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Increased Plant Growth in the Northern High Latitudes from 1981 to 1991

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Abstract

Variations in the amplitude and timing of the seasonal cycle of atmospheric CO2 have shown an association with surface air temperature consistent with the hypothesis that warmer temperatures have promoted increases in plant growth during summer1 and/or plant respiration during winter2 in the northern high latitudes. Here we present evidence from satellite data that the photosynthetic activity of terrestrial vegetation increased from 1981 to 1991 in a manner that is suggestive of an increase in plant growth associated with a lengthening of the active growing season. The regions exhibiting the greatest increase lie between 45°N and 70°N, where marked warming has occurred in the spring time3 due to an early disappearance of snow4. The satellite data are concordant with an increase in the amplitude of the seasonal cycle of atmospheric carbon dioxide exceeding 20% since the early 1970s, and an advance of up to seven days in the timing of the drawdown of CO2 in spring and early summer1. Thus, both the satellite data and the CO2 record indicate that the global carbon cycle has responded to interannual fluctuations in surface air temperature which, although small at the global scale, are regionally highly significant.
... However, most studies have focused on community scales or small study areas because of their limitations in field measurements. With the rapid progress of remote sensing, a combination of remote sensing and ground observations datasets at different scales can be used to effectively estimate vegetation biomass (Myneni et al., 1997Piao et al., 2005Piao et al., , 2007Fang et al., 2007). For instance, Piao et al. (2003) estimated the magnitude and changes in grassland biomass in some ecosystems in China. ...
... Our results further showed that T min and T max had an asymmetric effect on the aboveground biomass of the investigated marsh wetland ( Table 1), suggesting that the increased maximum temperature in spring and winter may be associated with the temporal change in marsh AGB, especially during spring. Furthermore, our findings were consistent with previous studies showing that a warmer climate could lead to increase aboveground biomass as a consequence of enhanced photosynthetic rate and longer growth season (Myneni et al., 1997Los et al., 2001;Tucker et al., 2001;Zhou et al., 2001;Hicke et al., 2002;Slayback et al., 2003). First, warming during the day accelerates the reaction FIGURE 5 | Spatial distributions of correlation coefficients between the annual AGB and annual precipitation (A), annual mean temperature (B), annual maximum temperature (C), and annual minimum temperature (D) in the western Songnen Plain marshes. ...
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Understanding the spatiotemporal dynamics of aboveground biomass (AGB) is crucial for investigating the wetland ecosystem carbon cycle. In this paper, we explored the spatiotemporal change of aboveground biomass and its response to climate change in a marsh wetland of western Songen Plain by using field measured AGB data and vegetation index derived from MODIS datasets. The results showed that the AGB could be established by the power function between measured AGB density and the annual maximum NDVI (NDVImax) of marsh: Y = 302.06 × NDVImax1.9817. The averaged AGB of marshes showed a significant increase of 2.04 g⋅C/m2/a, with an average AGB value of about 111.01 g⋅C/m2 over the entire western Songnen Plain. For the influence of precipitation and temperature, we found that the annual mean temperature had a smaller effect on the distribution of marsh AGB than that of the total precipitation in the western Songnen Plain. Increased precipitation in summer and autumn would increase AGB by promoting marshes’ vegetation growth. In addition, we found that the minimum temperature (Tmin) and maximum temperatures (Tmax) have an asymmetric effect on marsh AGB on the western Songnen Plain: warming Tmax has a significant impact on AGB of marsh vegetation, while warming at night can non-significantly increase the AGB of marsh wetland. This research is expected to provide theoretical guidance for the restoration, protection, and adaptive management of wetland vegetation in the western Songnen Plain.
