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Mining the various records of plant phenology before the era of modern weather observations is an important but challenging task. We mined descriptions of plant phenology in Kanazawa, Japan, during the first half of the nineteenth century in the Kakuson Diary. We retrieved records of full bloom of 28 plant species, appearance of 31 seasonal foods, and peak leaf colouring. In particular, we found more than 10 years of records of plum, peach, cherry blossoms, udo, and bamboo shoots in spring; watermelon in summer; and persimmon, chestnut, and peak leaf colouring in autumn. The records suggest that spring phenology during 1807 to 1838 was later and autumn phenology was earlier than now. Despite spatio-temporal uncertainty in records in old diaries, we need to mine records of plant phenology in more old diaries and publish them in English. [ABSTRACT FROM AUTHOR]

Eucommia ulmoides 'Hongye' is a new ornamental variety of E. ulmoides with excellent red or purple foliage. We found that E. ulmoides 'Hongye' exhibited a gradual change from green to red colour under light conditions. However, the colouring mechanism in the leaves of E. ulmoides 'Hongye' remains unclear. In this study, we compared the pigment content and leaf colour index of E. ulmoides 'Hongye' at five stages with those of E. ulmoides 'Xiaoye', which was used as the control variety. The transcriptome sequencing data of the first-period (H1, green) and fifth-period (H5, red) leaves were also analysed and compared. The corresponding gene regulation in anthocyanin-related metabolic pathways was then analysed. Physiological results indicated that the contents of flavonoids and anthocyanins in red leaves (H5) were significantly higher than those in green leaves (H1), whereas the chlorophyll content in red leaves (H5) was lower than that in green leaves (H1). Moreover, the carotenoid content did not significantly differ between the two varieties. A transcriptome analysis identified 4240 differentially expressed genes (DEGs), and 20 of these genes were found to be involved in flavonoid and anthocyanin biosynthesis pathways. The results provide a reference for further study of the leaf colouration mechanism in E. ulmoides. [ABSTRACT FROM AUTHOR]

Leaf senescence is a major event in a plant's life history as autumn marks the end of the growing season. The optimal timing of leaf senescence is crucial to both minimise risks of low temperature events and to maximise carbon gain during the growing season. As abiotic conditions are currently changing at unprecedented rates, it is important to study how leaf senescence of different species is responding to these changes in order to forecast future growing season length and carbon sequestration potentials. In contrast to flowering phenology, data on autumn events are scarce and even more so for herbaceous than for woody plants, thus more information on this phenological stage is urgently needed.We studied leaf senescence in 632 populations from 17 herbaceous species located along elevational gradients. We focussed on the beginning (5% of the population senesce, LS5) and peak (50% senesce, LS50) of leaf senescence. To see whether we can predict species‐specific changes, we studied the link between LS5 and LS50 and flowering phenology as well as leaf functional traits related to plant performance. We looked at first and last flowering day and flowering duration as well as the traits specific leaf area (SLA), leaf dry matter content (LDMC), area‐based leaf nitrogen and carbon content, carbon isotope discrimination (Δ13C) and the stomatal pore area index.We found species‐specific slopes of the beginning of leaf senescence along the elevational gradient. The peak of leaf senescence was uniformly delayed with increasing elevation across all species. Flowering phenology as well as leaf functional traits had a close relationship with leaf senescence and thus can be used to forecast species‐specific responses to changes in abiotic conditions. High SLA and high leaf nitrogen were related to earlier senescence while high LDMC, high Δ13C and high stomatal pore area index were related to later senescence.Synthesis. The link between senescence, flowering phenology and plant functional traits will help to fine‐tune predictions of future growing season length and ecosystem function. To date, most analyses are based on spring phenology and traits, for which data are more abundant than data on autumn senescence. [ABSTRACT FROM AUTHOR]

