Effects of thinning and fertilization on the growth and yield of coastal Sitka spruce - western hemlock stands on the Queen Charlotte Islands (EP 1097)


Mixed second growth stands of western hemlock (Hw) and Sitka spruce (Ss) make up nearly half of the timber harvesting land base on Haida Gwaii, and are representative of other second-growth mesic sites found within the Coastal Western Hemlock biogeoclimatic zone (CWH) in B.C. Intensive silviculture was strongly supported with government sponsored forestry programs in the 1980’s and 1990’s; to monitor the effectiveness of  these programs, an experiment consisting of a series of juvenile spacing and fertilizer treatments was established on Graham Island, British Columbia in 1991. Given the magnitude of mid-term Hw/Ss stands to be relied upon in the CWH, results from this long term study can be used to guide local management practices.


  1. To investigate tree and stand growth responses to thinning and nitrogen and phosphorus fertilization in a Sitka spruce - Western Hemlock ecosystem.  
  2. To use the results in the development of silvicultural and management prescriptions, and in the construction of growth models.


This experiment was established on Graham Island in Haida Gwaii. The experiment used an incomplete factorial treatment arrangement, in a randomized complete block design. Three blocks contained 12 plots each for a total of 36 treatment units. Each plot is 0.0625 ha (25 x 25 m), with a 10-m buffer which received the plot’s treatment. Within each block, there are nine plots in mixed hemlock and spruce stands, and three plots in pure hemlock or spruce. The experiment included five thinning regimes and two fertilization levels: Unthinned (T0); 1600 (T1); 1200 (T2); 800 (T3); 400 (T4); and with (T1) fertilization of a blend of 250 kgN/ha + 100kgP/ha; and without fertilizer (T0). The following combinations were applied: T0F0, T1F0, T2F0, T3F0, T4F0, T0F1, T1F1, and T3F1.