Seasonal changes in camera-based indices from an open canopy black spruce forest in Alaska, and comparison with indices from a closed canopy evergreen coniferous forest in Japan

Nagai, Shin; Nakai, T.; Saitoh, Taku M.; Busey, R.; Kobayashi, Hideki; Suzuki, Rikie; Muraoka, Hiroyuki; Kim, Yongwon

doi:10.1016/j.polar.2012.12.001

Cited by 13 publications

(8 citation statements)

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“…The year-to-year variation in the timing of flowering, leaf flush, and leaf fall for the whole canopy and for each tree species in deciduous forests can be detected by analyzing RGB time series (Ide and Oguma 2010 ; Nagai et al 2011a ; Inoue et al 2014 ). The seasonal variation of these values correlates well with that of gross primary production (GPP) in this forest (Saitoh et al 2012 ), deciduous coniferous forest (larch ( Larix kaempferi ) forest; Ide and Oguma 2011 ), and evergreen coniferous forest (Japanese cedar forest; Saitoh et al 2012 ; Nagai et al 2013a ). Nagai et al ( 2013a ) examined differences between the seasonal variation in RGB-derived indices between a Japanese closed canopy evergreen coniferous forest (Japanese cedar, Cryptomeria japonica ) and an Alaskan open canopy evergreen coniferous forest (black spruce, Picea mariana ).…”

Section: Phenological Observations By Digital Cameras and Spectral Rasupporting

confidence: 52%

“…The seasonal variation of these values correlates well with that of gross primary production (GPP) in this forest (Saitoh et al 2012 ), deciduous coniferous forest (larch ( Larix kaempferi ) forest; Ide and Oguma 2011 ), and evergreen coniferous forest (Japanese cedar forest; Saitoh et al 2012 ; Nagai et al 2013a ). Nagai et al ( 2013a ) examined differences between the seasonal variation in RGB-derived indices between a Japanese closed canopy evergreen coniferous forest (Japanese cedar, Cryptomeria japonica ) and an Alaskan open canopy evergreen coniferous forest (black spruce, Picea mariana ). However, insufficient comparative studies have been conducted in Japan.…”

Section: Phenological Observations By Digital Cameras and Spectral Rasupporting

confidence: 52%

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Review: advances in in situ and satellite phenological observations in Japan

et al. 2015

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To accurately evaluate the responses of spatial and temporal variation of ecosystem functioning (evapotranspiration and photosynthesis) and services (regulating and cultural services) to the rapid changes caused by global warming, we depend on long-term, continuous, near-surface, and satellite remote sensing of phenology over wide areas. Here, we review such phenological studies in Japan and discuss our current knowledge, problems, and future developments. In contrast with North America and Europe, Japan has been able to evaluate plant phenology along vertical and horizontal gradients within a narrow area because of the country’s high topographic relief. Phenological observation networks that support scientific studies and outreach activities have used near-surface tools such as digital cameras and spectral radiometers. Differences in phenology among ecosystems and tree species have been detected by analyzing the seasonal variation of red, green, and blue digital numbers (RGB values) extracted from phenological images, as well as spectral reflectance and vegetation indices. The relationships between seasonal variations in RGB-derived indices or spectral characteristics and the ecological and CO2 flux measurement data have been well validated. In contrast, insufficient satellite remote-sensing observations have been conducted because of the coarse spatial resolution of previous datasets, which could not detect the heterogeneous plant phenology that results from Japan’s complex topography and vegetation. To improve Japanese phenological observations, multidisciplinary analysis and evaluation will be needed to link traditional phenological observations with “index trees,” near-surface and satellite remote-sensing observations, “citizen science” (observations by citizens), and results published on the Internet.

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Section: Phenological Observations By Digital Cameras and Spectral Rasupporting

confidence: 52%

Section: Phenological Observations By Digital Cameras and Spectral Rasupporting

confidence: 52%

Review: advances in in situ and satellite phenological observations in Japan

et al. 2015

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“…Snow melt and continuous snow cover occurs in late April to May and in October [14,41], respectively. The leaf emergence of understory plants occurs soon after the snow melt and senescence starts in late August [22,42].…”

Section: Study Sitementioning

confidence: 99%

In Situ Observations Reveal How Spectral Reflectance Responds to Growing Season Phenology of an Open Evergreen Forest in Alaska

et al. 2018

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Plant phenology timings, such as spring green-up and autumn senescence, are essential state information characterizing biological responses and terrestrial carbon cycles. Current efforts for the in situ reflectance measurements are not enough to obtain the exact interpretation of how seasonal spectral signature responds to phenological stages in boreal evergreen needleleaf forests. This study shows the first in situ continuous measurements of canopy scale (overstory + understory) and understory spectral reflectance and vegetation index in an open boreal forest in interior Alaska. Two visible and near infrared spectroradiometer systems were installed at the top of the observation tower and the forest understory, and spectral reflectance measurements were performed in 10 min intervals from early spring to late autumn. We found that canopy scale normalized difference vegetation index (NDVI) varied with the solar zenith angle. On the other hand, NDVI of understory plants was less sensitive to the solar zenith angle. Due to the influence of the solar geometry, the annual maximum canopy NDVI observed in the morning satellite overpass time (10-11 am) shifted to the spring direction compared with the standardized NDVI by the fixed solar zenith angle range (60−70 •). We also found that the in situ NDVI time-series had a month-long high NDVI plateau in autumn, which was completely out of photosynthetically active periods when compared with eddy covariance net ecosystem exchange measurements. The result suggests that the onset of an autumn high NDVI plateau is likely to be the end of the growing season. In this way, our spectral measurements can serve as baseline information for the development and validation of satellite-based phenology algorithms in the northern high latitudes.

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“…We determined snow-free seasons based on images obtained by a digital camera system (Coolpix 4500; Nikon, JAPAN) with a fisheye lens (FC-E8; Hayasaka Rikoh, JAPAN) mounted on the top of the scaffold tower (Nagai et al, 2013) (Table 1). This study focused on snow-free season; however, other seasons (snow-disappearing, snow-covering, and snow-covered seasons) were also determined for the purpose of quality controls of EC data.…”

Section: Snow-free Seasonsmentioning

confidence: 99%

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

Ikawa

Nakai

Busey

et al. 2015

Agricultural and Forest Meteorology

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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.

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Seasonal changes in camera-based indices from an open canopy black spruce forest in Alaska, and comparison with indices from a closed canopy evergreen coniferous forest in Japan

Cited by 13 publications

References 40 publications

Review: advances in in situ and satellite phenological observations in Japan

Review: advances in in situ and satellite phenological observations in Japan

In Situ Observations Reveal How Spectral Reflectance Responds to Growing Season Phenology of an Open Evergreen Forest in Alaska

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

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