In permafrost regions, vegetation growth is influenced by both climate conditions and the effects of permafrost degradation. Climate factors affect multiple aspects of the environment, while permafrost degradation has a significant impact on soil moisture and nutrient availability, both of which are crucial for ecosystem health and vegetation growth. However, the quantitative analysis of climate and permafrost remains largely unknown, hindering our ability to predict future vegetation changes in permafrost regions. Here, we used statistical methods to analyze the NDVI change in the permafrost region from 1982 to 2022. We employed correlation analysis, multiple regression residual analysis and partial least squares structural equation modeling (PLS-SEM) methods to examine the impacts of different environmental factors on NDVI changes. The results show that the average NDVI in the study area from 1982 to 2022 is 0.39, with NDVI values in 80% of the area remaining stable or exhibiting an increasing trend. NDVI had the highest correlation with air temperature, averaging 0.32, with active layer thickness coming in second at 0.25. Climate change plays a dominant role in NDVI variations, with a relative contribution rate of 89.6%. The changes in NDVI are positively influenced by air temperature, with correlation coefficients of 0.92. Although the active layer thickness accounted for only 7% of the NDVI changes, its influence demonstrated an increasing trend from 1982 to 2022. Overall, our results suggest that temperature is the primary factor influencing NDVI variations in this region.

Environmental changes, such as climate warming and higher herbivory pressure, are altering the carbon balance of Arctic ecosystems; yet, how these drivers modify the carbon balance among different habitats remains uncertain. This hampers our ability to predict changes in the carbon sink strength of tundra ecosystems. We investigated how spring goose grubbing and summer warming-two key environmental-change drivers in the Arctic-alter CO2 fluxes in three tundra habitats varying in soil moisture and plant-community composition. In a full-factorial experiment in high-Arctic Svalbard, we simulated grubbing and warming over two years and determined summer net ecosystem exchange (NEE) alongside its components: gross ecosystem productivity (GEP) and ecosystem respiration (ER). After two years, we found net CO2 uptake to be suppressed by both drivers depending on habitat. CO2 uptake was reduced by warming in mesic habitats, by warming and grubbing in moist habitats, and by grubbing in wet habitats. In mesic habitats, warming stimulated ER (+75%) more than GEP (+30%), leading to a 7.5-fold increase in their CO2 source strength. In moist habitats, grubbing decreased GEP and ER by similar to 55%, while warming increased them by similar to 35%, with no changes in summer-long NEE. Nevertheless, grubbing offset peak summer CO2 uptake and warming led to a twofold increase in late summer CO2 source strength. In wet habitats, grubbing reduced GEP (-40%) more than ER (-30%), weakening their CO2 sink strength by 70%. One-year CO2-flux responses were similar to two-year responses, and the effect of simulated grubbing was consistent with that of natural grubbing. CO2-flux rates were positively related to aboveground net primary productivity and temperature. Net ecosystem CO2 uptake started occurring above similar to 70% soil moisture content, primarily due to a decline in ER. Herein, we reveal that key environmental-change drivers-goose grubbing by decreasing GEP more than ER and warming by enhancing ER more than GEP-consistently suppress net tundra CO2 uptake, although their relative strength differs among habitats. By identifying how and where grubbing and higher temperatures alter CO2 fluxes across the heterogeneous Arctic landscape, our results have implications for predicting the tundra carbon balance under increasing numbers of geese in a warmer Arctic.

The Arctic has warmed nearly four times faster than the global average since 1979, resulting in rapid glacier retreat and exposing new glacier forelands. These forelands offer unique experimental settings to explore how global warming impacts ecosystems, particularly for highly climate-sensitive arthropods. Understanding these impacts can help anticipate future biodiversity and ecosystem changes under ongoing warming scenarios. In this study, we integrate data on arthropod diversity from DNA gut content analysis-offering insight into predator diets-with quantitative measures of arthropod activity-density at a Greenland glacier foreland using Structural Equation Modelling (SEM). Our SEM analysis reveals both bottom-up and top-down controlled food chains. Bottom-up control, linked to sit-and-wait predator behavior, was prominent for spider and harvestman populations, while top-down control, associated with active search behavior, was key for ground beetle populations. Bottom-up controlled dynamics predominated during the early stages of vegetation succession, while top-down mechanisms dominated in later successional stages further from the glacier, driven largely by increasing temperatures. In advanced successional stages, top-down cascades intensify intraguild predation (IGP) among arthropod predators. This is especially evident in the linyphiid spider Collinsia holmgreni, whose diet included other linyphiid and lycosid spiders, reflecting high IGP. The IGP ratio in C. holmgreni negatively correlated with the activity-density of ground-dwelling prey, likely contributing to the local decline and possible extinction of this cold-adapted species in warmer, late-succession habitats where lycosid spiders dominate. These findings suggest that sustained warming and associated shifts in food web dynamics could lead to the loss of cold-adapted species, while brief warm events may temporarily impact populations without lasting extinction effects.

