Comparison of the litterfall and forest floor organic matter and nitrogen dynamics of upland forest ecosystems in north central Wisconsin

It has been suggested that a feedback exists between the vegetation and soi l whereby fertile (vs infertile) sites support species with shorter leaf li fe spans and higher quality litter which promotes rapid decomposition and h igher soil nutrient availability. The objectives of this study were to (1) characterize and compare the C and N dynamics of dominant upland forest eco systems in north central Wisconsin, (2) compare the nutrient use efficiency (NUE) of these forests, and (3) examine the relationship between NUE and s ite characteristics. Analyzing data from 24 stands spanning a moisture/nutr ient gradient, we found that resource-poor stands transferred less C and N from the vegetation to the forest floor, and that N remained in the forest floor at least four times longer than in more resource-rich stands. Analyzi ng data by leaf habit, we found that less N was transferred to the forest f loor annually via litterfall in conifer stands, and that N remained in the forest floor of these stands nearly three times longer than in hardwood sta nds. NUE did not differ among forests with different resource availabilitie s, but was greater for conifers than for hardwoods. Vitousek's (1982) index of nutrient use efficiency (I-NUE1 = leaf litterfall biomass/leaf litterfa ll N) was most closely correlated to litterfall specific leaf area and perc ent hardwood leaf area index, suggesting that differences in species compos ition may have been responsible for the differences in NUE among our stands . NUE2, defined as ANPP/leaf litterfall N, was not closely correlated to an y of the site characteristics included in this analysis.