Sunday, July 1, 2018

What is CAI and MAI?



CAI is the increment which a tree puts on in a single year. The CAI varies from year to year being affected by seasonal conditions and treatments.

MAI is the mean volume of a tree or crop put on from origin up to the desired age i.e. the total increment up to a given age divided by that age.

If when the curves of Current and Mean annual increments are plotted over tree age, the two do not coincide with each other through out the life of the tree except at two periods one at the end of first year and the other at the culmination of MAI.The CAI rises to maximum and then gradually fall off.The MAI also increases to a maximum at a later age but with much lower rate.The MAI continues to rise towards maximum even after the CAI has started falling. 

When the CAI falls to such an extent it is equal to MAI, the MAI reaches its highest points. This is the year of culmination of the MAI. At later stage, the CAI is less than the MAI, and MAI also beings to drop but not as rapid as that of CAI. THE CAI will be zero and also negative when there is rot or other damages resulting in negative CAI. But the  MAI value is never Zero and negative like CAI.


What is DBH ?

DBH is defined as the average stem diameter outside bark at the point of 1.3m or 1.37m (FAO) above the ground as measured.

  • It is a convenient height for taking measurement as it does not require bending down or stretching up to reach a lower or higher point.

  • It is a place on a tree stem, which is free from obstructions from thorny shrubs  and abnormalities like root swell, etc.

  • It gives uniform point of measurement and therefore standardizes measurement.

  • It shows strong correlation to the volume or weight of the stem for most tree species.

Rules of the DBH Measurement

  • Loose barks, mosses, lichens that are found on the tree must be removed before measuring the diameter over bark.

  • Breast Height (BH) should be measured by means of a measuring stick on standing trees at 1.3m or 1.37m (FAO)  above the ground level.

  • BH should be marked by intersecting vertical and horizontal lines 12 cm long painted with white paint.

  • On sloping land, the diameter at BH should be measured on uphill side.

  • In case of the tree is leaning, DBH is measured along the tree stem and not vertically, on the side of the lean for trees growing on flat ground and on uphill side, for trees growing on sloping ground.

  • BH should be taken at the lowest point above which the buttress formation is not likely to extend.

  • When the tree is forked above the BH, it is counted as one tree, but when it is forked below BH, each fork should be treated as though it were a separate tree.

Instruments used in Diameter measurement of trees

1. Diameter Tape

  The Diameter of a tree cross section  may be obtained with a flexible tape by measuring the circumference of the tree. A diameter tape is a measuring tape that has scale on both sides: one side is specially marked to show the diameter of a tree, and the other is a normal scale.


2. Calipers

Calipers are often used to measure tree DBHor when diameters are less than about 60cm. A Caliper may be constructed of metal, plastic or wood, consists of a graduated beam with two perpendicular arms. One arm  is fixed at the origin of the scale and the other arm slides.When the beam is pressed against the tree and the arms closed, the beam of the Caliper can be read on the scale.


3. Wooden Scale

It is generally a two feet folding scale used to measure diameters of logs at their end cross sections.