Decomposition of the Leaves of Some Forest Trees under Field Conditions.

In the main the few studies that have been made on the decomposition of leaves have either been made under highly artificial conditions (5) or else over a short period of time (1, 3, 4). Therefore an experiment intended to supply natural conditions as nearly as possible and lasting a number of years was set up in the fall of 1934. Leaves of sugar maple, hickory (several species), white oak and black oak (several species) were collected from the ground during the period of leaf fall; needles from the red pine were collected from the tree, using needles ready to fall. Weighed quantities of air dry leaves were placed in wire baskets 24 x 24 x 6 inches made from galvanized wire. Half-inch mesh wap used for all leaves except pines for which quarter-inch mesh was used to keep the needles from falling out. All baskets were supplied with a cover made from the same material as the rest of the basket. The baskets were placed in the field on November 17. The pine needles were placed under the trees from which they had been collected. The others were placed in a mixed hardwood stand. Before the baskets with the leaves were put in place all fresh leaves were removed from the ground so that they rested on partly decayed leaves. The baskets were placed on level ground to insure that all parts came in intimate contact with the soil. Besides the single species or mixture of species as indicated above, the oak leaves and pine needles were mixed in the order of 72 per cent. of the former to 28 per cent. of the latter. This was done to simulate mixed stands of hardwood and conifers, and to discover whether there is any foundation for the general belief among foresters that there is more rapid decomposition when pine and hardwood leaves occur together than when alone. The amount of leaves placed in each basket was not the same except in pine, because the leaves were put in weighed baskets first and then weighed. The pine needles were weighed separately and 400 grams put into each basket. The amount of the other leaves varied from about 200 to 300 grams per basket. This quantity of leaves was undoubtedly larger than that which would normally have accumulated on an area of four square feet during one season. The oven dry weight of corresponding samples of leaves were made so that every year comparisons could be made between oven dry leaves. At the time of setting up the experiments it was thought that maple and hickory leaves would decay very rapidly and therefore only four baskets were made up of these leaves, whereas eight baskets of the others were prepared. The original intention was to remove a basket each spring and fall, 1 Paper from the Department of Botany of the University of Michigan, no. 822. 704