Global climate changes have a great impact on terrestrial ecosystems. Vegetation is an important component of ecosystems, and the impact of climate changes on ecosystems can be determined by studying vegetation phenology. Vegetation phenology refers to the phenomenon of periodic changes in plants, such as germination, flowering and defoliation, with the seasonal change of climate during the annual growth cycle, and it is considered to be one of the most efficient indicators to monitor climate changes. This study collected the global land surface satellite leaf area index (GLASS LAI) products, meteorological data sets and other auxiliary data in the Three-River headwaters region from 2001 to 2018; rebuilt the vegetation LAI annual growth curve by using the asymmetric Gaussian (A-G) fitting method and extracted the three vegetation phenological data (including Start of Growing Season (SOS), End of Growing Season (EOS) and Length of Growing Season (LOS)) by the maximum slope method. In addition, it also integrated Sen’s trend analysis method and the Mann-Kendall test method to explore the temporal and spatial variation trends of vegetation phenology and explored the relationship between vegetation phenology and meteorological factors through a partial correlation analysis and multiple linear regression models. The results of this study showed that: (1) the SOS of vegetation in the Three-River headwaters region is concentrated between the beginning and the end of May, with an interannual change rate of −0.14 d/a. The EOS of vegetation is concentrated between the beginning and the middle of October, with an interannual change rate of 0.02 d/a. The LOS of vegetation is concentrated between 4 and 5 months, with an interannual change rate of 0.21 d/a. (2) Through the comparison and verification with the vegetation phenological data observed at the stations, it was found that the precision of the vegetation phonology extracted by the A-G method and the maximum slope method based on GLASS LAI data is higher (MAE is 7.6 d, RMSE is 8.4 d) and slightly better than the vegetation phenological data (MAE is 9.9 d, RMSE is 10.9 d) extracted based on the moderate resolution imaging spectroradiometer normalized difference vegetation index (MODIS NDVI) product. (3) The correlation between the SOS of vegetation and the average temperature in March–May is the strongest. The SOS of vegetation is advanced by 1.97 days for every 1 °C increase in the average temperature in March–May; the correlation between the EOS of vegetation and the cumulative sunshine duration in August–October is the strongest. The EOS of vegetation is advanced by 0.07 days for every 10-h increase in the cumulative sunshine duration in August–October.

https://www.mdpi.com/2072-4292/14/15/3748/pdf?version=1660004199

LAI-Based Phenological Changes and Climate Sensitivity Analysis in the Three-River Headwaters Region

Temperate forests are particularly exposed to climate change and the associated increase in weather extremes. Droughts, storms, late frosts, floods, heavy snowfalls, or changing climatic conditions such as rising temperatures or more erratic precipitation are having an increasing impact on forests. There is an urgent need to better assess the impacts of climate change and extreme weather events (EWEs) on temperate forests. Remote sensing can be used to map forests at multiple spatial, temporal, and spectral resolutions at low cost. Different approaches to forest change assessment offer promising methods for a broad analysis of the impacts of climate change and EWEs. In this review, we examine the potential of Earth observation for assessing the impacts of climate change and EWEs in temperate forests by reviewing 126 scientific papers published between 1 January 2014 and 31 January 2024. This study provides a comprehensive overview of the sensors utilized, the spatial and temporal resolution of the studies, their spatial distribution, and their thematic focus on the various abiotic drivers and the resulting forest responses. The analysis indicates that multispectral, non-high-resolution timeseries were employed most frequently. A predominant proportion of the studies examine the impact of droughts. In all instances of EWEs, dieback is the most prevailing response, whereas in studies on changing trends, phenology shifts account for the largest share of forest response categories. The detailed analysis of in-depth forest differentiation implies that area-wide studies have so far barely distinguished the effects of different abiotic drivers at the species level. 

