The timing of spring leaf-out in temperate and boreal trees greatly affects ecosystem functioning and global biogeochemical cycles. Yet, spring phenological responses to climate change remain uncertain due to the complex, interacting effects of environmental triggers. While spring temperature, winter chilling and day length have traditionally been accepted as the main drivers of spring phenology, recent research suggests that additional factors, such as solar radiation and air humidity in spring and leaf-out timing and temperatures in the preceding year, play an important role, too, further complicating predictions of spring phenology. Here, I test for the relative importance of each driver using ground-sourced and satellite-derived phenology observations from the Northern Hemisphere. The results show that, consistent with the ongoing advances in spring leaf-out, spring temperature remains the dominant driver of spring phenology across the vast majority of temperate and boreal forests. By contrast, winter temperatures played only a minor role, suggesting that, despite generally warmer winters, trees’ chilling requirements are mostly met. After controlling for spring climate and temporal autocorrelation in the data, spring phenology and climate of the preceding year did not affect leaf-out timing, contradicting recent observational studies. Overall, the strong and consistent effect of spring temperature predicts that the arrival of spring will continue to advance in the future, with multiple cascading effects on species interactions, forest productivity and other ecosystem functions.

How to cite: Zohner, C.: Testing the relative importance of the various environmental triggers of spring leaf-out, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1924, https://doi.org/10.5194/egusphere-egu23-1924, 2023.

The ongoing climate change has primarily affected snowmelt and greenup timings, which are the two crucial regulators for every component of biogeochemical cycles of the terrestrial ecosystems in high-latitude regions. Previous studies, using various datasets at different regional scales, have focused on either trend, therefore not thoroughly analyzing relative long-term changes in both timings over the entire high-latitudes. In this study, we assessed the four decades (1982-2021) of trends in those two timings for the regions (latitude > 45°N). First, we used Google Earth Engine to derive snowmelt and greenup timings based on normalized indices (i.e., normalized difference snow index and normalized difference vegetation index) that were retrieved from the surface reflectance of Advanced Very High Resolution Radiometer (AVHRR, daily at 0.05°) from National Oceanic and Atmospheric Administration (NOAA) Climate Data Record (CDR). Then, we evaluated those timings against various ground datasets and remote sensing-based estimates, such as PhenoCam, PEP725, SNOTEL, and MODIS. Finally, we investigated the meteorological and geographical effects on the long-term trends of the two timings across the high-latitude regions. Our results imply that the increases in the spatial heterogeneity on snow-free days may considerably alter the spatiotemporal pattern of the vegetation growth and, therefore, the relevant carbon cycle across the high-latitudes.

This study is supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MSIT) (2020R1A2C2007670, 2020R1C1C1014886 and 2022R1C1C2009543).

How to cite: Kim, J. and Kim, Y.: Four Decades of Trends in Snowmelt and Greenup over High-latitude Terrestrial Ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2988, https://doi.org/10.5194/egusphere-egu23-2988, 2023.

Knowledge of the phenological dynamics of various flowering plants is important for food supply and essential for analysing and modelling adaption of pollinators, especially the honey bees, Apis melifera. The increased frequency of extreme events associated with climate change has resulted in new challenges for farmers as well as beekeepers, and has made research on this issue a priority for adaptation planning. Satellite products can be used for phenological monitoring and detection with good spatial coverage providing valuable information for agriculture and beekeeping. In this study, we investigated the flowering period and dynamics of the two most important honey crops in Hungary, Sunflower (Helianthus annuus L.) and Oil Seed Rape (Brassica napus L.). To generate flowering time series data from Sentinel-2 we used the MSIL2A product in 20-meter resolution, which contains 10 spectral bands with 5 days revisit days. This product also contains additions mapping data helping the classification of the studied area. The research has been created using the Ecosystem Map of Hungary, which also a 20-meter-resolution map helping us to describe the agricultural land developed in 2020. To find the honey producing crops, we used machine learning applications for classification of the arable lands and these desired parcels. Subsequently, flowering timeline was estimated from NDVI and NDYI fields obtained from Sentinel-2 satellite data. Hive weight time series was measured locally with automatic hive scales during the flowering seasons of 2021-2022. The scales grants the apiarists supplementary information like weight in a 10-minute interval. This provide essential information about the health and productivity of the colony and enables information to be gathered before winter season or swarming events. We examined the results of the satellite data against the hive weight data during the honey collecting period and investigated with the actual meteorological conditions to determine a multiplex relationship between the parameters. A method is presented to apply local honey collection data to evaluate and downscale satellite-based phenological estimates for applications in beekeeping.

