Response of Soil Health Indicators to Organic Matter Removal and Compaction Manipulations at Six LTSP Sites in the Western US

Forest soils control many ecosystem services that enable and support primary forest productivity. Therefore, maintaining the health of the soil is critical to sustainable forest management. The long-term soil productivity (LTSP) experiment was initiated to increase our understanding of how the soil responds to pulse harvest disturbance and experiments have enabled tracking of soil health parameters across many diverse forest types. The purpose of this study was to investigate the effect of organic matter (OM) removal and compaction manipulations on soil health indicators at six long-term LTSP sites (study durations 16?25 years) in the Pacific Northwest and Northern California, USA. We hypothesized that only the most severe OM removal treatment would exhibit decreased soil nutrient pools and reduced biological processes and compaction would have less detrimental impact on soil properties than OM removal treatments. We collected mineral soil samples at six LTSP sites and measured soil health properties related to nutrient pools (total soil carbon (C) and nitrogen (N), active C) and biological processes (C and N mineralization and enzymatic potential activity). Our results indicate that the effects of OM removal treatments are more prominent than those effects of compaction treatments. Despite variation in inherent site properties, we did find consistent evidence that severe harvesting treatments may disrupt mineral soil functions and remain detrimental to most soil health measurements, even after 16?25 years. In contrast, bole-only and whole-tree removal treatments did not have this effect on soil parameters indicating these practices may not incur such long-lasting or deleterious effects. These results indicate the importance of reducing soil disruption due to harvesting in order to maintain ecosystem functions and highlights the importance of understanding the range of impact harvesting practices may have on forest soil health.