Buffer strip dynamics in the western Oregon Cascades

Although buffer strips have long been used as aprotection tool when logging near streams, long-termstudies investigating buffer strip dynamics are rare.Steinblums et al. (1984) inventoried 40 buffer strips 1 to15 years old in the western Oregon Cascades beginning inthe summer of 1975. Numerous site and stand
characteristics were evaluated and regional regressionequations were developed to predict survival of the bufferstrips (Steinblums et al. 1984).
During the summer of 1990, 20 of the original bufferstrips (Steinblums et al. 1984) were selected forreinventory to assess overstory conifer changes and densityof conifer regeneration. Three sites had experiencedsevere windthrow followed by salvage logging, and a fourthcould not be matched with original field notes. The 1990comparison utilized the 16 remaining sites.
Four diameter classes (10-14 inches DBH, 15-29 inchesDBH, 30-44 inches DBH, and >45 inches DBH) were used to
evaluate changes in overstory conifers since the originalstudy. Density and basal area of each class were evaluatedfor each of the three common coniferous species (westernhemlock, western redcedar, and Douglas-fir), and combinedconifers. Average combined conifer densities of these latesuccessional buffer strips increased from 54 to 59 treesper acre since the earlier study (Steinblums et al. 1984);average combined conifer basal area decreased from 299 to263 ft2 per acre since the original study.
Ingrowth was most common in the two smallest diameterclasses, with the majority of buffer strips showingincreases in density and basal area. Average combinedconifer density increased from 32 to 41 trees per acre;average combined conifer basal area increased from 64 to 76ft2 per acre. Western hemlock was the major contributor tothe increases. Western redcedar and Douglas-firrepresented relatively minor components of the two smallestdiameter classes in both samplings. While combined coniferbasal area increases were small, density increased as muchas 900%.
Decreases in density and basal area were common forconifers 30-44 inches DBH, with the majority of lossesevident among western hemlock. However, Douglas-fir alsoexhibited some declines in this class. Western redcedarwas relatively unchanged since the original study. Densitylosses ranged from 0 to 50% of the original buffer; basalarea losses ranged from 0 to 72%. Density and basal area losses typically occurred amongconifers ^45 inches DBH. Though trees of this size werenot prevalent, basal area losses from this class rangedfrom 0 to 84% of the original sample value.
Conifer regeneration data indicate these buffer stripsare sufficiently stocked to maintain conifers over time.Average densities of saplings (3 feettall) ranged from nearly 200 to 3600 trees per acre.