Effects of climate variability on carbon sequestration among adjacent wet sedge tundra and moist tussock tundra ecosystems

Kwon, Hyojung; Oechel, W. C.; Zulueta, R. C.; Hastings, Steven J.

doi:10.1029/2005jg000036

Cited by 85 publications

(118 citation statements)

References 109 publications

(168 reference statements)

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“…The vegetation communities at Ivotuk are dominated by tussock sedge, dwarf shrubs and mosses [23]. All four tower sites are located on areas of continuous permafrost with an active layer thaw depth of approximately 37 cm [52] for Barrow-BEO/Barrow-BES, 43 cm for Atqasuk [53] and 25 cm for Ivotuk [50]. There is no substantial polygon formation located here, with the site consisting of a gentle northwest facing slope and a wet meadow on the margins of a stream.…”

Section: Study Areamentioning

confidence: 99%

Mapping Arctic Tundra Vegetation Communities Using Field Spectroscopy and Multispectral Satellite Data in North Alaska, USA

et al. 2016

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Abstract:The Arctic is currently undergoing intense changes in climate; vegetation composition and productivity are expected to respond to such changes. To understand the impacts of climate change on the function of Arctic tundra ecosystems within the global carbon cycle, it is crucial to improve the understanding of vegetation distribution and heterogeneity at multiple scales. Information detailing the fine-scale spatial distribution of tundra communities provided by high resolution vegetation mapping, is needed to understand the relative contributions of and relationships between single vegetation community measurements of greenhouse gas fluxes (e.g.,~1 m chamber flux) and those encompassing multiple vegetation communities (e.g.,~300 m eddy covariance measurements). The objectives of this study were: (1) to determine whether dominant Arctic tundra vegetation communities found in different locations are spectrally distinct and distinguishable using field spectroscopy methods; and (2) to test which combination of raw reflectance and vegetation indices retrieved from field and satellite data resulted in accurate vegetation maps and whether these were transferable across locations to develop a systematic method to map dominant vegetation communities within larger eddy covariance tower footprints distributed along a 300 km transect in northern Alaska. We showed vegetation community separability primarily in the 450-510 nm, 630-690 nm and 705-745 nm regions of the spectrum with the field spectroscopy data. This is line with the different traits of these arctic tundra communities, with the drier, often non-vascular plant dominated communities having much higher reflectance in the 450-510 nm and 630-690 nm regions due to the lack of photosynthetic material, whereas the low reflectance values of the vascular plant dominated communities highlight the strong light absorption found here. High classification accuracies of 92% to 96% were achieved using linear discriminant analysis with raw and rescaled spectroscopy reflectance data and derived vegetation indices. However, lower classification accuracies (~70%) resulted when using the coarser 2.0 m WorldView-2 data inputs. The results from this study suggest that tundra vegetation communities are separable using plot-level spectroscopy with hand-held sensors. These results also show that tundra vegetation mapping can be scaled from the plot level (<1 m) to patch level (<500 m) using spectroscopy data rescaled to match the wavebands of the multispectral satellite remote sensing. We find that developing a consistent method for classification of vegetation communities across the flux tower sites is a challenging process, given the spatial variability in vegetation communities and the need for detailed vegetation survey data for training and validating classification algorithms. This study highlights the benefits of using fine-scale field spectroscopy measurements to obtain tundra vegetation classifications for landscape analyses and use in carbon flux scaling studies. Improved...

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Section: Study Areamentioning

confidence: 99%

Mapping Arctic Tundra Vegetation Communities Using Field Spectroscopy and Multispectral Satellite Data in North Alaska, USA

et al. 2016

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“…Chapin et al, 2000;McGuire et al, 2003). Major conclusions of these experiments are that the fluxes, particularly those of methane, show a high spatial variability due to heterogeneity in topography, vegetation and hydrology, even at the smallest scales of polygons and floodplains (van Huissteden et al, 2005;Kwon et al, 2006). Decomposition of soil carbon is sensitive to temperature changes and enhanced thawing (Zimov et al, 2006;Wagner et al, 2007), but growth of tundra ecosystems is nitrogen limited, which would reduce the sensitivity to climate warming .…”

Section: Introductionmentioning

confidence: 99%

The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia

et al. 2007

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Abstract. Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, R eco and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m −2 yr −1 , which is composed of an R eco =+141 g C m −2 yr −1 and GPP=−232 g C m −2 yr −1 . This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14 • C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (R g <200 W m −2 ), whereas R eco depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO 2 e m −2 yr −1 , so that the greenhouse gas balance was −64 g C-CO 2 e m −2 yr −1 . Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition.

