REU Projects 2015

2015 Projects:

Asymbiotic Nitrogen Fixation in Yosemite National Park: Mentors: Dr. Carolin Frank (UC Merced) and Dr. Stephen C. Hart (UC Merced)

Climate Responses of Sierra Nevada Conifer Forests: Mentor: Dr. Emily Moran (UC Merced)

Distribution and Frequency of Willow Species Browse on Tuolumne River, and Dana and Lyell Fork Segments: Mentors: Tim Kuhn (NPS) and Joy Baccei (NPS)

Effects of Altitude on Monkeyflower Mating Systems and Pollination: Mentor: Dr. Jason Sexton (UC Merced)

Forest Effects on Snow Accumulation and Melt: Mentors: Jim Roche (NPS, UC Merced) and Dr. Roger Bales (UC Merced)

Influence of the Rim Fire on Great Gray Owls and Spotted Owls: Mentor: Sarah Stock (NPS)

Red-fir Forest Structure and Health in Active Fire Regime Landscapes: Mentor: Marc Meyer (USDA Forest Service Pacific Southwest Region)

Effects of Fire on Seedling Germination of the Giant Sequoia: Mentor: Thomas Reyes (NPS)

 

Asymbiotic Nitrogen Fixation in Yosemite National Park

 

Mentors: Dr. Carolin Frank (UC Merced) and Dr. Stephen C. Hart (UC Merced)

 

All plants and animals live in association with bacteria or ‘microbiomes’ that are essential for health, development, and disease protection. For most organisms, especially those in natural ecosystems, the role of such symbiotic bacteria has not been investigated. Recently, scientists at UC Merced discovered that the subalpine conifer limber pine hosts bacteria called endophytes inside its needles, and that these bacteria can reduce, or ‘fix’ atmospheric nitrogen (N) to ammonium. Nitrogen is essential to all life on Earth, but is a growth-limiting nutrient in most ecosystems. The discovery that conifers host N-fixing bacteria is important since previously only a small number of plants—legumes for example—were known to host them, and only inside specialized organs called nodules. Our hypothesis is that the ability to fix N is widespread in conifers, and that fixation rates depend on ecosystem N supply and possible other co-factors (e.g., phosphorus, molybdenum, or iron) that are required for N fixation. This project will assay and compare foliar and soil rates of N fixation across conifer species and environmental gradients of soil nutrient availability and climate (temperature and moisture) in Yosemite National Park (YNP). We will use the acetylene reduction method and measurements of the natural abundance of the stable isotope N-15 to evaluate N fixation rates. This project will include field work in remote sites within YNP, as well as laboratory analyses to be conducted at UC Merced.

 

 

 

Climate Responses of Sierra Nevada Conifer Forests

 

Mentor: Dr. Emily Moran (UC Merced)

 

This project will examine how climate variation affects growth, survival, and/or reproduction in mountain conifer species. It will make use of four long-term plots located just north of the Yosemite Valley: two diverse lower-elevation stands (comprised of white fir, cedar, sugar & ponderosa pine, Douglas-fir, and oak) and two higher-elevation stands dominated by white fir. The student will have access to long-term tree and seedling census data (going back 20 years in the case of adult trees) and long-term climate data. The student will also have the opportunity to collect new data on seedling recruitment (which is likely to have been affected by the recent drought) and/or adult growth (from tree-bole increment cores).

 

 

 

Distribution and Frequency of Willow Species Browse on Tuolumne River, and Dana and Lyell Fork Segments

 

Mentors: Tim Kuhn (NPS) and Joy Baccei (NPS)

 

Resources Management and Science staff at Yosemite National Park are seeking to improve understanding of the distribution of willows (Salix spp.) and frequency of browse within meadow systems on the Tuolumne River (i.e., Tuolumne Meadows), and on the Lyell Fork. Willow species have been reported as an important component of streambank stability, exerting hydrogeomorphic effects on channel roughness and shear forces during high flow events. Willows are also reported to provide important structural habitat for numerous terrestrial and avian wildlife species, and to contribute allocthonous organic material valuable to aquatic invertebrates. Browse of apical meristems may affect annual productivity of willows, and thereby reduce hydrogeomorphic control exerted by willows or habitat quality. An investigation of the distribution of willows and frequency of browse would contribute information vital to the on-going management of these river corridors. This research complements an on-going experimental (i.e., exclosure) study among park and academic researchers on the effects of browse on productivity and on hydrogeomorphic contribution by willows. The student involved on this project may also gain additional field and data analysis experience by assisting park staff with the installation and survey of permanent channel and meadow cross-sections in meadows on the Lyell Fork of the Tuolumne River.

