Spring Phenophases Research Articles

Spring phenological models combining the effects of temperature and photoperiod are successfully transferred to various spatial and temporal scales: a case study of Aesculus hippocastanum L.

Abstract On the basis of long-term, high-quality in situ observations on phenological and meteorological data, we parameterised and examined the performances of four single-phase and two two-phase models for the prediction of the leaf unfolding and flowering dates of horse chestnut (Aesculus hippocastanum L.). Amongst models, those combining the effects of temperature and photoperiod showed the best phenophase prediction, suggesting the influence of photoperiod on the leaf unfolding and flowering of A. hippocastanum. The obtained coefficients showed that the effect of photoperiod was greater on leaf unfolding than on flowering. Comprehensive assessment revealed that the single-phase BCdoy model demonstrated the best fitting for both phenophases. This model also showed sufficiently high accuracy and the transferability of results in time and space. The proposed models can be used to predict the spring phenophases of A. hippocastanum in European and Asian countries, where this ornamental tree species is widely used in urban landscaping, and to optimise control methods against Cameraria ohridella Deschka & Dimić (Lepidoptera, Gracillariidae). For C. ohridella, the first flying out of adults after overwintering begins at the onset of horse chestnut leaf unfolding and mass flight occurs during the full flowering period.

Analysing long-term spatiotemporal land surface phenology patterns over the Iberian Peninsula using 250 m MODIS EVI2 data

Iberian Peninsula ecosystems are especially vulnerable to global warming, and variations in climate patterns may alter the wide variety of services they provide. Despite this, seasonal variations in Iberian ecosystems have been understudied. Thus, this study aims to characterise land surface phenology (LSP) patterns in the Iberian Peninsula over 21 years (2001−2021), considering three phenometrics: the start (SOS), the end (EOS), and the length of the growing season (LOS). These were estimated from 8-day image composites of EVI2 (Two-band Enhanced Vegetation Index), derived from the surface reflectance product MOD09Q1 at a 250-metre spatial resolution. Phenometrics and in-situ human phenological observations of plant phenophases were also compared. Pearson's correlation coefficient, p-value, and absolute differences between paired phenometrics and phenophases were calculated to quantify uncertainty between both phenological approaches.Generally, SOS and EOS dates were later in the Alpine and Atlantic biogeographic regions. SOS occurred in March–April and EOS between October–December. Natural vegetation land cover types had similar phenological dynamics, with SOS occurring between late winter and spring and EOS between autumn and early winter. However, phenometric dates were earlier in Mediterranean savannas, grasslands, and scrublands. Atlantic evergreen broadleaf vegetation showed the strongest correlations between SOS and the first (r = 0.96) and second (r = 0.68) leaf unfolding. In contrast, Mediterranean evergreen broadleaf vegetation had unclear correlations. Atlantic deciduous broadleaf vegetation showed a moderate correlation between SOS and first (r = 0.52) and second (r = 0.57) leaf unfolding. The correlation between SOS and the first (r = 0.14) and second (r = 0.13) leaf unfolding was weaker for Mediterranean deciduous broadleaf vegetation. EOS and autumn phenophases generally showed unclear consistency. Higher spatial resolution satellite data may improve the consistency between EOS and autumn phenophases in Iberian ecosystems, as well as between SOS and spring phenophases in heterogeneous Mediterranean ecosystems.

