	Coniferous trees			Broadleaved trees	Total
	Spruce Picea	Pine, Pinus	Total
	million cubic meters
Eastern Norway	113	48	161	18	179
Southern Norway	18	20	38	10	48
Western Norway	-	10	10	7	17
Trøndelag	35	8	43	9	52
Northern Norway	5	4	9	18	27
All Norway	171	90	261	62	323

The volume of the most important broadleaved trees was distributed approximately as follows: birch, Betula, 79 percent; aspen, Populus, 8 percent; alder, Alnus, 6 percent; oak, Quercus, 3 percent; mountain ash, Fraxinus, 2 percent; totalling 98 percent. The remaining 2 percent was made up of willow, Salix; beech, Fagus; ash, Fraxinus; linden, Tilia; maple, Acer; bird-cherry, Cerasus; hazel, Corylus; and other broadleaved trees.

The percentage distribution of the volume by breast-height dimensions for the whole country is given in Table 3, and annual volume growth is shown in Table 4.

TABLE 3. - PERCENTAGE DISTRIBUTION OF VOLUME, BY DIAMETER GROUPS

	Under 10 cm.	10-20 cm.	20-30 cm.	Over 30 cm.	Total
	percent
Spruce	9	44	38	9	100
Pine	6	35	43	16	100
Broadleaved trees	28	50	16	6	100

TABLE 4. - ANNUAL VOLUME GROWTH

Region	Coniferous trees			Broadleaved trees	Total
	Spruce	Pine	Total
	10,000 million cubic meters
Eastern Norway	409	135	544	71	615
Southern Norway	70	70	140	39	179
Western Norway	-	28	28	28	56
Trøndelag	91	16	107	25	132
Northern Norway	14	5	19	44	63
All Norway	584	254	838	207	1,045

On comparing Tables 2 and 4 with Table 1 it is found that volume and increment per hectare in the forests of Norway are very low. This is chiefly due to the fact that a major part of the forest area lies close to the climatic limit of forest growth along the mountain regions, or to the north. About 1.2 million hectares of forest, or about 16 percent of the total forest area of the country, lies north of the polar circle.

The mean volume and volume growth per hectare of coniferous forest are shown in Table 5.

Results of the second national strip survey

Since 1938 five counties have been resurveyed, namely Nos. 1, 2, 4, 5, and 15 (see Figure 1). Some of the most important results of the second survey are shown in Tables 6 to 11.

TABLE 5. - VOLUME AND ANNUAL GROWTH PER HECTARE

Region	Spruce	Pine	Broadleaved trees	Total	Spruce	Pine	Broadleaved trees	Total
	cubic meters
Eastern Norway	35	15	4	54	1.3	0.4	0.1	1.8
Southern Norway	20	22	5	47	0.8	0.8	0.2	1.8
Western Norway	0.6	34	2	37	-	1.0	0.1	1.1
Trøndelag	37	8	5	50	1.0	0.2	0.1	1.3
Northern Norway	18	12	6	36	0.4	0.2	0.2	0.8
All Norway	31	15	4	50	1.0	0.4	0.2	1.6

TABLE 6. - AREA OF PRODUCTIVE FOREST LAND DISTRIBUTED AMONG THE INDIVIDUAL SITE CLASSES

County number and name	Area, by site class					Total
	1	2	3	4	5
	1,000 hectares
1 Ostfold	17	46	59	54	37	213
2 Akershus	20	60	152	69	12	313
4 Vestfold	22	31	51	16	9	129
5 Hedmark	22	93	461	409	211	1,196
15 Nord-Trøndelag	5	30	178	173	106	492
Total	86	260	901	721	373	2,343
	percent
Percentage distribution	4	11	38	31	16	100
	cubic meters
Yield capacity per hectare	9.2	6.5	4.3	2.7	1.6	-

TABLE 7. - AREA OF INDIVIDUAL CUTTING CLASSES

County number and name	Area, by site cutting class					Total
	I	II	III	IV	Va-Vb
	1,000 hectares
1 Ostfold	4	12	40	73	84	213
2 Akershus	5	6	62	87	153	313
4 Vestfold	7	2	16	33	171	129
5 Hedmark	37	45	222	334	558	1,196
15 Nord-Trøndelag	9	7	52	122	2302	492
Total	62	72	392	649	1,168	2,343
	percent
Percentage distribution found	3	3	17	27	50	100
Yield capacity per hectare	6	31	28	28	7	100

¹ 5,000 hectares in Class Va and 66,000 hectares in Class Vb.
² 25,000 hectares in Class Va and 277,000 hectares in Class Vb.