Temporal variability of leaf senescence (autumn phenology) was observed in 2020 in 11 European beech (Fagus sylvatica) trees in Tivoli, Rožnik and Šišenski hrib Landscape Park in Ljubljana, Slovenia, and also observed for spring phenology in the same year. General leaf colouring, BBCH94, occurred between 19 and 24 October 2020, with lower inter-individual variability than that of leaf unfolding, BBCH11. The trees had active leaves (time between leaf unfolding and leaf colouring) between 177 and 199 days. In only three trees total leaf fall, BBCH97, occurred before 19 November 2020. Leaf colouring of the tree included in the long-term monitoring program of the Slovenian Environment Agency ARSO occurred on 24 October 2020. This is 7 days later than the 65-year average of the same tree/location and is ascribed to weather conditions. Investigation of tree tissues showed that the width of the last formed tree-ring in the wood varied between 0.39 and 9.61 mm and in the phloem between 0.09 and 0.26 mm, and that the tissues reflect the health condition of the trees.

Reliable phenological observations are important for studying the response of trees to climate and climate change. National phenological networks were not specifically established to monitor tree phenology within forests, yet they are often used to generalise tree phenological phases at national or regional scales. Our objective was to investigate whether a phenological monitoring network using trees in open areas can accurately predict phenology of European beech (Fagus sylvatica L.) located within forests by using two models: one with correlates of environmental variables and one with interpolated monthly air temperature and sun hours. The first leaf unfolding, general leaf colouring and leaf fall dates from 2004 through 2010 were modelled using data from 47 Slovene National Phenology Network (NPN) stations in open areas and tested on phenological observations within forests using data from the UNECE CRLTAP ICP Forests network. Good agreement was found between predicted and observed first leaf unfolding in the forest, while slightly lower agreement was detected for general leaf colouring and leaf fall. Suggestions for the improvement of national phenological network are discussed in order to better predict beech phenology in forest habitats.

We evaluated the spatial characteristics of the first day of peak leaf colouring (PLCstart) and their relationships with air temperature along latitudinal and elevational gradients in Japan from 2015 to 2017. Leaf colouring information collected from more than 740 sites via citizen science was analysed, representing elevations from 0 to 2800 m and latitudes from 32°N to 44°N. We found that locations with earlier PLCstart dates (day of year 265–294) displayed steeper slopes in elevation per degree of latitude than locations with later PLCstart dates (day of year 295–314). This statistically significant result indicates that the influence of elevation on PLCstart (vertical gradient) weakened as the leaf colouring season progressed in Japan. In addition to these spatial characteristics, the PLCstart and the warmth index (based on monthly mean air temperature) showed significant linear correlations for latitudinal and elevational gradients. This result suggests that the sensitivity of PLCstart to air temperature, as manifested in both latitudinal and elevational gradients, is constant. This study suggests that online phenological data may provide more accurate results for a regional scale (100–1000 km) than the datasets used by previous studies. [ABSTRACT FROM AUTHOR]

A paper published in Global Change Biology in 2006 revealed that phenological responses in 1971–2000 matched the warming pattern in Europe, but a lack of chilling and adaptation in farming may have reversed these findings. Therefore, for 1951–2018 in a corresponding data set, we determined changes as linear trends and analysed their variation by plant traits/groups, across season and time as well as their attribution to warming following IPCC methodology. Although spring and summer phases in wild plants advanced less (maximum advances in 1978–2007), more (~90%) and more significant (~60%) negative trends were present, being stronger in early spring, at higher elevations, but smaller for nonwoody insect‐pollinated species. These trends were strongly attributable to winter and spring warming. Findings for crop spring phases were similar, but were less pronounced. There were clearer and attributable signs for a delayed senescence in response to winter and spring warming. These changes resulted in a longer growing season, but a constant generative period in wild plants and a shortened one in agricultural crops. Phenology determined by farmers' decisions differed noticeably from the purely climatic driven phases with smaller percentages of advancing (~75%) trends, but farmers' spring activities were the only group with reinforced advancement, suggesting adaptation. Trends in farmers' spring and summer activities were very likely/likely associated with the warming pattern. In contrast, the advance in autumn farming phases was significantly associated with below average summer warming. Thus, under ongoing climate change with decreased chilling the advancing phenology in spring and summer is still attributable to warming; even the farmers' activities in these seasons mirror, to a lesser extent, the warming. Our findings point to adaptation to climate change in agriculture and reveal diverse implications for terrestrial ecosystems; the strong attribution supports the necessary mediation of warming impacts to the general public. [ABSTRACT FROM AUTHOR]

