Deciduous trees are a large and overlooked sink for snowmelt water in the boreal forest

Abstract

The terrestrial water cycle contains large uncertainties that impact our understanding of water budgets and climate dynamics. Water storage is a key uncertainty in the boreal water budget, with tree water storage often ignored. The goal of this study is to quantify tree water content during the snowmelt and growing season periods for Alaskan and western Canadian boreal forests. Deciduous trees reached saturation between snowmelt and leaf-out, taking up 21–25% of the available snowmelt water, while coniferous trees removed <1%. We found that deciduous trees removed 17.8–20.9 billion m3 of snowmelt water, which is equivalent to 8.7–10.2% of the Yukon River’s annual discharge. Deciduous trees transpired 2–12% (0.4–2.2 billion m3) of the absorbed snowmelt water immediately after leaf-out, increasing favorable conditions for atmospheric convection, and an additional 10–30% (2.0–5.2 billion m3) between leaf-out and mid-summer. By 2100, boreal deciduous tree area is expected to increase by 1–15%, potentially resulting in an additional 0.3–3 billion m3 of snowmelt water removed from the soil per year. This study is the first to show that deciduous tree water uptake of snowmelt water represents a large but overlooked aspect of the water balance in boreal watersheds.

Transpiration from subarctic deciduous woodlands: Environmental controls and contribution to ecosystem evapotranspiration

“…In contrast, Kevo showed a substantial water surplus (Table ). Our measurements did not include the snowmelt period, but these sites can reach snowpack depths of >1 m (data not shown), and tree water uptake during this period, especially from deciduous species, can progressively deplete soil water sources (Young‐Robertson et al, ). This decline in soil water content after snowmelt is very clear in the seasonal course of SMD measured in Abisko in 2008 and 2009 (outside our measurement period in Abisko, Figure S5).…”

“…Higher transpiration rates by deciduous broadleaf forests could lead to stronger evaporative cooling locally (Chapin et al, ), although, in a regional context, the effects of the expansion of deciduous broadleaf trees into the tundra zone can be more complex and actually enhance Arctic warming (Swann et al, ). Moreover, increased soil moisture uptake by deciduous trees could lead to faster depletion of snowmelt water during the shoulder season, triggering further hydrological changes (Young‐Robertson, Bolton, Bhatt, Cristóbal, & Thoman, ). Therefore, a greater understanding of the magnitudes and controls of evapotranspiration in deciduous woodlands is needed to predict future changes in land–atmosphere interactions in subarctic forest–tundra ecotones.…”

Differential declines in Alaskan boreal forest vitality related to climate and competition

“…For example, temperature sensitivity of spring tree growth, water use, and successional strategy vary dramatically between the dominant angiosperm and gymnosperm species (Drobyshev, Gewehr, Berninger, Bergeron, & Mcglone, ; Euskirchen, Carman, & Mcguire, ; Hollingsworth, Johnstone, Bernhardt, & Chapin, ; Johnstone & Chapin, ; Trugman et al., ; Young‐Robertson, Bolton, Bhatt, Cristobal, & Thoman, ). Site‐level studies have shown that angiosperm water use greatly exceeds that of gymnosperm species in the Alaskan boreal forest, such that angiosperm species consume >20% of total snowmelt water in comparison to the <1% associated with gymnosperm species (Young‐Robertson et al., ). Understanding angiosperm vs. gymnosperm responses to climate change is particularly important given that recent fires in Alaska have the potential to increase angiosperm coverage by up to 20% (Barrett, Mcguire, Hoy, & Kasischke, ).…”

Towards improved parameterization of a macroscale hydrologic model in a discontinuous permafrost boreal forest ecosystem

“…3c, Table 3). The permafrost coverage is different between the two sub-basins, with approximately 2 and 53 % in the LowP and HighP sub-basins, respectively (Table 1; Rieger et al, 1972;Yoshikawa et al, 2002).…”

“…Location and permafrost extent (light blue shading) in the Caribou Poker Creek Research Watershed, Alaska, and the two subbasins of interest (low permafrost or LowP sub-basin and high permafrost or HighP sub-basin). The permafrost map of CPCRW was produced by a small-scale observation across the watershed (Rieger et al, 1972;Yoshikawa et al, 2002). hydrological model. The sub-grid parameterization method proposed in this study closely fits the MPR approach.…”