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The taiga ecosystem in northeastern Siberia, a nitrogen-limited ecosystem on permafrost with a dry climate, changed during the extreme wet event in 2007. We investigated the normalized difference vegetation index (NDVI) as a satellite-derived proxy for needle production and compared it with ecosystem parameters such as soil moisture water equivalent (SWE), larch foliar C/N ratio, δ13 C and δ15 N, and ring width index (RWI) at the Spasskaya Pad Experimental Forest Station in Russia for the period from 1999 to 2019. Historical variations in NDVI showed a large difference between typical larch forest (unaffected) and the sites affected by the extreme wet event in 2007 because of high tree mortality at affected sites under extremely high SWE and waterlogging, resulting in a decrease in NDVI, although there was no difference in the NDVI between typical larch forest and affected sites before the wet event. Before 2007, the NDVI in a typical larch forest showed a positive correlation with SWE and a negative correlation with foliar C/N. These results indicate that not only the water availability (high SWE) in the previous summer and current June but also the soil N availability likely increased needle production. NDVI was also positively correlated with RWI, resulting from similar factors controlling them. However, after the wet event, NDVI was negatively correlated with SWE, while NDVI showed a negative correlation with foliar C/N. These results indicate that after the wet event, high soil moisture availability decreased needle production, which may have resulted from lower N availability. Foliar δ15 N was positively correlated with NDVI before 2007, but foliar δ15 N decreased after the wet event. This result suggests damage to roots and/or changes in soil N dynamics due to extremely high soil moisture. As a dry forest ecosystem, taiga in northeastern Siberia is affected not only by temperature-induced drought but also by high soil moisture (led by extreme wet events) and nitrogen dynamics. [ABSTRACT FROM AUTHOR]

The taiga ecosystem in northeastern Siberia, a nitrogen-limited ecosystem on permafrost with a dry climate, changed during the extreme wet event in 2007. We investigated the normalized difference vegetation index (NDVI) as a satellite-derived proxy of needle production and compared it with ecosystem parameters such as soil moisture water equivalent (SWE), foliar C/N ratio, δ13C and δ15N, and ring width index (RWI) at the Spasskaya Pad Experimental Forest Station in Russia for the period from 1999 to 2019. Historical variations in NDVI showed a large difference between typical larch forest (unaffected) and the sites affected by the extreme wet event in 2007 because of high tree mortality at affected sites under extremely high SWE and waterlogging, resulting in a decrease in NDVI. Before 2007, the NDVI in a typical larch forest showed a positive correlation with SWE and a negative correlation with foliar C/N. These results indicate that not only the water availability (high SWE) in the previous summer and current June but also the soil N availability increased needle production. NDVI was also positively correlated with RWI, resulting from similar factors controlling them. However, after the wet event, NDVI was negatively correlated with SWE, while NDVI showed a negative correlation with foliar C/N. These results indicate that after the wet event, high soil moisture availability decreased needle production, which may have resulted from lower N availability. Needle δ15N was positively correlated with NDVI before 2007, but after the wet event, needle δ15N decreased. This result suggests damage to roots and/or changes in soil N dynamics due to extremely high soil moisture. [ABSTRACT FROM AUTHOR]

The taiga forest, a semi-arid and nitrogen-limited ecosystem on permafrost, has changed under extreme wet events. This study aims to understand the changes that occurred in a larch forest in Eastern Siberia after the wet event of 2006–2007. In the summer of 2018, studies were conducted at the Spasskaya Pad Experimental Forest Station near Yakutsk, Russia, where a transect (60 m × 510 m) with 34 plots (30 m × 30 m) was set. It included intact sites and affected sites with different levels of forest damage, owing to the extreme wet event. We observed spatial variations in the normalized difference vegetation index (NDVI) calculated from Landsat satellite-observed data, and the foliar δ13C, δ15N, and C/N (carbon/nitrogen) ratio obtained from the needle samples of 105 mature larch trees. Our results reveal that the affected plots had a lower NDVI than the intact plots, resulting from a difference in tree stand density. In addition, the stand density is suggested to be a controlling factor in the spatial variations in the foliar C/N and δ13C values based on their significant relationships with the NDVI in June. We concluded that the larch trees from the regenerating forests in the affected areas have a higher nitrogen level and light availability (relatively low C/N and high δ13C) because of the slight competition for resources, owing to a low-stand density. This may lead to further succession of the larch forests after the extreme wet event. [ABSTRACT FROM AUTHOR]

Arctic and boreal permafrost ecosystems in Eastern Siberia, considered crucial to the climate system and global carbon cycle, are particularly vulnerable to climate change. This study investigates carbon dioxide (CO 2) exchange fluxes over northeastern Siberia from 2013 to 2015 in a taiga–tundra boundary ecosystem for which such measurements are scarce. The growing season (May–September) net CO 2 exchange flux (NEE) was −39.4 (−60.1 to −20.2) gCm−2, with ecosystem respiration (RE) = 306.2 (288.1–317.9) gCm−2 and gross primary production (GPP) = −345.5 (−372.5 to −317.7) gCm−2. Microclimatic factors determining these CO 2 exchange fluxes change seasonally. These fluxes are significantly affected by the timing of the onset of C uptake, which is reflected by changes in the soil temperature in spring and early summer, following which fluxes respond well to the photosynthetic photon flux density, especially for NEE. These CO 2 exchange fluxes at the northeastern Siberian taiga–tundra boundary ecosystem are significantly smaller than those previously reported at southern-taiga forest sites. Spring snow meltwater-rich soil moisture conditions render southern-taiga sites as stronger CO 2 sinks in June than taiga–tundra boundary ecosystem, which may be largely responsible for the pronounced north–south gradient in growing season NEE. [ABSTRACT FROM AUTHOR]