B. HUSCH
B. HUSCH is Chief, Forest Resource Surveys Section, Forestry and Forest Products Division, FAO, This article is based on an excerpt from a speech delivered to the Division of Forest Mensuration, Society of American Foresters' National Meeting, held from 27-30 September 1964 in Denver, Colorado, U.S.A. in which the items are presented is not rigid and is subject to some modification although the sequence is in most cases logical.
IT HAS BECOME very apparent that foresters have neglected placing the proper emphasis on the planning of a forest inventory in the rush to get to work, to do photointerpretation, to get out in the field, and to measure trees and gather data. It should be said at the outset that the most difficult and the key part of an inventory takes place before a tree is ever measured, in the brain of the forester or team that designs the procedure in all its details. This article is, therefore, not directed primarily to the inventory experts who are certainly cognizant of the points to be raised, but to those foresters who must carry out inventory work as part of their varied duties. It is hoped, however, that the ideas presented will interest the specialists also, if no more than by attempting to summarize and emphasize what they have been saying for many years.
Although the reasons for carrying out inventories may vary there is a unity in their planning and execution regardless of the diverse ends to which the resultant information may be directed. Thus the need for inventory information may vary from the national level for overall planning and development of forestry and forest industries to detailed data concerning a privately owned forest tract. But the intent in all cases is to provide knowledge about the forest resource. To utilize and manage a forest resource wisely on whatever scale demands knowledge of the location of the forest areas, estimates of the quantity, quality and availability of timber, and its growth and yield. This is the information a forest inventory can provide.
To gather this information efficiently and provide it in a useful form is by no means a simple task. Preparing a program which will have as its end product the required information requires much thought and planning. The important points which must always be considered in this planning stage are briefly summarized here: considered and not included, for not all items always have the same emphasis nor need be included in all inventories. But for planning purposes they should always be considered and, if found not applicable, then eliminated. In short, the points mentioned should be viewed as a check list when planning an inventory. The order
1. A first stage in planning requires the compilation and study of all existing available information concerning the forest area. This should include any past surveys, reports, maps or photographs, if available. If at all possible, reconnaissance trips to the field prove useful in learning the forest types and are essential if photointerpretation is contemplated as a part of the inventory procedure. It is also desirable to gain at least a rough idea of the characteristics of the timber, its range of volume per unit area, and an idea of its variability. Information on the transportation system present in the form of railroads, roads, rivers, and trails is important as it can influence the method of travel and of distributing sample plots. The type of transportation - airplane, helicopter, boat, vehicle, horse, or by foot - will be influenced by the transportation network. In the course of reconnaissance, the manner of affording logistical support for the future inventory must be kept in mind. By logistical support is meant the provision of lodging, feeding, and supplies to field crews.
2. The next stage of planning is to decide what information the inventory will provide. This is a critical phase of planning and one that has far too often been neglected or at best kept hovering in the background without recognition of its vital contribution. It is very strongly emphasized that, at this stage of planning, decisions should be made as to exactly what kind of information will appear in the final results of the inventory. It is essential that all the people concerned with the inventory work or the use to which the final report will be put have detailed discussions or reach agreement before proceeding to subsequent planning. It is important to include descriptions of the stand parameters, units, and the desired limits of accuracy for the estimate. In planning an inventory it is of basic importance to decide on the allowable error and the specified probability early in the planning process. This should be decided upon after considering for what the information will be used and what accuracy is needed. One need not blindly follow some conventionally accepted error or probability. Rather, the accuracy decided on should be sufficient for the use of the information: greater accuracy means waste of money. It is further recommended that at this time the outlines be prepared of the tables which appear in the final report. These outlines should include all titles, column headings, class Emits, and measurement units. This may seem burdensome and a task that can be put off until after the data is gathered, but it is extremely important in terms of sequence, since all subsequent inventory work is dependent on the decisions made at this time.
