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forest area (young forest according to type of damage) #209
Forest area closest to young forest plants with a particular type of damage. Young forest plants are trees and shrubs ≥10 cm in height and ≤11.9 cm in diameter at breast height (dbh). However, depending on the inventory, only trees ( NFI3, NFI5) or only trees and selected shrub species (NFI4) were recorded as the nearest young forest plant. Since a young forest plant may have several different types of damage, it can contribute to areas with several different damage types at the same time.

forest area (young forest assessed) #198
Forest area closest to young forest plants with a certain characteristic (e.g. damage). Young forest plants are trees and shrubs ≥10 cm in height and ≤11.9 cm in diameter at breast height (dbh). However, depending on the inventory, only trees ( NFI3, NFI5) or only trees and selected shrub species (NFI4) were recorded as the nearest young forest plant.

size classe (young forest; 3 classes) #2010
Size of young forest plants ≥10 cm in height and ≤11.9 cm in diameter at breast height (dbh) – in three classes (two height classes and one dbh class). Reference: Field Survey (MID 507: Jungwaldklasse)

damage to young forest plants #1882
Damage to young forest plants ≥10 cm in height and ≤11.9 cm in diameter at breast height (dbh), whereby browsing is only assessed on specimens ≤129 cm in height, – in eight classess. Reference: Field Survey (MID 127: Gipfeldürre, MID 174: Verbiss des Leittriebes, MID 977: Fegeschaden, MID 987: Schälschaden, MID 184: Krankheit; MID 183: Holzereischaden, MID 185: anderer Schaden)

protection forest region #829
Demarcation of Switzerland used in NFI for protection forest analyses. The six protection forest regions were derived from the economic regions by combining individual regions according to natural and statistical criteria.

stockable and accessible forest without shrub forest NFI2-NFI5 #2615
Forest that was less than two-thirds covered with shrubs in the four inventories NFI2 (1993-1995), NFI3 (2004-2006), NFI4 (2009-2017) and NFI5 (2018-2026), was accessible on foot and could be stocked, i.e. did not contain forest roads, recreational facilities, streams, avalanche paths, etc.

1.4 km grid, subgrids 1-5 #1746
Sub-grids 1, 2, 3, 4 and 5 of the field surveys on the sampling grid with a mesh size of 1.4 km (base grid).

Estimates and standard error of the estimates

The results published in the NFI tables are estimates for variables in the Swiss forest (population parameters) whose true values are not known and must therefore be extrapolated (estimated) from the NFI sample data.

The extrapolations carry uncertainties. However, the accuracy of the extrapolations can be reliably estimated from the NFI sample, which is designed to be a random sample. To this end, all NFI tables include a second figure in addition to the estimate itself, namely the standard error of the estimate.

In most tables the percent standard error is reported (±%), but the absolute standard error (±) is also reported occasionally, especially for estimated percentages. The relationship between absolute and percent standard error is as follows:

percent standard error = absolute standard error / estimate × 100

absolute standard error = percent standard error × estimate / 100

Information on the forest road network is based on a full survey of all forest roads. In this case, there is no need to specify a standard error because there is no uncertainty caused by sampling.

Confidence interval of the estimate

With the estimate and the standard error of the estimate, the limits of the so-called confidence interval of the estimate can be calculated as:

lower limit = estimate – tQ × absolute standard error

upper limit = estimate + tQ × absolute standard error

If the simple standard error is used for the calculation (tQ = 1), then the 68% confidence interval is formed. In this case, the true value of the population parameter has a 68% probability of lying within this confidence interval of the estimate. If the double standard error is used (tQ = 2), then there is a 95% probability that the true value lies within this 95% confidence interval.

Significance of the estimate

The confidence interval can be used to statistically test whether the estimated population parameter is larger or smaller than a specific reference or target value, or whether two estimated population parameters truly differ (in the real population). For practical applications, proceed as follows: if a reference value lies outside the confidence interval, the estimated population value can be interpreted as being significantly different from it; if it lies within the confidence interval, the difference between the estimated population parameter and the reference value can be interpreted as random or not significant. When two population parameters are compared, they can be interpreted as differing significantly if their confidence intervals do not overlap.