How to cite: Vincze, C., Leelőssy, Á., Vincze, F., and Mészáros, R.: Flowering dynamics of nectar and pollen sources in Hungary based on Sentinel-2 satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11562, https://doi.org/10.5194/egusphere-egu23-11562, 2023.

The most reliable method for monitoring plant phenology and changes in vegetation development is ground observation (in-situ). However, this method is difficult to implement on a larger spatial scale. For that reason, remote sensing data have begun to be used to quantify vegetation phenology in recent decades. Information about phenology is derived from remote sensing data using ie. phenological metrics. In this study, we used 3 base metrics - the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LGS) for evaluating changes in the phenology of four land covers (coniferous forest, broadleaf forest, field, and grassland) in the European region (approx. 30 countries). For their determination, Enhanced Vegetation Index2 (EVI2) was used based on images from The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Satellite images were obtained at a spatial resolution of 5 x 5 km in the time period from 2000 to 2022. For four land covers within the 22-year period, it was evaluated that the SOS significantly shifted to an earlier date in about half of the evaluated states. The EOS significantly shifted to a later date in almost all evaluated states. Based on these results, we evaluated the whole length of the growing season and found a significant shift to a later date also in almost all evaluated states.

Acknowledgement: This work was supported by an individual IGA project - Determination of vegetation time and its spatiotemporal variability using remote sensing of the Earth (AF-IGA2022-IP-067) and by SustES project – Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797), which provided essential data and software access.

How to cite: Dížková, P., Bartošová, L., Balek, J., Semerádová, D., Žalud, Z., and Trnka, M.: Analysis of changes in the timing of the growing season in the Europe using remote sensing data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14824, https://doi.org/10.5194/egusphere-egu23-14824, 2023.

Understanding grassland phenology responses to climate change is of crucial importance for revealing regional and species differences in ecosystem processes. By means of thousands of ground observations and the counterparts derived from long-term remote sensing data, the spatiotemporal patterns of grassland phenology and its links to climate changes and biotic factors were investigated over the Northern Hemisphere. In site-species scale, the leaf-out date did not show significant variation trend for 68.6% of the site-species, while the leaf senescence date has significantly delayed for 31% of the site-species during 1982-2011 over China. Sunshine hours, temperature, precipitation, and the leaf-out date primarily explained the variation of leaf senescence for 36.6%, 31.7%, 22.0%, and 9.8% of the investigated site-species, respectively. Sunshine hours were the foremost factor in controlling leaf senescence for 60.1% of graminoid species and temperature for 42.3% of forb species. Specifically, in the Inner Mongolia Grassland, a predominant significant positive correlation between the leaf-senescence date and previous precipitation in 54.6% of site species. In pixel-landscape scale, a significant advance (P < 0.05) of the start of growing season (SOS) was detected in 23.2% of grid cells, while a predominantly and significantly delaying trend (P < 0.05) of the end of growing season (EOS) was identified in 20.5% of grid cells during 1981–2014 over the grasslands in the Northern Hemisphere. They jointly resulted in a primarily significant prolongation trend of growing season length in 22.7% of grid cells. Meanwhile, the time span of SOS/EOS (from the earliest SOS/EOS to the last SOS/EOS) and the growing season length (from SOS to EOS) have extended for the entire study region. For the Inner Mongolia Grassland, SOS was mainly controlled by pre-SOS precipitation with the sensitivity being largest in desert steppe. EOS was closely connected with pre-EOS air temperature in meadow steppe and typical steppe, but more closely related to pre-EOS precipitation in desert steppe. Moreover, a significant negative correlation between EOS and SOS was observed in part of grassland areas, but no significant relationship between NPP and EOS was observed. Aside from correlation analysis, a newly model by incorporating the effect of drought stress (CDDP) into the traditional chilling-degree-days (CDD) model was developed to simulate the leaf senescence. CDDP model was selected as the optimal model for 73% of site species with insufficient water supply in preseason, while CDD model was selected as the optimal model for 18% of site species with a relatively wet but cold preseason. Overall, they highlight the diverse responses in the timing of spring and autumn phenology to preceding temperature and precipitation in different grassland types and their dependence on species, functional-types, and geographical gradients. 

