Zeide, B. 1998.
Generalized site index curves for fast-growing tree
species. In Modelling Growth of Fast-Growing Species. September
3-5, 1997. Valdivia, Chile.
(in press)
To construct a site index curve we measure height of forest
stands at, say, 5, 10, 15, 20, and other ages. Do we need ten
points or would five suffice? The answer is that two points are
necessary and sufficient to reconstruct the entire growth
sequence of average height, diameter, and other stand variables.
Using this concept growth types, or generalized site index
curves, were constructed for fast-growing tree species by
combining 354 site index curves of seven southern pine species at
two ages. This study introduced the harmonizing function that
permits the compression of growth information to one guide type.
The harmonizing function complements growth equations: it
describes the cross-section of growth curve families, that is,
their values at the same age. As compared with the
Chapman-Richards equation, the types require less information
(two versus at least three points) and yet they are more accurate
than the equation fitted to three points. As compared with the
one-point approach realized in regular site index curves, the
deviation of the types from the actual growth is three times
smaller. The types uncover the information implicit in the two
measured heights and are capable of representing stand growth in
both stable and variable environments.