Changes In Vegetation Phenology Research Articles

Sentinel-2 time series: a promising tool in monitoring temperate species spring phenology

Abstract The changes in vegetation phenology observed in recent decades may have significant implications for carbon, water, and energy fluxes as well as ecosystem productivity. Phenology is an important indicator of a changing environment, and studying species-specific phenology can help understand their responses to varying climate conditions. While satellite-based phenology provides long-term information for large areas, it describes different traits than ground-based phenology. Nonetheless, emerging research on remote sensing-based phenology has shown its usefulness in determining inter- and intra-specific differences, as well as interannual changes. In this study, we examined the potential of the Sentinel-2 time series from 2018 to 2022 in assessing the spring phenology of seven temperate tree species. Three vegetation indices were calculated, namely, the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index, the Normalized Difference Vegetation Index, and the Enhanced Vegetation Index. We examined interspecific variations in the start of the season (SOS) and interannual variability. Additionally, we explored intraspecific variations in spring phenology among common beech stands across an elevation gradient. Our findings reveal substantial differences in Sentinel-2-derived phenology across species, with larch, birch, and hornbeam displaying an earlier SOS compared with oak and alder. The latest SOS dates were observed in 2021, whereas the earliest occurred in 2018 and the difference exceeded 20 days. It corresponded to the diverse spring meteorological conditions in the examined years, with the highest heat accumulation in 2018 and the lowest in 2021. Additionally, the three examined indices showed different phenological curves, with MERIS Terrestrial Chlorophyll Index exhibiting distinct patterns with a delayed start of the spring increase compared with the other two indices. The relationship between elevation and SOS dates was generally positive, but there was high variability in some years. The earliest SOS dates occurred at ~600 m a.s.l. and larger interannual variations were observed for stands located on the highest elevations. These results underscore the potential of Sentinel-2 in monitoring the spring phenology of temperate species, offering insights into inter- and intra-specific variations, as well as year-to-year changes. In the future, longer Sentinel-2 time series will improve estimates and facilitate the tracking of long-term changes. Such advancements hold relevance for forest management, carbon budget predictions, and understanding ecosystem dynamics.

Study on the Spatial and Temporal Distribution of Urban Vegetation Phenology by Local Climate Zone and Urban–Rural Gradient Approach

Understanding variations in the temporal and spatial distribution of vegetation phenology is essential for adapting to and mitigating future climate change and urbanization. However, there have been limited vegetation phenology studies within small-scale areas such as urban environments over the past decades. Therefore, the present study focuses on Jinan city, Shandong Province, China as the study area and employs a more refined local climate zone (LCZ) approach to investigate spatial and temporal variations in vegetation phenology. The three phenological indicators used in this study from 2007 to 2018, namely, the start of growing season (SOS), the end of growing season (EOS), and the length of growing season (LOS), were provided by MODIS satellite data. The SOS, EOS, and LOS were superimposed on the LCZ and urban–rural gradient to analyze the changes in vegetation phenology, and the applicability of these two analysis methods in the study of urban vegetation phenology was compared by the honest significant difference test. We found that the SOS, EOS, and LOS of vegetation in the study area generally showed an advance, delay, and extension trend, respectively. The means of the SOS and EOS along different LCZ types varied noticeably more than those along urban–rural gradients. In 2016, 77.5%, 80.0%, and 75.8% of LCZ pairs indicated statistically significant differences for SOS, EOS, and LOS, respectively. This study provides a new perspective for the study of urban vegetation phenology which can help in management of urban-scale environments, identification of areas rich in biodiversity, and conservation and restoration of biodiversity in urban areas.

