© 1994 Heron Publishing—Victoria, Canada
Use of the crown competition factor concept to select clones and spacings for short-rotation woody crops
R. B. Hall
Department of Forestry, Iowa State University, Ames, Iowa 50011, USA / Received September 10, 1993
Summary
Plantation spacing and rotation age are interrelated critical factors in optimizing production of short-rotation woody crops
(SRWC). Different genotypes have different spacing and rotation-age optima. I have developed a method for estimating the optimum
for new Populus clones based on a modification of the crown competition factor (CCF) concept, which was originally developed for conventional
forestry practices with older trees. Measurements of as few as 100 trees of a new clone over a relatively short time period
could be used to predict the optimum spacing and rotation age combinations for that clone. The technique could also be used
to quantify basic differences in crown architecture and yield physiology among genotypes.
One set of at least 20 trees is planted at an open-grown spacing and measured annually for crown and basal stem diameters.
The regression of crown diameter on stem diameter is used to calculate the land area that would be occupied per open-grown
tree at various stem diameters. This allows prediction of the spacing needed to reach the minimum density for maximum stand
growth at a given age or stem size. A second set of 80 measurement trees is planted in a closely spaced set of Nelder arcs
to force overstocking within the first few years of growth. Productivity measurements on these trees establish the upper limit
on CCF for maximum stand growth. The data are then used to calculate the best spacing and rotation age combination for a new
clone.
Application of this model may lead to a better understanding of the productive advantages of the sylleptic branch habit, different
branch angles and seasonal growth rates, different carbon allocation strategies, and responses to competition.
Keywords:
branch habit, carbon allocation, crown architecture, genotype, Populus, productivity, rotation age.
