Photoperiod decelerates the advance of spring phenology of six deciduous tree species under climate warming

Long-term species-level observations indicate the critical role of soil moisture in regulating China's grassland productivity relative to phenological and climatic factors

As a sensitive indicator of climate change and a key variable in ecosystem surface-atmosphere interaction, vegetation phenology, and the growing season length, as well as climatic factors (i.e., temperature, precipitation, and sunshine duration) are widely recognized as key factors influencing vegetation productivity. Recent studies have highlighted the importance of soil moisture in regulating grassland productivity. However, the relative importance of phenology, climatic factors, and soil moisture to plant species-level productivity across China's grasslands remains poorly understood. Here, we use nearly four decades (1981 to 2018) of in situ species-level observations from 17 stations distributed across grasslands in China to examine the key mechanisms that control grassland productivity. The results reveal that soil moisture is the strongest determinant of the interannual variability in grassland productivity. In contrast, the spring/autumn phenology, the length of vegetation growing season, and climate factors have relatively minor impacts. Generally, annual aboveground biomass increases by 3.9 to 25.3 g∙m2 (dry weight) with a 1 % increase in growing season mean soil moisture across the stations. Specifically, the sensitivity of productivity to moisture in wetter and colder environments (e.g., alpine meadows) is significantly higher than that in drier and warmer environments (e.g., temperate desert steppes). In contrast, the sensitivity to the precipitation of the latter is greater than the former. The effect of soil moisture is the most pronounced during summer. Dominant herb productivity is more sensitive to soil moisture than the others. Moreover, multivariate regression analyses show that the primary climatic factors and their attributions to variations in soil moisture differ among the stations, indicating the interaction between climate and soil moisture is very complex. Our study highlights the interspecific difference in the soil moisture dependence of grassland productivity and provides guidance to climate change impact assessments in grassland ecosystems.

A Long-Lived Alpine Perennial Advances Flowering under Warmer Conditions but Not Enough to Maintain Reproductive Success

AbstractAssessing whether phenological shifts in response to climate change confer a fitness advantage requires investigating the relationships among phenology, fitness, and environmental drivers of selection. Despite widely documented advancements in phenology with warming climate, we lack empirical estimates of how selection on phenology varies in response to continuous climate drivers or how phenological shifts in response to warming conditions affect fitness. We leverage an unusual long-term dataset with repeated, individual measurements of phenology and reproduction in a long-lived alpine plant. We analyze phenotypic plasticity in flowering phenology in relation to two climate drivers, snowmelt timing and growing degree days (GDDs). Plants flower earlier with increased GDDs and earlier snowmelt, and directional selection also favors earlier flowering under these conditions. However, reproduction still declines with warming and early snowmelt, even when flowering is early. Furthermore, the steepness of this reproductive decline increases dramatically with warming conditions, resulting in very little fruit production regardless of flowering time once GDDs exceed approximately 225 degree days or snowmelt occurs before May 15. Even though advancing phenology confers a fitness advantage relative to stasis, these shifts are insufficient to maintain reproduction under warming, highlighting limits to the potential benefits of phenological plasticity under climate change.

Plant species phenology differs between climate and land-use scenarios and relates to plant functional traits

Phenological shifts due to changing climate are often highly species and context specific. Land-use practices such as mowing or grazing directly affect the phenology of grassland species, but it is unclear if plants are similarly affected by climate change in differently managed grassland systems such as meadows and pastures. Functional traits have a high potential to explain phenological shifts and might help to understand species-specific and land-use-specific phenological responses to changes in climate. In the large-scale field experiment Global Change Experimental Facility (GCEF), we monitored the first flowering day, last flowering day, flowering duration, and day of peak flowering, of 17 herbaceous grassland species under ambient and future climate conditions, comparing meadows and pastures. Both climate and land use impacted the flowering phenology of plant species in species-specific ways. We did not find evidence for interacting effects of climate and land-use type on plant phenology. However, the data indicate that microclimatic and microsite conditions on meadows and pastures were differently affected by future climate, making differential effects on meadows and pastures likely. Functional traits, including the phenological niche and grassland utilization indicator values, explained species-specific phenological climate responses. Late flowering species and species with a low mowing tolerance advanced their flowering more strongly under future climate. Long flowering species and species following an acquisitive strategy (high specific leaf area, high mowing tolerance, and high forage value) advanced their flowering end more strongly and thus more strongly shortened their flowering under future climate. We associated these trait-response relationships primarily with a phenological drought escape during summer. Our results provide novel insights on how climate and land use impact the flowering phenology of grassland species and we highlight the role of functional traits in mediating phenological responses to climate.