Higher risk of spring frost under future climate change across China's apple planting regions

Spring frost is one of major agro-meteorological disasters impacting apple production. Previous studies focused on the impacts of spring frost during the flowering period on apples, however, the frost events occurring at both pre- and post-flowering phases have significant impacts on apples. Our study employed four phenology models (parallel model, M1 model, sequential model, and growing degree hour model), along with their ensemble model driven by five global climate models (GCMs) to predict the key spring phenphases of apple across China’s apple planting regions under two emission scenarios (SSP245 and SSP585) during the 2050 s (2040–2069) and 2080 s (2070–2099). A new spring frost assessment index (FI) combining frequency and intensity of spring frost was developed to evaluate the impacts of climate change on spring frost risk of apple. The results showed a large spatial variation in projected spring phenophases across China’s apple planting regions. Projected budbreak (BBCH 09), initial flowering (BBCH 60), and final flowering (BBCH 69) would advance 5.6–15.9 days, 5.7–14.8 days, and 5.6–14.5 days, respectively, in regions I, II, and V of northern China apple planting regions. However, in regions III and IV of southern China apple planting regions, projected budbreak, initial flowering, and final flowering would delay –9.2–21.5 days, –7.5–20.6 days, and –6.8–20.8 days in the future climate scenarios, compared with the baseline (1980–2009). Projected last spring frost date considering the entire spring phenphases would advance 3.7–11.8 d in the future climate scenarios, compared with the baseline. Projected spring frost risk would increase in all the three growth stages including budbreak to initial flowering, flowering period, and final flowering to the last spring frost date across all the China's apple plating regions in future climate scenarios except southward China's apple plating region under the SSP585 in the 2080 s. Our study provides an important reference for early warning, prevention and mitigation of spring frost disasters, and the layout of the apple industry.

Modern Aspects of Studying The Phyllophagous Insects Role in Forest Communities

This paper presents a review of publications on the relationship between the phyllophagous insects and the forest communities in the current ecological situation, when ongoing climate changes, manifested primarily in an increase in the air temperature and a change in the precipitation amount and distribution, affect all processes in natural communities. Changes in the ranges of many plants and animals species are observed – moving up northwards and up in altitude. The spring phenophases come earlier, the autumn ones come later, the vegetation period lengthens and the terrestrial plants biomass increases. Such phenomena, together with changes in climatic parameters, affect herbivorous animals, which include insects with various food specialisations and different life cycles. As before, despite the growing number of observations in different parts of the Earth, there remains a lot of uncertainty about how individual plant and insect species and their functional groups function under the changing external conditions. It is emphasized that it is necessary to continue long-term studies in specific natural conditions in order to more accurately determine the reaction of the interactions’ participants to local climate changes and understand what the forestry strategy should be in the current and the predicted future situation.

Spring and Autumn Phenology in Sessile Oak (Quercus petraea) Near the Eastern Limit of Its Distribution Range

Due to the visible and predictable influence of climate change on species’ spatial distributions, the conservation of marginal peripheral populations has become topical in forestry research. This study aimed to assess the spring (budburst, leaf development, and flowering) and autumn (leaf senescence) phenology of sessile oak (Quercus petraea), a species widespread across European forests close to its ranges’ eastern limit. This study was performed in Romania between spring 2017 and 2020, and it included a transect with three low-altitude populations, a reference population from its inner range, and a sessile oak comparative trial. The temperature was recorded to relate changes to phenophase dynamics. We identified small variations between the reference and peripheral populations associated with climatic conditions. In the peripheral populations, budburst timing had day-of-year (DOY) values <100, suggesting that sessile oak may be more susceptible to late spring frost. Furthermore, we found spring phenophase timing to be more constant than autumn senescence. Moreover, budburst in the sessile oak comparative trial had obvious longitudinal tendencies, with an east to west delay of 0.5–1.4 days per degree. In addition, budburst timing influenced leaf development and flowering, but not the onset of leaf senescence. These findings improve our understanding of the relationship between spring and autumn phenophase dynamics and enhance conservation strategies regarding sessile oak genetic resources.

