{"title":"Evaluation of the Normalized Differential Vegetation Index as a Source of Information on Aboveground Phytomass in Steppes","authors":"A. V. Khoroshev, O. G. Kalmykova, G. Kh. Dusaeva","doi":"10.1134/s0001433823090116","DOIUrl":null,"url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Labor consumption of phytomass measurements on sample plots hinders the extrapolation of point data to areas comparable to commercial lands or landscape units. Vegetation indices calculated from satellite images are usually considered indicators of green phytomass; they are used for its areal estimates. The task of this study is to establish the informativity of the normalized differential vegetation index (NDVI) depending on the fractional structure of living and dead aboveground phytomass, seasonal dynamics of the biological cycle, hydrothermal conditions, and landscape position. The results of monthly measurements of aboveground phytomass fractions on 13 sites in phytocenoses of forest feather grass and feather grass formations in the Burtinskaya steppe (Orenburg Nature Reserve) from May to September 2015–2020 were used. The NDVI values were calculated for each period from Landsat satellite images at all sites. Hypotheses about geobotanical, hydrothermal, phonological, and landscape factors of NDVI informativity were tested by calculating the Spearman correlation coefficients using the dispersion and multiregression analysis. The discrepancy between the seasonal peaks of the NDVI and green phytomass is not consistent with the common concept of a direct indicator value of the NDVI. The total live biomass correlates more clearly with the index in June and July; the correlation is lower in the end of the season. The NDVI index turned out to be sensitive not so much to the reserves of green phytomass, but more to the mass and proportion of forbs and the ratio of live and dead phytomass. In late spring and early summer, the NDVI is most closely associated with forbs and, in July, with cereals. The hypothesis about the possibility of screening green mass with standing dead biomass was confirmed, which leads to a decrease in the NDVI despite the preservation or growth of green phytomass. The NDVI may underestimate the real green phytomass if there is a sharp increase in the mass of standing dead biomass, usually in the second half of summer and early autumn. The NDVI more adequately reflects the state of the aboveground phytomass of steppe communities that have not been exposed to fires for a long time when compared with burned communities and fallows.</p>","PeriodicalId":54911,"journal":{"name":"Izvestiya Atmospheric and Oceanic Physics","volume":null,"pages":null},"PeriodicalIF":0.9000,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Izvestiya Atmospheric and Oceanic Physics","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1134/s0001433823090116","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"METEOROLOGY & ATMOSPHERIC SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
Labor consumption of phytomass measurements on sample plots hinders the extrapolation of point data to areas comparable to commercial lands or landscape units. Vegetation indices calculated from satellite images are usually considered indicators of green phytomass; they are used for its areal estimates. The task of this study is to establish the informativity of the normalized differential vegetation index (NDVI) depending on the fractional structure of living and dead aboveground phytomass, seasonal dynamics of the biological cycle, hydrothermal conditions, and landscape position. The results of monthly measurements of aboveground phytomass fractions on 13 sites in phytocenoses of forest feather grass and feather grass formations in the Burtinskaya steppe (Orenburg Nature Reserve) from May to September 2015–2020 were used. The NDVI values were calculated for each period from Landsat satellite images at all sites. Hypotheses about geobotanical, hydrothermal, phonological, and landscape factors of NDVI informativity were tested by calculating the Spearman correlation coefficients using the dispersion and multiregression analysis. The discrepancy between the seasonal peaks of the NDVI and green phytomass is not consistent with the common concept of a direct indicator value of the NDVI. The total live biomass correlates more clearly with the index in June and July; the correlation is lower in the end of the season. The NDVI index turned out to be sensitive not so much to the reserves of green phytomass, but more to the mass and proportion of forbs and the ratio of live and dead phytomass. In late spring and early summer, the NDVI is most closely associated with forbs and, in July, with cereals. The hypothesis about the possibility of screening green mass with standing dead biomass was confirmed, which leads to a decrease in the NDVI despite the preservation or growth of green phytomass. The NDVI may underestimate the real green phytomass if there is a sharp increase in the mass of standing dead biomass, usually in the second half of summer and early autumn. The NDVI more adequately reflects the state of the aboveground phytomass of steppe communities that have not been exposed to fires for a long time when compared with burned communities and fallows.
期刊介绍：
Izvestiya, Atmospheric and Oceanic Physics is a journal that publishes original scientific research and review articles on vital issues in the physics of the Earth’s atmosphere and hydrosphere and climate theory. The journal presents results of recent studies of physical processes in the atmosphere and ocean that control climate, weather, and their changes. These studies have possible practical applications. The journal also gives room to the discussion of results obtained in theoretical and experimental studies in various fields of oceanic and atmospheric physics, such as the dynamics of gas and water media, interaction of the atmosphere with the ocean and land surfaces, turbulence theory, heat balance and radiation processes, remote sensing and optics of both media, natural and man-induced climate changes, and the state of the atmosphere and ocean. The journal publishes papers on research techniques used in both media, current scientific information on domestic and foreign events in the physics of the atmosphere and ocean.
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