... Previous findings have demonstrated that changes in VPD, temperature, and atmospheric CO 2 concentration can significantly influence plant growth by controlling photosynthetic rate, stomatal conductance, CO 2 assimilation, and other physiological pathways (Bonan et al., 2014;Green et al., 2020;Lopez et al., 2021;Piao et al., 2013;Wang et al., 2020). Moreover, the remotely sensed indicators such as Vegetation Indices (VIs) and Leaf Area Index (LAI) were used to investigate the relationships between terrestrial ecosystems and climate change at regional and global scales (Myneni et al., 1997;Nemani et al., 2003;Zhang, Song, et al., 2017;Zhu et al., 2016). Recent studies suggested that satellite-derived measurements of solar-induced chlorophyll fluorescence (SIF) can capture climate change impacts on vegetation productivity better than other indicators (Dechant et al., 2020;Fournier et al., 2012;Migliavacca et al., 2017;Song et al., 2021). ...
... Multiple lines of evidence indicated that global vegetation productivity has increased over the last two decades (Figure 2). Similar to the previous results based on VIs (Myneni et al., 1997;Zhang, Song, et al., 2017;Zhu et al., 2016), our results showed that SIF (or GPP) has increased over more than half (approximately 66.5%-72.2%) of the globally vegetated areas. Most of the upward trends were found in East Asia, South Asia, Central Africa, central North America, and continental Europe. ...
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Rising atmospheric dryness [vapor pressure deficit (VPD)] can limit photosynthesis and thus reduce vegetation productivity. Meanwhile, plants can benefit from global warming and the fertilization effect of carbon dioxide (CO2). There are growing interests to study climate change impacts on terrestrial vegetation. However, global vegetation productivity responses to recent climate and CO2 trends remain to be fully understood. Here, we provide a comprehensive evaluation of the relative impacts of VPD, temperature, and atmospheric CO2 concentration on global vegetation productivity over the last two decades using a robust ensemble of solar‐induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) data. We document a significant increase in global vegetation productivity with rising VPD, temperature, and atmospheric CO2 concentration over this period. For global SIF (or GPP), the decrease due to rising VPD was comparable to the increase due to warming but far less than the increase due to elevated CO2 concentration. We found that rising VPD counteracted only a small proportion (approximately 8.1%–15.0%) of the warming and CO2‐induced increase in global SIF (or GPP). Despite the sharp rise in atmospheric dryness imposing a negative impact on plants, the warming and CO2 fertilization effects contributed to a persistent and widespread increase in vegetation productivity over the majority (approximately 66.5%–72.2%) of the globally vegetated areas. Overall, our findings provide a quantitative and comprehensive attribution of rising atmospheric dryness on global vegetation productivity under concurrent climate warming and CO2 increasing.
... The high positive trend in the maximum annual NDVI index value in the southern part of Iceland is in line with the widespread afforestation of that region (Fries 2017). The other studies about northern latitude's vegetation variations, indicate that there is a great increase in vegetation coverage between 45°N and 70°N (Myneni et al. 1997;Huang et al. 2017). ...
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Changes in the vegetation of the Arctic and sub-Arctic regions have been used as indicators of the impact and seriousness of climate change. In this study, 342 MODIS NDVI images were used to monitor and assess the variability and long-term changes in the vegetation in Iceland in the period 2001–2018. An insignificant trend in the changes of the vegetation coverage (R = 0.16, p-value = 0.05) was obtained, however, it also resulted that the area with the low values of the NDVI (< 0.6) is decreasing, whereas the area with higher values of the NDVI (> 0.6, mostly forests) is increasing. The NDVI index during the study period rose for the area of about 3260 km2, while it declined for 1635 km2. The results of this study can be used for organizing the strategies preventing climate change and global warming.
... Remote and near-surface spectral observations provide Vegetation Indices (VIs) sensitive to canopy greenness (Tucker, 1979;Huete et al., 2002;Richardson et al., 2009), which can be used to monitor canopy development, phenology, and vegetation functioning (Wu et al., 2009;Migliavacca et al., 2011;Toomey et al., 2015). This linkage between the variation of greenness and vegetation functioning is strong in canopies with a pronounced seasonal dynamics of leaf area index (LAI) and chlorophyll content (Myneni et al., 1997;Zhang et al., 2003;Migliavacca et al., 2015) like grassland and deciduous forests. By contrast, evergreen forests, especially those with broadleaf trees, exhibit low temporal variability in their canopy greenness Moser et al., 2020), which results in a desynchronization between seasonal changes in canopy-scale greenness and seasonality of vegetation functioning such as carbon and water fluxes . ...
