Olympic Habitat Development Study



The structural complexity of mature forests includes not only living features such as large diameter trees and multilayered canopies; it also includes standing and down dead wood (also called coarse woody debris). Logs on the forest floor serve as nurseries for seedlings and provide hiding and foraging cover for invertebrates, amphibians, small mammals and birds. Young stands lack trees large enough to provide material for the large logs (another old-growth element) Old-growth characteristics

    •  Large (>80cm) or old (>200 years) trees
    •  2 or more species with a wide range in ages and sizes
    •  Deep, multi-layered canopy
    •  Large conifer snags
    •  Large diameter and long logs

(For more detailed information, see the link located in Resources.)

found in old-growth stands. As a solution for this, we consolidated small logs together into structures nicknamed "log pyramids". A log pyramid is intended to equal the mass and volume of a much larger log, thus providing some of the same benefits of larger logs. The study created 5 to 7 structures per ha.2 to 3 structures per acre Each structure was 1.0 to 1.5 m35 to 50 inches wide, 0.5 to 1.0 m20 to 40 inches wide and 9 to 15 m30 to 50 feet long. Log structures will decay more rapidly than a solid log of the same dimensions but this can be a plus if woody material in a range of decay classes is missing. (Learn more about decay classes here).

Log pyramids can be created at the time of thinning. This has the advantage that people and equipment that might be useful in "making" logs are already on site so the log structures can probably be constructed more economically. Combining thinning and creation of wildlife enhancement structures cannot always be done at the same time (some organizations may have restrictions). We decided to wait until 2 winter seasons had passed so we could take advantage of any windthrow(trees blown over in wind storms) that might occur after the thinning. Trees in recently thinned stands have not adjusted to their new environments (by increasing root growth and diameter growth low on the stem) and they are more likely to be wind thrown the first few years after thinning.

Log structures began decaying rapidly on Fresca and have been colonized by mosses, liverworts, fungi, and are serving as nurse logs for western hemlock and Sitka spruce regeneration. Log pyramids on other sites are decaying more slowly and have different plants growing on them.

Another wildlife enhancement treatment included in the study was the creation of "slash piles" They were made as large as practical (about 2 m 6.5 feet high and 3 m10 feet in diameter with hand labor to keep them functional for as long as possible, since a small pile will "melt" quickly under the wet conditions of the Olympic Peninsula.


Log pyramid at Fresca shortly after creation.
Log pyramids are the equivalent of voluminous natural debris, like this decaying log at our plot in Clavicle. Log pyramid at Fresca shortly after creation. Log pyramids at Fresca were quickly colonized by mosses and liverworts, and a few years later, by conifer seedlings. (photo taken 12 years after structure was built)
Log pyramid at Fresca shortly after creation.