Optimizing growth and development of 2-0 Douglas-fir seedlings by altering light intensity

Abstract

Douglas-fir (Pseudotsitgamenziesii (Mirb.) Franco) seedlings were grown outdoors in pots under 71% of full light the first growing season and full light the second. Another group of seedlings was given full light continuously for 2 years. At the end of the 1st year, seedlings given initial shade had grown larger in total weight (root + shoot) than those grown under full light. With removal of shading, the larger plants with lower shoot/root ratios began to allocate increased dry matter to root development relative to their shoots. By the end of 2 years, shoot/root ratios for the two groups were no different, yet the plants shaded in their 1st year were 69% larger in dry weight. By proper use of shading during development, larger 2-0 planting stock having good root development may be produced. Such stock, grown without the use of costly fertilizer, may be better suited to regeneration of droughty sites in the Northwest than the usual 2-0 planting stock, nursery grown under full light.