Responses of spring leaf phenological and functional traits of two urban tree species to air warming and/or elevated ozone

Climate warming and surface ozone (O3) pollution are important global environmental issues today. However, the combined impacts of air warming and O3 on phenology and its functional traits of urban trees are still poorly understood. Here, an experiment was performed to explore the variations of the spring phenological and functional traits in leaves of Populus alba 'Berolinensis' and Forsythia suspensa under ambient air (15.8 °C, 35.7 ppb), increased air temperature (IT, ambient air temperature + 2 °C, 17.9 °C), elevated O3 (EO, ambient air O3 concentrations + 40 ppb, 77.4 ppb), and their combined treatments (17.7 °C, 74.5 ppb). Our results showed that: IT advanced the beginning of leaf bud expansion phase of P. alba 'Berolinensis' and F. suspensa for 6 d and 5 d, respectively, increased leaf unfolding rate, leaf area and dry weight, and enhanced photosynthesis and antioxidative enzyme activities. EO delayed the beginning of leaf bud expansion phase of P. alba 'Berolinensis' for 5 d, decreased leaf area and biomass, and inhibited photosynthesis and caused oxidative damage of plant leaves. Compared to EO, the combined treatment advanced the spring phenophase, increased growth and induced the higher level of photosynthetic rate and antioxidative enzymes activities in plant leaves, which indicated that the positive effects of increased temperature (17.7 °C) alleviated the inhibition of growth and photosynthesis induced by ozone. Our findings can provide a theoretical reference for predicting the adaptation of functional traits of the two trees blossomed early under warming and O3 pollution at spring phenological stage.

Spring phenology of some ornamental species, as an indicator of temperature increase in the urban climate area

The aim of this study is to provide information on the phenology of urban spring season, of some species of ornamental trees and shrubs, in the light of climate changes occurred over the recent decades. Ten species of ornamental shrubs and trees cultivated in two areas of a town located in southwestern Romania were studied. It was found that the spring season phenology of the studied species is dependent on the climatic year, in recording differences between the number of days from November 1 and the beginning of each spring phenophase, both from one species to another and from one climatic year to another, and also from one area to another; the spring phenology starting earlier in the urban area regardless of the species and the climatic year. Higher temperatures, rising from one year to another, are speeding-up the onset and development of spring phenology, regardless of species, and the urban climate through the effect of urban heat island leads to even earlier onset of spring phenophases and shortening of the growing season, so that by phenological differences existing within the species from one climatic year to another and from one climatic zone to another, spring season phenology can be considered an indicator of temperature rise.

Phenological niche overlap between invasive buckthorn (Rhamnus cathartica) and native woody species

Common buckthorn (Rhamnus cathartica L.) is a prolific invader of forest understories throughout eastern North America. Its ability to invade is partially attributable to its relatively high shade tolerance and ability to capture light both early and late in the growing season because of its phenological differences from native species. Competitors that mitigate this phenological advantage by casting shade early and late in the growing season may therefore increase biotic resistance against invasion. However, controlled comparisons between buckthorn and other woody understory species are scarce and to what extent buckthorn’s phenology is truly exceptional is incompletely known. Here, we compare the spring and autumn phenologies of five shade tolerant, native woody species (Sambucus canadensis, Sambucus racemosa, Corylus americana, Cornus racemosa, and Acer saccharum) to those of buckthorn in two common garden experiments. Spring phenology of buckthorn was often comparable to the five native species considered. All native species broke bud no later than 7 days after buckthorn, with S. racemosa reaching spring phenophases consistently earlier than buckthorn. In contrast to spring, buckthorn fall phenology was distinct in comparison to some natives but not all. Native species started to senesce up to 20 days earlier than buckthorn, but both Sambucus species senesced slowly and held their leaves equally long as buckthorn. These findings illustrate that buckthorn does not possess unique phenology amongst understory species. Forest communities rich in deciduous shrubs or trees that are phenologically similar to buckthorn (particularly S. racemosa) likely limit buckthorn's critical spring and fall carbon gains and exert greater biotic resistance to invasion by buckthorn.

