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Altitude above sea level in classes of 200 m. Reference: Digital height model DHM 25 from Swisstopo

Altitude above sea level in classes of 400 m. Reference: Digital height model DHM 25 from Swisstopo

Altitudinal vegetation belts in the system used in the guidelines for monitoring the sustainability and performance of protection forests (NaiS; Frehner et al. 2005) – in ten classes, whereby the classes «hyperinsubric», «colline» and «colline with beech» and «lower and upper montane» only occur in the Southern Alps (S), the classes «submontane», «lower montane», «upper montane» only in the Northern Alps (N) and the classes «high montane», «subalpine» and «upper subalpine» on both sides of the Alps. The information is based on the altitudinal vegetation belts determined by experts (accessible forest sample plots of NFI4 on the 1.4-km network; Arge Frehner et al. 2020), as well as on the altitudinal vegetation belts modelled for the period 1981-2010 (other sample plots; Zischg et al. 2021). n/a: located above the forest boundary modelled by Zischg et al. and sometimes in the area of lakes, which were relatively roughly cut out by Zischg et al.

Altitudinal vegetation belts in the system used in the guidelines for monitoring the sustainability and performance of protection forests (NaiS; Frehner et al. 2005), reduced to three classes. The variable represents a simplification of the NaiS altititudinal vegetation belts in six classes (NAISHSTKOMB6KL) in which the class «hyperinsubric and colline» is mearged with «submontane» to form the class «hyperinsubric, colline, submontane», the class «lower and upper montane» with «high montane» to form the class «montane» and the class «subalpine» with «upper subalpine» to form the class «subalpine». The information is based on the altitudinal vegetation belts determined by experts (accessible forest sample plots of NFI4 on the 1.4-km network; Arge Frehner et al. 2020), as well as on the altitudinal vegetation belts modelled for the period 1981-2010 (other sample plots; Zischg et al. 2021). n/a: located above the forest boundary modelled by Zischg et al. and sometimes in the area of lakes, which were relatively roughly cut out by Zischg et al.

Altitudinal vegetation belts in the system used in the guidelines for monitoring the sustainability and performance of protection forests (NaiS; Frehner et al. 2005), reduced to six classes. The variable represents a simplification of the NaiS altitudinal vegetation belts with ten classes (NAISHSTKOMB) in which the classes «hyperinsubric» and «colline» are merged with «colline with beech» to form the class «hyperinsubric and colline» and the class «lower montane» with «upper montane» and «lower/upper montane» to form the class «lower and upper montane». The information is based on the altitudinal vegetation belts determined by experts (accessible forest sample plots of NFI4 on the 1.4-km network; Arge Frehner et al. 2020), as well as on the altitudinal vegetation belts modelled for the period 1981-2010 (other sample plots; Zischg et al. 2021). n/a: located above the forest boundary modelled by Zischg et al. and sometimes in the area of lakes, which were relatively roughly cut out by Zischg et al.

Sample plots without/with gaps ≥100 m² from canopy edge to canopy edge that intersect with the interpretation area (50 × 50 m), classified according to the area of the largest gap into five classes. Reference: aerial photo interpretation

Aspect, classified into the following five classes: North, East, South, West and indeterminate. «Indeterminate» means that the slope is ≤10%. Reference: Field Survey (MID 191: Azimut der Exposition)

Aspect, classified into the following nine classes: North, North-East, East, South-East, South, South-West, West, North-West and indeterminate. «Indeterminate» means that the slope is ≤10%. Reference: Field Survey (MID 191: Azimut der Exposition)

Type of subsidised measure implemented since the last Inventory as part of the biodiversity promotion programme. Reference: Forest Service Survey (MID 2016: Biodiversitätsmassnahmen)

Proportion of the ground area covered by tree crowns according to the aerial photo interpretation – in five 20-percent classes. The percentage is calculated using the 25 grid points on the interpretation area (50 × 50 m). Reference: aerial photo interpretation

Combination of the 18 groups of NaiS site types, each with a similar objective for the main tree species (NAISGGROB20), into 10 large associations known as «forest formations». *As the characterisation of the site types in the NaiS-NFI project is on a small scale, it is possible that non-forest site types such as meadow, pasture and rock may be present in sample plots that are classified as «forest» in NFI. Similarly, «forest without shrub forest“ may also contain «shrub forest» site types.

