Olympic Habitat Development Study

Welcome to the Olympic Habitat Development Study!

The information presented here is the result of a long-term scientific study that started in 1994 as a cooperative effort between the Pacific Northwest Research Station and the Olympic National Forest.

Forests and ecosystems change in time, maturing or “aging” just as any other living thing. A stand of young trees will grow into a mature forest and as more time goes by, this mature forest eventually develops into an old-growth 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.)

forest. As a forest becomes older, it increases in structural complexity and the array of organisms it supports changes. Logging during the 20th century greatly reduced the area of old-growth forests in the Pacific Northwest, thus reducing the habitat available for species which depend on this forest type.

Over the past 30 years there has been much greater recognition of the links between the amount of old-growth habitat and populations of specific species (e.g., spotted owl and marbled murrelet as well as a large number of other species). We need to increase the amount of suitable habitat if we want to ensure survival and long-term viability of these species. This has led managers to ask, “Can we use forest management practices in ways which will accelerate the development of specific characteristics associated with old-growth forests?” The Olympic Habitat Development Study (OHDS) was designed to answer this question by applying management treatments in 40- to 80-year-old conifer stands on the Olympic Peninsula.

Active Management

The OHDS is testing if active management of young conifer stands can accelerate the development of structures and ecological communities associated with old-growth forests. We can't use our wizardly powers to speed-up the “aging” of a stand but we might be able to shorten how long it takes to produce specific characteristics associated with old-growth stands -- such as large diameter trees or multi-layered canopies -- without creating some of the problems that may be associated with other timber harvesting practices. We are doing this through a novel system called “Variable-Density Thinning” (VDT) (A type of thinning used by forest managers to increase the variation in tree spacing across the stand (spatial heterogeneity) and promote the development of multiple canopy layers (structural complexity). Such thinnings usually maintain large numbers of trees in some areas and reduce stand density or create gaps in other areas.) as well as using some wildlife enhancement treatments.(Treatments designed to add habitat features. Examples would be topping trees to create snags, adding nest boxes, creating cavities, or increasing coarse wood) Our VDT treatments included skips (unthinned areas) and gaps. (created openings in the forest canopy) They were designed to create a mosaic of habitat conditions, favor structural complexity (e.g. multilayered canopy), and increase tree growth and the productivity and diversity of plant communities.


Our OHDS sites on the Olympic Peninsula.
Our OHDS sites on the Olympic Peninsula.


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