Twenty-year response of Douglas-fir to logging debris manipulation and vegetation control at two sites with contrasting soil quality

Abstract

Reforestation practices have potential to alter site productivity and influence forest stand development. We evaluated the effects of logging debris (LD) manipulation (LD dispersed, LD piled, and LD removed) and competing vegetation control (VC; initial VC only or annual VC for five years) on Douglas-fir stand characteristics at two sites in western Washington and Oregon, USA that contrasted strongly in soil quality (SQ). Annual VC had a pronounced effect on stand volume compared to initial VC, but the magnitude of effect was greater at the low SQ site (~50 % increase in volume) than at the high SQ site (~25 % increase). Volume effects of VC at the low SQ site were due to differences in proportionate survival between treatments (0.15 lower with initial VC vs. annual VC) and will likely persist to end of rotation; effects at the high SQ site were due to greater growth with annual VC, but differences between VC treatments are decreasing with time. Effects of LD treatments were muted and primarily associated with the piling treatment. Total volume was ~25 % greater with LD piling compared to LD removal at the low SQ site only. At both sites, soils sampled under piles had higher extractable nutrients and nitrogen mineralization compared to soils between piles, which may have provided benefits to tree growth at the low SQ site. The contrasting site responses and decreasing effects of VC treatment at the high SQ site highlight the importance of understanding mechanisms of treatment response when making inferences for similar sites.

Citation

Slesak, Robert A.; Dahms-May, Scout M.; Harrington, Timothy B. 2026. Twenty-year response of Douglas-fir to logging debris manipulation and vegetation control at two sites with contrasting soil quality. Forest Ecology and Management. 603: 123434. https://doi.org/10.1016/j.foreco.2025.123434.