Article
Remote sensing capabilities to monitor evergreen broadleaved vegetation are limited by the low temporal variability in the greenness signal. With canopy greenness computed from digital repeat photography (PhenoCam), we investigated how canopy greenness related to seasonal changes in leaf age and traits as well as variation of trees’ water fluxes (characterized by sap flow and canopy conductance). The results showed that sprouting leaves are mainly responsible for the rapid increase in canopy green chromatic coordinate (GCC) in spring. We found statistically significantly differences in leaf traits and spectral properties among leaves of different leaf ages. Specifically, mean GCC of young leaves was 0.385 ± 0.010 (mean ± SD), while for mature and old leaves was 0.369 ± 0.003, and 0.376 ± 0.004, respectively. Thus, the temporal dynamics of canopy GCC can be explained by changes in leaf spectral properties and leaf age. Sap flow and canopy conductance are both well explained by a combination of environmental drivers and greenness (96% and 87% of the variance explained, respectively). In particular, air temperature and vapor pressure deficit (VPD) explained most of sap flow and canopy conductance variance, respectively. Besides, GCC is an important explanatory variable for variation of canopy conductance may because GCC can represent the leaf ontogeny information. We conclude that PhenoCam GCC can be used to identify the leaf flushing for evergreen broadleaved trees, which carries important information about leaf ontogeny and traits. Thus, it can be helpful for better estimating canopy conductance which constraints water fluxes.
... It is worth noting that both T day and T night had intensive influences on vegetation dynamics according to their proportions of significant pixels ( Fig. 5 and Fig. 7). On the contrary, daytime warming in the same cold Arctic regions has been reported to be more positively influential for vegetation and is probably due to the much shorter duration of nighttime during the growing season (Piao et al., 2015;Shen et al., 2016;Myneni et al., 1997). The ongoing drastic nighttime warming in alpine ecosystems like HMA should receive more attention. ...
Article
Meteorological records over the past five decades have shown that climate warming has been faster during the nighttime than during the daytime. However, the responses of vegetation development to asymmetric warming are not well understood due to the misinterpretation of phenology that have resulted from the snowmelt effect. We applied normalized difference vegetation index (NDVI) sources from Global Inventory Modeling and Mapping Studies (GIMMS:1982-2015) and Moderate Resolution Imaging Spectroradiometer (MODIS: 2000-2020) to reveal maximum greenness in high-mountain Asia (HMA). The snow-free normalized difference phenology index (NDPI), which is a 3-band vegetation index that designed to best contrast vegetation from soil and snow, was applied for estimating the start of the growing season (SOS). We found that alpine pastures in HMA generally became greener and the SOS was delayed. Preseason daytime temperatures (T day) and nighttime temperatures (T night) had opposite effects on maximum greenness, with T day being negative and T night being positive. The responses of SOS to T day and T night were highly related with the frequency of meteorological drought events during 2000-2020. In regions with lower frequency of drought events, both daytime and nighttime warming could advance SOS. In regions with higher frequency of drought events, daytime warming could delay SOS, but nighttime warming could advance SOS. The results of our study are of great significance to understand the responses of alpine ecosystems to asymmetric climate warming. Such an understanding is quite valuable for pasture management and future vegetation climate projections.
... Vegetation index (NDVI) changes. The Normalized Difference Vegetation Index (NDVI) is an important indicator of vegetation growth 24 . The study results reveal that the NDVI of the lower reaches of the Tarim River increased from 0.14 in 2000 to 0.21 in 2020, representing a rise of about 33.3%. ...
