Variation in stemflow volume and chemistry in black birch (Betula lenta L.) in relation to tree size and associated bark textural changes
Date
2011
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Stemflow can be described as the transfer of precipitation by gravity along the stem of a plant to the surface of the ground during and as a result of precipitation events. It has been shown to be an important component of the hydrology and nutrient-cycling systems of forested areas. Although stemflow is a spatially-
concentrated source of nutrients and water, its effects are wide-ranging. In addition to having local effects on flora, fauna, and soil characteristics, stemflow can move through the soil matrix through root channels and other chasms in the soil strata. This allows for rapid translocation of water and chemical compounds downslope to wetlands and streams, thereby affecting a greater area. This study focuses on the variation in stemflow volume and chemistry from Betula lenta L. in relation to tree size and associated bark textural changes. Betula lenta L., known commonly as black birch, is a deciduous canopy tree native to the Eastern United States. This species was chosen for the study because it exhibits a dramatic contrast in bark texture as a function of tree size and age. Twenty-four trees were selected for inclusion in the study, encompassing three size-classes. The size-
classes, which are classified as small, medium, and large, are defined respectively by the following values in dbh (diameter at breast height): 10-30, 30-50, 50-70 cm. Twenty-two rain events were sampled for stemflow volume during the period, of which ten were also sampled for chemical ion concentration for Ca2+, K+, Mg2+, and Mn2+. The results of the study showed that the variation in mean stemflow volume among the three size-classes was statistically significant; in support of the hypothesis that the medium size-class would generate the highest mean stemflow volumes. The large size-class generated the lowest mean stemflow volumes, with the small size-class in between. The results of the chemical analyses showed that the large size-class produced higher mean stemflow chemical concentrations for the four ions than for the other two size-classes. This difference was statistically significant, and supported the hypothesis that the large size-class would generate higher mean stemflow chemical concentrations for the four ions. Although the mean chemical concentrations in the medium size-class were consistently higher than for the small size-class, the differences were not statistically significant. The results of this study, while supporting the hypotheses set forth at the inception of the study, also shed light on the ultimate ecological and environmental effects of variations in stemflow volume and chemistry. By combining the volumes and chemistry for the ten precipitation events for which both datasets were collected, a mean value for total stemflow chemical ion input was calculated for the three size-classes. The difference showed the small size-class consistently and statistically significantly, the smallest producer of total stemflow chemical ion input. For Ca2+ and K+, the large size-class was greater than the medium size-class, and for Mg2+ and Mn2+, the medium size-class was greater than the large. The differences for the large and medium classes were not statistically significant. This study clearly showed a correlation between size-class and stemflow volume and chemistry in B. lenta. In addition, this study has the potential to spawn future research related to the intraspecific variations in stemflow parameters for other co-occurring tree species to derive a more accurate picture of forest-stand-scale hydrologic budgets and nutrient-cycling systems. From a forest management perspective, this study has identified possible considerations for determining timber-harvesting cycles, specifically in relation to tree age and nutrient management. From an ecological management perspective, the implications of the variation in stemflow volume and chemistry can be considered from many angles. Among these are plant community assemblages, soil fauna, plant-soil interactions, and invasive-species ecology.