Dealing with missing values

When calculating a results table, data are not always available for all combinations of characteristics^* of the classification variables and regional demarcation applied. In most cases, this indicates that the attribute estimated with the respective target variable does not occur or occurs only very rarely. Usually, the value 0 is used (imputed). However, as this value is not based on direct measurements, the associated standard error is represented with a full stop [.]. If the imputed value of 0 is referred to in the calculation, e.g. in the case of percentages or certain change estimates, no value can be entered. In this case, the estimated value and standard error are both represented with a full stop [.].

For example, no Arolla pines have been found and measured in the Swiss Plateau to date (growing stock of Arolla pines by production region). The values can be assumed to be missing because Arolla pine does not occur in the Swiss Plateau and therefore the growing stock there must be 0.

^* e.g. ‘Arolla pine’ characteristic of the classification variable ‘tree species’ and ‘Swiss plateau’ characteristic of the ‘regional demarcation’

Changes

There are two types of changes in the NFI:

The first type involves specific target variables relating to components of change, such as increment, fellings, mortality and losses. These target variables are only available for two consecutive inventory cycles, e.g. NFI3–NFI4. In the evaluation of components of change, the classification variable characteristic of the second inventory cycle is assigned to the first inventory cycle. These evaluations therefore do not take into account potential changes in a classification variable characteristic from the earlier to the later inventory (e.g. from private to public ownership).

With the second type of change, the difference in target variables, such as number of stems, growing stock or forest area, is used to assess the change between two inventory cycles. Target variables are generally used to represent states, such as that in NFI4, but can also indicate the net change between any two inventory cycles, e.g. NFI1–NFI4. In evaluations of change using these target variables, the change in a classification variable characteristic is considered in the analysis. Consequently, one can detect, for example, that the forest area without shrub forest increased between the two inventory cycles. This only has an effect on classification variables whose characteristic (class) can actually change, e.g. the affiliation with a forest area or the tree condition.