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Water system management is a worldwide challenge, especially in arid and semi-arid regions. Ecological water conveyance projects aim to raise the groundwater table, thereby saving natural vegetation and curbing ecological deterioration. Since 2000, these projects have been implemented in the arid zone of northwest China, with generally successful outcomes. Taking a portion of the lower reaches of the Tarim River as the study area, this paper analyzes in detail the ecohydrological effects which have occurred since the launching of artificial water conveyance 20 years ago. The results show that the groundwater table in the upper, middle and lower segments of the Tarim River’s lower reaches has been raised on average 4.06, 4.83 and 5.13 m, respectively, while the area of surface water bodies connected to those sections has expanded from 49.00 km² to 498.54 km². At the same time, Taitema Lake, which is the terminal lake of the Tarim River, has been revived and now boasts a water area of 455.27 km². Other findings indicate that the surface ecological response is extremely sensitive and that the area of natural vegetation has expanded to 1423 km². Furthermore, the vegetation coverage, vegetation index (NDVI), and Net Primary Productivity (NPP) have increased by 132 km², 0.07 and 7.6 g C m⁻², respectively, and the Simpson dominance, McIntosh evenness, and Margalef richness indices have risen by 0.33, 0.35 and 0.49, respectively, in the monitored sample sites. As well, the carbon sink area has expanded from 1.54% to 7.8%. Given the increasing intensity of the occurrence of extreme hydrological events and successive dry years, similar ecological water conveyance projects should be considered elsewhere in China and in other parts of the world. The water conveyance scheme has generally proven successful and should be optimized to enhance the benefits of ecological water conveyance under water resource constraints.
... The Arctic (north of 66.5 • N) and boreal region (between 45 and 65 • N) have undergone dramatic temperature and ecological changes over the past century, and the rate of this change has accelerated in recent decades (Cohen et al., 2014). Satellite-based observations of leaf area index (LAI) and normalized difference vegetation index (NDVI) suggest that northern high latitudes have shown a significant trend of greening in the past three decades as a result of vegetation growth (Bhatt et al., 2017;Keeling et al., 1996;Myers-Smith et al., 2011;Myneni et al., 1997;Xu et al., 2013;Zhou et al., 2001;, in part because the temperature is the limiting factor for vegetation growth in this region (Nemani et al., 2003). In the meantime, boreal forest fires have shown an increasing trend over the past few decades, which is likely to continue (Abatzoglou and Williams, 2016). ...
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Here we use satellite observations of formaldehyde (HCHO) vertical column densities (VCD) from the TROPOspheric Monitoring Instrument (TROPOMI), aircraft measurements, combined with a nested regional chemical transport model (GEOS-Chem at 0.5×0.625∘ resolution), to better understand the variability and sources of summertime HCHO in Alaska. We first evaluate GEOS-Chem with in-situ airborne measurements during the Atmospheric Tomography Mission 1 (ATom-1) aircraft campaign. We show reasonable agreement between observed and modeled HCHO, isoprene, monoterpenes and the sum of methyl vinyl ketone and methacrolein (MVK+MACR) in the continental boundary layer. In particular, HCHO profiles show spatial homogeneity in Alaska, suggesting a minor contribution of biogenic emissions to HCHO VCD. We further examine the TROPOMI HCHO product in Alaska in summer, reprocessed by GEOS-Chem model output for a priori profiles and shape factors. For years with low wildfire activity (e.g., 2018), we find that HCHO VCDs are largely dominated by background HCHO (58 %–71 %), with minor contributions from wildfires (20 %–32 %) and biogenic VOC emissions (8 %–10 %). For years with intense wildfires (e.g., 2019), summertime HCHO VCD is dominated by wildfire emissions (50 %–72 %), with minor contributions from background (22 %–41 %) and biogenic VOCs (6 %–10 %). In particular, the model indicates a major contribution of wildfires from direct emissions of HCHO, instead of secondary production of HCHO from oxidation of larger VOCs. We find that the column contributed by biogenic VOC is often small and below the TROPOMI detection limit, in part due to the slow HCHO production from isoprene oxidation under low NOx conditions. This work highlights challenges for quantifying HCHO and its precursors in remote pristine regions.
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