Trends in the timing of spring and autumn phenophases of Betula pubescens were investigated in the southern, middle, and northern boreal zones in Finland. The field observations were carried out at 21 sites in the Finnish National Phenological Network in 1997-2013. The effective temperature sum of the thermal growth period, i.e. the sum of the positive differences between diurnal mean temperatures and 5 °C (ETS1), increased annually on average by 6-7 degree day units. Timing of bud burst remained constant in the southern and middle boreal zones but advanced annually by 0.5 day in the northern boreal zone. The effective temperature sum at bud burst (ETS2) showed no trend in the southern and middle boreal zones, whereas ETS2 increased on average from 20-30 to 50 degree day units in the northern boreal zone, almost to the same level as in the other zones. Increase in ETS2 indicates that the trees did not start their growth in very early spring despite warmer spring temperatures. The timing of leaf colouring and leaf fall remained almost constant in the southern boreal zones, whereas these advanced annually by 0.3 and 0.6 day in the middle boreal zone and by 0.6 and 0.4 day in the northern boreal zone, respectively. The duration of the growth period remained constant in all boreal zones. The results indicate high buffering capacity of B. pubescens against temperature changes. The study also shows the importance of the duration of phenological studies: some trends in spring phenophases had levelled out, while new trends in autumn phases had emerged after earlier studies in the same network for a shorter observation period. [ABSTRACT FROM AUTHOR]

Ecosystem productivity is influenced by the start and end of the growing season, and ecosystem models that simulate productivity need reliable representations of the phenology. For the seasonal development, autumn events are less understood than spring events, with comparatively fewer modelling attempts have been made for leaf senescence than for budburst. The few existing models for autumn phenology represent the influence of temperature and photoperiod. In this study, the aim was to evaluate which type of temperature response, photoperiod requirement and interaction between temperature and photoperiod captured the variation in leaf colouring more accurately. We tested existing models on a large dataset and developed new models by combining seven model components: linear or sigmoid temperature response above or below a base temperature, with or without modification by photoperiod, and photoperiod requirements (starting day of temperature response). Potential photoperiod requirement for leaf senescence induction was assessed by using a calibrated starting day or day of budburst that instead of a requirement represent the start of the ageing processes. Day of leaf colouring was simulated using 37 models for birch, beech and oak in Austria, Germany and the United Kingdom, in total 111 model runs that was compared to average day of leaf colouring. In 109 out of 111 simulations, average day of leaf colouring provided a better estimate. Some of the better performing models resembled average day of leaf colouring by counting number of days. Overall, the results indicate that the models estimated response to temperature and photoperiod do not support the use of a fixed degree-day requirement, especially across large regions. No photoperiod requirement could be inferred, and photoperiod in combination with temperature response provided little or no improvement on model performance. [ABSTRACT FROM AUTHOR]

