Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis
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 the climate-sensitive tundra. Space-borne remote sensin...
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ftcopernicus:oai:publications.copernicus.org:bg67975 2023-05-15T15:19:39+02:00 Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis Walther, Sophia Guanter, Luis Heim, Birgit Jung, Martin Duveiller, Gregory Wolanin, Aleksandra Sachs, Torsten 2019-01-09 application/pdf https://doi.org/10.5194/bg-15-6221-2018 https://www.biogeosciences.net/15/6221/2018/ eng eng doi:10.5194/bg-15-6221-2018 https://www.biogeosciences.net/15/6221/2018/ eISSN: 1726-4189 Text 2019 ftcopernicus https://doi.org/10.5194/bg-15-6221-2018 2019-12-24T09:49:46Z 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 the climate-sensitive tundra. Space-borne 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 it highly challenging. Here, we conduct an extensive analysis of the timing of peak vegetation productivity as shown by satellite observations of complementary indicators of plant greenness and photosynthesis. We choose to focus on productivity during the peak of the growing season, as it importantly affects the total annual carbon uptake. The suite of indicators are as follows: (1) MODIS-based vegetation indices (VIs) as proxies for the fraction of incident photosynthetically active radiation (PAR) that is absorbed (fPAR), (2) VIs combined with estimates of PAR as a proxy of the total absorbed radiation (APAR), (3) sun-induced chlorophyll fluorescence (SIF) serving as a proxy for photosynthesis, (4) vegetation optical depth (VOD), indicative of total water content and (5) empirically upscaled modelled gross primary productivity (GPP). Averaged over the pan-Arctic we find a clear order of the annual peak as APAR ≦ <math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="normal">GPP</mi><mo><</mo><mi mathvariant="normal">SIF</mi><mo><</mo><mi mathvariant="normal">VIs</mi><mo>/</mo><mi mathvariant="normal">VOD</mi></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="112pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="cd46dc2fef72916ed36fc73b3985dd60"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-6221-2018-ie00001.svg" width="112pt" height="14pt" src="bg-15-6221-2018-ie00001.png"/></svg:svg> . SIF as an indicator of photosynthesis is maximised around the time of highest annual temperatures. The modelled GPP peaks at a similar time to APAR. The time lag of the annual peak between APAR and instantaneous SIF fluxes indicates that the SIF data do contain information on light-use efficiency of tundra vegetation, but further detailed studies are necessary to verify this. Delayed peak greenness compared to peak photosynthesis is consistently found across years and land-cover classes. A particularly late peak of the normalised difference vegetation index (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 or 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. Text Arctic Tundra Copernicus Publications: E-Journals Arctic Biogeosciences 15 20 6221 6256 |
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Open Polar |
collection |
Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
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 the climate-sensitive tundra. Space-borne 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 it highly challenging. Here, we conduct an extensive analysis of the timing of peak vegetation productivity as shown by satellite observations of complementary indicators of plant greenness and photosynthesis. We choose to focus on productivity during the peak of the growing season, as it importantly affects the total annual carbon uptake. The suite of indicators are as follows: (1) MODIS-based vegetation indices (VIs) as proxies for the fraction of incident photosynthetically active radiation (PAR) that is absorbed (fPAR), (2) VIs combined with estimates of PAR as a proxy of the total absorbed radiation (APAR), (3) sun-induced chlorophyll fluorescence (SIF) serving as a proxy for photosynthesis, (4) vegetation optical depth (VOD), indicative of total water content and (5) empirically upscaled modelled gross primary productivity (GPP). Averaged over the pan-Arctic we find a clear order of the annual peak as APAR ≦ <math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="normal">GPP</mi><mo><</mo><mi mathvariant="normal">SIF</mi><mo><</mo><mi mathvariant="normal">VIs</mi><mo>/</mo><mi mathvariant="normal">VOD</mi></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="112pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="cd46dc2fef72916ed36fc73b3985dd60"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-6221-2018-ie00001.svg" width="112pt" height="14pt" src="bg-15-6221-2018-ie00001.png"/></svg:svg> . SIF as an indicator of photosynthesis is maximised around the time of highest annual temperatures. The modelled GPP peaks at a similar time to APAR. The time lag of the annual peak between APAR and instantaneous SIF fluxes indicates that the SIF data do contain information on light-use efficiency of tundra vegetation, but further detailed studies are necessary to verify this. Delayed peak greenness compared to peak photosynthesis is consistently found across years and land-cover classes. A particularly late peak of the normalised difference vegetation index (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 or 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. |
format |
Text |
author |
Walther, Sophia Guanter, Luis Heim, Birgit Jung, Martin Duveiller, Gregory Wolanin, Aleksandra Sachs, Torsten |
spellingShingle |
Walther, Sophia Guanter, Luis Heim, Birgit Jung, Martin Duveiller, Gregory Wolanin, Aleksandra Sachs, Torsten Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
author_facet |
Walther, Sophia Guanter, Luis Heim, Birgit Jung, Martin Duveiller, Gregory Wolanin, Aleksandra Sachs, Torsten |
author_sort |
Walther, Sophia |
title |
Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
title_short |
Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
title_full |
Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
title_fullStr |
Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
title_full_unstemmed |
Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
title_sort |
assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis |
publishDate |
2019 |
url |
https://doi.org/10.5194/bg-15-6221-2018 https://www.biogeosciences.net/15/6221/2018/ |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic Tundra |
genre_facet |
Arctic Tundra |
op_source |
eISSN: 1726-4189 |
op_relation |
doi:10.5194/bg-15-6221-2018 https://www.biogeosciences.net/15/6221/2018/ |
op_doi |
https://doi.org/10.5194/bg-15-6221-2018 |
container_title |
Biogeosciences |
container_volume |
15 |
container_issue |
20 |
container_start_page |
6221 |
op_container_end_page |
6256 |
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1766349853898571776 |