Phenological response of European beech (Fagus sylvatica L.) to climate change in the Western Carpathian climatic-geographical zones

Introduction

The paper analyzes the results of 26 years (1996-2021) of phenological observations of the vegetative organs of European beech (Fagus sylvatica L.) in the Western Carpathians. It evaluates the influence of the heterogeneity of this territory, including relief and elevation, based on climatic-geographical types.

Methods

Phenological stages, including leaf unfolding, full leaves, leaf coloring, and leaf fall, were monitored at 40 phenological stations across eight elevation zones. The study assesses trends in the occurrence of phenological stages, the length of the growing season, and phenological elevation gradients.

Results

The results indicate a statistically significant earlier onset of spring phenological phases and delay in autumn phases, resulting in an average extension of the beech growing season by 12 days. Our findings confirm that the lengthening of the growing season due to warming, as an expression of climate change, is predominantly attributed to the warming in the spring months. The detected delayed onset of autumn phenophases was not due to warming in the autumn months, but other environmental factors influence it. The trend of elongation of the growing season (p<0.01) is observed in all elevation zones, with a less significant trend observed only in zones around 400 and 600 m a.s.l, signaling changes in environmental conditions across most of the elevation spectrum. Moreover, the heterogeneity of climatic-geographical types within each elevation zone increases the variability in the duration of the growing season for sites with similar elevations. By extending the growing season, it is assumed that the beech area will be changed to locations with optimal environmental conditions, especially in terms of adverse climatic events (late spring frosts, drought) during the growing season. The phenological elevation gradients reveal an earlier onset of 2.2 days per 100 m for spring phenophases and a delay of 1.1-2.9 days per 100 m for autumn phenophases.

Discussion

These findings highlight the specific environmental conditions of European beech in the Western Carpathians and their potential for anticipating changes in its original area. Additionally, these observations can aid in forecasting the further development of phenological manifestations related to climate change.

Soil freeze-thaw cycles affect spring phenology by changing phenological sensitivity in the Northern Hemisphere

The use of frozen soil-vegetation feedback for predictive models is undergoing enormous changes under rapid climate warming. However, the influence of soil freeze-thaw (SFT) cycles on vegetation phenology and the underlying mechanisms remain poorly understood. By synthesizing a variety of satellite-derived data from 2002 to 2021 in the Northern Hemisphere (NH), we demonstrated a widespread positive correlation between soil thawing and the start of the growing season (SOS). Our results also showed that the SFT cycles had a significant impact on vegetation phenology mainly by altering the phenological sensitivities to daytime and nighttime temperatures, solar radiation and precipitation. Moreover, the effects of SFT cycles on the sensitivity of the SOS were more pronounced than those on the sensitivity of the end of the growing season (EOS) and the length of growing season (LOS). Furthermore, due to the degradation of frozen soil, the changes in phenological sensitivity in the grassland and tundra biomes were significantly larger than those in the forest. These findings highlighted the importance of incorporating the SFT as an intermediate process into process-based phenological models.

Warming increases the differences among spring phenology models under future climate change

Phenological models are built upon an understanding of the influence of environmental factors on plant phenology, and serve as effective tools for predicting plant phenological changes. However, the differences in phenological model predictive performance under different climate change scenarios have been rarely studied. In this study, we parameterized thirteen spring phenology models, including six one-phase models and seven two-phase models, by combining phenological observations and meteorological data. Using climatic data from two Shared Socioeconomic Pathways (SSP) scenarios, namely SSP126 (high mitigation and low emission) and SSP585 (no mitigation and high emission), we predicted spring phenology in Germany from 2021 to 2100, and compared the impacts of dormancy phases and driving factors on model predictive performance. The results showed that the average correlation coefficient between the predicted start of growing season (SOS) by the 13 models and the observed values exceeded 0.72, with the highest reaching 0.80. All models outperformed the NULL model (Mean of SOS), and the M1 model (driven by photoperiod and forcing temperature) performed the best for all the tree species. In the SSP126 scenario, the average SOS advanced initially and then gradually shifted towards a delay starting around 2070. In the SSP585 scenario, the average SOS advanced gradually at a rate of approximately 0.14 days per year. Moreover, the standard deviation of the simulated SOS by the 13 spring phenology models exhibited a significant increase at a rate of 0.04 days per year. On average, two-phase models exhibited larger standard deviations than one-phase models after approximately 2050. Models driven solely by temperature showed larger standard deviations after 2060 compared to models driven by both temperature and photoperiod. Our findings suggest investigating the release mechanisms of endodormancy phase and incorporating new insights into future phenological models to better simulate the changes in plant phenology.

