Dendrometry

Dendrometry is the branch of forestry that is concerned with the measurement of the various dimensions of trees, such as their diameter, size, shape, age, overall volume, thickness of the bark, etc., as well as the statistical properties of tree stands, including measures of central tendency and dispersion of these quantities, wood density, or yearly growth, for instance.
The most frequent measurements acquired in the field include

the Diameter at Breast Height
the height of the tree
measures contraction and relaxation of vessels
the horizontal dimension of the canopy

These key measurements are used to infer, through allometric relations, other tree properties that may be of greater interest but are harder to measure directly, such as the quantity of commercial wood retrievable, or the amount of carbon sequestered in the plants.