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Methodology and definitions



General remarks

The coverage for the developed countries* part of the global assessment was the whole of Europe (the countries as they were before the changes that began in 1989 in central and eastern Europe), the former USSR, Canada and the United States of America, Australia, Japan and New Zealand. All these countries carry out national forest inventories on either a continuing or ad hoc basis. Consequently, the approach used for the collection of forest resource information for the 1990 assessment was, as for earlier assessments, to rely to the greatest possible extent on the agencies responsible for the national forest inventories. In this, as in other respects, the assessment for the developed countries was markedly different from that for the developing countries, described later.

Because each country has tended to develop its own definitions and to have its own particular information needs, however, and in order to obtain as comparable information as possible, special emphasis was placed on drawing up a common classification and set of definitions and getting countries to adapt, where necessary, their national data to conform to the internationally agreed classification and definitions. For this purpose, the classification framework and definitions in the FAO publication “Toward a common framework for world forest resources assessments” were closely followed in the preparations for the assessment.

Another important consideration was the need to collect information for the 1990 assessment that was as comparable as possible with that obtained from earlier assessments.

The system used, which was a repetition of the one successfully followed in the previous (1980) assessment, was two-pronged: (1) circulation of a questionnaire, after approval by the Joint FAO/ECE Working Party on Forest Economics and Statistics, to all countries; (2) appointment by each country of a correspondent or correspondents responsible for collecting the national data, completing the questionnaire and assisting the secretariat in checking, clarifying and supplementing the information given in the questionnaire, including where necessary making estimates or providing unofficial data when official statistics were not available. An important aspect of this work was the attachment to the statistical replies of notes explaining, where necessary, how the data had been obtained, giving an indication of its reliability, and whether and why it may not have corresponded to the classification and definitions provided with the questionnaire. The correspondents proved to be a key element in the data collection system.

The first draft of the questionnaire for the developed countries was presented for discussion at the ad hoc FAO/ECE/FINNIDA Meeting of experts on forest resource assessment, held in Kotka, Finland in October 1987 (Kotka I). It was subsequently amended in the light of the Kotka discussions, further revised by an FAO/ECE team of specialists on forest resource assessment and approved by the the Joint FAO/ECE Working Party on Forest Economics and Statistics, before being circulated to countries.

In drawing up the questionnaire, a number of basic principles were followed, including: (1) the information being requested should be of interest and relevance at the international level; (2) there had to be some compromise between what it would be interesting and useful to collect and what it was reasonable to expect countries to be able to provide; (3) the majority of countries should be able to provide most of the information requested, either as official data or as informed estimates (it was recognized that not all countries would be able to answer all the questions); (4) where data were provided which did not conform to the internationally agreed classification and definitions, accompanying notes should explain the differences.

The questionnaire consisted of two parts:

I. General forest resource information;

II. The role of the forest in providing environmental and other non-wood goods and services (non-wood benefits).

Part I was almost entirely quantitative information, so that the answers were in the form of statistics, supplemented by explanatory notes. On the other hand, Part II dealt far more with qualitative matters, the possibilities to obtain statistics on non-wood benefits being much more limited than on the wood production aspects. Answers to Part II had very often to be based on subjective judgement, and their quality was highly dependent on the expertise and experience of the correspondents.


General forest resource information

This review must, for reasons of space, be limited to the methodology applied to the collation of national information at the international level, rather than the inventory methods applied at the national level for the actual collection of data. National inventory methodologies vary in function of the extensiveness of the resource, the importance attached to the forest resource and its various uses by policy makers in individual countries and the resources available for the work. Generally speaking, much of of the information for the 1990 assessment was gathered by ground surveys using sampling methods, and often as a regular monitoring system. Some countries obtained part of their inventory information from aerial surveys or other remote sensing (satellite) systems. Certain data, such as on ownership, were taken from other sources, such as cadastral records. Where national inventory systems did not exist, a number of countries built up their countrywide database from local sources, such as management plans.

The first section of Part I concerned the place of forest and other wooded land within the total area of land. For this, the key definition is that of “forest and other wooded land”, which occasionally proved to be not as straight-forward as it might seem. The agreed definition of “land under natural or planted stands of trees, whether productive or not, including land from which forest has been cleared but that will be reforested in the foreseeable future, and including areas occupied by roads, small cleared tracts and other small open areas within the forest which constitute an integral part of the forest” raised some questions of interpretation of terms such as “land under trees”, the length of time a deforested area remained “forest” and of “foreseeable future” for reforestation.