Non-symmetric responses of leaf onset date to natural warming and cooling in northern ecosystems

The northern hemisphere has experienced regional cooling, especially during the global warming hiatus (1998-2012) due to ocean energy redistribution. However, the lack of studies about the natural cooling effects hampers our understanding of vegetation responses to climate change. Using 15,125 ground phenological time series at 3,620 sites since the 1950s and 31-year satellite greenness observations (1982-2012) covering the warming hiatus period, we show a stronger response of leaf onset date (LOD) to natural cooling than to warming, i.e. the delay of LOD caused by 1°C cooling is larger than the advance of LOD with 1°C warming. This might be because cooling leads to larger chilling accumulation and heating requirements for leaf onset, but this non-symmetric LOD response is partially offset by warming-related drying. Moreover, spring greening magnitude, in terms of satellite-based greenness and productivity, is more sensitive to LOD changes in the warming area than in the cooling. These results highlight the importance of considering non-symmetric responses of spring greening to warming and cooling when predicting vegetation-climate feedbacks.

Climatic drivers and ecological implications of variation in the time interval between leaf-out and flowering

Leaf-out and flowering in any given species have evolved to occur in a predetermined sequence, with the inter-stage time interval optimized to maximize plant fitness. Although warming-induced advances of both leaf-out and flowering are well documented, it remains unclear whether shifts in these phenological phases differ in magnitudes and whether changes have occurred in the length of the inter-stage intervals. Here, we present an extensive synthesis of warming effects on flower-leaf time intervals, using long-term (1963-2014) and in situ data consisting of 11,858 leaf-out and flowering records for 183 species across China. We found that the timing of both spring phenological events was generally advanced, indicating a dominant impact of forcing conditions compared with chilling. Stable time intervals between leaf-out and flowering prevailed for most of the time series despite increasing temperatures; however, some of the investigated cases featured significant changes in the time intervals. The latter could be explained by differences in the temperature sensitivity (ST) between leaf and flower phenology. Greater ST for flowering than for leaf-out caused flowering times to advance faster than leaf emergence. This shortened the inter-stage intervals in leaf-first species and lengthened them in flower-first species. Variation in the time intervals between leaf-out and flowering events may have far-reaching ecological and evolutionary consequences, with implications for species fitness, intra/inter-species interactions, and ecosystem structure, function, and stability.

Satellite observed reversal in trends of spring phenology in the middle-high latitudes of the Northern Hemisphere during the global warming hiatus

The start of the growing season (SOS) is essential to track the responses of vegetation to climate change. However, recent findings on whether the SOS in the middle-high latitudes of the Northern Hemisphere (NH) continued to advance or reversed during the global warming hiatus were not consistent. It is necessary to investigate the causes of this controversy and to examine the relationship between the SOS and preseason temperature trends. To this end, we first applied four widely used phenology extraction methods to derive the SOS from the GIMMS NDVI3g dataset and then used the ensemble empirical modal decomposition (EEMD) method to extract the nonlinear trends of the SOS and preseason temperature. Our results clarify, for the first time, that the limitations of the linear assumption-based trend analysis methods are an important but overlooked cause of the discrepancies among existing studies on whether the SOS was advanced or delayed in the NH (>30° N) during the global warming hiatus. We further revealed the range of the mismatches between the SOS and preseason temperature trends at the latitude, altitude and biome levels. Specifically, we discovered that the SOS in the NH (>30° N) obtained by the four phenology extraction methods showed a significant reversal from advance to delay during the global warming hiatus, and the corresponding average rate of change was very small. The area showing increasing preseason temperatures decreased during the global warming hiatus, but it always occupied most of the NH (>30° N). However, delayed SOS trends were dominant in the NH from 50° N to 60° N, above 3000 m and in biomes other than TBMF and BF. Accordingly, using an EEMD-like approach to evaluate the changes in the SOS and preseason temperature is necessary for improving our understanding of the changes in the SOS and their association with climate.

