EFFECTS OF SCLEROPHYLLOUS SHRUB COMPETITION ON ROOT AND SHOOT DEVELOPMENT AND BIOMASS PARTITIONING OF DOUGLAS-FIR SEEDLINGS

Effects of sclerophyllous shrub sprout competition on the morphological development of 1+0 containerized Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were monitored above- and below-ground for 5 years after planting. Seedlings were planted among dead shrub sprouts 0.25 m in height (treatment C1), stumps of mature shrubs slashed just before planting (treatment C2), and shrub sprouts 0.5 m in height (treatment C3). In treatments C2 and C3, stumps sprouted quickly and sprouts grew vigorously, whereas C1 seedlings grew initially without competition. Above- and below-ground growth were reduced substantially and similarly by increasing competition. Root and shoot biomass of C1 seedlings were approximately 9-10 times and 22-25 times larger than that of C2 and C3 seedlings, respectively. During the first growing season, root biomass of seedlings in all three treatments increased relatively more than did shoot biomass. This growth pattern was reversed during subsequent seasons, and over the 5-year period resulted in greater growth in shoot biomass than in root biomass. Both shoot/root and height/diameter ratios increased over time in C2 and C3 seedlings. In contrast, the shoot/root ratio increased and the height/diameter ratio decreased in C1 seedlings. Allometric regression analyses showed no significant difference in biomass allocation to shoot and root among treatments over time.