In the Northeastern United States, invasive Acer platanoides (Norway Maple) trees have been out-competing native Acer saccharum(Sugar Maple) through changes in leaf phenology which alter ecosystem level processes such as seasonal changes in light and availability of belowground resources. Here we are evaluating the effect of the invasive trees on litter decomposition rates (LDR), which can be used as a proxy for availability of belowground resources. Specifically, we are testing two hypotheses: 1. The Home Field Advantage (HFA) hypothesis states that litter decomposition is accelerated underneath a conspecific canopy (home) that underneath a heterospecific canopy (away; and 2) the substrate quality-matrix quality interaction (SMI) hypothesis states that decomposers should break down the substrate (leaf litter) more slowly as the substrate and the matrix (environmental litter) become increasingly different.
The field test consisted of a reciprocal transplant decomposition experiments using litterbags with varying proportions (0, 25, 50, 75 and 100%) of Norway Maple and Sugar Maple leaves combinations placed under the canopy of Norway Maple and Sugar Maple trees in the Crum Woods of Swarthmore College. We deployed 380 litterbags collected 4 times during 24 months. We quantified decomposition by mass loss and performed fiber analyses to characterize the amount of soluble cell contents, lignin, hemicellulose, and cellulose.
We found no significant difference in mass loss during the decomposition of each of the five leaf litter combinations, regardless of the canopy under which they decomposed. The fiber analyses showed that cellulose and lignin were not significant between the five litter combinations. However, the bag containing 100% of Norway maple leaves had the highest proportion of soluble cell contents and nitrogen and both were significantly different than that of the bags containing 100% of sugar maple leaves. Our data does not support either the HFA or the SMI hypotheses. It is not clear yet how Norway maple leaves are influencing the decomposition of native species and the availability of belowground resources