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

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

Radiation-constrained boundaries cause nonuniform responses of the carbon uptake phenology to climatic warming in the Northern Hemisphere

Climatic warming has lengthened the photosynthetically active season in recent decades, thus affecting the functioning and biogeochemistry of ecosystems, the global carbon cycle and climate. Temperature response of carbon uptake phenology varies spatially and temporally, even within species, and daily total intensity of radiation may play a role. We empirically modelled the thresholds of temperature and radiation under which daily carbon uptake is constrained in the temperate and cold regions of the Northern Hemisphere, which include temperate forests, boreal forests, alpine and tundra biomes. The two-dimensionality of the temperature-radiation constraint was reduced to one single variable, θ, which represents the angle in a polar coordinate system for the temperature-radiation observations during the start and end of the growing season. We found that radiation will constrain the trend towards longer growing seasons with future warming but differently during the start and end of season and depending on the biome type and region. We revealed that radiation is a major factor limiting photosynthetic activity that constrains the phenology response to temperature during the end-of-season. In contrast, the start of the carbon uptake is overall highly sensitive to temperature but not constrained by radiation at the hemispheric scale. This study thus revealed that while at the end-of-season the phenology response to warming is constrained at the hemispheric scale, at the start-of-season the advance of spring onset may continue, even if it is at a slower pace.

Disorder or a new order: How climate change affects phenological variability

Advancing spring phenology is a well documented consequence of anthropogenic climate change, but it is not well understood how climate change will affect the variability of phenology year to year. Species' phenological timings reflect the adaptation to a broad suite of abiotic needs (e.g., thermal energy) and biotic interactions (e.g., predation and pollination), and changes in patterns of variability may disrupt those adaptations and interactions. Here, we present a geographically and taxonomically broad analysis of phenological shifts, temperature sensitivity, and changes in interannual variability encompassing nearly 10,000 long-term phenology time series representing more than 1000 species across much of the Northern Hemisphere. We show that the timings of leaf-out, flowering, insect first-occurrence, and bird arrival were the most sensitive to temperature variation and have advanced at the fastest pace for early-season species in colder and less seasonal regions. We did not find evidence for changing variability in warmer years in any phenophase groups, although leaf-out and flower phenology have become moderately but significantly less variable over time. Our findings suggest that climate change has not to this point fundamentally altered the patterns of interannual phenological variability.

Estimating phenological sensitivity in contemporary vs. historical data sets: Effects of climate resolution and spatial scale

PREMISE

Phenological sensitivity, or the degree to which a species' phenology shifts in response to warming, is an important parameter for comparing and predicting species' responses to climate change. Phenological sensitivity is often measured using herbarium specimens or local studies in natural populations. These approaches differ widely in spatiotemporal scales, yet few studies explicitly consider effects of the geographic extent and resolution of climate data when comparing phenological sensitivities quantified from different data sets for a given species.

METHODS

We compared sensitivity of flowering phenology to growing degree days of the alpine plant Silene acaulis using two data sets: herbarium specimens and a 6 yr observational study in four populations at Niwot Ridge, Colorado, USA. We investigated differences in phenological sensitivity obtained using variable spatial scales and climate data sources.

RESULTS

Herbarium specimens underestimated phenological sensitivity compared to observational data, even when herbarium samples were limited geographically or to nearby weather station data. However, when observational data were paired with broader-scale climate data, as is typically used in herbarium data sets, estimates of phenological sensitivity were more similar.

CONCLUSIONS

This study highlights the potential for variation in data source, geographic scale, and accuracy of macroclimate data to produce very different estimates of phenological responses to climate change. Accurately predicting phenological shifts would benefit from comparisons between methods that estimate climate variables and phenological sensitivity over a variety of spatial scales.

