Thursday, August 9, 2007 - 10:50 AM

COS 118-9: Riparian forest restoration planting assemblages have effects on in-stream detrial decomposition

Joshua A. Jones and Christopher M. Swan. University of Maryland, Baltimore County

Riparian zones play a vital role in stream ecosystems and perform essential ecosystem services. Riparian restoration projects have been implemented on agricultural lands and the types of species planted directly influence the species of leaf litter entering streams during leaf fall.  Given inter-specific variation in leaf palatability to in-stream consumers and the role these organisms play in decomposing this material, the tree species planted can have implications for in-stream leaf decomposition. While we know litter mixing often results in an antagonistic effect (i.e., litter mixtures decompose slower than single species treatments) for pristine communities, this relationship is not known for restoration communities.  We chose leaf litter from two forest communities, one natural assemblage (Tulip Poplar, Red Maple, Red Oak) and one restoration assemblage (Dogwood, Green Ash, Sycamore), and estimated decay of all single and mixed-species combinations for each separately.  We carried this out in three locations: one stream restored ~2 years ago, one restored ~4 years ago, and a pristine stream.  Our results revealed the emergent effect of litter mixing from the restored community was synergistic (i.e., mixtures lost more mass than the average of the single species) at the pristine site, mass loss was higher in the restoration community at the younger site, but no affect was observed between or within communities at the older site.  These results have a number of implications:  1) the effects of diversity may differ depending on the species composition of the riparian community; 2) the effects of diversity may be a function of time since restoration; and 3) the species within the restored community may affect the way in which decomposition proceeds.  Riparian community structure does show to have an effect on the in-stream ecosystem function, a consequence that needs to be further investigated with species used in riparian restoration projects.