Potential of Earth Observation to Assess the Impact of Climate Change and Extreme Weather Events in Temperate Forests—A Review

Rapid urbanization has led to extensive effects on the spatio-temporal patterns of the carbon sources and sinks in ecosystems. However, due to the lack of long-term continuous land use/cover change (LUCC) data, there has been limited discussion on the spatio-temporal impacts of urbanization on carbon sources/sinks and the non-linear characteristics of urban changes over time. This study focused on the impact of urbanization on vegetation net ecosystem productivity (NEP) in 31 provincial capital cities in China from 1990 to 2019, using land use change data and NEP indicators, to analyze the change patterns and response modes of urbanization intensity and NEP. The study found that: (1) During the period of 1990–1995, almost all cities in China experienced a turning point of urbanization rate from decreasing to increasing, while after 2000, the urbanization rate declined significantly; (2) Climate background affects the negative impact of urbanization on NEP, especially in warm and humid climate background, while the direct impact of urbanization on vegetation is more significant; (3) Overall, urbanization in China aggravated the negative impact of urbanization on NEP from 1990 to 2019, especially in cold and arid climate background, which would further exacerbate the negative impact of urbanization. This study helps us better understand the impact of Chinese urbanization on ecosystem carbon sinks and mitigating the carbon emissions pressure of urban environments. 

How urbanization shapes the ecosystem carbon sink of vegetation in China: A spatiotemporal analysis of direct and indirect effects

Carbon uptake of vegetation is controlled by phenology and photosynthetic carbon uptake capacity. However, our knowledge of the seasonal responses of vegetation productivity to phenological and physiological changes in alpine ecosystems is still weak. In this study, we quantified the spatio-temporal variations of vegetation phenology and gross primary productivity (GPP) across the source region of the Yellow River (SRYR) by analyzing MODIS-derived vegetation phenology and GPP from 2001 to 2019, and explored how vegetation phenology and maximum carbon uptake capacity (GPPmax) affected seasonal GPP over the region. Our results showed that the SRYR experienced significantly advanced trends (p &lt; 0.05) for both start (SOS) and peak (POS) of the growing season from 2001 to 2019. Spring GPP (GPPspr) had a significantly increasing trend (p &lt; 0.01), and the earlier SOS had obvious positive effects on GPPspr. Summer GPP (GPPsum) was significantly and negatively correlated to POS (p &lt; 0.05). In addition, GPPmax had a significant and positive correlation with GPPsum and GPPann (p &lt; 0.01), respectively. It was found that an earlier spring-summer phenology and higher photosynthetic peak enhanced the photosynthetic efficiency of vegetation in spring and summer and altered the seasonal patterns of vegetation productivity in the SRYR under warming and wetting climates. This study indicated that not only spring and autumn phenology but also summer phenology and maximum carbon uptake capacity should be regarded as crucial indicators regulating the carbon uptake process in alpine ecosystems. This research provides important information about how changes in phenology affect vegetation productivity in alpine ecosystems under global climate warming. 

Earlier Spring-Summer Phenology and Higher Photosynthetic Peak Altered the Seasonal Patterns of Vegetation Productivity in Alpine Ecosystems

Warming associated with climate change will likely continue to advance the onset of spring phenology for many forest plants across the eastern United States. Understory forbs and spring ephemerals which fix a disproportionate amount of carbon during spring may be negatively affected by earlier canopy closure (i.e., phenological windows), however, information on the spatial patterns of phenological change for these communities is still lacking. To assess the potential for changes in spring phenological windows we synthesized observations from the Appalachian Mountain Club’s (AMC) Mountain Watch (MW) project, the National Phenology Network (NPN), and AMC’s iNaturalist projects between 2004 and 2022 (n = 118,250) across the length of the Appalachian Trail (AT) Corridor (34°N-46°N latitude). We used hierarchical Bayesian modeling to examine the sensitivity of day of year of flowering and leaf-out for 11 understory species and 14 canopy tree species to mean spring temperature (April-June). We conducted analyses across the AT Corridor, partitioned by regions of 4° latitude (South, Mid-Atlantic, and North). Spring phenologies for both understory plants and canopy trees advanced with warming (∼6 days/°C and ∼3 days/°C, respectively). However, sensitivity of each group varied by latitude, with phenology of trees and understory plants advancing to a greater degree in the mid-Atlantic region (∼10 days/°C) than the southern or northern regions (∼5 days/°C). While we find evidence that phenological windows remain stable in southern and mid-Atlantic portions of the AT, we observed an expansion of the spring phenological window in the north where there was greater understory temperature sensitivity compared to trees (∼1.6 days/°C). Our analyses indicate differential sensitivity of forest plant phenology to potential warming across a large latitudinal gradient in the eastern United States. Further, evidence for a temperature-driven expansion of the spring phenological window suggests a potential beneficial effect for understory plants, although phenological mismatch with potential pollinators is possible. Using various extensive citizen-science derived datasets allows us to synthesize regional- and continental-scale data to explore spatial and temporal trends in spring phenology related to warming. Such data can help to standardize approaches in phenological research and its application to forest climate resiliency.

