Olympic Habitat Development Study
US FOREST SERVICE

 

Station 4 - GAPS

Our thinning prescription for Fresca included installing a series of gaps throughout the stand. Gaps were 20 m by 20 m;66 feet by 66 feet they were established at a minimum distance of 20 m 66 feet from a skip, so the increased light reaching the ground in and around the gaps (and increased air movement which will reduce relative humidity) will have minimal effects on the desired intact stand conditions associated with skips. Gaps were designed to be small to reduce the chance for windthrow along the edges of the gaps. (gaps were smaller in diameter than the height of the dominant trees) These gaps accounted for 15% of the total area of the stand. In the gaps we removed all trees with a diameter greater than 20 cm 8 inches except for hardwoods or uncommon species. Because large trees were only removed in gaps (plus a few in skid trails), gaps provided most of the merchantable timber in the VDT. (variable-density thinning)

The purpose of these gaps is to increase structural and compositional heterogeneity of the stand. Some specific processes that will be enhanced are:

•  Trees in or around the edges of the gaps will have much more growing space than those in the general thinned matrix area. Thus, gap creation increases growth of overstory trees --especially stem diameter growth.

•  Trees in and around the gaps will develop long crowns and large branches. In addition, some species such as Sitka spruce will form epicormic branches.(new branches which develop from buds under the bark in response to a major change in light environment or to damage)
(Learn more about spruce on the Natural History Tour.)

•  Understory development will be enhanced in and around the gaps. This includes tree regeneration.

•  Gap creation will favor growth of many understory and midstory species

We did some planting in gaps. We wanted to use the gaps to promote regeneration of species that alter soil properties through mycorrhizal diversity,(mycorrhizae are a symbiotic relationship (partnership) between a fungus and the roots of a plant. Some mycorrhizal fungi produce truffles which can be an important food source for small mammals)
(For more detailed information, see the link located in Resources.)
nitrogen fixation (root nodules on red alder take in nitrogen from the air and convert it to a form the alder can utilize)
(Learn more about alder on the Natural History Tour)
and calcium cycling (western redcedar or maple). Areas of hardwoods and shrubs in conifer forests are promoted by gaps; these plants provide important habitat for several species of lichens.(lichens are interesting partnerships between a fungus and a photosynthetic partner) (Learn more about lichens here)


 

Gap overhead view.
Gap at the Snow White research plot. Gap overhead view. Gaps provide habitat for sun-loving species.
Gap overhead view.