Continued spring phenological advance under global warming hiatus over the Pan-Third Pole

The global surface temperature has witnessed a warming hiatus in the first decade of this century, but how this slowing down of warming will impact spring phenology over Pan-Third Pole remains unclear. Here, we combined multiple satellite-derived vegetation indices with eddy covariance datasets to evaluate the spatiotemporal changes in spring phenological changes over the Pan-Third Pole. We found that the spring phenology over Pan-Third Pole continues to advance at the rate of 4.8 days decade^-1 during the warming hiatus period, which is contrasted to a non-significant change over the northern hemisphere. Such a significant and continued advance in spring phenology was mainly attributed to an increase in preseason minimum temperature and water availability. Moreover, there is an overall increasing importance of precipitation on changes in spring phenology during the last four decades. We further demonstrated that this increasingly negative correlation was also found across more than two-thirds of the dryland region, tentatively suggesting that spring phenological changes might shift from temperature to precipitation-controlled over the Pan-Third Pole in a warmer world.

Quantifying the importance of day length in process-based models for the prediction of temperate spring flowering phenology

Owing to climate change and frequent extreme weather events, changes in spring flowering phenology have been observed in temperate forests. The flowering time response to climate change is divergent among species and is difficult to predict due to the complexity of flowering mechanisms. To compare the effects of spring warming, winter chilling, and day length on spring flowering time, we evaluated eight process-based models (two types of forcing models, two types of chilling-forcing models, and four models with the effect of day length added to the aforementioned four models). We used flowering data of seven temperate species (Cornus officinalis, Rhododendron mucronulatum, Forsythia koreana, Prunus yedoensis, Rhododendron yedoense f. poukhanense, Rhododendron schlippenbachii, and Robinia pseudoacacia) observed in nine different arboretums in South Korea over 9 years. Generally, the forcing model performed better than the sequential chilling-forcing model, regardless of the species. The performance gap between the models was reduced when day length term was included in model, but the chilling-forcing model did not outperform the forcing model. The effect of day length on flowering time differed depending on the species. Prunus yedoensis, which had a particularly low warming sensitivity compared to other species, was more dependent on day length than other species. On the other hand, day length had little effect on the flowering time of Robinia pseudoacacia and Cornus officinalis, mostly found in the early successional stage. These findings imply that the effect of chilling on flowering time would be minor for the seven species inhabiting the warm-temperate forest, and the effect of day length on flowering time was species-specific and dependent on species' temperature (warming) sensitivity and life strategy. In the future warm climate, the flowering time of day length sensitive species would not advance significantly, which may result in a phenological mismatch and endanger their life.

Stomatal Limitation Is Able to Modulate Leaf Coloration Onset of Temperate Deciduous Tree

Autumn phenology, determined mainly by temperature and photoperiod, is essential for ecosystem carbon sequestration. Usually, the variations in the maximum rate of Rubisco (Vcmax) and the maximum rate of ribulose-bisphosphate regeneration (Jmax) are taken as the mechanism regulating the seasonal pattern of photosynthetic rates and autumn phenology. In this study, we used Quercus mongolicus seedlings as an example to examine the photosynthetically physiological mechanism of leaf coloration onset (LCO) responding to different warming and photoperiod treatments based on experimental data acquired from large artificial climate simulation chambers. The results indicated that: (1) LCO and the net CO2 assimilation rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), Vcmax, and Jmax of Quercus mongolicus seedlings were significantly affected by the changes of photoperiod. (2) LCO was significantly correlated only with the Pn approach, supporting the view that leaf senescence is the result of a trade-off between nutrient resorption and reserves. (3) The major variation in stomatal conductance (Gs) is the mechanism by which photoperiod regulates the seasonal pattern of photosynthetic rates, implying that both limitations of stomatal and photosynthetical capacity (Vcmax and Jmax, non-stomatal limitation) are able to modulate LCO. Our study riches the knowledge of phenology and provides a reference for phenological modelling and ecosystem carbon estimation.

