Understory CO2, sensible heat, and latent heat fluxes in a black spruce forest in interior Alaska

Abstract

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.

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

“…When explaining seasonal variability in T birch / ET eco , we found that T birch / ET eco strongly depended on VPD and PAR, with T birch / ET eco saturating at high VPD, but this environmental control on T birch / ET eco was stronger in Abisko. Therefore, our results show an increased relative role of mountain birch in controlling ecosystem evapotranspiration as evaporative demand increases, especially in denser forests, in contrast with studies on waterlogged peatlands where understorey contribution increases with VPD (Ikawa et al, ). In our sites, mountain birch roots possibly access soil moisture at greater depths (Hunziker, Sigurdsson, Halldorsson, Schwanghart, & Kuhn, ), supplying water to meet the increasing evaporative demand and causing the increase in T birch / ET eco .…”

Quantifying the Feedback Between Rice Architecture, Physiology, and Microclimate Under Current and Future CO2 Conditions

“…By doing so, we were able to get an understanding of the in‐canopy to above‐canopy interactions occurring in the ambient and FACE setup. Footprint analysis showed that nearly all of our measurements originate within 5 m from the IRGASON device (Figure S5; Matthes et al, , Ikawa et al, ). Cospectral analysis revealed minimal flux loss at higher frequencies.…”

“…The points represent the measurement heights for air temperature, relatively humidity, CO 2 concentration and photosynthetic active radiation. Ikawa et al, 2015). Cospectral analysis revealed minimal flux loss at higher frequencies.…”

Evapotranspiration in a rice paddy field over 13 crop years

“…The rice paddy water was drained in late August and no further irrigation was applied until harvesting. Nonetheless, no relation was found between the ET / E P values and the normalized soil moisture data calculated following Ikawa et al 2015 . The variation in the timing of the water drainage was also not enough to explain the variation of the ET / E P values because 2009 exhibited higher ET / E P values than expected given the precipitation measurements, even though the water drainage started early August 12 .…”