Bulldozing stumps and nitrogen fertilization affect growth of Douglas-fir seedlings
Eight treatments involving stump removal by bulldozing in combination with nitrogen fertilization were applied to 0.04-ha circular plots in a clear-cut on the Olympic Peninsula, Washington. Treatments included stump removal (either all stumps removed or the plot left undisturbed) and broadcast fertilization with ammonium nitrate (0, 336, 672, or 1345 kg N ha−1). Diameter at breast height and height of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings, planted several months after treatment, were recorded five and eight seasons after outplanting. The results showed that either bulldozing stumps from the site or fertilizing with ammonium nitrate increased growth of seedlings through their eighth growing season. After eight growing seasons, bulldozing had increased seedling height by 23% and diameter at breast height by 43%; fertilizing produced increases of 13% in height and 17% in diameter at breast height.