It has been all too often the case that this initial stage has been entirely neglected in planning an inventory. Far too frequently inventory planning consists of deciding on the number and distribution of photo and field plots followed by making the specified measurements. A mass of data is gathered and then thoughts turn to how to extract some information and in what form to present it. Often complaints come from people that the inventory data is in an inconvenient form; something has been left out or excess information included.
The proper procedure is exactly the reverse; the kind and form of the final results should be decided upon first and then the inventory procedures designed to provide the information required. Part of the preliminary stage should include decisions on the auxiliary information to be shown, such as maps, overlays, soil information, land-use patterns, transport routes, etc.
3. A very important aspect in inventory planning is the question of the time and funds available for the inventory. In the planning operation this question does not suddenly arise as a separate step, but permeates the entire planning sequence, and it is mentioned now only to bring out its importance and no because it occurs uniquely at this stage.
A fixed amount of money may be available for an inventory, and it is then necessary to fit the entire inventory to this limitation. On the other hand, the available funds may be flexible and it is then necessary to estimate the cost of an inventory operation and see if the money needed is available or will be approved. In either case it is necessary to make cost estimates of all inventory phases as a part of the planning procedure. This is especially important since all stages of the inventory will be affected. To mention but a few, the size and competence of the staff, the kind of equipment and instruments, the use of existing or new aerial photography, the number and distribution of samples will all be influenced by their costs.
The time available for an inventory must also be kept in mind as its effects are very similar to those mentioned in regard to costs. Sometimes it may become necessary to have results of lower accuracy available in a short time rather than spending a longer period obtaining more accurate estimates.
4. Once past the critical stage of deciding what the inventory is to show, one can get down to the details of the design. In the majority of cases, of any size require the use of some sampling technique. However, there are occasions when a complete or 100 percent inventory is best. These opportunities are few although at least passing consideration should be given if the possibility exists. In the following paragraphs it will be assumed that the inventory will utilize some sampling scheme.
5. The possibility of utilizing aerial photography as a part of the inventory design should then be considered. If aerial photographs are available, their utility will depend upon the photo characteristics with which we must work. Existing photography cannot be changed; so procedures to utilize it must be designed to fit its specifications. If new photography is used, it is possible to write the specifications which will make the photos most useful to the particular inventory. In any case, if at all possible, aerial photographs should be utilized in the inventory design. In most inventory practices, aerial photographs find their main utility in permitting stratification of the forest area. This entails photointerpretation requiring knowledge of forest conditions and the ability to identify differences on the aerial photographs. It is essential that inventory planning include a period for training photointerpreters to recognize the strata established for subdividing the forest area. Where photointerpreters have worked in a specific area for long periods, their past experience may allow the elimination of this phase. But where inventories are carried out in new regions or at least regions unfamiliar to the photointerpreter, time must be allotted for photointerpretation training including field checking. Detailed instructions must be prepared on the photointerpretation classification system, distribution of photo plots, if used, and the measurements to be made on the photographs.
6. The sampling design for obtaining measurements requires the integration of information desired from the inventory, the forest, topographic and logistic conditions, and the ingenuity of the designer to prepare a statistically sound sampling scheme which will provide the desired information within the limits of the allowable error and desired probability with the available resources in the required time. Care should be take to avoid the antiquated approach, all too often followed, of choosing an intensity of sampling as a first step in designing an inventory rather than deciding on acceptable limits of error and then estimating the intensity needed to stay within these limits.
It is in the planning stage that the creative ability of the inventory planner is given full play. There can be no one recommended procedure since many designs can be prepared depending on the skill, intelligence, and experience of the designer. At this time only those items are mentioned which must be considered in the sampling scheme; they are:
(a) preparation of a stratification system;(b) decision on the use of random or systematic sampling;
(c) estimation of the required number of photo and field samples to yield the desired estimate within the limits of accuracy;
(d) size and shape of sample plots;
(e) distribution of sample photo and field plots to the strata.