Permafrost, widely distributed in the Northern Hemisphere, plays a vital role in regulating heat and moisture cycles within ecosystems. In the last four decades, due to global warming, permafrost degradation has accelerated significantly in high latitudes and altitudes. However, the impact of permafrost degradation on vegetation remains poorly understood to date. Based on active layer thickness (ALT) monitoring data, meteorological data and normalized difference vegetation index (NDVI) data, we found that most ALT-monitored sites in the Northern Hemisphere show an increasing trend in NDVI and ALT. This suggests an overall increase in NDVI from 1980 to 2021 while permafrost degradation has been occurring. Permafrost degradation positively influences NDVI growth, with the intensity of the effects varying across land cover types and permafrost regions. Furthermore, based on Mann-Kendall trend test, we detected abrupt changes in NDVI and environmental factors, further confirming that there is a strong consistency between the abrupt changes of ALT and NDVI, and the consistency between the abrupt change events of ALT and NDVI is stronger than that of air temperature and precipitation. These findings work toward a better comprehending of permafrost effects on vegetation growth in the context of climate change. Our research focuses on the influence of permafrost degradation on vegetation in high-latitude and high-altitude regions of the Northern Hemisphere. By analyzing permafrost monitoring and vegetation data, we have observed a widespread occurrence of permafrost degradation and vegetation greening in recent years across the Northern Hemisphere. Our analysis has revealed a strong connection between permafrost degradation and vegetation greening in permafrost areas, and the impact varies with different vegetation and permafrost types. In addition, we further investigated the consistency of abrupt changes in the vegetation growth with various environmental factors. It can be seen that despite the significant influence of air temperature changes on vegetation growth in permafrost regions of the Northern Hemisphere, the abrupt change of vegetation growth is consistent with the abrupt change in the process of permafrost degradation, indicating that vegetation growth displays a heightened sensitivity to permafrost degradation. These findings provide valuable insights into the ecological consequences of permafrost changes in high-latitude and high-altitude areas under the influence of climate change. Vegetation in the Northern Hemisphere shows a greening trend, and permafrost shows a degradation trend Permafrost degradation positively influences vegetation growth, with the intensity of the effects varying by vegetation and permafrost types Abrupt changes in vegetation growth are more consistent with abrupt permafrost degradation than with meteorological factors

As an essential link between terrestrial and climatic ecosystems, vegetation has been altered by the soil hy-drological environment associated with frozen soil thaw. However, it is not clear whether fluctuating soil moisture (SM) within the frozen soil zone alters the hydrologic environment to alleviate water stress in plants further, and there are scant previous studies at large scale on whether there is a threshold for SM on vegetation greening. This study integrated SM monitoring data at 125 stations from existing studies, then quantified the advantages of six remote sensing/reanalysis SM products: QTP-DNN-Sm, Global Land Data Assimilation System (GLDAS-Noah), European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5-Land), European Space Agency Climate Change Initiative (ESA CCI), Global-SM, and QTP-SM. Moreover, we assessed the influence of single and multiple regional environmental elements (temperature, precipitation, land surface temperature (LST), normalized difference vegetation index (NDVI), and snow) on SM, as well as identified four trends of SM and vegetation growth for 51.26% of the Tibetan Plateau (TP). The results are as follows: 1) The overall performance of QTP-DNN-Sm products was slightly better than that of Global-SM, GLDAS-Noah, QTP-SM, ESA CCI, and ERA5-Land, with higher median Pearson correlation coefficient (R) value (0.685, 0.686, 0.699, 0.704, 0.300, and 0.582 for QTP-DNN-Sm, Global-SM, GLDAS-Noah, QTP-SM, ESA CCI, and ERA5-Land, respectively) and lowest median unbiased Root Mean Square Error (ubRMSE) (0.061, 0.064, 0.068, 0.064, 0.042, 0.076, and 0.047 m3/m3 for QTP-DNN-Sm, Global-SM, GLDAS-Noah, QTP-SM, ESA CCI, ERA5-Land, and ESA CCI, respectively). 2) NDVI in the frozen soil zone was the best variable to explain SM based on the GeoDetector-based factor detection, and interaction detection results indicated that the interaction between NDVI and temperature was gradually emerging to explain SM from permafrost zones to seasonally frozen ground zones. 3) The nonlinear relationship function between SM and NDVI showed that vegetation growth in 47.76% of the area (mainly distributed in the Changjiang River, Yarlung Zangbo River, and Yellow River basins) was more influenced by phenology. Thresholds existed in 3.49% of TP, where the cumulative effect of SM affects vegetation growth. In 0.65% of the regions, vegetation growth experienced eco-physiological processes of positive relief of water stress and physical processes of negative damage. The ease with which SM altered vegetation growth trends was consistent with the degradation degree of frozen soil type. Although the percentage of regions where the thresholds exist is relatively small, the positive/negative effects of the complex localized inter between SM and vegetation in these regions could threaten the balance and stability of fragile alpine ecosystems sustained by permafrost.