NFI4
forest area (young forest according to type of damage) divided by forest area (young forest assessed)
size classe (young forest; 3 classes) · damage to young forest plants
regional demarcation: protection forest region
unit: %, column total
evaluation area: stockable and accessible forest without shrub forest NFI2-NFI5
grid: 1.4 km grid, subgrids 1-5
state 2009/17
		protection forest region
		Jura + Plateau		Northwestern Alps		Northeastern Alps		Southwestern Alps		Southeastern Alps		Southern Alps		Switzerland
size classe (young forest; 3 classes)	damage to young forest plants	%	±	%	±	%	±	%	±	%	±	%	±	%	±
n/a	n/a	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	no damage	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	dry top	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	fraying damage	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	disease	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	harvesting damage	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	other damage	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	browsing of shoot 1	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	total	.	.	.	.	.	.	.	.	.	.	.	.	.	.
height 10-39 cm	n/a	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	no damage	18.9	0.5	18.0	0.7	18.3	0.9	14.7	1.0	15.0	0.9	12.5	0.9	17.2	0.3
	dry top	0.5	0.1	0.1	0.1	0.2	0.1	0.1	0.1	0.2	0.2	0.0	.	0.3	0.1
	fraying damage	0.1	0.0	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	0.0
	disease	0.2	0.1	0.6	0.2	0.0	.	0.1	0.1	0.2	0.2	0.2	0.2	0.3	0.1
	harvesting damage	0.2	0.1	0.0	.	0.0	.	0.0	.	0.1	0.1	0.0	.	0.1	0.0
	other damage	1.8	0.2	1.2	0.3	2.4	0.5	2.1	0.5	2.1	0.5	1.5	0.4	1.8	0.1
	browsing of shoot 1	3.6	0.3	4.4	0.5	4.7	0.7	4.1	0.7	4.4	0.7	4.9	0.7	4.1	0.2
	total	.	.	.	.	.	.	.	.	.	.	.	.	.	.
height 40-129 cm	n/a	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	no damage	17.8	0.5	16.8	0.7	16.7	0.9	14.1	1.0	17.0	1.0	11.6	0.9	16.4	0.3
	dry top	0.6	0.1	0.5	0.2	0.5	0.2	1.4	0.4	0.9	0.3	0.9	0.3	0.7	0.1
	fraying damage	0.2	0.1	0.3	0.1	0.5	0.2	0.4	0.2	0.3	0.2	0.5	0.2	0.3	0.1
	disease	0.6	0.1	0.5	0.2	0.8	0.3	0.7	0.3	0.8	0.3	0.6	0.2	0.6	0.1
	harvesting damage	0.6	0.1	0.4	0.1	0.2	0.2	0.1	0.1	0.1	0.1	0.2	0.2	0.4	0.1
	other damage	2.7	0.3	2.8	0.4	4.6	0.7	3.2	0.6	5.8	0.8	4.0	0.6	3.4	0.2
	browsing of shoot 1	4.9	0.4	5.0	0.5	5.3	0.7	5.4	0.8	4.2	0.6	7.8	0.8	5.3	0.2
	total	.	.	.	.	.	.	.	.	.	.	.	.	.	.
dbh 0.1-11.9 cm	n/a	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	no damage	37.4	0.6	36.6	1.0	32.9	1.3	36.0	1.6	35.9	1.4	34.4	1.4	36.2	0.4
	dry top	1.9	0.2	2.0	0.4	2.3	0.5	3.0	0.7	0.5	0.2	6.5	0.9	2.4	0.2
	fraying damage	1.0	0.2	0.9	0.2	2.0	0.5	2.1	0.6	2.0	0.5	1.9	0.5	1.4	0.1
	disease	1.7	0.2	1.4	0.3	1.9	0.5	0.9	0.4	0.6	0.3	1.4	0.4	1.4	0.1
	harvesting damage	2.3	0.3	1.6	0.4	0.8	0.3	0.3	0.2	0.6	0.3	0.7	0.3	1.5	0.1
	other damage	6.6	0.4	9.6	0.8	12.0	1.1	16.2	1.5	13.8	1.2	16.7	1.2	10.4	0.3
	browsing of shoot 1	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	total	.	.	.	.	.	.	.	.	.	.	.	.	.	.
total	n/a	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.	0.0	.
	no damage	74.2	0.8	71.4	1.2	68.0	1.7	64.8	2.1	67.8	1.9	58.4	1.9	69.8	0.6
	dry top	3.1	0.3	2.6	0.4	2.9	0.6	4.5	0.9	1.6	0.5	7.5	0.9	3.4	0.2
	fraying damage	1.3	0.2	1.2	0.3	2.5	0.6	2.6	0.7	2.3	0.5	2.4	0.6	1.8	0.2
	disease	2.5	0.3	2.5	0.4	2.6	0.6	1.8	0.6	1.6	0.5	2.1	0.7	2.3	0.2
	harvesting damage	3.2	0.3	1.9	0.4	1.0	0.4	0.4	0.3	0.8	0.3	0.9	0.3	2.0	0.2
	other damage	11.1	0.6	13.6	0.9	18.9	1.5	21.5	1.9	21.8	1.7	22.2	1.5	15.6	0.4
	browsing of shoot 1	8.6	0.5	9.4	0.8	10.1	1.0	9.5	1.2	8.6	1.0	12.7	1.1	9.4	0.3
	total	.	.	.	.	.	.	.	.	.	.	.	.	.	.

Table citation

Abegg, M.; Ahles, P.; Allgaier Leuch, B.; Cioldi, F.; Didion, M.; Düggelin, C.; Fischer, C.; Herold, A.; Meile, R.; Rohner, B.; Rösler, E.; Speich, S.; Temperli, C.; Traub, B.,
2023: Swiss national forest inventory - Result table No. 1267444. Birmensdorf, Swiss Federal Research Institute WSL

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