Organic matter and nitrogen content of the forest floor in even-aged northern hardwoods

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Abstract
Organic content of the forest floor decreases for several years and clear-cutting, and then slowly recovers. Thickness, bulk density, organic matter, and nitrogen content of forest floors were measured for 13 northern hardwood stands in the White Mountains of New Hampshire [USA]. Stands ranged from 1 to about 100 yr in age. Forest-floor thickness varied significantly with stand age, but bulk density, organic fraction, and nitrogen fraction were independent of age. Total organic content of the forest floor agreed very well with data from Covington''s (1981) study of the same area. Both studies indicated that mature forest floors have about 80 Mg organic matter .cntdot. ha and 1.9 Mg nitogen .cntdot. ha. Within 10 or 15 yr after cutting, the organic matter content of the floor decreases to 50 Mg .cntdot. ha, and its nitrogen content to 1.1 Mg .cntdot. ha. The question whether the decrease is rapid and the minimum broad and flat, or if the decrease is gradual and the minimum sharp, cannot be answered. The subsequent increase to levels reached in mature forest requires about 50 yr. Some of the initial decrease in organic matter and N content of the forest floor may be caused by organic decomposition and N leaching, but mechanical and chemical mixing of floor into mineral soil, during and after the harvest operation, may also be important. The difference is vital with respect to maintenance of long-term productivity.