Planning a forest inventory

Forest Inventory lecturenotes

Category Forest Inventory lecturenotes not found

Introduction

Large parts of the AWF Wiki are devoted to [[Category:Sampling design|sampling] and plot design techniques and the impression could arise that forest inventory is nothing else than applied statistics. While applied sampling is a crucial part in forest inventory, it should also have become clear, that forest inventory is but one component in more general planning processes.

Also, forest inventories are projects that require project planning like any other project. In fact, proper and careful planning is essential to a successful forest inventory exercise. As technology advances, many situations change over years as do details of planning.

A most important aspect of a forest inventory is that there must be an explicit information requirement that justifies the need for an inventory to be carried out. This information requirement, at the best, is written down and needs to be translated and broken down into measurable attributes. It is not sufficient to say, for example, that we need to know the “forest structure” or the “biodiversity” or the “situation of the tree resource outside the forest” or the “sustainability of forest management” – but all such topics need to be expressed in terms of lists of variables (that serve as indicators) so that they become operational for a forest inventory.

It is helpful to actively search the discussion with the decision makers or those who request the information in order to make clear and illustrate the options and limitations of a forest inventory. This is at least as important as the efficient sampling and plot design.

It is difficult for many, to imagine what the results are that a forest inventory can yield. And it is a normal situation that the most concrete requirements are formulated but in the moment that the results are published, questions such as “why didn’t you also report on this and this …?” occur. While this is normal, it should be avoided to the largest possible extent through discussions prior to implementation of the inventory. In that context it is very relevant to be able to anticipate which groups of interested parties need to be interviewed. This is usually not only the foresters but possibly also experts from other sectors that are interested in forest or landscape level information such as conservation biologists, agronomists, tourism developers etc.

"Good" forest inventory

To the best knowledge of the senior author there is no such thing like “best practice” guide for forest inventories. Probably, it does not make sense to set up such a guide because the options are so manifold and the system to be sampled so complex that it is unlikely that there is one single clearly best option. It is more probably that there are various very good options. The major point is to avoid pitfalls and errors, and that is best done by consulting with experts in forest inventory sampling and those who have local expertise and can give practical advises.

There are certainly some criteria to which a forest inventory study should be conform to and that is (as in any empirical project):

• the project should be conform to the objectives;
• it should provide adequate precision;
• it should be methodologically sound and follow statistical sampling criteria;
• it should have comprehensive and transparent reporting and documentation;
• and the major criterion (to which all the above contribute) is that there is overall credibility.

Planning procedure

A forest inventory is a project like many other projects and general planning principles apply. Figure 1 illustrates this general procedure.

Some points are addressed in what follows:

• The objectives should be discussed in detail, and at best there should be a permanent discussion with potential users of the information to be produced also during the data collection and analysis phase. Mid-term meetings or workshops will help. The objectives determine number and type of variables to be collected. More attributes to be measured mean higher cost so that there must usually be a convincing justification as to integrate additional variables or target objects.
• A number of key features needs to be clearly and explicitly defined, although in many cases everything appears so obvious: population of interest, major attributes to be assessed, precision requirements for the major attributes and products expected such as maps (most appealing but least precise), statistics etc.;
• A forest inventory is a costly project, in particular when extensive field sampling is part of the exercise. Therefore, sufficient resources must be secured and available;
• Qualified experts, field crew leaders and teams for coordination and field work need to be found. This is not always an easy task. In what refers to field teams, thorough training is a must as is the writing of a detailed inventory manual. Only written definitions and inventory procedures guarantee that all field teams do exactly the same. Some more points about this extremely important point are discussed in the following;
• All available relevant a priori information should be compiled and evaluated such as models, maps and existing inventory reports; in this preparation phase, contact should be sought to those who know the region (forest service, forest owners association) and who possibly can give practical advises for inventory planning;
• The options should be checked whether the forest inventory can be combined with other natural resources assessments. While this appears to be a good idea, because the observation of additional variables in the field carries a relatively modest marginal cost, it is not frequently done; probably because the survey techniques and “philosophies” are so different between different disciplines;
• A decision must be made about the data sources to be used and analyzed (field data, remote sensing imager, interviews, etc.);
• A classification system needs to be devised, for example for forest types;
• A sampling and plot design needs to be defined; in the same step, the estimation design should be defined; sampling and plot design without estimation design can result in major problems at the end of the inventory if it turns out that statistically unbiased estimation is not possible under the chosen sampling and plot design;
  in that context, it is also recommendable to design a data base that is to receive the data, and to make a “pseudo”-analysis with dummy data in order to be sure that you can analyze the data as you would like it.
• If remote sensing is applied, specify the classification system for image interpretation including interpretation key;
• A detailed field manual needs to be written, which defines the protocol of the inventory, form sheets need to be designed or a software developed if portable data loggers are used;
• Organizing logistics such as transportation of the field crews, availability of measurement devices, maps, etc.; if an inventory is planned that requires the field teams to stay in the forest overnight, the logistics is complex. Organization of logistics is facilitated for the coordination team if the contracts with the field teams are formulated such that they are by themselves responsible for transport, measurement devices etc. Of course, the contract must then be accordingly. This type of contract guarantees much better that cars and measurement devices are carefully treated;
• A time table needs to be set up for field work and for image interpretation.