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Nutrient distributions, concentrations, and fluxes in two red spruce (Picearubens Sarg.) stands in the Great Smoky Mountains are described and used to evaluate various hypotheses for recent decline of this species. These forests, like others in the southern Appalachians, were relatively rich in N and low in base cation status. The combination of high atmospheric N and S deposition, little or no N or S retention, relatively high N mineralization, and extremely acid soils caused soil solutions to be dominated by NO3−, SO42−, Al, and H+. Soil solution Al in these sites (most of which was in monomeric form) occasionally reached levels noted to inhibit base cation uptake and root growth in solution culture studies. These pulses of Al were driven by pulses of NO3− and, to a lesser extent, SO42− in soil solution. However, fine roots were present at depths of up to 60 cm in the mineral soil, indicating that Al concentrations had not become consistently toxic to roots. Solution fluxes (both throughfall and soil leaching) exceeded litter-fall fluxes for all the macronutrients at both sites, a typical situation for K and S, but most unusual for N, P, Ca, and Mg. There are significant implications of these fluxes and of the apparent net uptake of N by foliage in terms of how vegetation uptake and translocation are calculated. Some new formulations are suggested, but measurement errors in systems with such a predominance of hydrologic fluxes make foliar leaching and, therefore, uptake and translocation calculations extremely uncertain. Although there are no outward signs of decline in these forests (other than balsam fir (Abiesbalsamea (L.) Mill.) mortality due to the balsam woolly adelgid (Adelgespiceae (Ratz.))), the high rates of NO3− leaching rates and the borderline soil solution Al values suggest that these systems are under stress. Whether these factors actually lead to a dieback or growth decline remains to be seen.

Forest soils represent a substantial portion of the terrestrial carbon (C) pool, and changes to soil C cycling are globally significant not only for C sequestration but also for sustaining forest productivity and ecosystem services. To quantify the effect of harvesting on soil C, we used meta-analysis to examine a database of 945 responses to harvesting collected from 112 publications from around the world. Harvesting reduced soil C, on average, by 11.2% with 95% CI [14.1%, 8.5%].There was substantial variation between responses in different soil depths, with greatest losses occurring in the O horizon (−30.2%). Much smaller but still significant losses (−3.3%) occurred in top soil C pools (0-15 cm depth). In very deep soil (60-100+ cm), a significant loss of 17.7% of soil C in was observed after harvest. However, only 21 of the 945 total responses examined this depth, indicating a substantial need for more research in this area. The response of soil C to harvesting varies substantially between soil orders, with greater losses in Spodosol and Ultisol orders and less substantial losses in Alfisols and Andisols. Soil C takes several decades to recover following harvest, with Spodosol and Ultisol C recovering only after at least 75 years. The publications in this analysis were highly skewed toward surface sampling, with a maximum sampling depth of 36 cm, on average. Sampling deep soil represents one of the best opportunities to reduce uncertainty in the understanding of the response of soil C to forest harvest.

No abstract

Forest soils are often deep and/or coarse‐textured, which does not always lend itself to easy unbiased sampling. Two important Pacific Northwest (PNW) forest soil series that are deep and coarse‐textured were studied to evaluate methods of estimating soil C: (i) a loamy sand glacial outwash soil (Indianola series, mixed, mesic Dystric Xeropsamments) and (ii) a very gravelly sandy loam glacial outwash soil (Everett series, sandy‐skeletal, isotic, mesic Vitrandic Dystroxerepts). Four methods were compared for estimating soil C, including: (i) large pit (0.5 m2) excavation, (ii) dug pit with 54‐mm hammer‐core bulk‐density sampling, (iii) 31‐mm soil push sampler, and (iv) clod method. Coarse (>2 mm) fragments were also collected, processed, and analyzed for soil C. Extending soil sampling deeper than 15 cm increased soil C estimates by as much as 120%. The pit excavation method with sand‐displacement volume measurements, which is by far the most labor‐intensive and time‐consuming, was considered the “standard” by which other methods were compared, as it didn't contain any obvious biases. Soil core methods overestimated the <2‐mm soil fraction (samples taken between large rocks). Biased methods are often accepted as the “best available” due to the high time requirement of pit excavation. The 31‐ or 54‐mm soil core methods often didn't work due to the high rock content (>50%) of the Everett soil. Including C analysis of the >2‐mm soil fraction increased soil C estimates by 170% for the Everett series soil (due to organic C contained in the rocks; there were no carbonates) but did not substantially increase the estimate in the Indianola series soil.