Japan Geoscience Union Meeting 2016

Presentation information

Oral

Symbol A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG22] Material Circulations in Land Ecosystems

Wed. May 25, 2016 9:00 AM - 10:30 AM 101B (1F)

Convener:*Tomomichi Kato(Research Faculty of Agriculture, Hokkaido University), Takashi Hirano(Research Faculty of Agriculture, Hokkaido University), Hisashi Sato(Department of Environmental Geochemical Cycle Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Ryuichi Hirata(National Institute for Environmental Studies), Chair:Takashi Hirano(Research Faculty of Agriculture, Hokkaido University)

9:00 AM - 9:15 AM

[ACG22-01] Understory CO2, sensible heat, and latent heat fluxes in a black spruce forest in interior Alaska

*Hiroki Ikawa1,2, Taro Nakai3,2, Busey Robert2, Kim Yongwon2, Hideki Kobayashi4, Shin Nagai4, Masahito Ueyama5, Kazuyuki Saito6, Hirohiko Nagano7,2, Larry Hinzman2, Rikie Suzuki4 (1.National Institute for Agro-Environmental Sciences, 2.International Arctic Research Center, 3.Hydrospheric Atmospheric Research Center, Nagoya University, 4.Department of Environmental Geochemical Cycle Research, Japan Agency for Marine-Earth Science and Technology, 5.Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 6.Department of Integrated Climate Change Projection Research, Japan Agency for Marine-Earth Science and Technology, 7.Faculty of Horticulture Chiba University)

Keywords:carbon cycle, boreal forest, understory

In this presentation, we would like to introduce our recent publication, Ikawa et al., 2015, Agricultural and Forest Meteorology: http://audioslides.elsevier.com//ViewerSmall.aspx?source=1&doi=10.1016/j.agrformet.2015.08.247
An open black spruce forest, the most common ecosystem in interior Alaska, is characterized by patchy canopy gaps where the forest understory is exposed. This study measured CO2, sensible heat, and latent heat fluxes with eddy covariance (EC) in one of those large canopy gaps, and estimated understory fluxes in a black spruce forest in 2011 – 2014. Then understory fluxes and ecosystem fluxes were compared. The understory fluxes during the snow-free seasons were determined by two approaches. The first approach determined understory fluxes as the fluxes from the canopy gap, assuming that fluxes under the canopy crown also had the same magnitude as the canopy gap fluxes. The second approach determined the understory fluxes by scaling canopy gap fluxes with a canopy gap fraction, assuming that only canopy gaps, which mostly constitutes the forest floor, contribute to fluxes. The true understory fluxes would be in between these two estimates. Overall, the understory accounted for 53 (39 – 66) %, 61 (45 – 77) %, 63 (45 – 80) %, 73 (56 – 90) %, and 79 (59 – 98) % of the total net ecosystem productivity (NEP), gross primary productivity (GPP), ecosystem respiration (RE), sensible heat flux (H), and latent heat flux (LE), respectively. The ratio of understory NEP (NEPU) to the ecosystem NEP (NEPE) and similarly calculated LEU/LEE during the daytime increased with vapor pressure deficit (VPD) at low VPD conditions (~ 2000 Pa) at half-hourly temporal scale. At high VPD conditions, however, NEPU/NEPE decreased with VPD, whereas LEU/LEE was maintained at the high level even at high VPD conditions. Despite large ranges of the estimates for the understory contributions, we conclude that the understory plays an important role in the carbon and energy balances of the black spruce ecosystem, and their contribution highly depends on the level of VPD.