Pruning and Spacing of Sitka spruce (EP 1065.04)


  1. To examine the rate of occlusion of pruned branch stubs, and the development of epicormic branches between different pruning and thinning treatments.
  2. To examine changes in stem form and crown dynamics between pruning and thinning treatments.
  3. To compare height and diameter growth between pruning and thinning treatments. 
  4. To compare wood quality between pruning and thinning treatments.

This experiment was established over existing provenance trials in 1994 at two sites, Area 2,3,4 and Rennel Sound, both located on the leeward side of Graham Island. 

  1. Area 2, 3 and 4 (formerly EP702.02) were planted in Sept. 1973 with seedlings from 38 Alaska and British Columbia provenances (from Sooke, B.C. to Duck Creek, Alaska).  Site 2 consists of 4 blocks, while sites 3 and 4 consist of 5 blocks.  Each block contains 38 randomly placed plots, each representing a provenance.  The plots consists of 9 trees spaced at 3 m intervals in a square.   The silvicultural treatments consists of 3 thinning regimes (0% removal, 25% removal, 50% removal) and 2 pruning regimes (prune to 2 m, prune to 6 m) applied to the original provenance trial at the block level.  All trees had been previously pruned to 2 m in July, 1984 to improve access to the tree stem during remeasurements.  Therefore, pruning to 2 m was not a new treatment.  The thinning treatments were not assigned randomly.  The blocks with lower survival rates were favoured for thinning to maintain as much of the original provenance trial as possible.      
  2. Rennell Sound (formerly EP702.05) has 9 blocks, each of  which consists of 10 provenances with 9 trees per provenance planted in a line and assigned randomly within the block.  Unlike Areas 2, 3 and 4, Rennell Sound lacked site replication, so the number of combinations of pruning and thinning treatments were limited.  Also, the area was too small to allow adequate buffers around individual plots.  For these reasons,  the provenance trial was split in a north-south direction, with those blocks to the west (1, 3, 5 and 7) receiving no thinning, and those blocks to the east (2, 4, 6, 8 and 9) receiving a thinning treatment of 50% stems  removed.   All trees were pruned to 6 m.  Tree numbers as tagged in the original provenance trial were not changed.  A single line of buffer trees surrounds the entire installation.