Canadian Forest Service Publications

Biomass and nutrient element dynamics in Douglas-fir: effects of thinning and nitrogen fertilization over 18 years. 1996. Mitchell, A.K.; Barclay, H.J.; Brix, H.; Pollard, D.F.W.; Benton, R.A.; deJong, R. Canadian Journal of Forest Research 26: 376-388.

Year: 1996

Issued by: Pacific Forestry Centre

Catalog ID: 4270

Language: English

CFS Availability: Order paper copy (free)

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Abstract

The effects of thinning (two-thirds of basal area removed) and N fertilization (448kg N/ha as urea) on biomass and nutrition of a 24-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand at Shawnigan Lake were studied over 18 years. At years 0, 9 and 18 after treatments, the aboveground biomass and N, P, K, Ca and Mg contents of stemwood, stem bark, foliage, and dead and live branches were determined (kg/ha) and increments in these properties (kg·ha-1·year-1) were calculated for the 0-9 and 9-18 year periods. Foliar biomass was increased by both treatments during the first period and also by thinning in the second period. Aboveground net primary production (ANPP) per unit of foliage biomass (foliage efficiency) was increased by treatments in the 0-9 year period. The combined effects of increased foliage mass and foliage efficiency resulted in increased total biomass production. Thinning and fertilization increased the uptake of all elements except for P with fertilization. This increase may have contributed to the long-term increase in stem growth. Retranslocation of elements before foliage shedding was important for tree nutrition, but was not improved by fertilization during the 9-18 year measurement period. The efficiency of N use in dry matter production (ANPP/unit of N uptake) was decreased by fertilization. This implied that poor sites would respond better to fertilization than rich sites.