Magnitude and direction of green-up date in response to drought depend on background climate over Mongolian grassland

Increasing drought is one major consequence of ongoing global climate change and is expected to cause significant changes in vegetation phenology, especially for naturally vulnerable ecosystems such as grassland. However, the linkage between the response characteristic of green-up date (GUD) to drought and background climate remains largely unknown. Here, we focused on how the GUD of Mongolian grassland responds to extreme drought events (EDE). We first extracted the GUD from the MODIS Enhanced Vegetation Index data during 2001–2020 and identified the preseason EDE using the standardized precipitation evapotranspiration index data. Subsequently, we quantified the response of GUD to preseason EDE (DGUD) in each pixel as the difference in GUD between drought and normal years. The effect of 12 factors on DGUD was analyzed using the random forest algorithm. The results showed that the GUD under EDE may delay or advance by > 20 days compared to normal years. For the regions with mean annual temperature > −2 °C, the GUD was delayed under EDE due to the dominant role of water restriction on GUD, while the GUD was advanced under EDE in colder areas due to the warmer temperature during drought. However, the magnitude of delay in GUD under drought was greater in regions with less precipitation and more severe droughts. Our results could help to develop appropriate management strategies to mitigate the impacts of drought on grasslands.

Spatial heterogeneity of vegetation phenology caused by urbanization in China based on remote sensing

Vegetation phenology changes caused by urbanization could lead to shifts in ecosystem services in urban areas and impact on human health. The characteristics of urbanization affect vegetation phenology need to be emphasized, especially in China with a complex natural environment and rapid urbanization background. In this study, we used remote sensing-based phenological data (MODIS MCD12Q2) to analyze the spatial heterogeneity of vegetation phenology caused by urbanization between urban and non-urban areas in 320 cities across China. We found a significant difference between vegetation phenology in urban and its corresponding non-urban area at national and the regional scale. For national scale, the start of the growing season (SOS) was significantly advanced by 2.53 days (P < 0.001), and the end of the growing season (EOS) was significantly delayed by 6.72 days (P < 0.001), resulting in the growing season length (GSL) was significantly extended by 9.25 days (P < 0.001). For regional scale, the changes of SOS, EOS, and GSL caused by urbanization varied from seven vegetation zones in China. As expected for the Tropical monsoon rain forest and rain forest zone (TR) and Tibetan plateau alpine vegetation zone (TP), and Warm-temperate broadleaf deciduous forest zone (WTB), vegetation phenology in other four vegetation zones shows significant differences between urban and non-urban areas. Furthermore, the potential factors driving phenological changes through urbanization were discussed, which will be of great help in understanding the urban ecological process in future studies.

Urban environments provide new perspectives for forecasting vegetation phenology responses under climate warming.

Given that already-observed temperature increase within cities far exceeds the projected global temperature rise by the end of the century, urban environments often offer a unique opportunity for studying ecosystem response to future warming. However, the validity of thermal gradients in space serving as a substitute for those in time is rarely tested. Here, we investigated vegetation phenology dynamics in China's 343 cities and empirically test whether phenological responses to spatial temperature rise in urban settings can substitute for those to temporal temperature rise in their natural counterparts based on satellite-derived vegetation phenology and land surface temperature from 2003 to 2018. We found prevalent advancing spring phenology with "high confidence" and delaying autumn phenology with "medium confidence" under the context of widespread urban warming. Furthermore, we showed that space cannot substitute for time in predicting phenological shifts under climate warming at the national scale and for most cities. The thresholds of ~11°C mean annual temperature and ~600 mm annual precipitation differentiated the magnitude of phenological sensitivity to temperature across space and through time. Below those thresholds, there existed stronger advanced spring phenology and delayed autumn phenology across the spatial urbanization gradients than through time, and vice versa. Despite the complex and diverse relationships between phenological sensitivities across space and through time, we found that the directions of the temperature changes across spatial gradients were converged (i.e., mostly increased), but divergent through temporal gradients (i.e., increased or decreased without a predominant direction). Similarly, vegetation phenology changes more uniformly over space than through time. These results suggested that the urban environments provide a real-world condition to understand vegetation phenology response under future warming.