Spatiotemporal Characteristics and Heterogeneity of Vegetation Phenology in the Yangtze River Delta

Vegetation phenology and its spatiotemporal driving factors are essential to reflect global climate change, the surface carbon cycle and regional ecology, and further quantitative studies on spatiotemporal heterogeneity and its two-way driving are needed. Based on MODIS phenology, meteorology, land cover and other data from 2001 to 2019, this paper analyzes the phenology change characteristics of the Yangtze River Delta from three dimensions: time, plane space and elevation. Then, the spatiotemporal heterogeneity of phenology and its driving factors are explored with random forest and geographic detector methods. The results show that (1) the advance of start of season (SOS) is insignificant—with 0.17 days per year; the end of season (EOS) shows a significant delay—0.48 days per year. The preseason temperature has a greater contribution to SOS, while preseason precipitation is main factor in determining EOS. (2) Spatial differences of the phenological index do not strictly obey the change rules of latitude at a provincial scale. The SOS of Jiangsu and Anhui is earlier than that of Zhejiang and Shanghai, and EOS shows an obvious double-clustering phenomenon. In addition, a divergent response of EOS with elevation grades is found; the most significant changes are observed at grades below 100 m. (3) Land cover (LC) type is a major factor of the spatial heterogeneity of phenology, and its change may also be one of the insignificant factors driving the interannual change of phenology. Furthermore, nighttime land surface temperature (NLST) has a relatively larger contribution to the spatial heterogeneity in non-core urban areas, but population density (PD) contributes little. These findings could provide a new perspective on phenology and its complex interactions between natural or anthropogenic factors.

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

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

Spatial Difference of Interactive Effect Between Temperature and Daylength on Ginkgo Budburst

Climate warming-induced shifts in spring phenology have substantially affected the structure and function of terrestrial ecosystems and global biogeochemical cycles. Spring phenology is primarily triggered by spring temperature and is also affected by daylength and winter chilling, yet the relative importance of these cues across spatial gradients remains poorly understood. Here, we conducted a manipulative experiment with two daylength and three temperature treatments to investigate spatial differences in the response of ginkgo budburst to temperature and daylength, using twigs collected at three sites across a spatial gradient: a control site at a low latitude and low elevation on Tianmu Mountain (TM_low), a low latitude and high elevation site on Tianmu Mountain (TM_high), and a high latitude site on Jiufeng mountain (JF). The mechanisms were also tested using in situ phenological observations of ginkgo along latitudes in China. We found that, compared to TM_low individuals, budburst dates occurred 12.6 (JF) and 7.7 (TM_high) days earlier in high-latitude and high-elevation individuals when exposed to the same temperature and daylength treatments. Importantly, daylength only affected budburst at low latitudes, with long days (16 h) advancing budburst in low-latitude individuals by, on average, 8.1 days relative to short-day (8 h) conditions. This advance was most pronounced in low-elevation/latitude individuals (TM_low = 9.6 days; TM_high = 6.7 days; JF = 1.6 days). In addition, we found that the temperature sensitivity of budburst decreased from 3.4 to 2.4 days °C^-1 along latitude and from 3.4 to 2.5 days °C^-1 along elevation, respectively. The field phenological observations verified the experimental results. Our findings provide empirical evidence of spatial differences in the relative effects of spring temperature and daylength on ginkgo budburst, which improved our understanding of spatial difference in phenological changes and the responses of terrestrial ecosystem to climate change.

Artificial light at night: an underappreciated effect on phenology of deciduous woody plants

Artificial light at night (ALAN), an increasing anthropogenic driver, is widespread and shows rapid expansion with potential adverse impact on the terrestrial ecosystem. However, whether and to what extent does ALAN affect plant phenology, a critical factor influencing the timing of terrestrial ecosystem processes, remains unexplored due to limited ALAN observation. Here, we used the Black Marble ALAN product and phenology observations from USA National Phenology Network to investigate the impact of ALAN on deciduous woody plants phenology in the conterminous United States. We found that (1) ALAN significantly advanced the date of breaking leaf buds by 8.9 ± 6.9 days (mean ± SD) and delayed the coloring of leaves by 6.0 ± 11.9 days on average; (2) the magnitude of phenological changes was significantly correlated with the intensity of ALAN (P < 0.001); and (3) there was an interaction between ALAN and temperature on the coloring of leaves, but not on breaking leaf buds. We further showed that under future climate warming scenarios, ALAN will accelerate the advance in breaking leaf buds but exert a more complex effect on the coloring of leaves. This study suggests intensified ALAN may have far-reaching but underappreciated consequences in disrupting key ecosystem functions and services, which requires an interdisciplinary approach to investigate. Developing lighting strategies that minimize the impact of ALAN on ecosystems, especially those embedded and surrounding major cities, is challenging but must be pursued.

