Response of a poor-site western redcedar stand to precommercial thinning and fertilization.

Abstract

Seven silvicultural treatments were applied in a 20-year-old natural western red-cedar (Thuja plicata) Donn ex D. Don) stand on a poor site in coastal Washington: (1) control (unthinned, unfertilized); (2) unthinned, fertilized with ammonium nitrate, monodicalcium phosphate, and potassium sulfate; (3) thinned, unfertilized; (4) thinned, fertilized with urea; (5) thinned, fertilized with ammonium nitrate; (6) same as treatment 5 plus monodicalcium phosphate; (7) same as treatment 6 plus potassium sulfate. Treatments 2 through 7 resulted in significantly better 3-year height and diameter growth of the 20 tallest trees per plot (250 tallest trees per hectare) than did the control treatment (1). Increases in growth over the control trees were least for treatment 3. Thinning alone (3) resulted in much smaller increases in growth than fertilization alone (2). There were no differences in growth between the thinned treatments fertilized with ammonium nitrate and urea (4 and 5), and both treatments had significantly better growth than thinning alone. The thinned treatment fertilized with monodicalcium phosphate plus ammonium nitrate (6) was more effective in increasing growth than the thinned treatment fertilized with ammonium nitrate alone (5). Addition of potassium sulfate (7) did not increase growth significantly over treatment 6. Three-year height and diameter growth of the 20 tallest trees per plot ranged from 1.1 m and 2.0 cm in treatment 1 to 1.8 m and 4.4 cm in treatment 7. Analysis of 2-year growth of the total stand showed that all sizes of trees responded to treatment. Foliar concentrations of nitrogen, phosphorus and sulfur were positively correlated with growth rates.

Citation

Harrington, Constance A.; Wierman, Charles A. 1985. Response of a poor-site western redcedar stand to precommercial thinning and fertilization. Res. Pap. PNW-RP-339. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 24 p