How can habitat size influence leaf litter decomposition in five mid-Appalachian springs (USA)? The importance of the structure of the detritivorous guild

Although habitat size is known to influence both structural and functional properties of ecosystems, there have been few attempts to assess the influence of habitat size on ecosystem processes. Here we investigated the relationships between leaf litter decomposition and ecosystem surface area, macroinvertebrates and physico-chemical factors in five freshwater springs located in Huntingdon County (Pennsylvania, U.S.A.). Leaves of Ulmus americana L. were used to study leaf litter breakdown with the litter-bag technique. Field work was carried out at one sampling station per spring, each with eight replicates per sampling time (3, 20, 40 days), from April to May 2004. American elm leaves decomposed at different rates in the different springs, varying inversely with the spring area. The leaf bags were colonized by 16 taxa of benthic macrofauna, amongst which scrapers and shredders were the most common guild. Macroinvertebrate species richness co-varied with spring area, but not with other physico-chemical variables. Moreover, a significant inverse relationship was observed between American elm leaf decay rate and taxonomic richness. In the studied springs, habitat area was an ecosystem feature indirectly affecting detritus processing by influencing the structure of the detrital food web within the systems.