Climate warming-induced phenology changes dominate vegetation productivity in Northern Hemisphere ecosystems

The climate change is expected to trigger changes in vegetation phenology, temperature, and soil moisture (SM), altering the productivity of ecosystems. Despite numerous existing efforts, however, their contradicting conclusions suggest that how vegetation productivity is impacted by these factors still remains unclear in the Northern Hemisphere ecosystems (≥25°N). This study used the optimal fingerprint (OFP) method and redundancy analysis (RDA) to attribute the importance of key drivers of vegetation productivity from 2001 to 2019 based on long-term remote sensing and FLUXNET observation data. The results showed that solar-induced chlorophyll fluorescence (SIF), gross primary productivity (GPP), and net primary productivity (NPP) were increased in 72.01% to 88.04% of the vegetation areas. We observed that the correlation between vegetation productivity and spring phenology, autumn phenology, growing season length (GSL), SM, temperature reached 99% significance level, where early spring phenology, delayed autumn phenology, extended GSL, increased SM, and elevated temperature all enhanced ecosystem productivity, with GSL being the most important factor driving vegetation productivity. In addition, the pixel-wise attribution analysis indicated that GSL, as the dominant driver, accounted for 30.24% of the vegetation productivity, followed by temperature (23.79%), spring phenology (19.56%), autumn phenology (14.09%), and SM (12.31%), all of which were dominated by positive effects (54.19% to 73.14%). The results from this study serve as important references that benefit our understanding of driving mechanisms of temperature-phenology-SM interactions on ecosystem productivity.

A dataset of vegetation phenology and change trends with a resolution of 500m of on the Mongolian Plateau (2001–2019)

Located in the highland of Eurasia, the Mongolian Plateau, a typical arid and semi-arid region, is highly sensitive to climate change. Vegetation phenology is the most intuitive and sensitive biological indicator of seasonal and interannual changes of climatic conditions. Vegetation phenology data can be used to explore the ecological situation and climate change of the Mongolian Plateau. Based on THE MODIS land cover Dynamic Product (MCD12Q2 C6), in this paper, we used non-parametric Theil-Sen Median trend analysis and Mann-Kendall significance test to extract sub-datasets, Mosaic, projection transformation and cropping. In this way, we obtained the data of four phenological periods (namely the beginning time, the end time, the length of the growing season and the peak time of the growing season) and the change trend data of vegetation of 500m resolution on the Mongolian Plateau from 2001 to 2019. This dataset can reflect the spatio-temporal changes of vegetation phenology in 19 years on the Mongolian Plateau. Combined with climate factors such as temperature and precipitation, it can be used to explore the response and feedback mechanism of vegetation phenology change to environmental factors, and provide data support for vegetation change analysis, climate change, carbon cycle and other studies.

A dataset of vegetation phenology of Inner Mongolia (2001-2020)

Vegetation phenology is one of the sensitive indicators reflecting global climate change and vegetation growth. Inner Mongolia is an important part of the ecological security barrier of the Mongolian Plateau, and a key area for resource development, environmental protection and ecological security in China. The study on the vegetation phenological changes of Inner Mongolia is of great significance for understanding the characteristics of climate change and extreme climate events in Inner Mongolia. Based on the normalized differential vegetation index (NDVI) in the high-spatial resolution MOD13Q1 data product, we used Google Earth Engine platform to process MODIS-NDVI raw data for format conversion, projection conversion and clipping, and exported NDVI long time series data from 2000 to 2021. Then, we adopted the dynamic threshold method to obtain a dataset of vegetation phenology of Inner Mongolia from 2001 to 2020. With a resolution of 250 m, this dataset contains remote sensing monitoring data of the start of growing season (SOS), the end of growing season (EOS), and the length of growing season (LOS) in Inner Mongolia from 2001 to 2019. It can provide data support for understanding the temporal and spatial variation of vegetation phenology in Inner Mongolia and its response to climate change.