TABLE 8. - VOLUME PER HECTARE (CONIFEROUS AND BROADLEAVED TREES) IN THE INDIVIDUAL SITE CLASSES

County number and name	Volume per hectare, by site class					Average for all productive forest land
	1	2	3	4	5
	cubic meters
1 Ostfold	113	93	75	58	39	71
2 Akershus	117	106	77	49	34	78
4 Vestfold	122	102	78	50	39	85
5 Hedmark	130	107	69	42	23	55
15 Nord-Trøndelag	108	110	80	51	30	61

TABLE 9. - VOLUME GROWTH PER HECTARE (CONIFEROUS AND BROADLEAVED TREES) IN THE INDIVIDUAL SITE CLASSES

County number and name	Increment per hectare for each site class					Average for all productive forest land
	1	2	3	4	5
	cubic meters
1 Ostfold	6.2	4.6	3.0	1.8	1.1	3.0
2 Akershus	6.6	5.0	2.9	1.4	0.8	3.2
4 Vestfold	6.7	4.8	3.1	1.7	1.2	3.8
5 Hedmark	7.2	5.1	2.6	1.3	0.6	2.1
15 Nord-Trøndelag	5.5	4.4	2.6	1.3	0.6	1.9

TABLE 10. - VOLUME PER HECTARE (CONIFEROUS AND BROADLEAVED TREES) FOR THE INDIVIDUAL CUTTING CLASSES

County number and name	Volume per hectare for each cutting class					Average for all productive forest land
	I-II	III	IV	Va	Vb
	cubic meters
1 Ostfold	40	73	86	(64---	---)	71
2 Akershus	20	70	112	(66---	---)	78
4 Vestfold	27	103	138	154	57	85
5 Hedmark	21	57	85	(42---	---)	55
15 Nord-Trøndelag	18	68	93	119	41	61

TABLE 11. - VOLUME GROWTH PER HECTARE (CONIFEROUS AND BROADLEAVED TREES) IN THE INDIVIDUAL CUTTING CLASSES

County number and name	Increment per hectare for each cutting class					Average for all productive forest land
	I-II	III	IV	Va	Vb
	cubic meters
1 Ostfold	2.7	4.0	3.5	(2.1---	---)	3.0
2 Akershus	1.6	4.2	4.5	(2.1---	---)	3.2
4 Vestfold	1.4	6.2	5.8	4.3	2.6	3.8
5 Hedmark	1.2	3.1	3.0	(1.2---	---)	2.1
15 Nord-Trøndelag	0.9	2.9	3.2	2.9	1.1	1.9

TABLE 12. - VOLUME AND INCREMENT; COMPARISON BETWEEN FIRST AND SECOND NATIONAL SURVEYS

¹ The total increment for these five counties constitutes about one-half of the volume growth of all the forests of Norway.

Comparison of results

On comparing Tables 8-11 with Table 5 it will be seen that the five counties resurveyed show considerably higher volumes and increments per hectare than the averages shown for their respective districts in the first survey (Table 5). Some of the causes for this are:

(1) The five counties resurveyed belong to the best forest counties and rank higher as to volume and volume growth per hectare than do the forests of Norway on the average.

(2) Fairly large areas of land have such a low yield capacity that they belong somewhere between productive forest land and nonproductive land. The qualifications for inclusion of a given stand under productive forest land were defined more closely in the second survey, and according to more rigid rules. As a result, the area of productive forest land found in the second survey is somewhat less than in the first, and the mean volume and the mean volume increment per hectare are somewhat greater.

(3) Part of the increase found is due to the use of improved methods of calculation in the second survey.

(4) The growing stock and increment of the forests of Norway have increased during the interval between the first and second survey.

This last factor is illustrated in Table 12 by a comparison between the two surveys with regard to the total volume and the total volume growth of coniferous trees (spruce and pine).

By this comparison the results of the first survey are corrected in such a way that they are directly comparable to those of the second survey.

The encouraging increase in volume and volume growth is probably due to several factors:

(1) The mean annual felling in the years between the two surveys has been somewhat less than the volume growth. This circumstance, however, can only partly explain the increase.

