[ Section 13: Table of Contents ]

[ Next: Study Questions ]

[ Bottom of Page ]

General Characteristics

Western hemlock was once considered to be a "weed" or "inferior" species in the Inland Mountain West. Today, western hemlock is managed for timber production because of good growth and ease of establishment. Western hemlock is very tolerant of shade and is considered to be the climax species in habitat types where it grows in the Inland Mountain West. Because of this species' shade tolerance, advance regeneration is common.

Release Interactions

Indian paint fungus is a serious heart rot in western hemlock. Both decay incidence and defect increase with tree age. The behavior of this fungus makes it a major consideration when releasing hemlocks and true firs.

Etheridge and Craig explained important factors leading to decay in western hemlock by Indian paint fungus. Infection occurs on stubs of shade-killed branchlets. About 40 years of suppressed growth is necessary to produce such conditions. After the stub heals over, the fungus can become dormant for up to 50 years. Infections are reactivated by mechanical injury such as logging scars, broken tops, broken branches, or frost cracks. Indian paint fungus was isolated only from branchlet stubs of suppressed trees. The length of time stubs were exposed before healing over was positively correlated with infection, suggesting that quick healing of branch stubs lowers susceptibility.

Other authors essentially agree with the findings of Etheridge and Craig(Aho for grand fir, Filip and Aho for white fire, Herring and Etheridge for Pacific silver fir (Abies amabilis Dougl. ex Forbes), and Smith and Craig for subalpine fir.

Response to Release

Possibly a greater proportion of released hemlock die than do other species discussed in this paper. For example, Tucker and Emmingham estimated that 95 percent of western hemlock died the year of release in a south-facing clearcut in Oregon. They estimated that 50 percent died in a shelterwood cutting at the same site. Needles of released western hemlock abscised prematurely, and needles formed the first year after release were about half normal size. Released hemlock in shelterwoods retained more pre-release crown and produced sun needles after release. Tucker and Emmingham recommended a shelterwood cutting, allowing 3 to 5 years before final overstory removal.

There is evidence that tall western hemlock are slower to respond and have slower growth after release than do shorter trees. Hoyer showed, from a sample of four trees, that the taller the tree at release, the slower the post-release height growth. Hoyer's tentative conclusion was that hemlock trees less than 30 ft. tall will release and closely match site index curves for western Washington. Trees taller than 30 ft. may not release well, thereby leading to an underestimate of site productivity. Additional evidence comes from Oliver, who found that taller hemlock trees take longer to respond to release. Weir and Hubert noted the effect of shock on released hemlock in northern Idaho. Following release, diameter growth response follows a sigmoid shape with increased growth up to about 7 years after overstory removal.

[ Section 13: Table of Contents ]

[ Next: Study Questions ]

[ Top of Page ]