Grazing alters vegetation phenology by regulating regional environmental factors on the Tibetan Plateau

Grazing can alter vegetation material and energy flow, influencing ecosystem structure and function. However, the direction and magnitude of the phenological response to grazing intensity remain relatively unexplored. Using grazing datasets encompassing 114 counties on the Tibetan Plateau (TP) combined with satellite retrievals of solar-induced chlorophyll fluorescence, we investigated the impact of grazing intensity on vegetation photosynthetic phenology from 2000 to 2015. Results showed earlier trends for the start of the growing season (SOS) and the end of the growing season (EOS) across an increased grazing intensity gradient. We found that the sensitivity of the SOS and the EOS to grazing intensity decreased with increasing grazing intensity level. Importantly, structural equation modeling (SEM) indicated that grazing indirectly contributed to the shift of SOS and EOS by regulating environmental factors. Specifically, decreasing grazing intensity increased soil moisture, which contributed to the earlier SOS under light grazing intensity level in spring. In contrast, higher near-surface maximum temperatures and decreased soil moisture induced by grazing promoted the earlier EOS in autumn under moderate and heavy grazing intensity levels. These findings improve our understanding of the response of vegetation phenology to grazing intensity and present new insights for assessing the effects of grazing on vegetation phenology changes.

Temporal and Spatial Changes of Vegetation Phenology and Their Response to Climate in the Yellow River Basin

Temporal and Spatial Changes of Vegetation Phenology and Their Response to Climate in the Yellow River Basin

Response of vegetation phenology to urbanization in urban agglomeration areas: A dynamic urban–rural gradient perspective

Being an important theme in global warming, the response of vegetation phenology to urbanization has become an increasing concern at both the local and global levels. Previous studies have focused on spatial or temporal responses across urban–rural gradients; thus, the influence of urbanization on vegetation phenology along the dynamic urbanization gradient has not been well quantified. In this study, we comprehensively analyzed the response of vegetation phenology to urbanization in the Guangdong–Hong Kong–Macao Greater Bay Area (GHM-GBA) from a dynamic urban–rural gradient perspective. The results show that the response of vegetation phenology to urbanization level has a distinct spatiotemporal difference across the urban–rural gradient. Compared to rural areas, the change rate of advancements in the start-of-season (SOS) in urban domains was 1.16 DOY/year and that of the end-of-season (EOS) was 0.63 days/year from 2001 to 2020. In the GHM-GBA region, 61.03 % of the remote sensing pixels showed an advancing trend for SOS and 55.75 % for EOS. Urbanization advanced the SOS and EOS but did not extend the growing season length, and the SOS and EOS were advanced by 7 and 6 days along the urban-to-rural gradient, respectively. For every 10 % increase in urbanization levels, the SOS and EOS advanced by 1.085 and 1.091 days across the urban–rural gradient, respectively; the spring land surface temperature (LST) advanced the SOS at a rate of 1.71 days/°C, while the autumn LST advanced the EOS at a rate of 1.88 days/°C. The phenological shift in the urban–rural gradient was more significant than that over time, which was mainly because of land surface warming under different urbanization levels. These quantitative findings are of great importance for understanding the complicated impacts of urbanization on vegetation phenology and for developing models to predict vegetation phenological changes under future urbanization.

Spatial–Temporal Pattern and Influencing Factors of Vegetation Phenology and Net Primary Productivity in the Qilian Mountains of Northwest China

Understanding how vegetation growth responds to climate change is a critical requirement for predicting future ecosystem dynamics. Global warming causes significant changes in the vegetation characteristics of mountain ecosystems, particularly affecting vegetation phenology and net primary productivity (NPP). The Qilian Mountains are located in an arid and semiarid region, and the mechanisms of vegetation phenology in response to climate change still need to be further explored. We used MODIS data (2001–2020) to extract vegetation phenology and NPP, quantitatively evaluated their spatial–temporal dynamics, and analyzed the response mechanism of vegetation phenology–climate and vegetation phenology–NPP combined with meteorological data. The results showed that from southeast to northwest, the vegetation phenology changes significantly with the change in vegetation type, with SOS (start of the growing season) advancing at a rate of −0.415 d/year, EOS (end of the growing season) and LOS (length of the growing season) delaying at a rate of 0.20 d/year and 0.374 d/year, respectively, and NPP continues to increase. There was also an elevation gradient effect, with SOS delayed by 15.6 d/km, EOS advanced by 12.02 d/km and LOS shortened by 19.24 d/km. We found that the preseason temperature and SPEI (standardized precipitation evapotranspiration index) have a strong influence on the SOS and EOS, with the mean minimum temperature being the most significant and requiring attention, while the influence of precipitation cannot be ignored. We also found that the vegetation phenology is closely related to NPP, and SOS has the most significant effect. This study will provide a scientific basis for the response mechanisms of vegetation phenology in arid and semiarid regions under climate change. It will provide a reference for the implementation of effective ecosystem management.

