Forest Mensuration and Management Quiz

Course Information

• Course title/code: Forestry Inventory and Mensuration (Frst 3052)
• Course credit: 3 Chr, 5 ETC
• Academic Year III, Semester I
• Program: BSc. Degree in Forestry
• Location: Gimbi, Ethiopia
• Year: 2021/22/23

Introduction to Forest Mensuration

• Mensuration is a branch of forestry concerned with determining dimensions (diameter, height, volume), form, age, and increment of trees, stands, or entire forests, whether standing or felled.
• It involves measurements of felled and standing trees, sawn wood, round logs, and other forest products (bamboos, charcoal, bark, fruits).
• Linear, area, volume, and weight (biomass) measurements are included.
• It provides quantitative information for forest management, planning, and research.
• It's fundamental to sustainable forest management, and the increasing demand on the world's forests requires more precise quantification of forest composition, structure, and the goods and services forests provide.

Forest Mensuration Role in Forest Management

• The main objective of forest mensuration is to provide quantitative information about the forest and its resources to support sound decisions regarding its destiny, use, and management.
• It's essential for planning, predicting growth and yield of forest resources, understanding how harvesting and other management activities influence resource flow, and making decisions on where, when, how, and how much forest land should be treated.

Forest Inventory

• Forest inventory is the systematic collection and analysis of forest data and information for assessment or analysis.
• It is about estimating the value and possible uses of timber and other resources.
• Critical factors include species, diameter at breast height (DBH), height, site quality, age, and defects.
• Inventories can include assessing timber and determining fire hazards.
• Results can support preventive actions and public awareness.
• Wildlife surveys may also be performed concurrently.
• It delivers comprehensive information about the state and dynamics of forests, crucial for strategic and management planning.
• Forest inventory is a record of quantity and value, similar to a store inventory.

Objectives of Forest Inventory

• Determine the volume of timber in a forest to estimate the yield.
• Assess the value of timber for sale or to estimate the return from clear-felled coupes.
• Determine the current periodic annual increment (growth).
• Prepare maps showing regions of high or low volume production to support decision-making in industry setup.
• Provide information for forest management planning and pre-investment decisions on forest industry establishment or expansion.
• Assess the feasibility of projects from economic, social, or other considerations.

Scope of Forest Inventory

• Provides a framework for measurement principles applicable to various forest measurement issues.
• Employs statistical theory and computer use for data processing.
• Predicts future yields.
• Includes the measurement not just of standing trees, but also felled timber and its conversion.

Methods of Tree Stand Measurement

• Measurement methods depend on the intended use and value of the product, the precision needed, and the cost.

Bias, Accuracy, and Precision

• Bias (systematic error) is the lack of accuracy and stems from flawed measurements or incorrect sampling methods.
• Accuracy is the closeness of an estimate to the actual true value. Though mensuration is a branch of mathematics, absolute mathematical accuracy isn't always achievable.
• Precision is the consistency of agreement between independent measurements. It's inversely related to uncertainty.

Causes of Bias in Measurement

• Improper instrument adjustment.
• Measuring units inconsistent with the instrument or technique.
• Consistent underestimation in measurements.
• Arbitrarily shifting field plot locations.

Measurement of Trees

• The primary goal of tree measurement is to estimate the quantity of timber, firewood, or other resources that can be obtained from them. Measurement incorporates techniques for DBH, height, logs, and fuelwood.

Diameter Measurement

• DBH (Diameter at Breast Height) is a crucial measurement for estimating tree volume, determining log volumes, and correlating height, volume, age, and tree increment.

DBH Measurement Rules and Instruments

• Standardized procedure of measuring 1.37m above ground.

• Rules for measuring trees tilted or with abnormalities.

Instruments for DBH/Girth Measurement

• Wooden scale, calipers, tape measure, Biltmore stick, Penta prism, and Barr and Stroud dendrometers are mentioned.

Principles of Height Measurement

• Total height is the distance from the top of the tree's leading shoot (or highest crown point) to the ground.
• Methods often use trigonometry and assume the tree is perpendicular to the ground.
• Instruments like hypsometers are crucial for precise height measurements.

Non-Instrumental Height Measurement

• Estimates tree height by eye (ocular method) or by using a pole to divide the tree into measurable segments.
• Shadow methods employ similar triangles formed by the pole and its shadow, compared to the tree and its shadow for calculations on clear days.
• Single pole method involves placing a pole at a specific distance from the observer to assist in the calculation of the tree's height.

Instrumental Height Measurement

• Hypsometers, altimeters, and clinometers use trigonometric principles to determine tree height from a distance.
• Different types of instruments like Abney level, Relaskop, and Haga altimeter are detailed.

Measuring Tree Volume

• Tree volume is complex due to tapering and shape variations, making simple formulas insufficient.
• Accurate volume calculation, like water displacement, is not always applicable in management settings.
• Geometrical shapes (like paraboloids and frustums) help in approximating volume to estimate timber volumes from measurements (girth and height) given form factors.

Measurement of Stem Volume by Form Factors

• Form factors measure the relationship between height and girth to calculate wood volume efficiently.
• This involves preparing tables of average form factors for various girth/height classes.
• Using the formula (V=FxAxH), the form factor (F), area (A), and height (H) are used to estimate the volume (V).