利用控制实验研究植物物候对气候变化的响应综述

物候是植物在长期适应环境过程中形成的生长发育节点。长时间地面物候观测数据表明，近50年全球乔木、灌木、草本植物的春季物候期受温度升高、降水与辐射变化等影响，以每10年2 d到10 d的速率提前。但因植物物候响应气候因子的机制仍不清楚，导致对未来气候变化情景下的植物物候变化预测存在较大的不确定性。在此背景下，控制实验成为探究气候因子对植物物候影响机制的重要手段。综述了物候控制实验中不同气候因子（温度、水分、光照等）的控制方法。总结了目前为止控制实验在植物物候对气候因子响应方面得到的重要结论，发现植物春季物候期（展叶、开花等）主要受冷激、驱动温度与光周期的影响，秋季物候期（叶变色和落叶）主要受低温、短日照与水分胁迫的影响。提出未来物候控制实验应重点解决木本植物在秋季进入休眠的时间点确定、低温和短日照对木本植物秋季物候的交互作用量化、草本植物春秋季物候的影响因子识别等科学问题。;Phenology is the occurrence time of plant growth and development events formed in the process of long-term adaptation to the environment. The long-term phenological observation data showed that the spring phenophases of trees, shrubs, and herbs advanced by 2 to 10 days per decade over the past 50 years, affected by temperature rises, precipitation, and radiation changes. However, the mechanism of plant phenology in response to climatic factors is still unclear, leading to greater uncertainty in predicting plant phenological changes under future climate change scenarios. In this context, the controlled experiments have become an important way to explore the mechanism of climatic factors affecting plant phenology. This study summarized firstly the control methods of different climatic factors (temperature, moisture, light, etc.) in the phenological experiments. Second, we summarized the critical conclusions of the controlled experiments about the response of plant phenology to climatic factors so far and found that the spring phenophases of plants (leaf-out, flowering, etc.) were mainly affected by chilling, forcing temperature and photoperiod, and the autumn phenophases (leaf coloring and fall) were mainly driven by low temperature, short daylength, and water stress. Finally, the study proposed that future controlled experiments should focus on determining the time for woody plants to enter dormancy in autumn, quantifying the interaction of low temperature and short daylength on autumn phenophase of woody plants, and identifying influencing factors for spring and autumn phenophases of herbaceous plants.

Mapping Temperate Forest Phenology Using Tower, UAV, and Ground-Based Sensors

Phenology is a distinct marker of the impacts of climate change on ecosystems. Accordingly, monitoring the spatiotemporal patterns of vegetation phenology is important to understand the changing Earth system. A wide range of sensors have been used to monitor vegetation phenology, including digital cameras with different viewing geometries mounted on various types of platforms. Sensor perspective, view-angle, and resolution can potentially impact estimates of phenology. We compared three different methods of remotely sensing vegetation phenology—an unoccupied aerial vehicle (UAV)-based, downward-facing RGB camera, a below-canopy, upward-facing hemispherical camera with blue (B), green (G), and near-infrared (NIR) bands, and a tower-based RGB PhenoCam, positioned at an oblique angle to the canopy—to estimate spring phenological transition towards canopy closure in a mixed-species temperate forest in central Virginia, USA. Our study had two objectives: (1) to compare the above- and below-canopy inference of canopy greenness (using green chromatic coordinate and normalized difference vegetation index) and canopy structural attributes (leaf area and gap fraction) by matching below-canopy hemispherical photos with high spatial resolution (0.03 m) UAV imagery, to find the appropriate spatial coverage and resolution for comparison; (2) to compare how UAV, ground-based, and tower-based imagery performed in estimating the timing of the spring phenological transition. We found that a spatial buffer of 20 m radius for UAV imagery is most closely comparable to below-canopy imagery in this system. Sensors and platforms agree within +/− 5 days of when canopy greenness stabilizes from the spring phenophase into the growing season. We show that pairing UAV imagery with tower-based observation platforms and plot-based observations for phenological studies (e.g., long-term monitoring, existing research networks, and permanent plots) has the potential to scale plot-based forest structural measures via UAV imagery, constrain uncertainty estimates around phenophases, and more robustly assess site heterogeneity.