Long-term vegetation phenology changes and response to multi-scale meteorological drought on the Loess Plateau, China

Investigating the response of vegetation phenology to meteorological drought can provide insight into the feedback mechanisms of ecosystems to environmental and climate change. These key phenological parameters of vegetation are extracted on the China's Loess Plateau (LP) based on TimeSat using MODIS remote sensing data, and their trends are estimated using Sen's slope. Then, response of key physical parameters of vegetation phenology to multi-scale drought was investigated using Standardized Precipitation Evapotranspiration Index (SPEI). The results show that: 1) LP vegetation Start of Season (SOS) and Peak of Season (POS) are delayed from south (low elevation) to north (high elevation). End of Season (EOS) is delayed from northeast to southwest. Length of Season (LOS) show decrease trend with altitude and latitude increasing. Besides, temporal variation of different vegetation phenological periods is highest in farmland and is lowest in the forest. 2) Vegetation SOS and POS are advanced in the eastern part of LP and delayed in the western part. Meanwhile, EOS and LOS are advanced in the southern part of LP. 3) The POS and EOS of LP vegetation responded more significantly to drought. The western Longzhong Plateau of LP was susceptible to the negative effects of preseason drought, and the eastern Northern Shaanxi Plateau and Taihang Mountains were susceptible to the positive effects. Moreover, monthly- and seasonal-scale droughts have significantly effects on vegetation phenology than annual-scale drought. 4) Compared to forest and grassland, the vegetation phenology of farmland is more sensitive to monthly- and seasonal-scale droughts. However, the response of forest to annual-scale drought is more significant. The results of the study could provide scientific basis for crop yield stabilization and agricultural disaster warning in the LP. Keywords: Vegetation phenology; TimeSat; Drought response; Loess Plateau.

Spatial and Temporal Variation in Alpine Vegetation Phenology and Its Response to Climatic and Topographic Factors on the Qinghai–Tibet Plateau

Vegetation phenology changes are able to reveal climate-change-associated ecosystem feedback mechanisms. In this study, Qinghai–Tibet Plateau (QTP) alpine vegetation phenological information was extracted from the normalised difference vegetation index of the MOD13Q1 product collected from 2001 to 2020 using TIMESAT3.3 and S-G filtering and threshold dynamics methods. An analysis of data from the start of growth (SOG) and end of growth (EOG) seasons using a Theil–Sen median slope trend and partial correlation analyses revealed spatial and temporal variations in vegetation phenology related to climate change and topography, including: (1) significant spatial variation, gradually increasing southeast-to-northwest SOG delays and northeast-to-southwest EOG delays, with significant variations across vegetation types; (2) significant altitude-associated variations in the meadow, steppe, and shrub alpine vegetation types with high-altitude boundaries of 2400 m, 2800 m, and 2600 m, respectively, with delayed and earlier SOG and EOG below and above each boundary, respectively; and (3) spatial variations in relationships between vegetation phenology changes and climatic factors, where SOG negatively and EOG positively correlated with temperature and precipitation. The mean temperature in the 30 days before SOG and mean total precipitation in the 30 days before EOG were significantly correlated with SOG and EOG timing both negatively and positively, respectively. These results provide guidance for the monitoring of the alpine vegetation phenology on the QTP.

Acceleration of vegetation phenological changes.

Piao et al. (2022) presents an interesting study on vegetation phenology from a novel angle. The study examined the speed of canopy development and senescence, or the "acceleration of vegetation phenological changes", and investigated its relationship with the trend of vegetation greening/browning and the underlying climate driving factors. It is an important contribution to the understanding of vegetation response to climate change, and may inspire new directions of vegetation phenology research.