(2) Some of the increase in increment is due to draining of bogs and waterlogged forest land. The area of productive forest land, on the other hand, has become somewhat reduced by new cultivation (arable land and cultivated pasture). The forest production gained by draining, however, exceeds that lost to agriculture. The net increase of all this hardly amounts to 10 percent of the apparent total increase in increment.

(3) The growth of the forest for the individual years varies with the climate (summer temperature, precipitation, etc.). In the two surveys carried out the increment has been calculated by means of the widths of the tree-rings for 10 years preceding the surveys. Climatic changes occurring between these two 10-year periods may, therefore, account for some of the increase in volume growth.

Material required for an accurate estimate of the effect of this factor is lacking. According to investigations so far, only part, and probably a small part, of the increase in volume growth can be due to climatic variations.

(4) A considerable part of the increase in increment is due to more rational forest management during the last 20 to 25 years.

Measures for increasing forest output

In spite of the considerable increase in volume and increment during the last 20 to 25 years, the condition of the forests in Norway is by no means what it ought to be. The division into cutting classes shows that for the five counties resurveyed since 1937 class Vb occupies more than 40 percent of the total area of productive forest land. This means that in these counties about 40 to 50 percent of the forest area has an unsatisfactory growing stock and increment. The future production of these areas can be increased considerably by improved forest management.

The total increment in the forests of Norway in the course of 50 to 60 years can be increased by about 50 percent. If the annual felling quantity in the transition period corresponds to the mean felling quantity in the years preceding World War II, this great increase in growth may still be within reach. If, on the other hand, the felling quantity is increased much beyond this level the wood-manufacturing industries may be faced with a timber shortage within 20 or 30 years.

The restoration of the forests will require a large amount of capital and working power. Very comprehensive forest cultivation is required to create satisfactory regeneration and to establish young stands in many of the forests which at present have but a small production and grow under difficult conditions of regeneration. The Government Forestry Board of Norway has been working for a long time to promote forest production. Under the Forest Protection Act of 1932 and the Reforestation Plan of 1937, the work has been mapped out by the Director of Forestry.

The Forest Protection Act provides that no cutting shall take place in younger stands, except when it is conducive to the further development of the stand. Cuttings in older stands shall not be performed in such a way, nor shall the ground be so treated after cutting, that these activities spoil or endanger the natural regeneration of the forests. As long as the Forest Control Officer finds that the forest owner works his forest according to the rules of good forest management, the forest owner shall have the right to manage his own forest. If the Control Officer finds that the forest owner is not complying with these rules in his cutting, he can prohibit cutting, order forest management by forest control officers, or order artificial regeneration. Under this law the private forest owner is free to manage his forest in his own way, provided he possesses a sufficient sense of responsibility. This course of action seems to lead to better results than the use of direct compulsory measures.

View of forest in Stor-Elvdal, Hedmark county

Pine forest in Buskerud county. The trees are about 140 years old, the standing volume 450 m³ per hectare By a thinning just carried out 140 m³ were cut per hectare. The annual increment is 7 m³ per hectare.

Photographs by courtesy of the Norwegian Forest Service

Other measures put into effect by the authorities for the intensification of forest management include:

(1) Information work and guidance of private forest owners by forest control officers.

(2) Payment by forest owners of 2 percent of the gross value of all timber sold or used for industrial production. The funds accruing from this source are paid back to the forest owner as soon as he carries out artificial regeneration.

(3) Direct subsidies by the government for: (a) forest cultivation, up to 50 percent of cost, and (b) building of forest motor roads.

By these measures, and others, the authorities have attempted to bridge the gap previously existing between forestry as a private and as a public enterprise. In this way an attempt is made to prepare the ground so that a method of forest management considered expedient from the point of view of public utility will also prove the most profitable one for the private forest owner.

The efforts made by the authorities brought good results during the prewar years. The area of artificial regeneration greatly increased from year to year up to 1940. During the war there was a heavy decline in forest cultivation activities. Simultaneously the occupation forces during the last years of war carried out a number of large clear cuttings. This was especially the case in the northernmost parts of Norway, but in southern Norway large clear cuttings also took place, particularly in the forests adjoining railways and roads.

When the war came to an end there was a greater need for forest cultivation than ever before. Difficulties arose from the manpower shortage and from various other circumstances attendant on the war. Nonetheless, great efforts are now being made to increase forest production through intensifying silvicultural treatment and improving forest management as a whole.