The vegetation and ecosystem in the source region of the Yangtze River and the Yellow River (SRYY) are fragile. Affected by climate change, extreme droughts are frequent and permafrost degradation is serious in this area. It is very important to quantify the drought-vegetation interaction in this area under the influence of climate-permafrost coupling. In this study, based on the saturated vapor pressure deficit (VPD) and soil moisture (SM) that characterize atmospheric and soil drought, as well as the Normalized Differential Vegetation Index (NDVI) and solar-induced fluorescence (SIF) that characterize vegetation greenness and function, the evolution of regional vegetation productivity and drought were systematically identified. On this basis, the technical advantages of the causal discovery algorithm Peter-Clark Momentary Conditional Independence (PCMCI) were applied to distinguish the response of vegetation to VPD and SM. Furthermore, this study delves into the response mechanisms of NDVI and SIF to atmospheric and soil drought, considering different vegetation types and permafrost degradation areas. The findings indicated that low SM and high VPD were the limiting factors for vegetation growth. The positive and negative causal effects of VPD on NDVI accounted for 47.88% and 52.12% of the total area, respectively. Shrubs were the most sensitive to SM, and the response speed of grassland to SM was faster than that of forest land. The impact of SM on vegetation in the SRYY was stronger than that of VPD, and the effect in the frozen soil degradation area was more obvious. The average causal effects of NDVI and SIF on SM in the frozen soil degradation area were 0.21 and 0.41, respectively, which were twice as high as those in the whole area, and SM dominated NDVI (SIF) changes in 62.87% (76.60%) of the frozen soil degradation area. The research results can provide important scientific basis and theoretical support for the scientific assessment and adaptation of permafrost, vegetation, and climate change in the source area and provide reference for ecological protection in permafrost regions.

The increase in deciduous shrub growth in response to climate change throughout the Arctic tundra has uncertain implications, in part due to a lack of field observations. Here we investigate how increasing alder shrub growth in alpine tundra in Interior Alaska corresponds to active layer thickness and soil physical properties. We documented increased alder growth by combining biomass harvests and dendrochronology with the analysis of remotely sensed Normalized Difference Vegetation Index and fire history. Active layer thickness was measured with a tile probe and carbon and nitrogen pools were assessed via elemental analysis. Shallower organic layers under increasing alder growth indicate that nitrogen-rich, deciduous litter inputs may play a role in accelerating decomposition. Despite the observed reduction in organic carbon stocks, active layer thickness was the same under alder and adjacent graminoid tundra, implying deeper thaw of the underlying mineral soil. This study provides further evidence that the widely observed expansion of deciduous shrubs into graminoid tundra will reduce ecosystem carbon stocks and intensify soil-atmosphere thermal coupling. Two consequences of rapid climate warming in the Arctic, where grass-like plants dominate under very cold conditions, are an increased growth and occurrence of shrubs and associated thaw of frozen ground. This exposes organic matter in soils to microbes that can decompose it into carbonaceous greenhouse gases, but some of this carbon loss may be offset by the increased plant growth. Here, we investigate the impacts of greater shrub presence on soil properties at five sites in Alaska. We documented shrub growth by analyzing satellite images, which can help us understand the productivity and/or leaf coverage at each site back in time, and annual growth rings in shrub stems, which show how old the shrubs are and how much they grow each year. We also measured the depth of soil thaw in the field and its organic matter content in a laboratory. Where shrubs were more common, we found a thinner layer of organic matter at the soil surface. Thaw depth remained the same, which may indicate that the presence of shrubs results in deeper thaw of the mineral soil. Our findings support the hypothesis that shrub expansion will further enhance warming-driven increases of greenhouse gas emissions from Arctic landscapes. Trends in dendrochronology and Normalized Difference Vegetation Index reveal increasing growth of alder shrubs in Interior Alaska.More alder cover results in the loss of the soil organic layer and thus soil C and N that is not offset by more shrub biomass.Increasing alder growth may promote permafrost thaw not captured by tile probe active layer thickness monitoring.

