Carbon and nutrients in the forest floor and mineral soil were measured to determine amounts and variation among eighteen 0.081‐ha plots in a Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] plantation growing with volunteer red alder (Alnus rubra Bong.). Ten years earlier, the preceding mature conifer stand was clearcut and nearly all logging slash and forest floor were consumed by slash fire. Forest floor mass in the 9‐yr‐old plantation averaged 9.86 Mg ha‐1, with 3.71 Mg C, 98.0 kg N, 10.6 kg P, and 8.4 kg S ha‐1. Mineral soil to 1‐m depth averaged 176 Mg C, 8330 kg N, 3340 kg P, and 605 kg S ha‐1 in the <2‐mm fraction. The 2‐ to <6‐mm soil fraction averaged an additional 100 Mg C, 4480 kg N, and 1700 kg P ha‐1. Net mineralizable N as NH4 (anaerobic N mineralization index) totaled 99 kg N ha‐1 in the top 45 cm of the mineral soil and 62 kg N ha‐1 in the 45‐ to 100‐cm depth. Density fractionation showed that the light fraction (<1.65 Mg m‐3) was only 13.4% of the fine soil mass of the 0‐ to 15‐cm depth, yet contained about 40% of the total C and N capital in the <2‐mm size fraction. The substantial amounts of C and nutrients in this low‐bulk density soil (<2‐mm fraction, 0.30 Mg m‐3) indicate a fertile soil despite large previous losses of organic matter and N from the site.
Application. Heat damage to natural and planted seedlings can be prevented by recognizing adverse conditions, identifying susceptible seedlings, and taking preventive measures, such as shading, planting resistant seedlings, and modifying the soil environment. Shade from live vegetation can prevent heat damage, but the associated competition may kill seedlings.Abstract. Tree seedlings start to suffer stem damage or tissue death when the temperature at the soil surface reaches approximately 52 *C. Seedling mortality rate accelerates as temperatures increase. Resistance to heat damage increases with size as the ability of a seedling to shade its base increase. Small newly germinated seedlings are at risk in late spring and early summer, while larger nursery-grown seedlings are at risk in mid to late summer, especially on soils with low heat capacity or conductivity, or with surfaces that are dry, dark colored or covered with organic matter. Heat damage to natural and planted seedlings usually occurs on flat or south-facing sites in regions with hot dry summers and clear skies, but can also occur in wetter regions under dry clear conditions. Shading only the basal portion of the stem appears to be as effective in preventing heat damage as shading the entire stem and some foliage, which can also reduce transpiration. Overhead shade and shade from live plants can reduce growth and survival.
Localized log–log regression equations were developed for young red alder (Alnusrubra Bong.) and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) to predict branch and leaf dry weights from branch diameters, and leaf and branch dry weights (predicted from branch diameters), bole volumes and weights, and tree heights from stump and breast-height diameters. Correlation coefficients were generally greater than 0.9. These equations will be useful for similar sites in estimating aboveground biomass at precommercial thinning, fuel loadings, nutrient cycling, and productivity.
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