Graduate Thesis Or Dissertation
 

Sitka spruce and western hemlock regeneration after selective harvesting, Tongass National Forest, southeast Alaska

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  • The objectives of this study were to determine the species composition and density of natural conifer regeneration following selective logging in southeast Alaska. Therefore, we quantified the density and size of new cohort spruce and hemlock and current seedling bank in 17 selectively logged stands. All stands were in mixed hemlock-spruce forests that were logged between 1900 and 1984, located at or near sea level, and not managed after this first logging. New cohorts included trees that germinated after logging plus advanced regeneration that was shorter than 1.4 in (standard height for diameter measurement - diameter at breast height, d.b.h.) at time of logging. With the exception of one tree, we found new cohort spruce only in plots that had been logged. New cohort hemlock were common in both logged and unlogged plots. New cohort spruce basal area ranged from 2 to 19 m2 / ha. Individuals were as large as 104 cm d.b.h. but generally ranged between 19 and 55 cm d.b.h. New cohort hemlock basal area ranged from less than 1 to 32 m2 / ha. The largest tree was 102 cm d.b.h. but most ranged from 11 to 51 cm d.b.h. The absence of new spruce in unlogged plots strongly suggests that disturbance favors spruce recruitment. The seedling bank included trees 0 to 3 m tall and less than 2.5 cm d.b.h. These seedlings became established after logging. The seedling bank density of both species was high; spruce ranged from 3,000 to 114,000 and hemlock ranged from 47,000 to 723,000 seedlings / ha. Rooting substrate (logs or undisturbed forest floor) was significant for both species (spruce p = 0.05, hemlock p = 0.0001). There were always more seedlings on logs than on undisturbed forest floor. By leaving spruce seed trees, judicious soil disturbance, planned entries to regulate overstory density and possibly planting spruce seedlings where the seed source is poor, we believe spruce can be regenerated in these systems. Pre-commercial thinning may be necessary to keep vigorously growing cohorts of spruce and hemlock in these stands, just as it is necessary in young stands regenerated after clearcutting.
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file details Yount_Louise_S_1997.pdf 2017-08-19 Pubblico Scaricare