Growth of plants results from two opposing factors: the intrinsic tend
ency toward unlimited increase (biotic potential) and restraints impos
ed by environmental resistance and aging. The expansion tendency preva
ils in the beginning of a tree's life, while growth decline becomes pr
ominent toward the end. The existing growth equations can be transform
ed (by differentiation, decomposition into the division components, an
d taking logarithms) so that the components that correspond to these t
wo factors are exposed. This transformation reveals two basic forms in
trinsic in most of the analyzed equations. Their common feature is tha
t growth expansion is proportional to current tree size. Growth declin
e of individual trees appears to be more variable and can be rendered
with equal accuracy by a variety of expressions. This may reflect that
a greater number of factors hinder growth: scarcity of resources, com
petition, reproduction, diseases, herbivory, disturbances, etc. Conseq
uently, the growth path is inherently imprecise and can be viewed as a
wide valley rather than a single line. This analysis laid groundwork
for the classification of known equations and made possible the discov
ery of a promising new equation form.