How to cite: Ren, S.: Divergent responses of grassland vegetation phenology to climate change at different scales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13150, https://doi.org/10.5194/egusphere-egu23-13150, 2023.

Land surface phenology (LSP) has been increasingly retrieved from satellite observations over past two decades. It plays an important role in understanding atmosphere-vegetation carbon and energy exchanges. Although LSP has been frequently compared with in-situ observations in a simple way, their difference and comparability are poorly understood. We in this study investigated the scalability, consistency, and representativeness of in-situ observations of species-specific phenology from national phenology networks and PhenoCam networks and compared them with LSP from Visible Infrared Imaging Radiometer Suite (VIIRS) at 500m pixels. Specifically, we investigated four methods (mean, median, 30^th percentile, and minimum bias) to upscale in-situ observations collected from the Pan European Phenological database (PEP725, 9664 site-years) and the USA National Phenology Network (USA-NPN, 3144 site-years) spanning 2013–2020. The up-scaled in-situ observations were compared with the VIIRS LSP to address the optimal method of upscaling. The comparison differences were analyzed by associating with land cover and land surface heterogeneity to reveal the fundamental impact factors. Further, interannual variations and long-term trends in the species-specific phenological timing in the PEP725 and USA-NPN observations were correlated to VIIRS LSP, which was to expose the similarity of phenological variations under the same or similar weather conditions. Moreover, the daily variations in species-specific plant development were extracted from PhenoCam observations in the USA. The daily PhenoCam observations were fused with temporal trajectories obtained from harmonized Landsat and Sentienal-2 (HLS) at 30m pixels, which bridged field observations with satellite time series. The fused HLS-PhenoCam time series were applied to identify the phenometrics at 30m pixels, which were then linked to VIIRS LSP. Finally, we discussed the scalability and comparability of in-situ phenology observations to the LPS from moderate satellite pixels.

How to cite: Zhang, X., Ye, Y., and Tran, K.: Discrepancy and linkage of Satellite-derived Land Surface Phenology with in-situ Observations from National Phenology Networks and PhenoCam Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9227, https://doi.org/10.5194/egusphere-egu23-9227, 2023.

In recent decades climate warming accelerated substantially and consequences were especially pronounced in alpine ecosystems. Among others, alpine grasslands characterized by long lasting snow cover e.g., snowsbeds, will be especially threatened, as they are subjected to substantial shifts in phenological timing and development due to earlier snowmelt. To assess the impact of advancing snowmelt on the phenology of alpine snowbed communities, we have monitored two study sites in the Italian Alps for 3-years. While both study sites are characterized by the same vegetation community (Salicetum herbaceae), altitude, and topography, they differed in the amount of winter precipitation and as a consequence in the timing of snowmelt. We monitored the phenological development of five shared plant species between both study sites by deriving the “green chromatic coordinate” (gcc) from images of the Phenocams, installed at both study sites and in-situ phenological assessment, following a standardized protocol. We then compared results between the early and the late snowmelt site and related the results of the community level to those of the species level. The gcc identified the start of growing season (SOS), peak of growing season (POS) and end of growing season (EOS) at both study sites but failed to grasp the interspecific and inter-site differences on the species level. We found that a three-week earlier snowmelt at the early snowmelt site (DOY 176 vs. 197) did not extend (25 vs. 26 days) but only advance the POS by 20 days and resulted in a approx. 10% lower gcc-values at the early snowmelt site. At the same time, the in-situ monitoring highlighted species-specific responses of the study species. Within the study period we could identify changes in the speed of the phenological development for each study species in at least one year, with the interannual differences being greater than the differences between the study sites. Nevertheless, when compared to the late snowmelt site, the phenological development at the early snowmelt site was slower for some species (e.g., Poa alpina -24.2%) and faster for others (e.g., Euphrasia minima +70.4%). This indicates the ability of these species to modulate their phenology in response to shifting snowmelt dates. Relating the results of both approaches to each other led to mixed results, as the species-based approach only partially supported the results of the community-based approach and vice versa, with R²-values ranging from 0.1 (Euphrasia minima) up to 0.61 (Veronica alpina). These results highlight the importance of multi-level approaches when trying to identify the effects of climate change on alpine vegetation communities, as species specific results in most cases don’t represent the results on a community level and results on community level mostly fail to address the single species’ responses in these complex and heterogeneous habitats.

