1.4 Assessment of Non-Productive Forest Functions in the Swiss National Forest Inventory (NFI)
Peter Brassel
1.4.1 Introduction
The National Forest Inventory (NFI) furnishes important information on the protective functions of the forest, nature conservation and diversity of species within the forest and along its margins. This article describes how the long-term aims of the inventory are maintained in the second survey and how the aims have been adapted to current needs for information. Methods and execution are outlined. It is shown how information on non
productive functions can be won from the parameters recorded in field surveys. The potentials and limitations of a sampling survey as an instrument for planning forest functions are briefly discussed.
The first NFI survey was conducted from 1983 through 1985. This first survey primarily furnished information on the area of forest in Switzerland and its structure and condition.
Numerous parameters concerning forest functions were recorded. Some 11 000 sample plots were surveyed. The findings were published in 1988 (EAFV, BFL 1988). The NFI now stands before the second survey. The field work should be finished in 1995 and the findings published in 1999.
1.4.2 Aims of the NFI
The National Forest Inventory is a long-term undertaking which aims at providing well
founded information on the forests in Switzerland. It is part of a long-term, comprehensive monitoring program including inventories of forest damage, soil, and forest vegetation.
Reliable data on the state of health of the forest and its development are necessary to formulate a definite policy for forest maintenance. The NFI can help to cover important gaps in the information needed.
The subject of the NFI is the forest and its functions. Its flexible information system, based on various sources, can be adapted to include additional information as required.
The major units of reference are Switzerland as a whole, its major regions and the larger cantons.
The main goal of the second survey, already in train, is to determine changes, particularly in the development of timber reserves, drain, timber increment and species composition. It will identify changes in the area of the forest, its structure and condition as well as parameters regarding its protective functions. This second inventory will also allow a first assessment of the current productive potential over the entire country.
A second major aim is to determine the current condition of the forest. As in the first survey, forest area, stem counts, standing volume and assortments, species composition, forest structure, stand stability, the situation regarding regeneration and site conditions will all be investigated.
The aims of the second survey are wider than those of the first. A whole range of new parameters concerning nature protection, biodiversity and recreational functions are included so as to establish a basis for assessment in a third survey.
1.4.3 Methods
The NFI is a large-scale two-phase inventory conducted at intervals of about ten years. In the first phase, black-and-white air-photos (1:25 000) are used to define the forest area according to quantitative criteria (MAHRER 1976) and the magnitude of forest storeys over a five hundred meter grid. In the second phase, field surveys, sample plots were marked with metal tubes over a one kilometer grid; these will be surveyed again in the second survey. In two concentric circles of five and two ares each, trees with a DBH of 12 cm and 36 cm or more were measured in the first survey and will be measured again in the second. Further, numerous parameters on stand and site are included. Regeneration was and will be assessed in each of two additional concentric circles with an area of three or fourteen square meters. Besides these dendrometrical measurements, numerous characteristics of species diversity, nature protection and other forest functions will be estimated in the second survey.
The federal budget rendered it impossible to include all 11 000 sample plots surveyed in the first survey in the second. The number of sample plots to be inspected in the field had to be reduced by half. Consequently the main aim of the second survey can only be partially achieved, though the application of double sampling with stratification in the newly-elaborated design for the second inventory should produce only a similar estimation error to that of the first survey (KOHL 1994).
1.4.4 Assessment of Forest Functions in the NFI
Even in the first NFI survey, the evaluation of forest functions was important. Besides data on timber production, it aimed at furnishing information on functional potentialities such as stability, traces of rockfalls, avalanches, landslips and erosion.
The current interest in forest functions is due on the one hand to the demand for information from politicians and the general public and on the other to the stipulations of the new Forest Bill, set in force in 1993, which imposes a duty of planning for forest functions.
The question is whether it is worthwhile, in the long-term view, to promote the functions of the forest everywhere. An inaccessible forest has no productive potential, as the timber cannot be extracted. Nevertheless, the productive potential of the forest as a whole can be determined. Or, to give another example, a forest stand may protect a valley from avalanches or rockfalls, but is only worth maintaining if there is anything deserving the expenditure. Consequently, assessments of forest functions cannot be determined on the basis of the forest itself, only its potentials.
