Forest Mensuration And Biometry: A Complete Guide

by | Aug 10, 2023 | Conservation, Forest Management

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Forest mensuration is the field of forestry concerned with determining the dimensions (diameter, height, volume), shape, age, and increment of single trees, stands, or entire forests, whether standing or after falling.

Forest mensuration started to make forest measurements more scientific in Europe. It has always been an essential part of forest management practice. Quantitative remote-sensing techniques, in addition to traditional terrestrial approaches, are an important aspect of forest measurement.

The science of forest (Bio) measurement is known as forest biometrics (metrics). It includes the individual and collective measurement of biological and physical features of trees and related vegetation, insects, disease, animals, terrain, soils, and climate. All quantitative factors in forestry, both temporal and geographical, are included in these qualities.

Finally, forest mensuration is concerned with the technical elements of tree and forest stand measurements, including:

  • Diameter, height, basal area, bark characteristics, and volume of standing and destroyed trees are all factors to be measured.
  • Identifying the age and shape of trees and forest stands
  • Counting the number of trees that are still standing and those that have been fallen
  • Measurements of the live crown and foliage amount
  • Estimation of individual tree and stand biomass and biomass components
  • Estimation of total and merchantable stand volume, as well as distribution of size classes
  • Calculation of single tree and forest stand diameter, basal area, height, and volume growth
  • Determining the extent of damage to individual trees and forest stands, as well as their quality.
  • It also needs to deal with the creation of models for the building of tree volume, taper, and biomass functions, as well as the creation of stand tables and growth and yield models.

Basic Measurement

The methodologies and instruments for conducting such research are provided by forest mensuration. It focuses on the quantitative assessment of the tree and stand characteristics at a certain moment in time during the tree and stand’s life cycle and offers the data needed for effective forest management.

Mensuration aims at reasonable and relative accuracy, i.e., maximum accuracy, which is both economical and practically feasible.

The main aims of forest mensuration are:

a) Characteristics of trees

b) Varying methods and conditions of felling and conversion

c) Personal bias of the estimator

d) Biological character of the forest

e) The use to which the measurements are to be put

f) Cost

Precision in forest mensuration is the degree to which measurements of tree approach or estimate the average. It gives consistent results from repeated measurements, e.g., 4.44 is more precise than 2.4

The volume of a tree is dependent on diameter or girth at breast height, total height, and form factor. It is not only necessary for the calculation of the volume of logs but also necessary for making an inventory of growing stock and correlating height, volume, age, and increment of the tree. E.g., The height of the Standard Timber Bole is from the ground level to a diameter of over bark 20cm.

Forest Mensuration

Forest Biometry

Forest management would be reduced to a profession of observation and storytelling without the science of forest biometrics. Before or after a treatment action, attempts at silvicultural treatments would be haphazard and without specificity. The forest inventory, site growth capacity, forest health, and long-term capability of the forest would all be unknown. The capacity to quantify all qualities within a tolerable level of precision and consistency is the most important attribute of any science.

Xylometric Method

The volume of billets is calculated using the xylometer, which is based on the concept of water displacement and consists of a graded tank and a volume of wood. To determine the volume of a stack, the entire stack is weighed first, with only a section of it submerged.

Specific Gravity Method

Sp. gr. = Weight of wood/ Weight of the same vol. of water

= Density of wood/Density of water c.c.

Volume = Weight (in gm)/sp. Gr.

= Weight (in lbs)/sp. Gr. ×62.5 cft

Measurement of Tree Form: The rate at which a log or stem taper is defined as form. From the base to the top, the diameter of a tree or log’s stem decreases.

Plant and Animal Biomass Estimation

The entire amount of biomass on the planet is estimated to be over 550 billion tonnes. The majority of this biomass is located on land, with the seas accounting for just 5 to 10 billion tonnes.

Plant biomass (phytomass) is around 1,000 times that of animal biomass on land (zoomass). Land animals consume around 18% of this plant biomass. The animal biomass in the ocean, on the other hand, is roughly 30 times that of the plant biomass. Ocean creatures consume the majority of the biomass produced by ocean plants.

Direct or indirect sampling methods can be used to determine biomass. Techniques that weigh or estimate the actual biomass of plants in quadrats are referred to as direct approaches. Indirect techniques work by establishing a link between plant weight and a more easily measured property like plant height, rainfall, or cover.

The best method for calculating biomass in an inventory or monitoring program is determined by the kind of vegetation, observers’ abilities, sample size requirements, and time and budgetary restrictions.

Read More About Methods of Biomass Estimation

Direct Method

Biomass sampling is generally done with a sample unit with specified limits, such as a quadrat, so that biomass may be stated relative to a known region. The quadrats are directly examined to assess biomass using these procedures. This sampling method is best suited to regions where herbaceous or shorter shrub species predominate and may be accommodated in tiny quadrats.

Indirect Method

The development of a link between plant weight and an easier-to-measure parameter such as plant height, rainfall, or cover is used in indirect approaches to quantify biomass. This procedure is normally carried out in three steps. To begin, preparatory sampling must be carried out in order to establish the link using regression analysis using biomass as the dependent variable. Following the preliminary work, the indirect property is measured quickly in the field. The data is gathered and transformed into biomass values using the previously defined regression equation in the final stage.

Also Read: Can Wood Biomass Have A Positive Influence On Climate?

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