 

 

 

Effects of Altitude on Monkeyflower Mating Systems and Pollination

 

Mentor: Dr. Jason Sexton (UC Merced)

 

Variation in environmental quality can have strong effects on the ecology of plant reproduction and the evolution of mating strategies. This project will investigate whether altitude (elevation) affects mating systems among Yosemite monkeyflower (Mimulus) populations.  This will be a comparative project among several monkeyflower (Mimulus) species found within Yosemite National Park.  The student investigator will collect data across different altitudes in the park to understand how patterns of floral architecture, seed production, and pollination opportunities shift across this climate gradient and towards species range limits.  This study will further inform our understanding of how plants tolerate and respond to environments that differ greatly.

 

 

Forest Effects on Snow Accumulation and Melt

 

Mentors: Jim Roche (NPS, UC Merced) and Dr. Roger Bales (UC Merced)

 

Forest canopy density affects accumulation and melt of the seasonal snowpack that, in turn, impacts water availability for vegetation and runoff. This project will assess snow depth data in areas of differing forest canopy cover. The prospective students will gather forest canopy cover data in the field at instrumented locations and areas where snow depth has been determined by remote sensing methods such as LiDAR. Data analysis will consist of correlating snow depth and forest canopy cover metrics. As time allows, we may collect additional canopy cover data in plots burned in the recent Rim Fire in order to assess potential impacts of fire on snow accumulation and melt.

 

 

 

Influence of the Rim Fire on Great Gray Owls and Spotted Owls

 

Mentor: Sarah Stock (NPS)

 

The 2013 Rim Fire burned over 78,000 acres within Yosemite, altering important wildlife habitat. Two species of conservation concern that could be strongly affected are the Great Gray Owl and the Spotted Owl. Approximately 20% of the park’s known Great Gray Owl nesting sites is within or immediately adjacent to the fire footprint, as are about 50% of known Spotted Owl nest sites. Spotted Owls nest in similar habitat to Great Grays Owls, but studies have suggested they may be more resilient to fire within their breeding areas. The REU student will be responsible for surveying Great Gray Owls and Spotted Owls in burned and unburned areas and characterizing any differences or similarities in occupancy and habitat use.

 

 

 

Red-fir Forest Structure and Health in Active Fire Regime Landscapes

 

Mentor: Marc Meyer (USDA Forest Service Pacific Southwest Region)

 

Contemporary, unlogged landscapes with an active fire regime provide ideal reference sites for quantifying the Natural Range of Variation (NRV) with respect to stand and landscape-level variables in Sierra Nevada forests. Recent studies within these active fire regime landscapes have provided numerous insights in the NRV of mixed conifer and yellow pine forests, but currently this information is lacking for red fir (Abies magnifica) forest ecosystems in the bioregion. Such information is timely since many red fir forests in the region are exhibiting early signs of moisture stress and compromised health. We propose to address this information need by quantifying stand and health variables in reference red fir forests that have burned within their historic fire return interval. Our aim is to provide estimates of the NRV of red fir forest structure and health across a range of red fir forest types, topographies, and geographic regions of the Sierra Nevada. Results of this study will be supportive of forest management planning efforts in the Sierra Nevada.

 

Effects of Fire on Seedling Germination of the Giant Sequoia

Mentor: Thomas Reyes (NPS)

Giant sequoias (Sequoiadendron giganteum) can become ancient and massive trees but only exist in 74 groves scattered across the Sierra Nevada. A recent study of the three sequoia groves in Yosemite National Park provided a complete tree demography as well as valuable insight on the health and status of these unique ecosystems.  A startling finding was that there are few young trees and no seedlings in the Merced and Tuolumne Groves, likely a result of insufficient fire in past decades.  A long history of fire suppression has left these groves with few canopy openings for new seedlings to germinate and thrive. As a consequence of actions taken to fight the massive Rim Fire in 2013, these two adjacent groves (the Merced Grove prevented from burning; the Tuolumne Grove back-burned as a protection measure) have serendipitously become a controlled study testing the recommendation for increased clearing and understory burning. This study proposes to take advantage of this window of opportunity to examine the effects of fire on giant sequoia seedling germination at these groves.  The student will also be given the opportunity to develop their own research question that will help guide future management actions and ensure the development a healthy new generation of giant sequoias.