Olympic Habitat Development Study



The thinned matrix was intermediate in response between the skips and the gaps. The species which increased the most was bracken fern but it increased to 45% cover by year 7 (as opposed to 60% in the gaps). Other species which increased substantially in cover were: deer fern, wood sorrel, false lily-of-the valley - these 3 increased in cover by about 20% -- and red huckleberry which increased to about 7% by year 7.

Although many of the same species responded both to the natural disturbances in the control area (ice storms) and to our thinning, the thinning had a larger effect (graph).Changes over time in percent cover of herbaceous species in the control (unthinned) area and the plot which was variably thinned. For example, both the control area and the area that was going to be thinned had deer fern coverages of less than 2% at the beginning of the study. At year 3, the 2 areas had about the same cover of deer fern (3%). By year 7, the control had 4% coverage while the VDT (variable-density thinning) plot was at 22%. By year 10, the control area had returned to a deer fern coverage of 2% (back where it started) while the variable-density thinned area (weighted average of skips, gaps and the thinned matrix) had a deer fern cover of 12%. The cover of deer fern in the thinned areas changed very little between years 10 and 17. Thus, for deer fern, the short-term effect on cover was larger and it lasted longer.


The bracken fern (Pteridium aquilinum<) increased significantly with the VDT.
The red huckleberry (Vaccinium parvifolium) is another one of the species that increased its cover. Its berries were a common source of food among indigenous peoples. The bracken fern (Pteridium aquilinum) increased significantly with the VDT. Vegetation growing around a pyramid log (one of our wildlife enhancement treatments).
The bracken fern (Pteridium aquilinum) increased significantly with the VDT.