Forest functions of considerable local importance according to forest plans or an assessment by the local forest service. It's possible for there to be several forest functions of considerable local importance at the same time. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'agricultural use' according to forest plans or an assessment by the local forest service. The forest function 'agricultural use' generally includes wooded pastures and nut orchards. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'drinking-water protection' according to forest plans or an assessment by the local forest service. The forest function «drinking-water protection» generally includes groundwater protection zones and drinking-water catchment areas. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'game protection' according to forest plans or an assessment by the local forest service. As a rule, the forest function 'game protection' includes seasonal grazing areas and game reserves. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'landscape protection' according to forest plans or an assessment by the local forest service. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'military' according to forest plans or an assessment by the local forest service. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'nature conservation' according to forest plans or an assessment by the local forest service. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function «protection against natural hazards» according to forest plans or an assessment by the local forest service. The term «natural hazards» refers to avalanches, rockfall, landslides, landslides and channel processes. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'recreation' according to forest plans or an assessment by the local forest service. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'timber production' according to forest plans or an assessment by the local forest service. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Presence of the forest function 'windbreak' according to forest plans or an assessment by the local forest service. The forest function 'windbreak' generally includes the forests or forest strips that protect agricultural land against wind. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Indication as to whether forest planning documents exist at the local level (operational plan, silvicultural project, etc.) and/or at the cantonal level (forest development plan or regional/cantonal forest plan). These documents provide the basis for the forest manager to make silvicultural or operational decisions, irrespective of the year they were produced. Reference: Forest Service Survey (MID 2028: lokale forstliche Planungswerke, MID 803: Stand der Waldentwicklungspläne WEP)

Classification of forests into 12 classes («types») according to their development, structure and management. Unlike in the 17-class forest-type classification, in this 12-class classification all development stages (from young growth to timber) are subsumed in the class «uniform high forest». Reference: Field Survey (MID 255: Nutzungskategorie, MID 257: Waldtyp nach Aufnahmeanleitung LFI, MID 260: Waldform, MID 267: Bestandesstruktur, MID 261: Entwicklungsstufe)

Classification of forests according to their establishment, structure and management into 17 classes («types»). In contrast to the forest typology with 12 classes, the forest typology with 17 classes defines each development stage (young growth to timber) as an individual class. Reference: Field Survey (MID 255: Nutzungskategorie, MID 257: Waldtyp nach Aufnahmeanleitung LFI, MID 260: Waldform, MID 267: Bestandesstruktur, MID 261: Entwicklungsstufe)

Type of forest in two classes: «forest without shrub forest» or «shrub forest». Reference: Field Survey (MID 816) or - if the forest is inaccessible – aerial photo interpretation

Zones around groundwater wells and groundwater recharging facilities that are designated by the canton as in the public interest for protecting drinking water. How strict the property restrictions and/or management requirements are depends on the protection zone,. The variable reflects the protection zone categories applicable since 2016 in accordance with Art. 121 of the Waters Protection Ordinance (SR 814.201) and the status of designation by the cantons on 8 July 2022 (download of data from geodienste.ch).

Areas in higher and lower altitude zones classified according to the system used for altitudinal vegetation belts in the guidelines for monitoring the sustainability and performance of protection forests (NaiS; Frehner et al. 2005). The boundary between the higher and lower altitudes runs between the «upper montane» and «lower montane» levels on the Northern Alps and between the «high montane» and «upper/lower montane» levels to the Southern Alps. The information is based on the altitudinal vegetation belts determined by experts (accessible forest sample plots of NFI4 on the 1.4-km network; Arge Frehner et al. 2020), as well as on the altitudinal vegetation belts modelled for the period 1981-2010 (other sample plots; Zischg et al. 2021). n/a: located above the forest boundary modelled by Zischg et al. and sometimes in the area of lakes, which were relatively roughly cut out by Zischg et al.

Located in/outside a groundwater protection zone. The cantons demarcate groundwater protection zones around groundwater wells and groundwater recharging facilities to protect drinking water where this is in the public interest. The indicator variable combines the various protection zone categories in force since 2016 in accordance with Art. 121 of the Waters Protection Ordinance (SR 814.201) into one class. Data status: 8 July 2022 (download from geodienste.ch).

