GENETIC-VARIATION IN TREE STRUCTURE AND ITS RELATION TO SIZE IN DOUGLAS-FIR .1. BIOMASS PARTITIONING, FOLIAGE EFFICIENCY, STEM FORM, AND WOOD DENSITY

Genetic variation and covariation among traits of tree size and struct ure were assessed in an 18-year-old Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) genetic test in the Coast Range of Ore gon. Considerable genetic variation was found in size, biomass partiti oning, and wood density, and genetic gains may be expected from select ion and breeding of desirable genotypes. Estimates of heritability for partitioning traits, including harvest index, were particularly high. Foliage efficiency (stem increment per unit leaf area) was strongly c orrelated with harvest index and may represent an alternative measure of partitioning to the stem. Estimates of foliage efficiency where lea f area was estimated based on stem diameter or sapwood area were unrel ated to foliage efficiency where leaf area was measured directly. Stro ng negative genetic correlations were found between harvest index and stem size, and between wood density and stem size. Achieving simultane ous genetic gain in stem size and either harvest index or wood density would be difficult.