This project addresses an important question, based on surprising preliminary findings, about the role of deciduous shrubs and trees in the water balance of Arctic ecosystems. In the tundra and boreal forest, large amounts of water are released during a short period (2 to 3 weeks) in spring when the winter's snow rapidly melts. Most of this snowmelt water flows out through rivers, because the ground is mostly frozen during snowmelt, while the remaining sizable fraction of snowmelt water is thought to be lost through evaporation or sublimation, or to groundwater recharge in those areas where permafrost doesn't prevent it. Uptake and storage by plants at this time of year has been considered negligible. Preliminary data from a small watershed in interior Alaska shows that deciduous trees take up 25-40% of the snowmelt water prior to leaf out and draw from these stores throughout the summer, including during lengthy dry periods. Preliminary data also show that arctic deciduous shrub stems rise and fall diurnally as the snow melts, which the investigators suspect is linked with water uptake, but the link between shrub water content and snowmelt is unknown. Water uptake by deciduous trees and shrubs has important ecosystem implications, from the water balance to climate feedbacks to coping strategies of deciduous vegetation during dry periods. The observed expansion of deciduous shrubs and trees in Alaska during the 20th century is likely altering the water balance and Arctic ecosystem in ways currently not being considered.
The investigators ask: To what extent do deciduous vegetation (trees and shrubs) use snowmelt water? What are the consequences of deciduous tree and shrub expansion on the ecohydrology of northern ecosystems? What are the plant ecological consequences (such as buffering from weather variability) of the storage and use of snowmelt water? They propose to characterize shrub and tree physiology (water uptake, water stress, transpiration, growth, photosynthesis), as well as environmental variables, including snowmelt, across a climate gradient in Alaska. These data will be integrated into statistical models that will quantify the controls on snowmelt water uptake by trees and shrubs, and will quantify the role of snowmelt water in sustaining physiological activity during dry periods. The proposal addresses emerging avenues of ecohydrology by quantifying the role of deciduous plants on the pathways and reservoirs of snowmelt water, and by assessing the potential for stored snowmelt water to buffer vegetation during dry periods. The transformative nature of the proposed work lies in reconsidering the dogma that vegetation plays a minor role in snowmelt hydrological processes. This reconsideration is salient given the observed widespread expansion of deciduous trees and shrubs and observed advancing snowmelt dates. The project would support two early career investigators, a PhD student, and 3 undergraduate students. Several distinct outreach activities are proposed, including teacher workshops aimed at enhancing the science curriculum of local and rural Alaskan K-12 classrooms, a traveling museum exhibit, an art exhibit featuring the work of the lead PI, and a partnership with a science writer for statewide dissemination of one article per year in statewide (Alaska) news outlets.
This project will study varied climate zones in Alaska to measure snowmelt water uptake and flux by studying deciduous vegetation in the arctic and subarctic. Each summer from 2015-2017 researchers will conduct four week-long measurement campaigns at each site. Fieldwork will occur at 4 sites in the sub-arctic and arctic, along the highway system. Sites will be established in spring of 2015 and will be measured regularly through the final year. Some of the visited sites are part of the LTER network where the team will utilize resources, like ATV’s, historic data, and lodging (at Toolik).