Details of individual functions have long been known. The difficulty is to define them precisely and systematically register them on the basis of quantitative parameters.
The second survey of the NFI will provide extensive information on the functional potentials of the forest, in terms of data which can be recorded in the forest itself:
- wood production: standing volume, increment, drain, accessibility, structure, stage of development, age, size of stand;
A number of forest functions cannot be assessed from within the forest itself but only in its environs:
- avalanche defence;
flooding;
wind-breaks;
deadening of noise;
purity of drinking water;
protection against extremes of temperature;
landscape protection;
hunting;
filtering;
sink for CO 2.
The current demands on the forest can only be assessed through questionnaires circulated among the local authorities and forest services. This tactic will not be employed in the second survey. The determination of all forest functions will be a major factor in the elaboration of methods for the third survey.
The second survey will primarily furnish data for the evaluation of the functional potentialities of the forest. The separate parameters to be considered are listed in the instructions for the field surveys (STIERLIN 1994).
Table 1 summarises the possible application of the various parameters in terms of deductions from measurements, classified according to the six functional categories laid down in the UN-ECE/F AO publication "The Forest Resources of the Temperate Zone"
(1990).
Tables 2a to 2g give the full list of parameters registered in the field survey, supplemented with the main applications of the individual parameters within the six functional categories. Some of these parameters had already been recorded in the first NFI survey.
Table 1. Number and possible application of parameters in the second NFI survey for determining forest functions.
Wood production, stock, growth, yield Protection, avalanches, rockfall, erosion Biodiversity
Nature conservation Grazing
Recreation
Number of Parameters
in Field Survey 61 16 27 16 15 1
Table 2a. Data per area were recorded on interpretation plots of 50 x 50 m. Since this first survey various new parameters, especially regarding nature have been introduced.
Survey No Forest Function
Data on Sudy Area 1st 2nd first second third
Heaps of branches * nature
Trees, small woody plants outside forest * wood nature
Limits of stocking * * wood
Type of pasturage * * grazing protec.
Intensity of pasturage * grazing
Traces of forest fires * * wood recr. protec.
Recreational facilities * * recr.
Signs of erosion * * protect.
Geomorphological features * nature
Obstacles * * wood protect.
Type of break in forest (a meadow, etc) * protect. nature
Slope of sample area * * protect. wood
Relief * * protect. wood
Traces of landslips * * protect.
Snow movement (traces) * * protect.
Special site and bodies of water * nature
Traces of rockfall * * protect.
Human artifacts (rubbish dumps, etc) * recr. nature
Stumps and fallen trees * wood nature
Deadwood * nature
Stone walls * nature
Over-utilisation (damage by man) * recr.
Areas without vegetation * nature protect.
Table 2b. The survey of forest margins includes a new series of parameters giving keys to the functions of the forest in nature protection and public recreation as well as species diversity. In Central Europe, special attention is being paid to forest margins because, due to the dense population, the intensive agriculture, their ecological importance and the conflict of interests, they constitute a real battlefield. For this reason the second NFI survey includes a detailed assessment of forest margins.
Survey No Forest Function
Data on Forest Margin 1 st 2nd first second third
Percentage of each tree or shrub species * nature recr. biod.
Structure (steep - stepped) * nature recr. biod.
Border (road, fence etc.) * nature recr. biod.
Width of forest cover * nature recr. biod.
Width of shrub belt * nature recr. biod.
Width of herb belt * nature recr. biod.
Density ( open - dense) * nature recr. biod.
Exposure * nature recr. biod.
Table 2c. The stand data recorded in the first survey will be re-registered in the second survey. They serve mainly for the classification of the stands and of wood production; important characteristics for functional potentials will also be recorded.
Survey No Forest Function
Stand Data 1st 2nd first second third
Age •
•
woodNext silvicultural operation •
•
woodBerry bushes ( degree of cover, dom. species) • biod. nature
Stand limits • • wood
Ground vegetation (degree of cover) • biod . protect.