Sample plots with/without current recreational use within a radius of 100 m around the sample plot centre, classified according to visitor frequency as a measure of the intensity of recreational use. No recreational use: <10 persons/year; very low intensity: <1 person/day; low: 1-10 persons/day; moderate: 11-100 persons/day; high: 101-500 persons/day; very high: >500 persons/day based on the entire year or the relevant season, taking into account all types of recreational use. Reference: Forest Service Survey (MID 330: Intensität der aktuellen Erholungsnutzung)

Number of natural hazard processes that can occur simultaneously in forest designated «protection forest» by the cantons (as of 2022) according to the harmonised criteria of SilvaProtect-CH (as of 2022). The following four natural hazard processes can be considered: rockfall, avalanches, hillslope debris flows/landslides, channel processes. Reference: GIS data from the FOEN, 2022

Forest ownership, classified according to the two categories: 'public' and 'private'. Reference: Forest Service Survey (MID 365: Eigentum)

Ownership of the forest, categorised according to the 7 types 'federal government', 'canton', 'municipality', 'citizens' community', 'corporation', 'individual private ownership' and 'company'. Reference: Forest Service Survey (MID 365: Eigentum)

Level of potential demand for local recreation, classified into five classes according to a model that estimates the number of permanently occupied and temporarily occupied/unoccupied dwellings within a radius of two kilometres. The variable is only available for NFI2 and NFI3.

Type of the most important forest function relevant for managing the forest according to forest plans or an assessment by the local forest service during NFI4 (2009-2017). Reference: Forest Service Survey (MID 911: Vorrangfunktion 2)

Type of the most important forest function relevant for management according to forest plans or an assessment by the local forest service during NFI5 (2018-2026). Reference: Forest Service Survey (MID 911: Vorrangfunktion 2)

Presence of the primary function «nature and landscape conservation», classified into the four classes: «landscape protection», «nature conservation», «game protection» or «other» according to forest plans or an assessment by the local forest service during NFI5 (2018-2026). Reference: Forest Service Survey (MID 911: Vorrangfunktion 2)

Presence of the primary function: «nature conservation» according to forest plans or an assessment by the local forest service during NFI5 (2018-2026). Reference: Forest Service Survey (MID 911: Vorrangfunktion 2)

Area in/outside a forest that provides protection against avalanches which the cantons designated «protective forest» according to the harmonised criteria of SilvaProtect-CH in 2022. Reference: GIS data from FOEN, 2022

Area in/outside a forest that provides protection against channel processes which the cantons designated «protective forest» according to the harmonised criteria of SilvaProtect-CH in 2022. Reference: GIS data from FOEN, 2022

Area in/outside a forest that provides protection against hillslope debris flows/landslides which the cantons designated «protective forest» according to the harmonised criteria of SilvaProtect-CH in 2022. Reference: GIS data from FOEN, 2022

Area inside/outside the protective forest that the cantons had designated in 2022 according to the harmonised criteria of SilvaProtect-CH (Losey & Wehrli 2013). In 2022, Canton Aargau had not yet designated its protective forest. Reference: GIS data from FOEN, 2022

Sample plots with/without recreational use within a radius of 100 m around the sample plot centre, with details about the recreational activity (e.g. walking, jogging or biking). Recreational activities are recorded if the visitor frequency is ≥10 people per year. Reference: Forest Service Survey (MID 329: Art der aktuellen Erholungsnutzung)

Sample plots with/without current recreational use within a radius of 100 m around the sample plot centre, classified according to seasonality of recreational use (all year round, almost only during the growing season, almost only in winter). Reference: Forest Service Survey (MID 403: Saisonalität der aktuellen Erholungsnutzung)

Production capacity of the site in kilograms per hectare and year based on the total mean increment (TMI) according to Keller (1978) - in four classes. Low: TMI ≤1500 kg/(ha/year), moderate: TMI 1501-3000 kg/(ha/year), good: TMI 3001-4500 kg/(ha/year), very good: TMI >4500 kg/(ha/year).

Forest area under the same management – in eight classes. Several forest owners form a management unit («enterprise») if they have joined forces to manage their forests permanently (and not just for one logging operation). Reference: Forest Service Survey (MID 410: Grösse der Bewirtschaftungseinheit)

Slope in classes of 20%. Reference: Digital height model DHM 25 from Swisstopo

Slope in classes of 40%. Reference: Digital height model DHM 25 from Swisstopo

Presence of a forest function that is locally very important according to forest plans or an assessment by the local forest service – in two classes (present/absent). Forest functions include e.g. timber production, protection against natural hazards, nature conservation and drinking water protection. Reference: Forest Service Survey (MID 327: Spezielle Waldfunktionen)

Indication as to whether the current main stand (i.e. the trees of the upper layer) originated from natural regeneration (100% natural regeneration), artificial regeneration (<20% natural regeneration) or mixed regeneration (20-99% natural regeneration). Reference: Forest Service Survey (MID 404: Art der Bestandesentstehung)

