California Agriculture

If biomass utilization results in soil compaction and reduced forest productivity, the potential benefits may be considered to be not worth the long-term impacts. We analyzed soil strength, an indicator of soil compaction, prior to and following commercial thins (sawlog and biomass harvest) and mastication treatments in 24- to 30-year-old mixed-conifer plantations in the central Sierra Nevada. Soil strength in mature, untreated second-growth stands was also measured as a reference. Neither the commercial thins nor the mastication treatments resulted in statistically detectable increases in compaction. Most of the existing compaction came from the original regeneration harvest that established the plantations several decades earlier. It will be important to monitor repeat treatments and long-term effects, but this study suggests that managers should not expect large impacts from thinning treatments on soil compaction in forests such as the one studied here as long as best practices are used.