The factors affecting the details of the sampling design have been alluded to in earlier paragraphs; but, for clarification, they are consolidated briefly here; they are:
(a) kind and accuracy of the information wanted;(b) time and funds available or needed;
(c) availability or possibility of using aerial photo graphs;
(d) transportation, communication, and logistical facilities.
7. In the early stages of planning, it is necessary to consider the volume tables, volume relationships, or the relationships of other units of quantity which may be utilized in the inventory. Most inventories utilize volume tables, although other procedures can be devised to translate directly measurable tree characteristics to volume. It must also be remembered that inventories can also be designed to supply information on other stand characteristics, for example, weight. If volume tables are to be used, it is essential to see if appropriate tables are available and, if not, include procedures for their preparation, For existing volume tables, procedures must be devised to check their applicability in terms of range of tree sizes, merchantability specifications, and form suitability.
8. Detailed instructions must be prepared, describing the size and number of crews, their distribution in the inventory area, and their work schedules. Instructions should be prepared for each crew member so that all work is uniform. Transportation must be arranged and suitable communication facilities provided. Transportation may be by airplane, helicopter, jeep, horse, boat, or by foot; but, in any case, it must be planned in detail. Communications are important and in remote areas reliance may have to be placed on two-way radios.
If field crews are inexperienced, it is necessary to arrange for a period of field training, followed by repeated checking of work so that field measurements are properly carried out.
9. Detailed instructions must be prepared describing the procedures to be followed for field location of sample plots, establishment of the plot, and measurements on the plots. It is important to have the specification for the tree measurements on the plots consistent with the volume table or relationship to be used and also in agreement with the previously designed tables for the final results. This illustrates the importance of the early preparation of the form of the final tables since the field measurements are then made consistent.
Instructions must also be prepared for any additional measurements for growth and quality, and for any supplementary information which may be desired, such as on soil conditions, lesser vegetation, and reproduction.
Necessary instructions must be also prepared on the use of photographs in the field.
It is important to decide on the instruments to be used and be certain that all field crews are familiar with them. When required, training in the use of instruments must be given to assure a uniform standard of work.
10. Field recording forms should be designed to permit easy and accurate recording of the field measurements. Forms should be as simple as possible and, if convenient, designed for ease in later computation or transfer of data. When data processing systems are to be used, consideration should be given to direct recording on machine cards in place of office transfer from conventional field forms. It has proved useful to carry out a trial in the field on a field form before accepting and reproducing it in quantity. Field trial often indicates desirable changes on the recording forms impossible to visualize in the office.
11. Before starting operational work another important planning step is to design the compilation and calculation procedures. This should include description of the data processing techniques, whether by desk calculator or more sophisticated computers. It is important to use data processing equipment whenever possible, since it is faster and permits many types of calculations which would be too laborious when using desk calculators. One should remember it is possible to use computational equipment even on small inventories. It is frequently possible to send data to processing centers for computation rather than requiring that the machines be right in the office. As foresters become more conversant with programing and as more basic programs become available, it may well occur that all inventory calculations will eventually be carried out in this way. Formulas for the calculation of totals, averages, and sampling errors must be devised at this stage. In all cases, it is essential that the end products of the selected compilation and calculation procedures yield the desired results previously chosen and indicated in the outline for the final tables.
This approach to inventory planning may seem over-detailed and complicated, but experience has shown that it pays off in a more efficient inventory with less wasted time and effort and provides more usable information than an inventory haphazardly undertaken. Naturally, the time and intensity of preliminary planning will vary with the amount and detail of the information desired, the size of area to be inventoried, and the allowable error. A simple, small inventory will obviously require less preliminary planning than one for 100,000 hectares or more in remote underdeveloped forest areas. But the essential point is that, regardless of the type of inventory, the same topics must be considered while recognizing that the degree of planning intensity may vary.