Urgency of next operation
•
• woodStage of development (young - mature)
•
• wood natureSize of stand
•
woodMixture proportion (percentage of conifers) • • wood nature
Type of utilisation •
•
woodDensity ( crowded - loosened) • • wood
Stability
• •
protect. woodShrub layer (degree of cover) • biod
Structure (single-layers - multistoried)
• •
woodForest form * * wood
Forest type * * wood
Table 2d. Data on wood harvest and forest roads arc used to compute the accessibility of the standing volume, which is directly related to the productive functions of the forest.
Survey No Forest Function
Data on Wood Harvesting and Accessibility 1st 2nd first second third
Limitations for wood harvesting * * wood
Percentage of compulsory felling * wood
Number of years since the last harvest * • wood
Type of last harvest * wood
Means employed in last harvest * wood
Who was in charge of last harvest * wood
Limitations for logging * wood
Cost of harvesting ( computed ) * * wood
Bases for planning * wood
Logging distance * * wood
Means of logging * * wood
Logging depot • wood
Assortment - polewood or long wood * wood
Forest roads (length and surface type) * * wood nature
Table 2e. Conventional measurements of the trees included in the two concentric sample plots are recorded.
They mainly serve for the determination of sustained yield.
Survey No Forest Function
Data on Trees 1st 2nd first second third
Number of growth rings in felled trees * * wood
Species * * wood biod.
Height * * wood
Percentage of dry branches if over 20% * nature
Dead but still standing * * nature wood
Timber volume (computed tree volume) * * wood prot.
Timber increment (computed change) * wood
Crown form * wood
Crown length * wood
Fallen (still green or dry) * * wood prot.
J)amage (type, location, size, cause) * * wood prot.
Tined * wood
Storey * * wood
Social status * wood
Stem diameter at breast height * * wood
Stem diameter at 7 m * * wood
Stem circumference at breast height * wood
Stump sprouts * wood
Old standard * * wood
Forked, divided stem * * wood
Table 2f. In the second survey, young forests, plants with a height of more than ten centimetres and Jess than 12 twelve centimeters DBH will be recorded. Consequently, the findings will only be comparable to those of the first survey within limits. The data will primarily be used to assess sustainability, species diversity and wood production.
Survey No Forest Function
Data on Young Forests •) 1 st ld first second third
Number of plants • * wood
Tree or shrub species * * biod. wood
Degree of cover by predominant tree species * wood
Total degree of cover * wood
State of health (e.g. game damage) * * wood
Size class * * wood
Protective measures * * wood
Type of regeneration (natural/plantation) * * wood
Table 2g. Most of these interwoven parameters cannot be applied to any one particular forest function, yet they serve for the localisation of sample areas and sample trees and sample sites.
Survey No Forest Function
Miscellaneous Data 1st 2nd first second third
Forest/non-forest decision "' "'
Forest District "' "'
Elevation * "'
Exposure "' "'
Commune and canton "' "'
Coordinates "' "'
Region "' "'
Limits of accessibility "' "'
Ownership "' "'
Accessibility "' "'
Azimuth to sample plot centre (tree) "' "'
Distance from sample plot centre (tree) "' "'
Reaction to measuring mark (tree) "'
Tariff tree "' "'
Matured since previous survey (tree) * wood
Harvested (tree) * wood
Time needed for surveying and recording "' "'
Time needed to reach /return from the site * "'
1.4.5 Modelling of Forest Functions
Parameters assessed in the field alone do not allow classification of forest functions. It is necessary to elaborate from these parameters models for functions permitting a comparison between the functional capabilities of a stand with its present functions. In any case, models for classifying the functions of a stand are based on an evaluation of the parameters measured. Models for evaluation must allow the computation of deduced parameters which are easily interpretable. This will permit conclusions regarding features affecting nature protection such as stumps, fallen branches, dry stone walls and small-scale relief. Further, the diversity of flora can be deduced from the tree species composition, presence or absence of a shrub layer, and the frequency of species along the forest margins.
Additional information on protective functions can be gained from traces of natural events such as landslips, erosion, rockfalls, snow cover movements and forest fires.
Table 3 shows the regional distribution of such phenomena. In the Jura and the Mittelland they are relatively rare, but traces of rockfalls and snow movement are frequently to be found in the Pre-alps, the high Alps, and on the southern slopes. Traces of forest fires were only found on the southern side of the Alps. Hints on the functional potentials of the forest can be determined from such traces with simple methods.
