Effects of bark texture and lichen cover on stem flow volume and chemistry.

Abstract

During an eight week period, stem flow samples were collected among three different tree species of varying bark textures at the Ameriflux Tower site at the University of Michigan Biological Station in Pellston, MI, in order to see how bark texture and lichen cover affected stem flow volume and chemistry. Trends in volume, nitrogen concentration, and nitrogen input were seen along the gradient of tree bark texture. Trees selected were used as gradient of bark texture. Species of Fagus grandifolia (beech), Poplar grandidentata (aspen), and Querus rubra (oak) were used to explain differences in trends. Gutter-like apparatuses were built for eight specimens of each species to collect representative samples of stem flow that reached the base of the tree. Two sets of stem flow samples were collected from two events, one of which was short duration, high intensity event, whereas the other was a long duration, low intensity event; both events received nearly the same volume of precipitation. These samples were analyzed for total nitrogen content. Volumes of stem flow increased along the gradient as bark coarseness decreased and volumes for each species, on average, were significantly higher in the first event than in the second event. Nitrogen concentration along the gradient increased as bark coarseness increased and concentrations per species were significantly higher on average in the second event. Nitrogen concentration along the gradient of trees also increased as average lichen cover increased. Nitrogen inputs were significantly higher in the first event, despite higher concentrations in the first event. Stem flow volume played a more significant role in nitrogen input than concentration. The lower nitrogen concentration in the second event suggests that lichens release more nitrogen into stem flow during long, low intensity rain events. However, the high intensity rain events have higher inputs of nitrogen, implying that lichens also take up more nitrogen in low intensity rain events. With further studying, implications about soil biodiversity and root biomass density can be further explored with this knowledge of stem flow volume and resolved.