Olympic Habitat Development Study
US FOREST SERVICE

Station 2 -THINNED MATRIX

The thinning we designed was to help us achieve our management objectives(accelerate the development of old-growth characteristics and plant and animal communities associated with old-growth stands) for the stand conditions in the 8 stands in our study (40- to 80-year-old conifer stands on the Olympic Peninsula). We hope the ideas will be useful for other areas - but the specific "recipe" or prescription should be altered based on local stand conditions, management objectives, and the economic feasibility of specific practices.

One goal of our thinning prescription was to create a range of growing conditions within a stand. We did this by creating a thinned matrix with skips and gaps (more about the skips and gaps at other stations). The matrix area (75% of the stand) was lightly thinned (the volume of trees cut or removed was low) using a technique called thinning from below.(this means mostly smaller trees were cut in the thinning) The thinning in the matrix was designed to:

•  Accelerate the production of trees with larger stem diameters by increasing or maintaining rates of diameter growth in existing overstory trees. Large-diameter trees are a key component of old-growth stands. 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.)

Forests naturally develop wider spacings between trees over time, as some large trees survive and others die or are damaged. Thinning can accelerate the process of stand development and thus accelerate creating conditions which are suitable for foraging or nesting of species such as flying squirrels, marbled murrelets and spotted owls.

•  Improve growing conditions for trees in the midstory or understory. Creating multilayered canopies (an 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.)

is one of our goals and thinning can increase the light available for these trees and result in faster growth rates.

•  Produce or retain trees with large branches and large, long crowns. Large diameter branches are used for nesting by marbled murrelets and long crowns provide substrates for lichens and other epiphytes. (plants growing on other plants such as moss or lichens on tree bark)

•  Increase seed production of desired species. For example, Douglas-fir is a minor component of the overstory trees at Fresca but since it provides relatively large, nutritious seeds for small mammals and birds, it was not cut unless it was necessary to have access for equipment. Thinning generally enhances seed production.

•  Increase tree species diversity. Tree species which are not common in the Fresca area - such as western redcedar, red alder, and bigleaf maple -- were not cut and where possible were given additional growing space to increase the odds of their long-term survival.

•  Increase development of understory species (Take the Understory Tour).

•  "Wind proof" the stand. By increasing future diameter growth, thinning will slowly reduce the height to diameter ratio (the ratio will increase in unthinned stands). Reducing the ratio will make the stand less susceptible to blowdown in the future.

•  Thinning also provided economic benefits to the local community.


 

The light thinning in the matrix did not remove many trees but additional light makes it thru the overstory canopy layer after thinning.
Some trees are removed selectively in the thinned matrix. The light thinning in the matrix did not remove many trees but additional light makes it thru the overstory canopy layer after thinning. Thinned matrix provides higher structural complexity. (Thinned matrix of the Snow White research plot was thinned operationally in the mid 1970s and again in the late 1990s as part of OHDS.)
The light thinning in the matrix did not remove many trees but additional light makes it thru the overstory canopy layer after thinning.