The Granger Causality (GC) statistical test explores the causal relationships between different time series variables. By employing the GC method, the underlying causal links between environmental drivers and global vegetation properties can be untangled, which opens possibilities to forecast the increasing strain on ecosystems by droughts, global warming, and climate change. This study aimed to quantify the spatial distribution of four distinct satellite vegetation products' (VPs) sensitivities to four environmental land variables (ELVs) at the global scale given the GC method. The GC analysis assessed the spatially explicit response of the VPs: (i) the fraction of absorbed photosynthetically active radiation (FAPAR), (ii) the leaf area index (LAI), (iii) solar-induced fluorescence (SIF), and, finally, (iv) the normalized difference vegetation index (NDVI) to the ELVs. These ELVs can be categorized as water availability assessing root zone soil moisture (SM) and accumulated precipitation (P), as well as, energy availability considering the effect of air temperature (T) and solar shortwave (R) radiation. The results indicate SM and P are key drivers, particularly causing changes in the LAI. SM alone accounts for 43%, while P accounts for 41%, of the explicitly caused areas over arid biomes. SM further significantly influences the LAI at northern latitudes, covering 44% of cold and 50% of polar biome areas. These areas exhibit a predominant response to R, which is a possible trigger for snowmelt, showing more than 40% caused by both cold and polar biomes for all VPs. Finally, T's causality is evenly distributed amongst all biomes with fractional covers between similar to 10 and 20%. By using the GC method, the analysis presents a novel way to monitor the planet's ecosystem, based on solely two years as input data, with four VPs acquired by the synergy of Sentinel-3 (S3) and 5P (S5P) satellite data streams. The findings indicated unique, biome-specific responses of vegetation to distinct environmental drivers.

As an important component of the climate system, permafrost responds significantly to climate change, and its impact on the ecosystem cannot be ignored. In this study, we analyzed the temporal and spatial variation trends of the normalized difference vegetation index (NDVI) in Arctic permafrost regions and revealed the correlation between the active-layer thickness (ALT), soil temperature, and NDVI change. Using the partial correlation method, we assessed the ecological regulation service of permafrost to the ecosystem. The results showed that both the average annual maximum and summer NDVI values in the Arctic region followed a significant increasing trend from 1982 to 2015. The average correlation coefficient (ACC) between Arctic NDVI and ALT was 0.35, followed by the ACC (0.33) between NDVI and soil temperature at 7-28 cm depth, and had a lower ACC (0.31) at 0-7 cm ALT. When the precipitation and snow water equivalent (SWE) remained unchanged, the partial correlation between NDVI and ALT was 0.711, which was a significant positive correlation. It also showed that permafrost degradation was the dominant factor controlling Arctic NDVI increase, whereas precipitation and SWE had little effect. The study revealed the impact of permafrost on NDVI change, deepened our understanding of the importance of permafrost degradation for ecosystem services, and effectively filled the gap that tundra ecosystem services value has been ignored in the global ecological service value assessment.

As an important component of the climate system, permafrost responds significantly to climate change, and its impact on the ecosystem cannot be ignored. In this study, we analyzed the temporal and spatial variation trends of the normalized difference vegetation index (NDVI) in Arctic permafrost regions and revealed the correlation between the active-layer thickness (ALT), soil temperature, and NDVI change. Using the partial correlation method, we assessed the ecological regulation service of permafrost to the ecosystem. The results showed that both the average annual maximum and summer NDVI values in the Arctic region followed a significant increasing trend from 1982 to 2015. The average correlation coefficient (ACC) between Arctic NDVI and ALT was 0.35, followed by the ACC (0.33) between NDVI and soil temperature at 7-28 cm depth, and had a lower ACC (0.31) at 0-7 cm ALT. When the precipitation and snow water equivalent (SWE) remained unchanged, the partial correlation between NDVI and ALT was 0.711, which was a significant positive correlation. It also showed that permafrost degradation was the dominant factor controlling Arctic NDVI increase, whereas precipitation and SWE had little effect. The study revealed the impact of permafrost on NDVI change, deepened our understanding of the importance of permafrost degradation for ecosystem services, and effectively filled the gap that tundra ecosystem services value has been ignored in the global ecological service value assessment.