Doctoral Dissertation Research: High-Elevation Deciduous Forest Structure: A Test of the Slow-Seedling Hypothesis

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This doctoral dissertation research will investigate the relative contributions and interactions of seedling environment, canopy structure, climate variation, and the type and history of disturbance as factors contributing to dominance of deciduous broad-leaved species as opposed to needle-leaved conifers in alpine forests. Conventional understanding has held that alpine forests are dominated by needle-leaved conifers, but at some locales, broad-leaf alpine forests exist. A "slow-seedling" hypothesis articulated by William Bond posits that deciduous broad-leaved seedlings are superior competitors, largely because of their greater adaptability to localized changes in the availability of resources like light and soil moisture, while needle-leaved conifers are more tolerant to stressors like low temperatures and soil acidity. This project will increase knowledge regarding how species respond to variability in environmental conditions along an elevation gradient, especially at different stages of life. The project will help advance understanding in the geographic and biological sciences by improving basic knowledge of the controls on forest composition and structure of sensitive high-elevation forests. More specifically, the project will improve understanding of tree regeneration in alpine forest environments, especially when they are subjected to changes in climate or other environmental conditions. The project also will provide new insights regarding the ways in which shifts in the relative dominance of either deciduous broad-leaved species or needle-leaved conifers in the alpine environment would affect radiation absorption, the seasonality of carbon cycling, snow melt, and the susceptibility of forests to disturbance from fire or insect outbreaks. Data from this project will become available to other scholars through a set of databases. The project will provide special education and training opportunities for two undergraduate students, and an educational module will be developed and tested in middle-school classes. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.The doctoral student whose dissertation research will be supported by this award will examine the specific ecological correlates important for seedling establishment, including light, elevation, canopy cover, soil nutrients, and landscape curvature. She will measure how structural properties differ between forest types across the elevation gradient, and she will examine the response of trees to climatic and disturbances histories in each forest type using tree-ring methods. The research will be conducted at eight sites in the forests on the slopes of the Japanese Alps in Chubu-Sangaku National Park in central Japan in collaboration with an experienced Japanese ecologist, Koichi Takahashi. Although conducted in Japan, the research findings will have utility to better understand forest dynamics around the nation, including in alpine forests of the U.S.