Phenological variation among trees of different heights provides a small-scale ecological distinction within the forest, allowing the modulation of light interception and, consequently, net carbon gain. While spring phenological variations in temperate forests are well studied, for autumn phenology it is still unclear whether canopy vertical position (exposure), ontogeny or microclimatic factors are more decisive. We observed leaf colouring (LC) and leaf fall (LF) phenology of 166 Fagus sylvatica L. individuals (European beech; Fagaceae), twice/three times a week during autumn 2012 in a mixed forest in southern Germany. We aimed to determine: (1) the extent of variations in leaf senescence among F. sylvatica trees occurring in three different vertical canopy positions in the forest (overstorey, mesostorey and understorey); and (2) whether phenology varies between three different canopy height levels (upper, intermediate and lower). Possible microenvironmental drivers, such as air temperature, air humidity and light, were analysed in relation to autumn phenology. Air temperature and humidity data were obtained from HOBO loggers and light conditions from hemispheric fisheye photographs. Overstorey individuals were the first to start autumn phenology followed by mesostorey and understorey trees. For understorey individuals, the onset of LC and LF were observed 31 and 24 days later than for overstorey trees. The upper canopy parts of individual trees were characterised by the earliest appearance of autumn phases; mean difference in onset date of LC and LF between the upper and lower level was in each case -11 days. As peak dates did not differ, the duration of autumn phases were shorter at the lowest canopy height levels. We find a remarkable phenological avoidance of understorey trees and lower leaves compared to overstorey trees and upper canopy parts in F. sylvatica . We suggest that the observed differences were related to vertical variations in relative humidity and light availability, but also have an ontogenic cue. Since phenological variation in forest stands alters a range of environmental conditions, our study is useful from an ecological and microclimatic viewpoint. Moreover, since phenological development was shown to differ considerably, generalisations are limited when considering trees of different life stages within a forest. Further studies should focus on light conditions to investigate their influence on autumn phenology and importance for phenological avoidance. [ABSTRACT FROM AUTHOR]

We analyzed the leaf phenology of European beech ( Fagus sylvatica) and its variation due to spatial and temporal climatic variability, using a modified data set of the phenological network in Slovenia. We used first leaf unfolding (LU) and general leaf colouring (LC) time series of 47 sites (altitudes from 55 to 1,050 m a.s.l.) and corresponding climate series (52 of precipitation and 38 of temperature) for the period 1955-2007, collected by the Environmental Agency of the Republic of Slovenia. Across the network in average, LU occurred from 14 April until 13 May, and LC from 3 October until 29 October. LU was delayed by 2.6 days and LC was promoted by 1.9 days when the altitude increased by 100 m. Year-to-year variation of LU was significantly correlated with March and April temperatures. March temperatures had a greater effect at lower elevations and April ones at higher elevations. LC was related to August and September temperatures, and occurred later if the temperatures were higher. Recently, March and April temperatures showed an increasing trend and LU occurred 1.52 days earlier per decade at 1,000 m a.s.l. but no significant shifts were observed at lower altitudes. August temperatures were also increasing but the trends of LC were not significant and were not clearly related to altitude. Our detailed sub-regional data from a relatively small area with high geographic variability showed that changes in climate affect phenological response, mainly leaf unfolding, to a greater degree at higher altitudes than at lower ones. [ABSTRACT FROM AUTHOR]

Abstract: The annual timing of temperate forest leaf colouring is affected by climate change; to date, its modelling remains a challenge. We take advantage of a ca. 400 leaf colouring observations database acquired in France during the period of 1997–2006 in order to develop a new modelling framework aimed at predicting the spatial and year-to-year variability of leaf colouring in European beech and oak (Fagus sylvatica L., Quercus petraea (Matt.) Liebl. and Quercus robur L.). We postulate colouring to be the outcome of a one-way process triggered by photoperiod and progressing through a photoperiod-sensitive cold-degree day summation procedure. Observations were pooled according to genus for the fitting and ensuing validation procedures. Parameters of the model suggest that colouring processes start earlier, and are sensitive to higher temperatures for Quercus than for Fagus. Errors associated with the modelled predictions are up to 13.0 days in Fagus and 10.3 days in Quercus, which are significantly lower than errors associated with (1) the overall mean (null model) or (2) previously published modelling frameworks. When averaged on a site basis, model predictions reproduced spatial variability of leaf colouring over the French territory with good efficiency (modelling efficiencies: 0.44 for Fagus, 0.45 for Quercus). The interannual variability of leaf colouring over France was fairly reproduced (r 2 =0.74 for Fagus, 0.83 for Quercus). On that basis, we claim that the modelling framework developed herein can be efficiently integrated into more general schemes aimed at simulating matter and energy fluxes on a regional scale, and we provide a generic parameterisation of the model to be integrated into such schemes. When used in a prospective analysis, the model predicts a trend towards delay in leaf colouring of 1.4 and 1.7 days per decade in Fagus and Quercus, respectively, over the period of 1951–2099 in France. [Copyright &y& Elsevier]