Green with phenology

[Figure: see text].

Dissecting impacts of phenological shifts for performance across biological scales

Although phenological shifts in response to climate are often assumed to benefit species' performance and viability, phenology's role in allowing population persistence and mediating species-level responses in the face of climate change remain unclear. Here, we develop a framework to understand when and why phenological shifts at three biological scales will influence performance: individuals, populations, and macroecological patterns. Specifically, we highlight three underexplored assumptions: (i) individual variability in phenology does not affect population fitness; (ii) population growth rates are sensitive to vital rates affected by phenology; and (iii) phenology mediates species-level responses to climate change including patterns of extinction, invasion, and range shifts. We outline promising methods for understanding how phenological shifts will influence performance within and across biological scales.

Does Phenological Plasticity Help or Hinder Range Shifts Under Climate Change?

Climate warming is predicted to shift species’ ranges as previously uninhabitable environments just beyond the leading range edges become suitable habitat and trailing range edges become increasingly unsuitable. Understanding which aspects of the environment and species traits mediate these range shifts is critical for understanding species’ possible redistributions under global change, yet we have a limited understanding of the ecological and evolutionary responses underlying population spread or extinction at species’ range edges. Within plant populations, shifts in flowering phenology have been one of the strongest and most consistent responses to climate change, and are likely to play an important role in mediating population dynamics within and beyond species’ ranges. However, the role of phenological shifts, and particularly phenological plasticity, in species’ range shifts remains relatively unstudied. Here, we synthesize literature on phenology, plasticity, and adaptation to suggest ways in which phenological responses to climate may vary across species’ ranges and review the empirical evidence for and against these hypotheses. We then outline how phenological plasticity could facilitate or hinder persistence and potential consequences of phenological plasticity in range expansions, including phenological cues, shifts in correlated traits, altered species interactions, and effects on gene flow. Finally, we suggest future avenues for research, such as characterizing reaction norms for phenology across a species’ range and in beyond-the-range transplant experiments. Given the prevalence and magnitude of phenological shifts, future work should carefully dissect its costs and benefits for population persistence, and incorporate phenological plasticity into models predicting species’ persistence and geographic range shifts under climate change.

Extending the Cultivation Area of Pecan (Carya illinoinensis) Toward the South in Southeastern Subtropical China May Cause Increased Cold Damage

Pecan (Carya illinoinensis) is an important nut tree species in its native areas in temperate and subtropical North America, and as an introduced crop in subtropical southeastern China as well. We used process-based modeling to assess the effects of climatic warming in southeastern China on the leaf-out phenology of pecan seedlings and the subsequent risk of "false springs," i.e., damage caused by low temperatures occurring as a result of prematurely leafing out. In order to maximize the biological realism of the model used in scenario simulations, we developed the model on the basis of experiments explicitly designed for determining the responses modeled. The model showed reasonable internal accuracy when calibrated against leaf-out observations in a whole-tree chamber (WTC) experiment with nine different natural-like fluctuating temperature treatments. The model was used to project the timing of leaf-out in the period 2022-2099 under the warming scenarios RCP4.5 and RCP8.5 in southeastern China. Two locations in the main pecan cultivation area in the northern subtropical zone and one location south of the main cultivation area were addressed. Generally, an advancing trend of leaf-out was projected for all the three locations under both warming scenarios, but in the southern location, a delay was projected under RCP8.5 in many years during the first decades of the 21st century. In the two northern locations, cold damage caused by false springs was projected to occur once in 15-26 years at most, suggesting that pecan cultivation can be continued relatively safely in these two locations. Paradoxically, more frequent cold damage was projected for the southern location than for the two northern locations. The results for the southern location also differed from those for the northern locations in that more frequent cold damage was projected under the RCP4.5 warming scenario (once in 6 years) than under the RCP8.5 scenario (once in 11 years) in the southern location. Due to the uncertainties of the model applied, our conclusions need to be re-examined in an additional experimental study and further model development based on it; but on the basis of our present results, we do not recommend starting large-scale pecan cultivation in locations south of the present main pecan cultivation area in southeastern subtropical China.