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“…Alternatively, the tundra may have acclimated to temperature changes, and has once again turned back to a sink after acting as a source in the 1980s (Oechel et al 2000). Since climatic factors may vary widely from year to year, there is also a large degree of interannual variability in tundra NEE, gross primary productivity (GPP), and ecosystem respiration (ER) (Kwon et al 2006, Lafleur and Humphreys 2008, Lund et al 2010.…”

Section: Introductionmentioning

confidence: 99%

“…Historically, Arctic tundra has acted as a strong carbon sink because low temperatures and poor soil drainage limit decomposition more than primary production. However, some studies indicate that the Alaskan tundra is becoming a net source of CO 2 during the growing season, with larger positive values of net ecosystem exchange (NEE, where a positive value of NEE denotes a source of CO 2 , and a negative value denotes a sink; Oechel et al 1995, Kwon et al 2006). This switch is generally thought to be due to drying and warming of the tundra, and consequently higher rates of soil decomposition (Kwon et al 2006, Oberbauer et al 2007.…”

Section: Introductionmentioning

confidence: 99%

“…However, some studies indicate that the Alaskan tundra is becoming a net source of CO 2 during the growing season, with larger positive values of net ecosystem exchange (NEE, where a positive value of NEE denotes a source of CO 2 , and a negative value denotes a sink; Oechel et al 1995, Kwon et al 2006). This switch is generally thought to be due to drying and warming of the tundra, and consequently higher rates of soil decomposition (Kwon et al 2006, Oberbauer et al 2007. It is also possible that earlier snowmelt and a longer growing season will increase the sink strength of the tundra, with warming in both the spring and autumn that may enhance plant production (e.g., Aurela et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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Seasonal patterns of carbon dioxide and water fluxes in three representative tundra ecosystems in northern Alaska

et al. 2012

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Abstract. Understanding the carbon dioxide and water fluxes in the Arctic is essential for accurate assessment and prediction of the responses of these ecosystems to climate change. In the Arctic, there have been relatively few studies of net CO 2 , water, and energy exchange using micrometeorological methods due to the difficulty of performing these measurements in cold, remote regions. When these measurements are performed, they are usually collected only during the short summer growing season. We established eddy covariance flux towers in three representative Alaska tundra ecosystems (heath tundra, tussock tundra, and wet sedge tundra), and have collected CO 2 , water, and energy flux data continuously for over three years (September 2007-May 2011. In all ecosystems, peak CO 2 uptake occurred during July, with accumulations of ;51-95 g C/m 2 during June-August. The timing of the switch from CO 2 source to sink in the spring appears to be regulated by the number of growing degree days early in the season, indicating that warmer springs may promote increased net CO 2 uptake. However, this increased uptake in the spring may be lost through warmer temperatures in the late growing season that promote respiration, if this respiration is not impeded by large amounts of precipitation or cooler temperatures. Net CO 2 accumulation during the growing season was generally lost through respiration during the snow covered months of September-May, turning the ecosystems into net sources of CO 2 over measurement period. The water balance from June to August at the three ecosystems was variable, with the most variability observed in the heath tundra, and the least in the tussock tundra. These findings underline the importance of collecting data over the full annual cycle and across multiple types of tundra ecosystems in order to come to a more complete understanding of CO 2 and water fluxes in the Arctic.

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Effects of climate variability on carbon sequestration among adjacent wet sedge tundra and moist tussock tundra ecosystems

Cited by 85 publications

References 109 publications

Mapping Arctic Tundra Vegetation Communities Using Field Spectroscopy and Multispectral Satellite Data in North Alaska, USA

Mapping Arctic Tundra Vegetation Communities Using Field Spectroscopy and Multispectral Satellite Data in North Alaska, USA

The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia

Seasonal patterns of carbon dioxide and water fluxes in three representative tundra ecosystems in northern Alaska

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