Phenological changes in herbaceous plants in China's grasslands and their responses to climate change: a meta-analysis.

Plant phenological events are sensitive indicators of climate change, and their change could markedly affect the structure and function of ecosystems. Previous studies have revealed the spatiotemporal variations in the phenological events of woody plants. However, limited studies have focused on the phenophases of herbaceous plants. In this study, by using a meta-analysis method, we extracted information about the phenological changes in herbaceous plants in China's grasslands from existing studies (including the period, station, species, phenophases, phenological trends, and climatic determinants) and analyzed the patterns manifested in the dataset. The results showed that the spring phenophases (e.g., first leaf date and first flowering date) of the herbaceous plants mainly advanced over the past 30years, but a large difference existed across grassland types. The spring phenophases of forages (species from the Cyperaceae, Gramineae, and Leguminosae families) became earlier in the desert steppe and alpine steppe but showed no apparent trends in the alpine meadow and even became later in the meadow steppe and typical steppe. In most cases, the increase in spring temperatures and precipitation promoted the greening up of herbaceous plants, while sunshine duration was positively correlated with the green-up date of herbaceous plants. For the autumn phenophases, the proportions of the earlier and later trends were very close, but the trends varied among the grassland types. The leaf coloring dates of the forages were delayed in the meadow steppe and alpine steppe but showed no distinct pattern in the typical steppe or alpine meadow and even became earlier in the desert steppe. In most cases, the increase in growing season temperature led to an earlier leaf coloring date of the herbaceous plants, but the increase in the preseason precipitation delayed the leaf coloring date. Our results suggested that the phenophases of herbaceous plants have complicated responses to multiple environmental factors, which makes predicting future phenological changes difficult.

Enhanced spring temperature sensitivity of carbon emission links to earlier phenology

Phenology has a great effect on the carbon cycle. Significant relationships have been well demonstrated between phenology and photosynthesis. However, few studies have been undertaken to characterize relationships between phenology and ecosystem respiration (Re). We conducted a reciprocal transplant experiment among three elevations for two-years to measure Re over six phenological sequences throughout the growing seasons. Our results showed that changes in phenological duration were mainly determined by the onset of phenology, as one day advance of phenological onset could lengthen 0.13 days of phenological duration. Advances in early spring phenophases (i.e., first leaf-out, first bud/boot-set and first flowering) under warming strengthened the temperature sensitivity of Re. However, the late phenophases (i.e., first seeding-set, first post-fruiting vegetation and first leaf-coloring) had non-significant relationships with Re. In total, after pooling all the data, one day advance of phenophases would increase Re by 2.23% under warming. In particular, Re would increase by 29.12% with an advance of phenophases by 8.46 days of under a 1.5 °C warming scenario. Our analysis of the coupling between temperature/moisture–phenology–Re may further supplement evidence that warmer spring temperature increases carbon emission by advancing early phenophases. This points to a faster and easier way to investigate how aboveground functional traits (phenology) affect unseen functional traits (Re) on the Tibetan Plateau.

Phenological responses of apple tree to climate warming in the main apple production areas in northern China

