| Abstract
| - Acidity of aqueous extracts of several tree and shrub leaf litters was determined by titration to pH 7 with 0.01N NaOH. Bases were determined by back titration of 0.05N HCl extracts of ground litters and after ashing. Lowest acidity was found in the broadleaved species (except sycamore) and western red cedar; greatest acidity was found in western hemlock, grand fir, and one sample of Douglas fir. Largest contents of ash bases were found in some broadleaves plus western red cedar; the smallest contents were in most of the conifers. Excess ash bases (ash bases minus acidity) were greatest in elm, hawthorn, western red cedar, hazel, willow, ash, and southern beech, and were smallest in western hemlock, Douglas fir, lodgepole pile, Sitka spruce, grand fir, hybrid larch, Scots pine, and Norway spruce. Acidity, directly titratable and ash bases, and excess ash bases showed significant, and in some cases quite large, variation between sites for some species. There is some support for the suggestion that excess ash bases are greater in mull-forming than in mor-forming litters. Acidity was significantly greater for litters collected dry than for those collected wet. Litters which were stored air dry for several months showed increased acidity compared with their initial values.
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