EAGER: How genetic variation in riparian trees influences stream succession and ecosystem function

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Rivers are generally very old waterways that have been carving through canyons and valleys for thousands of years. Because new streams and rivers are rare, little is known about how they form. One place we can learn about this process is within volcanic landscapes. After catastrophic volcanic eruptions, water from springs and snowmelt carve fresh stream channels. The trees that line the newly formed rivers and streams then provide shade, shelter, and crucial inputs of leaves and nutrients into these aquatic systems. These trees also help shape the rivers themselves by stabilizing banks, creating meanders, and slowing erosion. This project examines willows that have colonized along streams that formed after the eruption of Mount St. Helens. Researchers will study the influence of genetic variation in these trees on the development, ecosystem structure, and successional processes of the associated stream communities. Understanding the impact that the genetics of trees plays in the development of river systems has the potential to transform our understanding of how aquatic ecosystems are structured. This research is also important for the management and conservation of rivers because it explores the critical roles trees play in the formation of river systems following disturbances. This project will also provide outreach that engages the public and middle school students and promotes the participation of girls in STEM. This study explores the novel role the genetics of colonizing trees may play in structuring stream networks; extending genes-to-ecosystems research into evolutionary geomorphology. Using established common gardens and four headwater streams at Mount St. Helens, this study will examine how male and female willow trees differ in terms of litter quality, herbivory-induced leaf chemical changes, and their subsequent influence on in-stream litter-dependent microbes, macroinvertebrates, and leaf litter decomposition. Plants that have been tagged as male or female and clones will be genotyped to determine genetic relatedness, using established primers for determining willow genotypes. CHN composition and condensed tannins will be measured for each willow genotype sampled from the common gardens and litterbags will be incubated in the streams to quantify the impact of genetic and chemical differences on riverine biotic communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.