• Roles of neighboring plants and temperature on growth and survival of white spruce seedlings along elevational gradients in Alaska

      Okano, Kyoko; Bret-Harte, M. Syndonia; Mulder, Christa P. H.; Juday, Glenn P. (2018-05)
      Seedlings are the most vulnerable stage of a tree's life and their successful survival and growth are critical to support future forests. Recent rapid warming in Alaska has promoted the movement of treeline upward in elevation, while trees at low elevations have decreased their growth. Understanding the direct effects of warming and the indirect effects induced by warming, such as species interactions, on the dominant treeline species, white spruce (Picea glauca) is key to sustaining boreal forests, from low elevations to above current treeline. The objectives of my thesis were to assess the roles that warming, neighboring interaction, habitat type, elevation and season play in the survival and growth of white spruce in Denali National Park and Preserve and Fairbanks, Alaska, USA. I planted spruce seedlings where I manipulated summer temperature and neighbor plants at seven sites (forest or tundra) along an elevational gradient that crossed treeline. I measured survival after winter and summer seasons, and harvested the seedlings for biomass after the third growing season. I found that competition -- particularly light competition where seedlings were shaded -- was the most important factor for seedling growth, while along elevational gradients, temperature and season had inverse effects on their survival: more seedlings at high elevations survived in summer and under warming, but more seedlings at low elevations survived in winter and under ambient temperatures. More seedlings with neighbors survived in summer and in forests, suggesting facilitation through shading. I found some evidence for a trade-off between growth and survival. Seedlings with a high relative growth in height (RGR height) in 2012 had a lower survival rate than seedlings with a low RGR height in the following hot and dry summer of 2013. More seedlings planted with neighbors that had a small diameter in 2012 also survived in 2013, but not without neighbors. These results suggest that a trade-off between survival and growth occurred only when competition for water can be expected. No difference in survival was found after the second winter and third summer. Altogether, I concluded the most important factor affecting seedling growth in my experiment was light competition, while the most important factors for seedling survival were warming and water availability for the first two years in the subarctic montane and interior Alaska.
    • The transport of aerosols into Denali National Park and Preserve

      Wallace, Ashley N. (2012-05)
      Denali National Park and Preserve (DNPP) is a federally protected Class I visibility area in Alaska. The Regional Haze Rule in the U.S. Clean Air Act requires the visibility in all Class I areas to be 'pristine.' According to the EPA DNPP does not have `pristine' air. Therefore, the Alaska Department of Environmental Conservation conducted a 15-month study of particulate matter smaller than 2.5 micrometers (PM2.5) from March, 2008 through June, 2009 to identify the aerosol sources in DNPP. DRUM aerosol impactors collected aerosols at four sites (DNPP Headquarters, Trapper Creek, McGrath, and Lake Minchumina) around DNPP. The aerosol data underwent a series of analyses including: a seasonal analysis of elemental composition, an analysis of potential source regions as identified by the HYbrid Single-Particle Lagrangian Integrated Trajectory ectory (HYSPLIT) model, and Chemical Mass Balance (CMB) analyses to identify specific aerosol sources. These analyses show that the predominant sources of aerosols impacting DNPP during winter and spring lie outside of Alaska and during summer and fall are from outside and local sources. Outside sources include deserts in China and industry in Russia. Because many of the aerosols impacting DNPP are produced internationally, the visibility in DNPP cannot be restored without international collaboration.