Written by: Ylva Melin, Swedish University of Agricultural Sciences, Dep. Forest Resource Management and Geomatics, 2004.
Before going into details about the inventory and data collection area in the other chapters in Part II, an overview is given of options available for acquiring data in a NFA. This section of the Knowledge Reference describes different options available to undertake a NFA in a country considering costs, existing technique and information requirements. It also briefly describes the development of NFAs from a historical perspective.
However, due to often high costs for personnel and logistics, it is important to weigh the value of the information generated from the data collection against the actual cost. It is not an easy task to determine the actual value of the information but what has to be considered is if the information can be used in an appropriate way in the planning process in the country. For more information visit: Rationale - Policy influence . Due to this, it is important to be careful when deciding what variables to collect in a country since more data about many variables do not necessarily result in a better outcome of the NFA, in terms of data usefulness. There is an obvious risk that the quality in the data actually collected will be poorer the higher the ambitions are. Moreover, there are examples of NFAs were data have been merely ¿stored¿ without providing any considerable positive return for the country.
The advantage of (medium resolution) satellite imagery is that large forest areas can be covered at low cost. Aerial photos usually give higher resolution but do not cover as large areas as satellite images, and thus the price per area unit will be higher than with satellite images. Because of this difference in costs, satellite images are commonly utilized in NFAs. However, what kind of remote sensing data to use depends also on other things such as what data are already available when the inventory starts, what kind of technique that is used traditionally and what data that is needed to complement available data to achieve the defined objectives of the assessment. The final issue that puts the limits for utilising the remote sensing technique is of course resources available for the assessments.
It should be noted that recent developments has led to satellite image data that are comparable to those of air photos in terms of resolution. However, the price for such images are still very high, and thus for most countries this is not an option.
During the last decade, also laser and radar technologies have found applications within forest assessments, but since these techniques still are only found on researchers¿ tables, and in addition are very expensive for assessment at larger scale, it is likely that these techniques will not be applicable for NFAs in the near future. For more information, visit: Remote sensing.
Due to this worldwide change in approaching the environment, today¿s perception of forests and trees as an integrated part of a system producing societal and environmental goods and services and not only timber has greatly influenced the NFAs in recent years. Variables with socio-economical importance, biodiversity, and non-wood forest products are some examples of variables in the ¿modern¿ NFA. To gather this kind of data, it is necessary also to go out in the field and meet people to interview. To do this there are certain methodologies available and some are described in the subject paper: Data collection through interviews.
Moreover, as mentioned previously the demand for new kinds of information is rising and it cannot always be physically measured. Thus, data also have to be collected through interviews focussing on the livelihood and land use practices of the rural population. A practical way of doing this is to add interviews to the traditional field surveys.
In some countries, integrated NFAs comprising both field surveys, remote sensing, and field interviews are supported by FAOs forest resource assessment programme.
Part II - Overview of options
Introduction
The way of gathering data in National Forest Assessments (NFA) has changed since the start of traditional forest inventories in the beginning of the 2000th century. This is mainly due to the increased demand for information from forests at both national and international level and also as a result of changes in interests and objectives for assessing forest resources over time. Along with this, new techniques have developed which have offered new opportunities for the approach to forestry inventories; the remote sensing technique is one of these and is further treated in the Knowledge Reference.Before going into details about the inventory and data collection area in the other chapters in Part II, an overview is given of options available for acquiring data in a NFA. This section of the Knowledge Reference describes different options available to undertake a NFA in a country considering costs, existing technique and information requirements. It also briefly describes the development of NFAs from a historical perspective.
Data collection in the field
Traditionally, data collection has been carried out through field surveys and there are many different sampling designs available for this purpose. For more information, visit Sample designs. Field sampling is a very straightforward and good way of collecting high quality data.However, due to often high costs for personnel and logistics, it is important to weigh the value of the information generated from the data collection against the actual cost. It is not an easy task to determine the actual value of the information but what has to be considered is if the information can be used in an appropriate way in the planning process in the country. For more information visit: Rationale - Policy influence . Due to this, it is important to be careful when deciding what variables to collect in a country since more data about many variables do not necessarily result in a better outcome of the NFA, in terms of data usefulness. There is an obvious risk that the quality in the data actually collected will be poorer the higher the ambitions are. Moreover, there are examples of NFAs were data have been merely ¿stored¿ without providing any considerable positive return for the country.
Remote sensing
During the second part of the 2000th century, remote sensing became an important tool within forest inventory practices. Throughout this period, aerial photography has been a very important technique, and additionally, in the 1980th satellite images brought new possibilities into the field of forest inventories. Initially, it was anticipated that the new method of taking pictures of the trees from the sky would solve many problems of forest inventory. However, the experiences are that the expectations of the output from the satellite images have often been too high. For example, fragmented forests are one item difficult to discern on a satellite image as well as trees outside forests, which for some countries are a very valuable resource. The bias in areas with this type of vegetation can therefore be very high when using images for the estimates. The opportunity to use satellite photos as a tool for stratification in order to make the sampling more cost-effective is frequently used.The advantage of (medium resolution) satellite imagery is that large forest areas can be covered at low cost. Aerial photos usually give higher resolution but do not cover as large areas as satellite images, and thus the price per area unit will be higher than with satellite images. Because of this difference in costs, satellite images are commonly utilized in NFAs. However, what kind of remote sensing data to use depends also on other things such as what data are already available when the inventory starts, what kind of technique that is used traditionally and what data that is needed to complement available data to achieve the defined objectives of the assessment. The final issue that puts the limits for utilising the remote sensing technique is of course resources available for the assessments.
It should be noted that recent developments has led to satellite image data that are comparable to those of air photos in terms of resolution. However, the price for such images are still very high, and thus for most countries this is not an option.
During the last decade, also laser and radar technologies have found applications within forest assessments, but since these techniques still are only found on researchers¿ tables, and in addition are very expensive for assessment at larger scale, it is likely that these techniques will not be applicable for NFAs in the near future. For more information, visit: Remote sensing.
Data collection through interviews
Forest inventories have been undertaken for almost 100 years in the boreal zone; Norway was the first country out. Initially, the inventories were performed mainly to assess the timber resources. With time the interest for a broader approach has grown, especially after the conference in Rio 1992, where the expression ¿sustainable development¿ spread over the world, which gave responses in all sectors working with environmental issues.Due to this worldwide change in approaching the environment, today¿s perception of forests and trees as an integrated part of a system producing societal and environmental goods and services and not only timber has greatly influenced the NFAs in recent years. Variables with socio-economical importance, biodiversity, and non-wood forest products are some examples of variables in the ¿modern¿ NFA. To gather this kind of data, it is necessary also to go out in the field and meet people to interview. To do this there are certain methodologies available and some are described in the subject paper: Data collection through interviews.
Combined surveys
Nowadays, a NFA usually is composed of a combination of different methods for data acquisition. Field inventory often is combined with remote sensing, whereby both high precision statistical estimates and maps of the forest resources can be obtained. Thus, air photos and satellite images are good complements to the traditional field based methods.Moreover, as mentioned previously the demand for new kinds of information is rising and it cannot always be physically measured. Thus, data also have to be collected through interviews focussing on the livelihood and land use practices of the rural population. A practical way of doing this is to add interviews to the traditional field surveys.
In some countries, integrated NFAs comprising both field surveys, remote sensing, and field interviews are supported by FAOs forest resource assessment programme.