To reveal the spatio-temporal variation characteristics of apple's phenology and their critical response time period and intensity to the temperature change in the main production areas of northern China, we chose Fushan, Wanrong and Akesu to respresent the Bohai Gulf, the Loess Plateau and Xinjiang apple production areas, respectively. Apple's phenology data of buds opening (BO), first leaf unfolding (LU), first flowering (FF), fruit maturing (FM), end of leaf coloring (LC) and the end of leaf fall (LF) at the three stations during 1996-2018 were used to analyze the changes of phenological occurrence dates and different growth stage lengths. Partial least squares (PLS) regression was applied to identify the impacts of climate warming on different phenology events at daily resolution. Results showed that regional mean occurrence dates of apple's BO, LU and FF advanced by a rate of 0.36, 0.33 and 0.23 day per year, respectively. However, apple's LF postponed by 0.68 d·a-1. The FM and LC showed different trends among all the sites. The length of fruit growing period (FG) and that of tree growing period (TG) extended at average rates of 1.20 and 0.82 day per year. Apple's spring phenophases dates at all stations correlated negatively with mean temperature during early January to pre-phenophases date, with a 1 ℃ increase inducing an advancement of 3.70, 3.47 and 3.48 days for apple's BO, LU and FF, respectively. In contrast, apple's autumn phenophases correlated positively with mean temperature 21-72 days before the phenophases date, and its correlation with mean temperature was lower than the correlation for spring phenophases. Generally, the effect of temperature on spring phenophase was stronger than that of autumn phenophase, and the extension of FG and TG was mainly caused by the advance of spring phenophase. The responses of apple's phenophases to climate warming differed across all the stations. Temperature had the greatest impact on the development of apple industry in Akesu, less in Wanrong, and with the least influence in Fushan. Our results could provide theoretical basis for response to climate change for apple industry in different areas of China.

Effects of multiple climate change factors on the spring phenology of herbaceous plants in Inner Mongolia, China: Evidence from ground observation and controlled experiments

AbstractIn a natural ecosystem or as climatic climax community, grassland is relatively dry with a strongly seasonal climate, and sensitive to climatic changes. Most of the previous studies used remote sensing data to investigate the phenological response of grassland to climate change, while ground‐based studies covering a large geographic area were limited. In this study, using the long‐term phenological data (1981–2012) of 16 herbaceous species observed at 20 stations in Inner Mongolia, China, we first investigated the trends in three spring phenophases, including the dates of bud‐burst, first leaf unfolding, and 50% of leaf unfolding. Subsequently, multiple linear regressions between phenophases and four climatic factors (spring temperature, soil moisture, chilling temperature, and insolation) were performed to determine the relative importance of each factor on the spring phenology. To validate the resulted regression coefficients, we developed a controlled environment to investigate the factors regulating the leaf unfolding time of one dominant species (Leymus chinensis). The results showed that the study area became warmer and drier from 1981 to 2012. However, the overall changes in spring phenophases were not apparent, as there was a similar proportion of significant earlier or later trends. Such phenological changes were driven by multiple climatic factors. The warmer temperature would advance the spring phenophases, while lower soil moisture would delay them. The impact of soil moisture was significant in the experimental data, but not significant in the observation data. In addition, leaf unfolding became faster when L. chinensis experienced more chilling days, but this effect was difficult to be detected in observation data due to the weak sensitivity of the leaf unfolding time to chilling days. These findings can help us to understand how the spring phenology of typical herbaceous species responds to multiple climatic factors under the background of climate change.

Differentiation and Non-Linear Responses in Temporal Phenotypic Plasticity of Seasonal Phenophases in a Common Garden of Crataegus monogyna Jacq.

Phenology in perennial plants implies the temporal occurrence of biological events throughout the year. Heritable phenotypic plasticity in the timing of the phenophases can be of importance in the adaptation of woody species to a quickly changing environment. We observed the timing of bud burst, flower opening, leaf senescence and leaf fall in two successive years in a common garden of Crataegus monogyna Jacq. in Belgium, consisting of six local and five non-local provenances. Data were processed with cumulative logistic mixed models. Strong auto-correlation was present among the spring phenophases as well as among the autumnal phenophases, with spring phenophases being negatively correlated with fall phenophases. The strongest between-provenance differentiation was found for the timing of bud burst in spring, followed by flower opening and finally by leaf senescence and leaf fall. Warmer spring temperatures in March 2017 advanced the timing of bud burst, and to a lesser extent of flower opening, in all provenances compared to 2016. However, the advancement was non-linear among the provenances, with the lower latitude provenances being relatively less early and the higher elevation provenances being more late than the local provenances in this year. It can be hypothesized that non-local provenances display larger temporal phenotypic plastic responses in the timing of their spring phenophases compared to local provenances when temperatures in the common garden deviate more from their home-sites.

