Forest Inventory and Assessment

Forest inventory and assessment play a pivotal role in the sustainable management of commercial forests. Accurate data regarding timber volume and the value of timber stands is essential for making informed decisions about harvesting, replanting, and ensuring the long-term profitability of forestry operations.

Date Posted:

August 10, 2023

Unveiling the Secrets of Timber Volume Estimation and Commercial Timber Stand Valuation

Forest inventory and assessment play a pivotal role in the sustainable management of commercial forests. Accurate data regarding timber volume and the value of timber stands is essential for making informed decisions about harvesting, replanting, and ensuring the long-term profitability of forestry operations.

In this comprehensive article, we delve into the process of forest inventory and assessment, uncovering the techniques used to estimate timber volume and determine the economic value of commercial timber stands.

Understanding Forest Inventory

Forest inventory involves systematically collecting data on a forest’s structure, composition, and health. This information provides valuable insights into the forest’s ecological health and is the foundation for effective forest management. The inventory process typically includes the following steps:

Sampling Design:

Foresters establish sampling plots or transects across the forest area to collect data representative of the entire stand. The selection of appropriate sample locations is crucial to ensure the accuracy and reliability of the results. According to the Food and Agriculture Organization of the United Nations, various types of sampling designs exist. We’ve listed some of the common ones below:

  • Simple random sampling: This sampling method is most used for the initial survey in an investigation and fpr smaller sample size areas.
  • Systematic sampling: This method involves selecting individual elements (trees) following a systematic pattern. Some of these patterns include square grids and sampling in narrow strips. This sampling technique provides a good representation of the forested area.
  • Stratified sampling: Here, diverse forest populations – heterogeneous populations – are divided into sub-populations of a known size. These sub-populations are called strata, and provide an effective cross-section of the population.
  • Multi-stage sampling: Sampling carried out in stages is often done as a cost or resource consideration, and to cater to different areas, conditions, and management levels according to a paper published in the journal Forests. Sampling in this way works effectively over the longer term, and “has the advantage of concentrating the sample around several ‘sample points’ rather than spreading it over the entire area to be surveyed,” says the Statistical Manual for Forestry Research.

Other sampling methods include Probability Proportional to Size (PPS) sampling, generalised random-tessellation stratified sampling (GRTS), cluster sampling and many others.

Vegetation Measurements:

Vegetation measurement can be used for both “inventory and monitoring, and for either site-specific or landscape-level applications” according to the Faculty of Forestry at the University of Toronto. And although our focus here is specifically on forestry, this measurement is also used on wetlands and grasslands. In the forestry context, data is collected in each sample plot on tree species, diameter at breast height (DBH), tree height, and crown size. This information becomes critical in forest planning, management and general research as outlined in the sixth edition of Forest Measurements and by the University of Toronto. Information about understory vegetation, shrubs, and ground cover is also recorded, considering broader ecology.

Site Conditions:

Understanding site conditions becomes important when considering forest regeneration, general growth and timber volume. This is crucial given the projection that “global timber volume produced in planted areas will increase from 1.4 billion m3 in 2005 to 1.7 billion m3 in 2030” according to iForest Biogeosciences and Forestry journal. Factors such as soil type, slope, aspect, and altitude are recorded as part of these site conditions. Data gathered also helps determine the climatic variation of certain forest species and how soil variation can, for example, impact tree size and productivity.

Health and Damage Assessment:

The inventory also includes evaluating the forest’s health and identifying any issues, such as pest infestations, disease outbreaks, or environmental stressors, that may affect timber quality. Natural disasters caused by climate change and unsustainable forest management practices make it more difficult for forests to handle external stressors. The use of global navigation satellite systems (GNSS) and remote sensing are essential in both predicting and reporting damaging forest events such as storms and wildfires.

Estimating Timber Volume

Once the forest inventory data is collected, foresters can estimate the timber volume present in commercial stands. In terms of timber, the volume of wood in a trunk – up to a specified top diameter – is considered ‘sellable,’ but this can vary dependent on market appetite. Accurate volume estimates mean more sustainable forest management, commercial harvesting, conservation, and trade.

Several methods are used for this purpose, and the choice depends on the forest type, species, and available resources. Some of these methods are below:

Volume Equations:

Volume equations are mathematical formulas developed based on statistical sample data analysis. These equations relate tree characteristics (e.g., DBH and height) to timber volume. When applied to the entire stand, they provide estimates of the total timber volume.

Cruise Methods:

Cruising involves physically measuring sample trees to determine their volume. This can be done using relascope, Biltmore stick, or similar instruments. The aggregated measurements from sample trees are then extrapolated to estimate the total volume of the timber stands in the form of a cruise report. Alongside total volume and trees per acre, this report also provides the range of tree species, sort, grade, age and other information.

Remote Sensing and GIS:

In recent years, remote sensing technologies, such as satellite and aerial imagery, have been increasingly used to estimate timber volume. Coupled with Geographic Information Systems (GIS), these tools provide accurate and efficient assessments over large forest areas. The bigger impact of these technologies is the creation of national forest resource maps to improve forestry management and sustainability at a local and, eventually, global scale. Global and local datasets that incorporate the use of stereo satellite imagery to capture height data from space as well as point cloud data from LiDAR and Drone data as well as some Radar datasets are also being utilised in the forestry industry more and more to make inventory studies better.

Determining the Economic Value of Timber Stands

Aside from estimating timber volume, assessing the economic value of timber stands is crucial for making profitable decisions in commercial forestry. Various factors influence the value of timber stands:

Market Prices:

The market demand and prevailing prices for different timber species and products significantly impact the economic value of a timber stand. Market research and price forecasting are essential to gauge the potential returns.

Quality and Grade:

The quality and grade of timber determine its suitability for specific end-uses and its market value. High-quality timber often commands a premium price. Part of this process is also understanding the volume loss or cull from timber stands, such as what’s lost through rot, splits and crooks. Certain defects, like knots, will also influence the value of timber.

Access and Logistics:

The accessibility of the timber stand and the ease of harvesting, transporting, and processing the timber affect its economic value. Remote or difficult-to-reach stands may incur higher operational costs. Difficulty can also arise when fluctuations in road traffic, variable road conditions and unsuitable weather enter the mix. Access and logistics are such critical issues that the Finnish government is focusing on enhancing wood purchasing efficiency to lower costs by 30% in the year 2025.

Environmental Considerations:

Sustainable forest management practices and forest certification can add value to timber stands, as eco-conscious consumers increasingly prioritise responsibly sourced products.

Forest inventory and assessment are the bedrock of commercial forestry, providing essential information for sustainable and profitable management practices. By understanding the process of inventory, timber volume estimation, and timber stand valuation, forest managers can make well-informed decisions that balance economic viability with ecological conservation. Integrating technology, market insights, and best management practices empowers the forestry sector to thrive while ensuring the longevity and health of our valuable forest resources for generations to come.


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