Effect of Altitude and Topography on Vegetation Phenological Changes in the Niubeiliang Nature Reserve of Qinling Mountains, China

Due to the fragility of the habitats in mountain nature reserves, the vegetation is extremely sensitive to climate change, and its phenological changes are more specific. Therefore, it is of great significance to study the effects of topography and climate on the vegetation phenology in mountain nature reserves. Based on the vegetation phenology data retrieved from MODIS EVI2 during 2000 to 2017, combined with temperature data, spatial trend analysis and correlation analysis methods were used to study the effects of topographic and climatic factors on vegetation phenology in the Niubeiliang Nature Reserve of the Qinling Mountains. The results showed that the GSS (growing season start) was advanced with a rate of 4.24 days/10a, and the rates in the northern and southern slopes were almost the same; the GSE (growing season end) was delayed with a rate of 3.29 days/10a, and the rate in the northern slope was faster; and the GSL (growing season length) was prolonged. There were seasonal differences and north–south differences in the effects of topography on the phenophase. The phenophase changed regularly with the increase in altitude. The higher the altitude, the more significant the effect. The steeper the slope, the later the GSS, the earlier the GSE, and the more significant its effect on the GSE. The aspect had little effect on GSS but a more significant effect on GSE, which was the latest on the sunny slope and the earliest on the zero slope. Temperature affected both the GSS advance and the GSE delay, and both had a time-lag effect of approximately 2–3 months. Its effect was more significant in the GSE, in the southern slopes, and in the high-altitude areas.

Photosynthesis phenology, as defined by solar-induced chlorophyll fluorescence, is overestimated by vegetation indices in the extratropical Northern Hemisphere

Vegetation phenology is highly sensitive to climate change, although the data and methods used to estimate key phenological states can influence this sensitivity. Because of its direct relation to leaf photosynthetic carbon uptake, remotely sensed solar-induced chlorophyll fluorescence (SIF) can provide new insight assessing changes in vegetation phenology. Here, we investigated the potential of using a SIF time series product named contiguous SIF (CSIF) to estimate spring, summer, and autumn phenology in the extratropical Northern Hemisphere (>30°N) and compared the results with those based on Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) for the period 2001–2018. Overall, we found similar spatial patterns in phenological states. However, specific dates of key phenological events differed when using CSIF vs. MODIS NDVI data. NDVI data indicated that the growing season started earlier (by 10.1 days on average) and ended later (11.5 days on average) relative to CSIF data. This implies that actual periods for photosynthetic activity are shorter (by 21.6 days on average) than those estimated from vegetation indices more directly related to changes in canopy structure. These large differences between results from NDVI and that from CSIF suggest that vegetation indices such as NDVI seem to overestimate the period for active photosynthesis over the extratropical Northern Hemisphere. Furthermore, while phenology of the early growing season is dominated by temperature for both NDVI and CSIF data, phenology of the late growing season is mainly controlled by temperature for NDVI but by precipitation for CSIF. Our findings were further confirmed by other SIF (GOME-2 SIF) and vegetation index (MODIS EVI) datasets. Phenology modes in Earth system modelling are often parameterized using leaf unfolding and senescence from either station or satellite observations. Our results imply that canopy structure-based parameterization schemes may have overestimated photosynthesis active period, and thus productivity responses. We conclude that SIF data offers a novel and unique approach for assessing phenological change - one that is more directly tied to the carbon cycle and how it is being influenced by climate change.

Vegetation Greening, Extended Growing Seasons, and Temperature Feedbacks in Warming Temperate Grasslands of China

Abstract Vegetation activity and phenology are significantly affected by climate change, and changes in vegetation activity and phenology can in turn affect regional or global climate patterns. As one of the world’s great biomes, temperate grasslands have undergone remarkable changes in recent decades, but the connections between vegetation activity and phenology changes and regional climate there have remained unclear. Using the observation minus reanalysis (OMR) method, this study investigated the possible effects of vegetation activity and vegetation growing season changes on air temperatures in temperate grasslands of China. The results showed that average NDVI of the temperate grassland significantly increased by 0.011 decade−1 for the growing season during 1982–2015. The growing season started earlier and ended later, resulting in an extension. Increased vegetation activity during spring and autumn significantly warmed spring and autumn air temperatures by reducing albedo. By contrast, summer greening had no significant effect on summer temperature, due to the opposing effects of decreased albedo and enhanced evapotranspiration on temperature. The earlier start and later end of the growing season contributed to warmer spring and autumn air temperatures. As phenological changes had no significant effect on summer temperature, the extended growing season warmed air temperature. Our results suggest that the climate change–induced increasing vegetation activity and extended growing seasons can further aggravate regional warming in temperate grasslands of China, implying that the effects of vegetation activity and phenology changes on regional climate should be considered in climate models for accurately simulating climate change in temperate grasslands.

