Addition of organic matter and elements to the forest floor of an old-growth Acersaccharum forest in the annual litter fall

Abstract

Litter fall and its content of N, P, K, Ca, Mg, S, Fe, Mn, Zn, and Cu were measured monthly over a 5-year period in an old-growth Acersaccharum Marsh, stand on a till site in central northern Ontario. Determined were the following: the amount, and the temporal and spatial distributions, of organic matter and elements deposited annually in the different litter fractions; the proportion of elements conserved within the tree phytomass through retranslocation versus that shed in the annual litter fall; and the residence time of litter-transported elements in the forest floor. Element transfer through the annual litter fall was also compared with that by other vectors of transport to the forest floor. Over the study period, total litter fall averaged 3730 kg•ha−1•year−1 (dry weight), with 78% consisting of leaves, 8% of flowers and fruits, and the remaining 14% mainly of twigs, branches, and bark slough. Annual element depositions (kg•ha−1) averaged as follows: N, 40.6; P, 1.8; K, 9.1; Ca, 37.6; Mg, 3.9; S, 3.0; Fe, 0.57; Mn, 2.67; Zn, 0.28; and Cu, 0.03. Turnover time of the forest floor was calculated as 7.4 years. Residence times (years) of elements in the forest floor were as follows: N, 18.3; P, 18.3; K, 1.5; Ca, 6.1; Mg, 6.8; S, 5.1; Fe, 257.2; Mn, 4.8; Zn, 18.1; and Cu, 5.8. Although the turnover time of forest-floor organic matter did not differ appreciably from values reported for A. saccharum forests elsewhere, residence times for elements suggested somewhat slower cycling, probably as a result of reduced uptake related to the advanced age of the stand. Potassium, followed by S, P, and N, were all conserved to a high degree by A. saccharum trees through retranslocation to the tree's perennial parts prior to leaf fall; Cu, Mn, and Mg were conserved to a lesser degree; Zn, Ca, and Fe were conserved very little. In comparing the leaching loss of elements from foliage with quantities conserved through retranslocation and quantities shed in the annual litter fall, the relative orders of magnitude do not give cause for concern that A. saccharum trees risk appreciable leaching losses of base cations, including K, from foliage as a result of acidified precipitation, at least at levels experienced in central northern Ontario during the early 1980s.