Status and type of certification. Reference: Forest Service Survey (MID 319: Art der Zertifizierung)

Status of the forest development plan or a comparable cantonal forest planning document. Reference: Forest Service Survey (MID 803: Stand der Waldentwicklungspläne)

Information on whether the forest road network has been completed or whether an improvment is in progress (construction, project planning) or planned according to the current transportation system plan. Reference: Forest Service Survey (MID 614: Erschliessungsabsichten)

Number of years since the last silvicultural treatment – in classes of ten years. Silvicultural treatments include harvesting and tending interventions, planting and afforestation, as well as sanitary and safety interventions. Reference: Forest Service Survey (MID: 607: Anzahl Jahre seit dem letzten Eingriff)

Information about the large- and small-scale infrastructure used for the extraction and transport of timber. Reference: Forest Service survey (MID 326: Erschliessungskonzept)

Year in which the forest was (re)afforested during past centuries – in classes of ten years. Reference: Forest Service Survey (MID 332: Jahr der Aufforstung)

Year in which the forest was (re)afforested in the past – in five classes: «before 1851», «1851-1900», «1901-1950», «1951-2006», or «no afforestation/afforestation unknown.». Reference: Forest Service Survey (MID 332: Jahr der Aufforstung)

Year in which the forest was (re)afforested in earlier periods in six classes: before 1851; 1851-1900; 1901-1950; 1951-2000; 2001-2020; oe «no afforestation/afforestation unknown». Reference: Forest Service Survey (MID 332: Jahr der Aufforstung)

Year in which the forest development plan or a comparable cantonal planning document was put into effect – in six classes. Reference: Forest Service Survey (MID 804: Kalenderjahr der Inkraftsetzung des Waldentwicklungsplans WEP)

Demarcation of Switzerland into five regions (Jura, Plateau, Pre-Alps, Alps and Southern Alps) with relatively uniform growth and timber production conditions. The production regions were established by the Federal Office of Forestry long before the first National Forest Inventory (NFI1, 1983-1985). With a small exception along Lake Geneva, the boundaries of the production regions still follow the municipal boundaries of the time. Unlike the NFI, the Forestry Statistics of the Federal Statistical Office don't use the production regions as demarcation but rather the forestry zones, whose boundaries are somewhat different.

Division of Switzerland into 14 regions (2 in the Jura, 3 on the Plateau, 3 in the Pre-Alps, 5 in the Alps and 1 in the Southern Alps). The economic regions are a subdivision of the production regions according to economic-geographical criteria.

Regional demarcation with the cantons as a unit, with the two half-cantons, Basel-Land and Basel-Stadt, combined into one canton for statistical reasons.

Demarcation of Switzerland into six regions with similar flora and fauna. The six regions correspond to the basic categories in the publication «The Biogeographical Regions of Switzerland», which was published by FOEN in 2022.

Regional demarcation with the forest districts as a unit. This variable is based on a survey of the cantonal forest services in winter 2022/2023.

Area accessible on foot that meets the NFI's definition of forest in both NFI4 (2009-2017) and NFI5 (2018-2026), i.e. was either «forest without shrub forest» or «shrub forest».

Forest of which less than two-thirds is covered with shrubs that can be accessed on foot.

Forest that was less than two-thirds covered with shrubs and accessible on foot in both NFI1 (1983-1985) and NFI2 (1993-1995).

Forest that was less than two-thirds covered with shrubs in the five inventories NFI1 (1983-1985), NFI2 (1993-1995), NFI3 (2004-2006), NFI4 (2009-2017) and NFI5 (2018-2026) and was accessible on foot.

Forest that was less than two-thirds covered with shrubs and accessible on foot in both NFI2 (1993-1995) and NFI3 (2004-2006).

Forest that was less than two-thirds covered with shrubs in both NFI3 (2004-2006) and NFI4 (2009-2017) and could be reached on foot.

Forest that was less than two-thirds covered with shrubs in both NFI4 (2009-2017) and NFI5 (2018-2026) and is accessible on foot.

Area that meets the NFI's definition of 'forest', i.e. is «a forest without shrub forest» or «a shrub forest».

Area that meets the NFI's definition of forest in both NFI4 (2009-2017) and NFI5 (2018-2026), i.e. was either «forest without shrub forest» or «shrub forest».

Stockable part of the accessible forest without shrub forest, i.e. accessible forest without shrub forest excluding the area of forest roads, recreational facilities, streams, avalanche paths, etc.

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.