Abstracts Biological Sciences

The effects of partial cutting on stand structure and growth, and forest plant communities of western hemlock-Sitka spruce stands in southeast Alaska

by Robert L. Deal

This study evaluated the effects of partial cutting on stand structure and growth, patterns of conifer regeneration, stand mortality and disease, and understory plant diversity and abundance. Seventy-three 1/5 ha plots were established in 18 partially cut stands throughout southeast Alaska. These stands were partially cut 12 to 96 years ago removing 16 to 96 percent of the original stand basal area. Partial cutting resulted in stands that had complex structures and these structures appear similar to uncut old-growth stands. Sitka spruce was maintained over a wide range of cutting intensities, and conversion to hemlock-dominated stands generally did not occur. New spruce regeneration was established in 23 of 55 partially cut plots compared with new spruce found in only 2 of the 18 uncut plots. The current stand basal area, tree species composition, and stand growth were strongly related to trees left after harvest. Trees that were 10 to 70 cm d.b.h. at time of cutting had the greatest tree diameter growth. Little of the stand growth since harvest came from new regeneration or trees greater than 70 cm d.b.h. The diameter growth of residual hemlock and spruce trees were similar The species richness of vascular plants and bryophytes was similar among uncut and partially cut plots and did not significantly change with different cutting intensities. Overall, plant community structures were similar between the uncut and partially cut plots. However, moderate and heavy cutting intensities resulted in stands that had significantly different plant community composition. The abundance of most deer forage plants did not significantly change after partial cutting. It appears that silvicultural systems that use single tree selection or small openings can be successful for timber management purposes in southeast Alaska. Concerns about changing tree species composition, lack of spruce regeneration, greatly reduced stand growth and vigor, increased dwarf mistletoe infection in hemlock trees, and higher incidence of tree wounding, decay, and mortality with partial cuts were largely unsubstantiated. Stand structural diversity, species richness and understory plant abundance were all greater in partially cut stands than in young-growth stands developing after clearcutting.