How to cite: Crepaz, H., Quaglia, E., Lombardi, G., Lonati, M., Rossi, M., Dullinger, S., Tappeiner, U., and Niedrist, G.: Phenological responses of Alpine snowbed communities to advancing snowmelt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13704, https://doi.org/10.5194/egusphere-egu23-13704, 2023.

The seasonality of development (phenology) of vegetation is sensitive to temperature. It is one of the most prominent biological markers of current global warming. The budburst period is of particular interest because the budburst date is decisive for the development and survival of deciduous trees. It reflects a trade-off between the need to maximize the growth period and the risks associated with late frost. Our study analyses the intra-community variability (ICV) of budburst dates acquired over 107 site-years in temperate deciduous forests located in the USA (67 site-years) and Europe (40 site-years) using phenological cameras. The average date of budburst shows a virtually identical sensitivity to temperature in American and European forests. The annual ICV of budburst was not significantly different in both continents (with an average value of 3 days, computed as the standard deviation of budburst across the community), despite a lower species richness in European forests (2 species on average) than in American forests (4.5 species on average). Earlier budburst and lower temperatures increased the ICV, which could reach up to 10 days. We suggest that the ecological consequences of the ICV of budburst should be investigated further. We show that over a growing season, the earliest trees of the community absorbed on average 10% more radiation than the latest trees (no difference across continents). This corresponds to a photosynthesis difference of 120 gC m^-2 yr^-1, the impacts of which in terms of individual growth, nutrient and water acquisition and/or exposure to water stress should be further investigated.

How to cite: Delpierre, N., Garnier, S., Treuil-Dussouet, H., Lin, J., Hufkens, K., Wilkinson, M., and Soudani, K.: Phenology across scales: an intercontinental analysis of budburst in temperate tree populations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16286, https://doi.org/10.5194/egusphere-egu23-16286, 2023.

Global warming has considerably advanced the start of the growing season of temperate trees. However, the rate of this phenological change does not necessarily track the changes in the date of the last spring frost, also induced by climate change, which may result in a higher risk of false spring. When a late spring frost (LSF) occurs during tree leaf emergence, it can lead to complete tree defoliation. Although the impacts of LSFs are rarely fatal for a tree, it is essential to identify those years to understand its effect on tree performance and vitality.

Here we aimed at identifying the years with potential frost damages, i.e., when frost have occurred around the time of leaf emergence of European beech (Fagus sylvatica L.) growing at two different elevations (1,065 and 1,365 m asl) at the Weissenstein (Swiss Jura mountains). We calibrated several phenological models using the Phenology Modeling Platform gathering various models considering forcing temperatures only or with a combination of chilling and photoperiod using high-resolution climate datasets and available phenological observations from a nearby station conducted from 2005 to 2022 (9 km away from our study sites, 1,120 m asl). The analyses are ongoing and will be compared to dendrochronology data collected from the same sites and be used to disentangle the pure effect of LSF from drought impacts on beech growth. Further investigations should be conducted on this aspect as the frequency and severity of extreme droughts are expected to increase while spring onset will continue to advance under a warmer climate, potentially increasing the risk of frost damage.

How to cite: Martínez-Sancho, E., Baumgarten, F., Reim, J., Gessler, A., and Vitasse, Y.: Identifying late spring frost impacts on European beech near its upper elevational limit using climatic and dendrochronology data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13305, https://doi.org/10.5194/egusphere-egu23-13305, 2023.

Systematic and regular monitoring phenology over a larger area is often based on cooperation with volunteers or workers who monitor the onset of phenophases and are thus part of phenological societies or national phenological networks. As part of our work and teaching at Mendel University in Brno (Bioclimatology courses) we have been cooperating with students since 2015 till now and one of the parts of their required semester work is the observation of the phenological development of selected species. At the beginning of the semester, students are thoroughly familiarized with the observation methodology and choose the plant species they will observe at regular visits during the semester (field crops, trees, shrubs or vineyards). Each student observes at least two trees or shrubs and one field crop and needs to visit the localities every three days (or more frequently if possible) and record the phenological development with cameras (using personal smartphones). During the semester or at the end of the semester, students upload pictures and terms of phenophases through the website www.fenofaze.cz. On this website, students' results and observations are displayed in real-time and are open to the general public. Student observations are strictly controlled and unusable data are taken out. We cooperate with c. 200 students each semester (i. e. 600 observations) and the first outputs showed that 50% of all observations are usable. Terms of phenophases are observed at the cadastre level and are aggregated to the district level to evaluate the long-term changes. In most cases, students approach vegetation phenological monitoring responsibly and with enthusiasm, and we consider it a reliable way of recording phenological changes and dates.