Later springs green-up faster: the relation between onset and completion of green-up in deciduous forests of North America.

In deciduous forests, spring leaf phenology controls the onset of numerous ecosystem functions. While most studies have focused on a single annual spring event, such as budburst, ecosystem functions like photosynthesis and transpiration increase gradually after budburst, as leaves grow to their mature size. Here, we examine the "velocity of green-up," or duration between budburst and leaf maturity, in deciduous forest ecosystems of eastern North America. We use a diverse data set that includes 301 site-years of phenocam data across a range of sites, as well as 22years of direct ground observations of individual trees and 3years of fine-scale high-frequency aerial photography, both from Harvard Forest. We find a significant association between later start of spring and faster green-up: - 0.47 ± 0.04 (slope ± 1 SE) days change in length of green-up for every day later start of spring within phenocam sites, - 0.31 ± 0.06days/day for trees under direct observation, and - 1.61 ± 0.08days/day spatially across fine-scale landscape units. To explore the climatic drivers of spring leaf development, we fit degree-day models to the observational data from Harvard Forest. We find that the default phenology parameters of the ecosystem model PnET make biased predictions of leaf initiation (39days early) and maturity (13days late) for red oak, while the optimized model has biases of 1day or less. Springtime productivity predictions using optimized parameters are closer to results driven by observational data (within 1%) than those of the default parameterization (17% difference). Our study advances empirical understanding of the link between early and late spring phenophases and demonstrates that accurately modeling these transitions is important for simulating seasonal variation in ecosystem productivity.

Machine learning modeling of plant phenology based on coupling satellite and gridded meteorological dataset

Changes in the timing of plant phenological phases are important proxies in contemporary climate research. However, most of the commonly used traditional phenological observations do not give any coherent spatial information. While consistent spatial data can be obtained from airborne sensors and preprocessed gridded meteorological data, not many studies robustly benefit from these data sources. Therefore, the main aim of this study is to create and evaluate different statistical models for reconstructing, predicting, and improving quality of phenological phases monitoring with the use of satellite and meteorological products. A quality-controlled dataset of the 13 BBCH plant phenophases in Poland was collected for the period 2007–2014. For each phenophase, statistical models were built using the most commonly applied regression-based machine learning techniques, such as multiple linear regression, lasso, principal component regression, generalized boosted models, and random forest. The quality of the models was estimated using a k-fold cross-validation. The obtained results showed varying potential for coupling meteorological derived indices with remote sensing products in terms of phenological modeling; however, application of both data sources improves models’ accuracy from 0.6 to 4.6 day in terms of obtained RMSE. It is shown that a robust prediction of early phenological phases is mostly related to meteorological indices, whereas for autumn phenophases, there is a stronger information signal provided by satellite-derived vegetation metrics. Choosing a specific set of predictors and applying a robust preprocessing procedures is more important for final results than the selection of a particular statistical model. The average RMSE for the best models of all phenophases is 6.3, while the individual RMSE vary seasonally from 3.5 to 10 days. Models give reliable proxy for ground observations with RMSE below 5 days for early spring and late spring phenophases. For other phenophases, RMSE are higher and rise up to 9–10 days in the case of the earliest spring phenophases.