Distinct latitudinal patterns of shifting spring phenology across the Appalachian Trail Corridor

Green vegetation plays a vital role in energy flows and matter cycles in terrestrial ecosystems, and vegetation phenology may not only be influenced by, but also impose active feedback on, climate changes. The phenological events of vegetation such as the start of season (SOS), end of season (EOS), and length of season (LOS) can respond to climate changes and affect gross primary productivity (GPP). Here, we coupled satellite remote sensing imagery with FLUXNET observations to systematically map the shift of SOS, EOS, and LOS in global vegetated area, and explored their response to climate fluctuations and feedback on GPP during the last two decades. The results indicated that 11.5% of the global vegetated area showed a significantly advanced trend in SOS, and that only 5.2% of the area presented significantly delayed EOS during the past two decades, resulting in significantly prolonged LOS in 12.6% of the vegetated area. The climate factors, including seasonal temperature and precipitation, attributed to the shifts in vegetation phenology, but with high spatial and temporal difference. LOS was positively and significantly correlated with GPP in 20.2% of the total area, highlighting that longer LOS is likely to promote vegetation productivity. The feedback on GPP from the shifted vegetation phenology may serve as an adaptation mechanism for terrestrial ecosystems to mitigate global warming through improved carbon uptake from the atmosphere.

Shifted Global Vegetation Phenology in Response to Climate Changes and Its Feedback on Vegetation Carbon Uptake

Forests play a vital role in sequestering carbon dioxide from the atmosphere. Vegetation phenology is sensitive to climate changes and natural environments. Exploring the patterns in phenological events of the forests can provide useful insights for understanding the dynamics of vegetation growth and their responses to climate variations. Deciduous forest in North America is an important part of global forests. Here we apply time-series remote sensing imagery to map the critical dates of vegetation phenological events, including the start of season (SOS), end of season (EOS), and growth length (GL) of the deciduous forests in North America during the past two decades. The findings show that the SOS and EOS present considerable spatial and temporal variations. Earlier SOS, delayed EOS, and therefore extended GL are detected in a large part of the study area from temporal trend analysis over the years, though the magnitude of the trend varies at different locations. The phenological events are found to correlate to the environmental factors and the impact on the vegetation phenology from the factors is location-dependent. The findings confirm that the phenology of the deciduous forests in North America is updated such as advanced SOS and delayed EOS in the last two decades and the climate variations are likely among the driving forces for the updates. Considering that previous studies warn that shifts in vegetation phenology could reverse the role of forests as net emitters or net sinks, we suggest that forest management should be strengthened to forests that experience significant changes in the phenological events.

https://www.mdpi.com/1999-4907/13/7/1137/pdf?version=1658385895

Phenological Shifts of the Deciduous Forests and Their Responses to Climate Variations in North America

Urban Growth and its Impact on Vegetation Carbon Sequestration: A National Scale Analysis

(1) Background: An estuary is a zone in which sea and river waters mix. It is a specific area with a very non-stable environment and salinity gradient. However, little is known about the diversity of ciliate communities in estuarine benthic ecosystems in the Arctic. The aim of this paper is to describe the diversity of intertidal ciliates in the Chernaya river estuary (Kandalaksha Gulf, White Sea), which is characterized by a pronounced salinity gradient (0–22‰), on the basis of a recently published dataset. (2) Methods: We conducted our own investigations during the summer periods of 1998–2000. Material was collected at five permanent stations along the salinity gradient (0–22%) of the estuary. For each observation, the coordinates of the sampling sites, the number of individuals observed and the sampling date were recorded. The total effort comprised 35 sampling days, with five sampling sites at each date. (3) Results: The dataset contains 4270 unique occurrences of 119 ciliates taxa (109 species, 8 unidentified species of the genus level and 2 unidentified species on the family level). The total number of specimens represented is 64,475. (4) Conclusions: The largest classes in terms of species diversity are Hypotrichea (27 species), Gymnostomatea (26 species), Oligohymenophorea (17 species) and Karyorelictea (16 species).

Biodiversity of Marine Interstitial Ciliates in the Intertidal Zone of the White Sea: A Dataset from the Chernaya River Estuary, Kandalaksha Gulf

Fine-scale mapping and spatiotemporal heterogeneity analysis of industrial CO2 emissions using nighttime light remote sensing in mainland China

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