Abstract
Silvicultural treatments applied prior to regeneration or during early stages of stand development can affect tree and stand productivity throughout the rotation. Most studies rarely extend measurements beyond the first decade after treatment, limiting our ability to properly assess long-term treatment efficacy. This is especially true in forests of the Inland Northwest. In 1982, a study was initiated on the Priest River Experimental Forest in northern Idaho to test the effects of different mechanical and chemical site preparation treatments on regeneration performance of interior Douglas-fir (Pseudotsuga menziesii var. glauca) and western white pine (Pinus monticola Dougl. ex. D. Don).
The study was replicated at two sites: a high elevation site and a low elevation site. Within each site four treatments were replicated 3 or 4 times, including (1) organic horizon removal and mineral exposure (scalping), (2) mixed organic and mineral soil bedding without competition removal, (3) organic soil bedding with chemical competition control, and (4) an untreated control. The objective of the study was to examine temporal trends in tree growth and growth efficiency to determine if tree productivity was substantially altered by the type of site preparation. Data collection occurred in the summer of 2017, 35 years after treatment. Seventy-five trees were destructively sampled to reconstruct patterns of stem height, diameter, and volume growth, as well as estimate growth efficiency at age 35. The combined bedding and herbicide treatment consistently increased cumulative stem size over time compared to the three other treatments, while scalping and bedding treatments at times resulted in decreased growth and productivity compared to the untreated control. Site preparation treatments did not significantly impact tree leaf area or growth efficiency for either tree species compared to the untreated control. Results of these studies provide a mechanistic context for the growth and productivity of P. menziesii and P. monticola in early maturity