Decomposition rates and colonizing benthic macroinvertebrate assemblages in invasive honeysuckle and native sugar maple leaf packs in southwestern Ohio

Background/Question/Methods

Streams in north temperate deciduous forests receive a peak in allochthonous inputs during autumn leaf fall. Honeysuckle (Lonicera maackii) is an invasive terrestrial plant that has become established in riparian zones in southwestern Ohio. We investigated the impacts of honeysuckle leaf fall on the stream community by comparing the rate of leaf decomposition and macroinvertebrate colonization of sugar maple (Acer saccharum) and honeysuckle. Based on observations in the terrestrial ecosystem, we expected honeysuckle to decompose more rapidly than maple leaves. Secondly, we hypothesized that the benthic macroinvertebrate assemblages colonizing maple leaf packs would be greater in population size and diversity than those colonizing honeysuckle leaf packs. We expected stream macroinvertebrates to prefer to colonize maple leaf packs over honeysuckle leaf packs because maple leaves are relatively high in nitrogen and honeysuckle has alleopathic qualities. We made 15x15cm mesh (5mm) bags and filled them with 5g of dried leaf matter. Four bags of each leaf type were placed pairwise at three sites along Jacoby Creek and the Little Miami River. The bags were removed from each site (in pairs) after one day, three days, ten days, and twenty-one days. We picked benthic macroinvertebrates from the leaf packs, identified them to the taxonomic level of family, and determined family abundances for each sample. After picking, the leaf samples were dried and weighed and the ratio of honeysuckle to maple decomposition was calculated.

Results/Conclusions

We found that honeysuckle leaves decomposed 1.5 times faster than maple leaves and that this difference was significant using a 95% confidence interval. An Analysis of Similarity (ANOSIM) for macroinvertebrates revealed that the abundances of families colonizing maple and honeysuckle leaf packs were not significantly different. Benthic macroinvertebrates did not appear to differentiate between leaves of the two species. Honeysuckle must decompose more rapidly than maple due to differences in some other mechanism such as microbial decomposition or fragmentation due to water flow. If honeysuckle is being decomposed by microbes this may alter the dynamics of the microbial loop, whereas if honeysuckle decomposition occurs at a faster rate because of fragmentation due to water flow, there could be a temporary pulse in food supply for filter feeders.