USE OF THE CROWN COMPETITION FACTOR CONCEPT TO SELECT CLONES AND SPACINGS FOR SHORT-ROTATION WOODY CROPS

Plantation spacing and rotation age are interrelated critical factors in optimizing production of short-rotation woody crops (SRWC). Differe nt genotypes have different spacing and rotation-age optima. I have de veloped a method for estimating the optimum for new Populus clones bas ed on a modification of the crown competition factor (CCF) concept, wh ich 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 spa cing 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 plan ted 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 give n 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 es tablish the upper limit on CCF for maximum stand growth. The data are then used to calculate the best spacing and rotation age combination f or a new clone. Application of this model may lead to a better underst anding of the productive advantages of the sylleptic branch habit, dif ferent branch angles and seasonal growth rates, different carbon alloc ation strategies, and responses to competition.