Foundation Species Loss Affects Leaf Breakdown and Aquatic Invertebrate Resource Use in Black Ash Wetlands

Abstract

The invasion by emerald ash borer (Agrilus planipennis) of extensive black ash wetlands in the upper Great Lakes region of North America is expected to alter plant community structure and composition and, therefore, abiotic factors like temperature and hydrology. We conducted two experiments to examine how changes in leaf litter could alter ecosystem function via 1) changes in litter breakdown and 2) aquatic invertebrate feeding. For the first experiment, we placed litter bags containing black ash (Fraxinus nigra), swamp white oak (Quercus bicolor), and lake sedge (Carex lacustris), in either control or clear-cut black ash plots. We found that black ash litter broke down 2-3 times faster than other species and broke down faster in control plots than in clear-cuts. There was no effect of clear cutting on swamp white oak or lake sedge breakdown rates. For the second experiment, we fed shredding caddisfly larvae (Limnephilus indivisus) one of six species: black ash, swamp white oak, lake sedge, balsam poplar (Populus balsamifera), American elm (Ulmus americana), or speckled alder (Alnus incana) for 14 days. Caddisflies had the highest survival and greater resource use when given black ash or speckled alder, which are abundant in black ash wetlands. These results suggest that loss of black ash will alter ecosystem processes via changes in the physical environment, changes in leaf litter properties, and changes in shredder processing rates of leaf litter.