The annual timing of leaf colouring of deciduous trees in temperate regions is not predictable using phenological models. In this analysis we show that commonly applied hypotheses of leaf colouring triggers have neither satisfactory explanatory power nor significant statistical proof. We tested meteorological parameters, such as monthly mean temperatures, threshold temperatures, monthly sums of precipitation and number of dry days per month of the year of the phenological event and of the previous year and the length of the vegetation period. Their influence on leaf colouring dates for 4 deciduous tree species (horse chestnut, beech, birch, oak) in Germany (1951-2003) was tested by Pearson's correlations. We created 3 different datasets: (A) phenological observations for single stations within 25 km of meteorological stations, (B) means of phenological observations around (<25 km) meteorological stations, and (C) phenological means for Germany. Only the mean temperature of September had a slight influence on the onset of leaf colouring (mean: rchestnut = 0. 45; rbeech = 0. 56; roak = 0. 51; rbirch = 0. 45). Taking all correlation coefficients r > 10. 31 into account, we can deduce that a warm September (all species) and August (oak, birch) delayed leaf colouring while a warm June (horse chestnut, oak) and May (horse chestnut) advanced leaf colouring. [ABSTRACT FROM AUTHOR]

The changes in precipitation and temperature regimes brought on by the current climate change have influenced ecosystems globally. The consequences of climate change on plant phenology have been widely investigated during the last few years. However, the underlying causes of the timing of autumn phenology have not been fully clarified yet. Here, we focused on the onset (10%) of leaf colouring—LCO—(Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie (BBCH) 92) of European beech (Fagus sylvatica, L.) as an important native tree species growing throughout Europe. Studied beech stands are located along the natural distribution range of the European beech in Western Carpathians (Slovakia) at different altitudes from lowlands (300 m a.s.l.) to uplands (1050 m a.s.l.) and climatic regions from warm to cold. To define limiting climate conditions for LCO, we established several bioclimatic indices as indicators of meteorological drought: climatic water balance (CWB), standardized precipitation index (SPI), standardized precipitation-evapotranspiration index (SPEI), dry period index (DPI), and heat waves (HW). In addition, meteorological variables such as monthly mean temperatures and precipitation totals were taken into account. Throughout the 23-year period (1996–2018) of ground-based phenological observations of temperate beech forests, the timing of LCO was significantly delayed (p ≤ 0.05) in the middle to high altitudes, while in the lowest altitude, it remained unchanged. Over the last decade, 2009–2018, LCO in middle altitudes started at comparable to low altitudes and, at several years, even later. This resulted mainly from the significant negative effect of drought prior to this phenological phase (p ≤ 0.01) expressed through a 1-month SPI in September (SPIIX) at the stand at the low-altitude and warm-climatic region. Our results indicate that the meteorological drought conditioned by lower total precipitation and higher evapotranspirative demands in the warmer climate advance leaf senescence. However, at present time, growth in rising temperature and precipitation is acceptable for most beech stands at middle to high altitudes. Beech utilizes these conditions and postpones the LCO by 0.3–0.5 and 0.6–1.2 day per year at high and middle altitudes, respectively. Although we show the commencing negative effect of drought at mid-altitudes with lower (below 700 mm) total annual precipitation, the trend of LCO in favourable warm climates is still significantly delayed. The ongoing warming trend of summer months suggests further intensification of drought as has started to occur in middle altitudes, spreading from the continual increase of evapotranspiration over the next decades. [ABSTRACT FROM AUTHOR]