The characteristics and fate of leaf litter inputs to boreal shield streams in relation to riparian stand structure

The implementation of riparian buffer guidelines is currently under review and partial-harvest logging is being considered as an alternative riparian management strategy. This thesis is an investigation of the input and decomposition rates of leaves within small headwater streams of Boreal Shield (mixedwood) forests. The goals of this thesis were (1) to provide information on the inputs of litter to Boreal Shield streams to determine if partial-harvest logging of commercial trees within riparian reserves has the potential to cause significant changes to litter inputs and (2) to measure the decomposition rates of alder, birch and poplar leaves and associated macroinvertebrate communities within undisturbed Boreal Shield streams.;Commercial deciduous tree species and understorey species were important to these small streams as they each accounted for approximately 50% of the total inputs of deciduous litter. Distance-weighted deciduous basal area was the best predictor of overstory deciduous litter (r2 = 0.597, p = <0.001), indicating that the size, abundance and proximity of deciduous trees to streams are important to the inputs of deciduous litter. The inputs of leaf litter to Boreal Shield streams can be effectively predicted by stem basal area. A linear regression model based on the basal area of deciduous tree is presented that can be useful to determine how many deciduous trees to retain within a riparian area to maintain the inputs of leaf litter at or near pre-harvest levels.;The rate of decomposition (k/day) of the three leaf species in coarse-mesh leaf packs suggests that a processing continuum exists in Boreal Shield streams throughout winter, where alder and birch were medium decomposing species (k = 0.0063 and 0.0053/d, respectively) and poplar decomposed more slowly (k = 0.0032/d). Birch decomposed faster in fine-mesh leaf packs. Macroinvertebrate communities on coarse-mesh leaf packs were significantly different between fall and spring collection dates regardless of leaf species. Birch leaf packs supported a higher density (individuals/g of leaves) of invertebrates in the fall while poplar supported greater shredder abundances (individuals/coarse-mesh leaf pack) in the spring.;The research shows that overstory and understorey deciduous riparian vegetation are equally important to leaf litter inputs to streams and that the diversity of leaves entering streams may be important in providing a sustained source of available leaf material to aquatic invertebrates. Careful consideration should be taken to maintain the inputs of leaf litter from overstory deciduous trees in the event of partial harvesting in the riparian area and to ensure that the species richness of leaf litter from deciduous trees is not altered as a result of the removal of specific commercial tree species from the riparian area.