Phenophase shifts across elevations on major mountains in North China

Previous studies have reported plant phenological changes along horizontal belts in North China, however, little is known about elevation effects on mountain phenophases in China, such as how vegetation phenophases shift across elevation on mountains, and how they change under background of global change. In this context, by application of remote sensing data, Moderate Resolution Imaging Spectroradiometer (MODIS), changes of spring phenophases across elevation on 6 typical mountains in North China, namely Wuling, Xiaowutai, Guandi, Migang, Huashan and Taibai Moutians, and the effects of elevation on phenophases along altitudinal gradients, were studied in current work. Preliminary results showed that, similar to our fi ndings of phenological changes in plain area in North China, the onset of vegetation phenophases in spring advanced on these mountains, while the ending time for autumn phenophases delayed in the past two decades. Trends for advanced spring phenophase increased signifi cantly with altitude in some mountain regions, and spring phenophase sensitivities to altitude are stronger in lower latitude than in higher latitude regions. Similar to foreign studies, it is reported for the fi rst time that global warming has led to a more uniform spring phenology across elevation in North China mountains in recent years. Findings will not only benefi t policy making for the government in the fi eld of ecological constructions, but also will be helpful to evaluate future climate change on vegetation in such areas.

Temporal coherence of phenological and climatic rhythmicity in Beijing.

Using woody plant phenological data in the Beijing Botanical Garden from 1979 to 2013, we revealed three levels of phenology rhythms and examined their coherence with temperature rhythms. First, the sequential and correlative rhythm shows that occurrence dates of various phenological events obey a certain time sequence within a year and synchronously advance or postpone among years. The positive correlation between spring phenophase dates is much stronger than that between autumn phenophase dates and attenuates as the time interval between two spring phenophases increases. This phenological rhythm can be explained by positive correlation between above 0°C mean temperatures corresponding to different phenophase dates. Second, the circannual rhythm indicates that recurrence interval of a phenophase in the same species in two adjacent years is about 365days, which can be explained by the 365-day recurrence interval in the first and last dates of threshold temperatures. Moreover, an earlier phenophase date in the current year may lead to a later phenophase date in the next year through extending recurrence interval. Thus, the plant phenology sequential and correlative rhythm and circannual rhythm are interacted, which mirrors the interaction between seasonal variation and annual periodicity of temperature. Finally, the multi-year rhythm implies that phenophase dates display quasi-periodicity more than 1year. The same 12-year periodicity in phenophase and threshold temperature dates confirmed temperature controls of the phenology multi-year rhythm. Our findings provide new perspectives for examining phenological response to climate change and developing comprehensive phenology models considering temporal coherence of phenological and climatic rhythmicity.

Phenological behaviour of early spring flowering trees in Spain in response to recent climate changes

This research reports the phenological trends of four early spring and late winter flowering trees in Spain (south Europe) from a recent period (1986–2012). The studied species were deciduous trees growing in different climatic areas: hazel (Corylus avellana L.), willow (Salix alba L.), ash (Fraxinus angustifolia Vahl.) and white mulberry (Morus alba L.). We analysed the response to climate and the trends of the following phenophases observed at the field: budburst, leaf unfolding, flowering, fruit ripening, fruit harvesting, leaf colour change and leaf-fall. The study was carried out in 17 sampling sites in the country with the aim of detecting the recent phenological response to the climate of these species, and the possible effect of climate change. We have observed differences in the phenological response to climate depending on each species. Sixty-one percent of studied sites suffered an advance of early spring phenophases, especially budburst on average by −0.67 days and flowering on average by −0.15 days during the studied period, and also in the subsequent fruit ripening and harvesting phases on average by −1.06 days. By contrast, it has been detected that 63% of sampling sites showed a delay in autumn vegetative phases, especially leaf-fall events on average by +1.15 days. The statistic correlation analysis shows in the 55% of the studied localities that phenological advances are the consequence of the increasing trend detected for temperature—being minimum temperature the most influential factor—and in the 52% of them, phenological advances occurred by rainfall variations. In general, leaf unfolding and flowering from these species showed negative correlations in relation to temperature and rainfall, whereas that leaf colour change and leaf-fall presented positive correlations. The results obtained have a great relevance due to the fact that they can be considered as reliable bio-indicators of the impact of the recent climate changes in southern Europe.