Nutrient Content of Litter Fall on the Hubbard Brook Experimental Forest, New Hampshire

Abstract

Litter fall was collected throughout the year beneath a mature northern hardwood forest in New Hampshire. The material, separated by species and plant part, was analyzed for dry weight and for 11 elements. Total aboveground litter fall average 5,702 kg/ha per year; leaves, branches, stems, and bark contributed 49.1%, 22.2%, 14.1%, and 1.7%, respectively. Other deciduous structures (i.e., bud scales, flowers, fruit), as well as insect frass and miscellaneous tissues, contributed 10.9%. The overstory contributed 98.0% of the total, and shrub and herbaceous layers contributed only 1.2% and 0.8%, respectively. The nutrient content of the litter totaled 140.4 kg/ha per year. The relative abundance for these 11 elements was N > Ca > K > Mn > Mg > S > P > Zn > Fe > Na > Cu. Nitrogen, Ca, and K accounted for 80.6% of the total, and Zn, Fe, Na, and Cu contributed only 0.8%. The overstory, shrub, and herbaceous layers suppled 96.6%, 1.7%, and 1.6% of the nutrients, respectively. Litter fall occurred throughout the year, but there were seasonal peaks for many types of tissues. Autumn was most important, accounting for 49.7% of the litter and 56.0% of the nutrients. Summer and winter seasons supplied similar quantities of the litter, 21.2% and 22.4%; however, 22.6% of the total nutrient fall occurred during summer compared with only 17.2% during the winter. Spring months supplied 6.7% and 4.1% of litter and nutrients, respectively. Storms were very important in the timing of litter and nutrient fall. The extreme variability of litter fall is the result of differences between species, tissues, vertical structure of the vegetation, elevation, site, and time of year. In spite of this variation, nutrient—budget studies reveal relatively small losses from the ecosystem. Larger fluctuations in rates of nutrient flow, via litter fall, are readily absorbed within the ecosystem, thus preventing nutrient loss and maintaining efficient nutrient cycling.