Table 3. Natural events damaging the forest (figures from the first NFI survey, 1988).
% of forest Jura Plateau Pre- Alps Southern Switzer-
with traces of: Region alps slopes land
Landslips 2 5 18 12 5 9
Erosion 2 7 22 15 10 12
Rockfalls 12 2 19 37 33 22
Snow movement 3 1 25 46 33 23
Forest fire 0 0 0 0 9 2
None 83 85 26 0 10 32
Modelling for avalanche protection is more complicated. The first step is to determine the avalanche break zones by means of a digital terrain model and then model the avalanche path. Endangered buildings and installations can then be identified by comparison with the help of digital maps {KELLER 1994). As a last step the protective function of the forest in avalanche zones can be determined. Similar models for protection against rockfalls are foreseen.
Models of forest functions are modelled for each sample area. It is to be expected that the forest fulfils several functions in each plot, but it is not possible to set priorities on the basis of sampling.
1.4.6 Sampling Inventories and Planning of Forest Functions
Sampling inventories provide spatial information to a given degree of precision. They allow the identification of major problems in various regions. As the NFI only furnishes data on potential forest functions, is incomplete and does not cover large areas, and further does not take conflicts of interests into account, it cannot be used as a basis for the planning of measures to be taken.
1.4. 7 Outlook
The evaluation of the data from the second NFI will be based on various sources. Not only aerial photos, field surveys and deductions from parameters will be applied, but also spatial information obtained from digital maps, topographical models, and data on areal statistics for Switzerland. The findings will be published before the turn of the century and should meet demands for many kinds of information.
The supply of scientific advice for politicians, practical foresters and researchers will be broadened. Such consultancy can include the optimisation of plans for sampling, training of field crews, recovery of data from the first and second NFI surveys, software for registering and storing data, and expertises on special problems. The methods employed in the NFI can replace forest enterprise inventories which are expensive but yield little valuable information.
1.4.8 Summary
The Swiss National Inventory is currently conducting its second survey.
The NFI has clear long-term aims yet can be adapted to meet immediate needs for information.
- In Switzerland, the non-productive functions of the forest are at present more important than pure supply of raw resources; nevertheless its productive function should not be neglected.
- The first and second NFI surveys record numerous parameters on non-productive functions.
- These parameters must be evaluated by means of models.
- Scientific advice on inventory methods can make a valuable contribution to the efficient collection of data on a regional basis.
1.4.9 References
EAFV (Eidg. Anstalt fiir das forstliche Versuchswesen), BFL (Bundesamt fiir Forstwesen und Landschaftsschutz (eds.) 1988: Schweizerisches Landesforstinventar: Ergebnisse der Erst
aufnahme 1982-1986. Ber. Eidgenoss. Forsch.anst. Wald Schnee Landsch. 305: 375 pp.
ECE/FAO 1990, 1993: The Forest Resources of the Temperate Zones; the UN-ECE/FAO 1990 Resource Assessment, Vol. I; United Nations, Geneva. 348 pp.
KELLER, M., 1994: Considerations to quantify Forest Functions by Means of a GIS; In: Proceedings EGIS/MARl'94: Fifth European Conference and Exhibition on Geographical Information Systems EGIS, Paris. March 29/April 1. 1994. 1676-1681.
KOHL, M. , 1994: Statistisches Design fi.ir das zweite Schweizerische Landesforstinventar: Ein Folgeinventurkonzept unter Verwendung von Luftbildern und terrestrischen Aufnahmen: Mitt.
Eidgenoss. Forsch.anst. Wald Schnee Landsch. 69, 1: 5-141.
MAHRER, F., 1976: Abgrenzungsnormen zur Erfassung der Waldflache im Schweizerischen Landesforstinventar (LFI). Ber. Eidgenoss. Forsch.anst. Wald Schnee Landsch. 167: 29-53.
STIERLIN, H.R.; B RANDL!, U.B.; HEROLD, ANNE; Z INGGELER, J., 1994: Anleitung fiir die Feldaufnahmcn der Erhebung 1993-1995. Birmensdorf, Eidgenossischc Forschungsanstalt fiir Wald, Schnee und Landschaft. 204 pp.
