Stand structure changes from year to year. These changes take place as a result of growth, death and cutting of trees. The growth of stand makes them the biggest renewable natural energy resource and, therefore numerous studies have been made to predict it, treating the stand as a unit as well as population of trees.

Treating the stand as a unit, growth function models have been suggested by many workers. Some of these models are given below:

1. Exponential, W=Be^kt
2. Time power, W=Bt^k
3. Monomolecular, W=A (1−Be^kt)
4. Auto catalytic or, Simple logistic, W=1/Be^−kt
5. Gompertz, W=AB^kt

Where, W = Plant characteristics, whose changing magnitude is measured. t = time, A, B & K = constant, e = Base of natural logarithm

Essentially, the growth of any stand parameter viz., height, diameter, volume or biomass, follows a pattern of slow growth in the beginning which becomes rapid at an early age and slows down in later years and culminates as an asymptote.

Methods of determining past growth of stands

The usual method of determining past growth of stands is by repeated measurement of sample plots as measurement of the whole stands is not a practical preposition.Even this could be done either by laying out temporary sample plots each time, an estimate of growth is to be made. The methods of laying out a temporary sample plot each time, growth is to be determined results in measuring different sample units each time and therefore the precision will be poorer and the accuracy generally lesser.

It can be done by laying permanent sample plots. The method of repeated measurements in permanent sample plots is better. The following two methods are commonly used for the purpose:

1. The method of control
2. Continuous forest inventory method

Method of predicting future growth of stands

Future growth of stands can be predicted with the help of yield tables prepared from the entire forest. Growth of a stand is a function of stand density and site quality. Therefore, before describing yield table, method of its preparation and its uses, it is necessary to have knowledge of stand density and site qualities and their effect on growth prediction.

Estimates of stand growth are needed to decide the health of the forest, the volume of material that can be harvested (yield) without violating the sustainability of the forest, the allowable cut, where the cut will be made and the trees which will comprise it.

In assessing stand growth, we need to consider each of the following components:

1. Regeneration and other non-measurable trees;
2. Accretion -the sum of the individual increases in size of the trees of measurable size present at the commencement of the growth period;
3. Ingrowth -the quantity of trees entering the measurable stand since the previous assessment;
4. Mortality -the quantity of trees lost through death;
5. Drain -the quantity of trees harvested during the growth period.