Natural regeneration of understory conifers was studied in 1988, 9–14 years after thinning of even-aged stands of western hemlock (Tsugaheterophylla (Raf.) Sarg.) and Sitka spruce (Piceasitchensis (Bong.) Carr.) on upland sites in southeast Alaska. Two age-classes of stands were compared: young stands, <30 years old that before thinning had open forest canopies and understories of conifer regeneration, shrubs, herbs, and forbs; and older stands, 31–98 years old, that before thinning had closed forest canopies and little or no understory vegetation. In 1988, dominant understory conifers in young stands were 2–4 m tall, and about the same age as trees in the overstory. In the older stands there was dense new regeneration that germinated 2–3 years after thinning and averaged 0.6–1.5 m tall. Seventy-two to 100% of all regeneration was hemlock. The rest was Sitka spruce. The amount of regeneration increased and the percentage of hemlock decreased with increasing thinning intensity. Thinning of young stands on upland sites appears to benefit understory conifers, which rapidly expand to fill in the available growing space. Heavy thinning in older stands promotes dense germination of understory conifers making it difficult for other understory plants to become established.
Data from 157 open-grown Sitka spruce (Piceasitchensis (Bong.) Carr.) and 102 western hemlock (Tsugaheterophylla (Raf.) Sarg.) at two locations in coastal Alaska and from 69 Sitka spruce on the Queen Charlotte Islands in British Columbia were used to develop height–diameter and crown width–diameter equations. Height–diameter relations for Sitka spruce were significantly different among all locations. Crown width–diameter relations were not significantly different. Common equations were fit to the spruce data and to the spruce and hemlock data independent of location and site index along the coast.
This study of response to partial cutting over a 17-year period in a 96-year-old stand of western hemlock-Sitka spruce at Karta Bay, Alaska, showed that crop trees left after partial cutting were able to increase or maintain about the same rate of diameter growth as before thinning, but growth in diameter of trees in an unthinned stand followed the normal pattern of decline. Opening the stand stimulated epicormic branching, thus reducing quality of trees in the future. Partially cut plots became well stocked with conifer regeneration, mostly western hemlock. Keywords: Thinning, rotation age, western hemlock, Tsuga heterophylla, Sitka spruce, Picea sitchensis. heterophylla (Raf.) Sarg.) related to stand structure and product development. Ph. D. dissertation on file at University of Washington, 138 p. , illus. , 1965. a,
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