The basic land use classification was:


Land area

    Non-forest land

      Agricultural land


    Forest & other wooded land




      Other wooded land

The assessment of forest and other wooded land was based on a kind of multi-directional matrix, so that there would be internal consistency between the different elements. Information was collected for a number of forest categories according to species groups and species, management and ownership status, age-class distribution, stocking, standing volume and growing stock, annual increment, and fellings and removals. In practice, the fullest information coverage in most countries is for the category “exploitable forest”, which is not surprising, given that management tends to be concentrated on this category and that by far the largest proportion of total wood supply comes from it (90 to 95 per cent in Europe). The definition of “exploitable forest” continues to raise certain difficulties, not only with regard to comparability of the concept of exploitability between countries but also between successive international assessments. In the past, other terms have been used to cover approximately the same concept, including productive forest, forest in use and operable forest. The term “production forest” is used in annex 2, table 3, which for the developed countries has the same connotation as exploitable forest. In all cases, the sense of the term is that such forests, whether managed or not and whether being currently used on a commercial scale or not, are available for wood production, i.e. there are not legal, physical or economic limitations on their use for this purpose.

The emphasis given to information relating to exploitable forest reflects the fact that forest management was until recently principally concerned with the production of wood. It is also the case that such information is mostly quantitative and can be scientifically obtained, which is often not so for information relating to the non-wood functions. For management for wood production, it is important to have good information relating to the growing stock, increment and drain, as well as to age or size class distribution, ownership and size of holdings and management status. It would also be valuable to have other information, such as economic accessibility and quality of growing stock, but here one is moving into parameters that are either variable over time (accessibility is a function of price, which can fluctuate considerably) or are difficult to assess in other than subjective terms (what is quality?). Accordingly, such data have not been collected at the international level. Regarding economic accessibility, it may be noted that the definition of “exploitable forest and other wooded land” is “land on which there are no legal, economic or technical restrictions on wood production...”, but no distinction is made between areas that are being exploited and those that are available for exploitation but where harvesting is not at present taking place.

Because more detailed information was not available from many developed countries, questions about changes in forest area had to be kept general. Countries were asked to provide data on the net change of the total area of forest and other wooded land over a recent ten-year period (if possible 1980 to 1990), the net change being the total increase due to natural regeneration and afforestation of non-forest land minus loss of forest and other wooded land to other uses. It would have been instructive to have more detailed change data, e.g on transfers to and from various categories of non-forest land and between the different categories of forest and other wooded land, but these were seldom available from countries. Even a reliable figure of net change of total forest and other wooded land was difficult for some to provide.

Comparison of data between one assessment and the next might be expected also to provide information on changes over time. In practice, the reliability of such data has proved to be variable, depending on whether there were changes in definitions, in countries* survey methodologies in the intervening period, or in the way in which nationally-derived data were converted into the standardized FAO format. Given the increasing demand for accurate knowledge about land use changes by different groups of information seeker, there is a clear need for improvements by developed countries in methodologies for assessing changes in forest and other wooded land. In this connection, the use of remote sensing offers considerable promise, at least for changes at an aggregrated level. Its worth has been proven for developing countries, as seen in Chapter 3.2.

The gradual shift in the use of energy away from non-renewable sources, notably fossil fuels, and towards alternative sources has increased interest in the potential availability of biomass for energy. The 1990 assessment for the developed countries collected this information on woody biomass in a somewhat more simplified form than in the experimental questionnaire used in the 1980 assessment. The approach suggested to countries was to derive, by the use of appropriate conversion factors, the volume and mass of above-ground forest biomass from the volume of inventoried tree biomass. Estimates could thereby be obtained for the biomass of the wood and bark components of inventoried material, and also that of other above-ground tree biomass (stems, branches, tops and other). Other conversion factors could also be used to estimate the biomass of other woody above-ground biomass (shrubs, seedlings) and of stumps and roots, and so obtain a figure for total woody biomass. This information could also be relevant for analyses on the carbon cycle and climate change and forests* potential for carbon sequestration.

Lastly, Part I of the assessment collected information on the wood drain, in other words fellings, which are the sum of the volume of wood removed from the forest and unrecovered fellings. Data on commercial fellings are generally available and probably reasonably accurate, but more difficulties arise with other cuttings, which are often not recorded and consist to a large extent of fellings by owners and others for their own use. As for other parameters, the most reliable and complete data on fellings exist for exploitable forest. They are particularly useful for comparing drain with net increment and growing stock data, which allows assessments to be made of the harvesting ratio (fellings as a per cent of increment or of growing stock or per hectare).


The role of the forest in supplying environmental and other non-wood goods

and services (non-wood benefits)

As mentioned earlier, the information collected in Part II of the assessment is much more of a qualitative nature than that in Part I. Nonetheless, an effort was made in designing the questionnaire to obtain as much quantitative information as possible, partly so as to allow comparative analysis. Part II consisted of the following sections:

Undisplayed Graphic Importance of forest functions by area;

Undisplayed Graphic Production of forest products other than wood;

Undisplayed Graphic Policy and planning activities relating to forest functions;

Areas of public concern and conflicts between forest functions.

