Effects of Fine-Scale Topography on CO<sub>2</sub> Flux Components of Alaskan Coastal Plain Tundra: Response to Contrasting Growing Seasons

Olivas, Paulo C.; Oberbauer, Steven F.; Tweedie, C. E.; Oechel, W. C.; Lin, David; Kuchy, Andrea

doi:10.1657/1938-4246-43.2.256

Cited by 36 publications

(56 citation statements)

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“…Adaptations to low temperatures and a short growing season require plants to respond to small changes in air temperature [4][5][6][7]. Therefore, changes in plant dominance and ecosystem function in the Arctic are largely driven by temperature, along with precipitation and growing season length [8][9][10][11][12]. Among the changes observed, most notable is that shrubs and graminoids are currently increasing in dominance [10,[13][14][15][16][17].…”

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confidence: 99%

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

et al. 2017

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Climate change is warming the temperatures and lengthening the Arctic growing season with potentially important effects on plant phenology. The ability of plant species to acclimate to changing climatic conditions will dictate the level to which their spatial coverage and habitat-type dominance is different in the future. While the effect of changes in temperature on phenology and species composition have been observed at the plot and at the regional scale, a systematic assessment at medium spatial scales using new noninvasive sensor techniques has not been performed yet. At four sites across the North Slope of Alaska, changes in the Normalized Difference Vegetation Index (NDVI) signal were observed by Mobile Instrumented Sensor Platforms (MISP) that are suspended over 50 m transects spanning local moisture gradients. The rates of greening (measured in June) and senescence (measured in August) in response to the air temperature was estimated by changes in NDVI measured as the difference between the NDVI on a specific date and three days later. In June, graminoid-and shrub-dominated habitats showed the greatest rates of NDVI increase in response to the high air temperatures, while forb-and lichen-dominated habitats were less responsive. In August, the NDVI was more responsive to variations in the daily average temperature than spring greening at all sites. For graminoid-and shrub-dominated habitats, we observed a delayed decrease of the NDVI, reflecting a prolonged growing season, in response to high August temperatures. Consequently, the annual C assimilation capacity of these habitats is increased, which in turn may be partially responsible for shrub expansion and further increases in net summer CO 2 fixation. Strong interannual differences highlight that long-term and noninvasive measurements of such complex feedback mechanisms in arctic ecosystems are critical to fully articulate the net effects of climate variability and climate change on plant community and ecosystem processes.

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Section: Introductionmentioning

confidence: 99%

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

et al. 2017

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“…Despite large carbon amounts being stored in the often permanently frozen grounds, net fluxes of carbon between the land surface and the atmosphere are small and their CO 2 balance is close to neutrality (McGuire et al, 2012). Because of their strong sensitivity to environmental conditions, carbon exchange processes are 5 highly variable in space and time (Olivas et al, 2011;Pirk et al, 2017;Lafleur and Humphreys, 2008;Welker et al, 2004) and an ecosystem might switch between being a carbon sink or source from year to year depending on the weather conditions (Huemmrich et al, 2010b).…”

Section: Introductionmentioning

confidence: 99%

“…However, their photosynthetic capacity is much lower (Yuan et al, 2014;Williams and Rastetter, 1999;Zona et al, 2011), and their seasonality is 5 often dissimilar (Gamon et al, 2013) as a consequence of their different sensitivities to environmental conditions (Zona et al, 2011). Micro-topography affects moisture conditions, even within small elevation changes of about one meter (Olivas et al, 2011;Gamon et al, 2013;Pirk et al, 2017). As a consequence, distinct spatial distributions of the plant functional types and highly variable patterns of photosynthetic light-use efficiency are observed.…”

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“…Vascular plants prefer lower, wetter places and their growth increases biomass, productivity, NDVI, and LAI. However, when the ground becomes drier, NDVI will increase, 10 but actual productivity decline (Olivas et al, 2011;Gamon et al, 2013;Buchhorn et al, 2013). Consequently, the wetness of the soil confounds the interpretation of spectral reflectance with respect to productivity, which is problematic as soils are often water-saturated (Stow et al, 2004).…”

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“…Consequently, the wetness of the soil confounds the interpretation of spectral reflectance with respect to productivity, which is problematic as soils are often water-saturated (Stow et al, 2004). Next to the confounding effect of moisture on spectral reflectance, changes in GPP have been observed to not necessarily translate into changes in NDVI (Olivas et al, 2011). In addition to these challenges, spectral reflectance observations are affected by large signals from the background and shadows cast by microtopography and 15 vegetation itself.…”

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confidence: 99%

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Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis

Walther¹,

Guanter²,

Heim³

et al. 2018

Preprint

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Abstract. High latitude treeless ecosystems represent spatially highly heterogeneous landscapes with small net carbon fluxes and a short growing season. Reliable observations and process understanding are critical for projections of the carbon balance of climate sensitive tundra. Spaceborne remote sensing is the only tool to obtain spatially continuous and temporally resolved information on vegetation greenness and activity in remote circumpolar areas. However, confounding effects from persistent clouds, low sun elevation angles, numerous lakes, widespread surface inundation, and the sparseness of the vegetation render this. Delayed peak greenness compared to peak photosynthesis is consistently found across years and land cover classes. A particularly late peak of NDVI in regions with very small seasonality in greenness and a high amount of lakes probably originates from artefacts. Given the very short growing season in circumpolar areas, the average time difference in maximum annual photosynthetic activity and greenness/growth of 3 to 25 days (depending on the data sets chosen) is important and needs to be considered when using satellite observations as drivers in vegetation models.

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Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

Newman

Throckmorton

Graham

et al. 2015

Geophysical Research Letters

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Polygonal ground is a signature characteristic of Arctic lowlands, and carbon release from permafrost thaw can alter feedbacks to Arctic ecosystems and climate. This study describes the first comprehensive spatial examination of active layer biogeochemistry that extends across high-and low-centered, ice wedge polygons, their features, and with depth. Water chemistry measurements of 54 analytes were made on surface and active layer pore waters collected near Barrow, Alaska, USA. Significant differences were observed between high-and low-centered polygons suggesting that polygon types may be useful for landscape-scale geochemical classification. However, differences were found for polygon features (centers and troughs) for analytes that were not significant for polygon type, suggesting that finer-scale features affect biogeochemistry differently from polygon types. Depth variations were also significant, demonstrating important multidimensional aspects of polygonal ground biogeochemistry. These results have major implications for understanding how polygonal ground ecosystems function, and how they may respond to future change.

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Effects of Fine-Scale Topography on CO₂ Flux Components of Alaskan Coastal Plain Tundra: Response to Contrasting Growing Seasons

Cited by 36 publications

References 58 publications

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis

Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

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Effects of Fine-Scale Topography on CO2 Flux Components of Alaskan Coastal Plain Tundra: Response to Contrasting Growing Seasons

Cited by 36 publications

References 58 publications

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis

Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

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Effects of Fine-Scale Topography on CO₂ Flux Components of Alaskan Coastal Plain Tundra: Response to Contrasting Growing Seasons