Buffer strip dynamics in the Western Oregon Cascades Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/js956j58h

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  • Although buffer strips have long been used as a protection tool when logging near streams, long-term studies investigating buffer strip dynamics are rare. Steinblums et al. (1984) inventoried 40 buffer strips 1 to 15 years old in the western Oregon Cascades beginning in the summer of 1975. Numerous site and stand characteristics were evaluated and regional regression equations were developed to predict survival of the buffer strips (Steinblums et al. 1984). During the summer of 1990, 20 of the original buffer strips (Steinblums et al. 1984) were selected for reinventory to assess overstory conifer changes and density of conifer regeneration. Three sites had experienced severe windthrow followed by salvage logging, and a fourth could not be matched with original field notes. The 1990 comparison utilized the 16 remaining sites. Four diameter classes (10-14 inches DBH, 15-29 inches DBH, 30-44 inches DBH, and 45 inches DBH) were used to evaluate changes in overstory conifers since the original study. Density and basal area of each class were evaluated for each of the three common coniferous species (western hemlock, western redcedar, and Douglas-fir), and combined conifers. Average combined conifer densities of these late successional buffer strips increased from 54 to 59 trees per acre since the earlier study (Steinblums et al. 1984); average combined conifer basal area decreased from 299 to 263 ft^2 per acre since the original study. Ingrowth was most common in the two smallest diameter classes, with the majority of buffer strips showing increases in density and basal area. Average combined conifer density increased from 32 to 41 trees per acre; average combined conifer basal area increased from 64 to 76 ft^2 per acre. Western hemlock was the major contributor to the increases. Western redcedar and Douglas-fir represented relatively minor components of the two smallest diameter classes in both samplings. While combined conifer basal area increases were small, density increased as much as 900%. Decreases in density and basal area were common for conifers 30-44 inches DBH, with the majority of losses evident among western hemlock. However, Douglas-fir also exhibited some declines in this class. Western redcedar was relatively unchanged since the original study. Density losses ranged from 0 to 50% of the original buffer; basal area losses ranged from 0 to 72%. Density and basal area losses typically occurred among conifers 45 inches DBH. Though trees of this size were not prevalent, basal area losses from this class ranged from 0 to 84% of the original sample value. Conifer regeneration data indicate these buffer strips are sufficiently stocked to maintain conifers over time. Average densities of saplings (<8 inches DBH and >3 feet tall) ranged from nearly 200 to 3600 trees per acre.
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