Acknowledgment: This research was funded by the Ministry of Education, Youth and Sports of the Czech Republic the project SustES—Adaptation strategies for the sustainability of ecosystem services and food security in adverse natural conditions (CZ.02.1.01/0.0/0.0/16_019/0000797). 

How to cite: Bartošová, L., Dížková, P., Fischer, M., Sedláček, F., Trnka, M., and Žalud, Z.: Monitoring phenology as part of university education, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13011, https://doi.org/10.5194/egusphere-egu23-13011, 2023.

The Phenological Network of Catalonia is a citizen science organization formed by 60 observers who constantly monitor 25 plants (wild and cultivated species), 14 birds and 6 butterflies. The first event of the phenophases related to plant species is submitted annually to the Pan-European Phenological Database, PEP725.

Since we were unaware of most of the varieties observed, we launched a project to improve the information on the varieties of cultivated plant species and improve the quality of the data sent to PEP725. Besides, this genetic analysis of fruit trees would help us to discriminate those early blooming varieties from the late ones; knowing if a fruit tree variety is early or late allows us to discriminate the phenological behavior due to environmental answer from the genetic predisposition to an early or late bloom.

The Meteorological Service of Catalonia has a collaboration agreement with the Institute of Agrifood Research and Technology (IRTA), which is related to the Center for Research in Agricultural Genomics (CRAG). We have developed a project to know the varieties of the 135 fruit and cereal samples of cultivated species observed in the Fenocat network through genetic analyzes conducted by the CRAG.

To carry out this project, we designed a system so that the observer himself could take the vegetal sample from the observed vegetal individual and send it directly to the CRAG laboratory in the shortest possible time in order to avoid sample damage due to the delay.

The CRAG laboratory analyzed the DNA of each sample and studied the genetic markers. With this, it has been possible to establish the similarity matrix of the samples analyzed with those of the IRTA database.

We have been able to find out the variety of the cultivated plant samples in some cases, while in other ones no identical result to any known variety has been found -only the degree of similarity to a specific variety has been determined-.

How to cite: Busto, M., Cunillera, J., and de Yzaguirre, X.: Genetic analysis of fruit trees and cereals observed in the Phenological Network of Catalonia (Fenocat), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6899, https://doi.org/10.5194/egusphere-egu23-6899, 2023.

Vegetation period of temperate tree species was projected to lengthen with climate warming by both advancing leaf-out during spring and delaying leaf senescence during autumn. However, this longer vegetation period does not necessarily translate into higher growth and carbon sequestration due to the increase in adverse weather conditions (e.g., severe drought) that occur during the growing season. Further, it remains unclear how species mixing might help benefit from a longer season and cope with extreme droughts compared to monocultures, i.e., whether diverse ecosystems are more resilient than monocultures. To tackle these questions, we set up experimental mesocosms using saplings from three species (i.e., Fagus sylvatica, Quercus petraea and Tilia cordata) grown either as monocultures or mixtures of two species. Each experimental unit was exposed to either (i) increased spring temperatures using a passive warming method, (ii) reduced precipitation (~ 50%) using rain shelters all year along, (iii) a combination of the two first treatments, or (iv) ambient conditions.

In spring 2022 we observed significantly earlier leaf-out of Quercus compared to Fagus and Tilia at ambient conditions and advanced leaf-out by about 4 days for all species when exposed to the passive warming treatment. In autumn 2022 we observed 50% senescence of Tilia several weeks before Fagus and Quercus at ambient conditions. Advanced leaf-out due to increased spring temperature and drought exposure did not affect senescence of any species growing in monocultures. However, the presence of Tilia in the same experimental unit delayed senescence of Fagus by 4 days and senescence of Quercus by 5 days, whereas neither species changed senescence when growing in Fagus-Quercus mixtures compared to growing in monocultures. A potential explanation could be the competition release for water and nutrients due to Tilia’s much earlier senescence. Although we expected saplings with earlier leaf-out to grow stronger and saplings exposed to drought to grow less, height increment of neither species was affected by any treatment.

How to cite: Walde, M. G., Moser, B., and Vitasse, Y.: Phenology and competitiveness of three temperate tree species in the juvenile stage under warmer springs and drier summers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11233, https://doi.org/10.5194/egusphere-egu23-11233, 2023.