Wood Productivity of Pacific Northwest Douglas-Fir: Estimates from Growth-and-Yield Models

摘要

With increases in harvest of forests in the Pacific Northwest during the late 1800s and early 1900s came a concern for future timber supplies. Unsuccessful attempts at selective logging in Douglas-fir (Pseudotsuga menziesii (Mirb.) France) and a better understanding of requirements for natural regeneration led to the adoption of moderate-sized clearcuts with adjacent uncut timber as a seed source (Curtis and Carey 1996). As a response of the need tor more depenctable regeneration, the 1950s saw a shift to artificial regeneration methods and the establishment of state forest practice regulations to insure prompt reforestation. This eliminated the need for leaving onsite seed sources, making further increases in cut unit size possible. Through the 1960s and 1970s, research improved the quality and survival of planted seedlings through the selection of genetically appropriate trees for individual sites, better nursery practices, site preparation, and early control of competing vegetation. Miller and others (1993) compared paired plots in naturally regenerated and planted Douglas-fir stands 35 to 38 years after harvest at seven locations in the Cascades of Oregon and Washington and found 40 percent more volume per acre and an 8 percent greater average diameter in the planted stands. The authors attributed the volume differential to differences in the pattern of stand development, e.g., planted stands reached breast height an average of 3 years sooner.