For the first three sections, countries were asked to complete tables with official data or informed estimates and to complement this information with explanatory notes or with additional information which did not fit into the form of the enquiry.

The approach for the first question - Importance of forest functions by area - was to ask countries to classify the importance of each of the seven selected functions into three classes of importance: high, medium and low. They were provided with guidelines to follow in assigning the importance of the function. They had to allocate a proportion of the total area of the category of forest and other wooded land in question to each level of importance so that the total came to 100 per cent. For example, suppose that the total area was one million ha and the importance reported for a given function was 50 per cent high, 30 per cent medium and 20 per cent low, this meant that 500 000 ha were classed in the high importance category, 300 000 ha in the medium, and 200 000 in the low.

The functions selected for assessment in this way were:

- Wood production;

- Protection;

- Water;

- Grazing (range);

- Hunting;

- Nature conservation;

- Recreation.

Because the importance of functions can differ considerably according to the category and ownership of forest and other wooded land, countries were asked to provide importance classifications of the functions for four categories:

- Publicly owned forest;

- Privately owned forest;

-Publicly owned other wooded land;

- Privately owned other wooded land.

In practice, most countries provided replies for the first two categories, sometimes however not being able to distinguish between public and private forest.

A supplementary question asked for information about the number and area of National Parks and nature reserves and the proportion of forest and other wooded land in such areas.

For forest products other than wood, the importance of which has been becoming increasingly recognized, countries were asked to list all the products which have some importance to them, providing to the extent possible annual quantities and values of production.

Since supply and demand of most non-wood forest functions are not regulated by the market and consequently government at various levels intervenes to regulate them, the third question on policy and planning activities relating to forest functions was aimed at information that could be helpful in planning and policy making and their implementation. The approach was to ask whether there had been changes in the importance attached to the different functions since the previous (1980) assessment; if so, in which direction: more emphasis or less. Countries were also asked whether explicit plans existed to change the importance given to the different functions in the coming decade; and if so, whether it would be greater or less. These answers should be supported by background information explaining the reasons for change, the nature of the plans or policies, and the means for implementation.

The fourth question arose from the growing public awareness and concern about forests and forestry matters and the conflicts between the different forest functions. Countries were asked to identify and describe the main issues and conflicts, which could only be dealt with in a descriptive and qualitative way.

Evaluation of the methodologies

As pointed out at the beginning of this section, the methodologies involved in the collection of forest resource information in the developed countries are the ones employed by the countries themselves in their forest inventories. The collation of general forest resource information (Part I) at the international level is in essence by means of circulating a questionnaire. The national correspondents who fill in the questionnaire have an important role in working with the compilers (FAO/ECE secretariat) in checking, explaining and supplementing the basic information. While the questionnaire-plus-correspondents approach works well for Part I of the assessment, the correspondents have a more difficult and even more important role in Part II (the role of the forest in supplying environmental and other non-wood goods and services), because of the much more qualitative and subjective nature of the information.

The experience of the 1990 assessment of the developed countries has shown that the quality of the information was in general reasonable, but varied quite considerably from country to country. More could no doubt have been done to raise the overall quality, but this would have required substantial additional input, both by the countries and the secretariat. With plans already in hand for the year 2000 assessment, some suggestions on ways in which future assessments might be improved may be offered:

1) Strengthening the dialogue between forest inventory managers and the users of their information, at the national and international level, to ensure the “right” information is being collected (this is liable to change from one assessment to the next);

2) Further streamlining of the questionnaire used to collect data at the international level to restrict it to the most important elements from the users* point of view;

3) At the same time, ensuring that comparability is maintained as much as possible with previous assessments;

4) A special effort to obtain better information on land use changes;

5) Strengthening cooperation between the more experienced countries in the field of forest inventory and the secretariat, on the one hand, and those needing to develop their inventory capabilities, on the other, in order to bring the quality of data from the latter to a higher level. Some of the countries of central and eastern Europe with economies in transition fall into the latter category;

6) For Part II, a reappraisal at the international level of the approach and methodology for collecting information, as well as of the type of information needed;

7) Above all, recognition by governments and the responsible agencies of the importance of forest resource inventory activities is a prerequisite for effective follow-up in the field of forestry to UNCED and other high-level meetings, such as the Ministerial Conferences for the Protection of Forests in Europe, in order to provide reliable and comprehensive information on the forest resource needed for policy-making. Such information can only be made available if inventory and assessment activities are adequately funded and supported politically. With few exceptions, this is not the case at present at the national level; it is manifestly not so at the international level.

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