Elm and maple processing rates : comparisons between and withinstreams

Abstract

Leaf breakdown rates of two species of elm (Ulmus) and two of maple (Acer) were investigated in two low orderstreams located in Western Maryland, U.S.A., and in Northern Appenins, Italy. Within each genus of leaf, one specieswas Italian and one was American. The role of macroinvertebrate shredders in leaf processing was also investigated. In both streams within the same genus of leaf the Italian leaves disappeared faster than the American leaves. Within the same species, the leaves were decomposed more rapidly in the Italian stream. Shredder biomass was always significantly higher on the leaves retrieved from the Italian stream suggesting that shredders had an important role in detritus processing. On the contrary, the comparison between leaf species showed a poor correlation between shredder biomass and leaf breakdown rate. Three hypotheses are proposed. The fact that native leaves were not processed at a faster rate, compared to the exotic leaves, support the notion that shredders do not specialize on litter of a given leaf species, but rather on appropriately conditioned leaf litter regardless of the species. Breakdown rates followed the same rank ordering in each stream : Acer pseudoplatanus > Ulmus minor > Ulmus americana > Acer rubrum indicating the existence of the same hierarchy in the availability of food to macroinvertebrates throughout the year.