Spatio-temporal monitoring of marsh vegetation phenology and its response to hydro-meteorological factors using CCDC algorithm with optical and SAR images: In case of Honghe National Nature Reserve, China

Vegetation phenology is a sensitive indicator which can comprehensively reflect the response of wetland vegetation to external environment changes. However, the time-series monitoring wetland vegetation phenological changes and clarifying its response to hydrology and meteorology still face great challenges. To fill these research gaps, this paper proposed a novel time-series approach for monitoring phenological change of marsh vegetation in Honghe National Nature Reserve (HNNR), Northeast China, using continuous change detection and classification (CCDC) algorithm and Landsat and Sentinel-1 SAR images from 1985 to 2021. We evaluated the spatio-temporal response relationship of phenological characteristics to hydro-meteorological factors by combining CCDC algorithm with partial least squares regression (PLSR). Finally, this study further explored the intra-annual loss and restoration of marsh vegetation in response to hydro-meteorological factors using the transfer entropy (TE) and CCDC-MLSR model constructed by CCDC and Multiple Linear Stepwise Regression (MLSR) algorithms. We found that the bimodal trajectory of phenology reflects two growth processes of marsh vegetation in one year, and high-frequency and high-amplitude loss occurred in shallow-water and deep-water marsh vegetation from April to October, resulting in the loss area within the year was significantly greater than the recovery area. We confirmed that the CCDC algorithm could track the evolution trajectory of time-series phenology of marsh vegetation. We further revealed that precipitation, temperature and frequency of water-level changes are the main driving factors for the spatio-temporal phenological evolution of different marsh vegetation. This study verified the effect of alternative changes of hydrology and climate on loss and recovery of marsh vegetation in each growth stage. The results of this study provide a scientific basis for wetland protection, ecological restoration, and sustainable development.

Distribution and Attribution of Earlier Start of the Growing Season over the Northern Hemisphere from 2001–2018

The start of the growing season (SOS) is a vital ecological indicator for climate change and the terrestrial ecosystem. Previous studies have reported that the SOS over the Northern Hemisphere (NH) has experienced remarkable changes in the past few decades. However, because of the different spatial and temporal coverages of existing SOS studies, a coherent and robust account for SOS changes in the NH has been lacking. Using satellite-retrieved vegetation-phenology datasets, ground observations, and several auxiliary datasets, this study evaluated the performance of the latest MODIS vegetation-dynamics dataset (MCD12Q2-C6) and explored the distribution and attribution of the SOS to climate change over the NH for the period 2001–2018. The validation results using the Chinese Ecosystem Research Network (CERN) and Lilac-leafing observations (Lilac) displayed that the MCD12Q2-C6 has a good performance in SOS monitoring over the NH mid-latitudes. Meanwhile, evidence from MCD12Q2-C6 pointed out that the SOS was advanced by 2.08 days on average over the NH during 2001–2018, especially for Europe, China, and Alaska, United States. In addition, detailed-sensitivity analysis showed that the increased surface air temperature (Ts) (−1.21 ± 0.34 days °C−1) and reduced snow-cover fraction (Sc) (0.62 ± 0.29 days%−1) were the key driving factors of the observed SOS changes over the NH during 2001–2018. Compared with Ts and Sc, the role of total precipitation (Pt) was minor in dominating the spring vegetation-phenology changes at the same period. The findings of this study contribute to our understanding of the responses of SOS to the competing changes of Ts, Pt, and Sc over the NH.