Spring Budburst Research Articles

Spring’s Signal: Can Bud Burst Timing Enhance Resistance to Ash Dieback in Europe?

Ash dieback (ADB), driven by the invasive fungus Hymenoscyphus fraxineus, poses a significant environmental and financial risk throughout Europe. Fraxinus excelsior (European ash), an essential part of forest ecosystems, has seen death rates as high as 85% in impacted areas, threatening its ecological roles and economic importance. This study examines the relationship between the phenological traits of ash clones, particularly the timing of spring bud burst, and their susceptibility to H. fraxineus infection. The study was conducted in a clonal seed orchard located in Northeastern Poland, encompassing 31 ash clones from different bioclimatic regions. Phenological analyses of bud burst were carried out from early April to late May during the years 2018–2020, and crown damage and defoliation levels were assessed multiple times throughout the growing season. The results confirm that clones with earlier bud burst exhibit significantly higher survival rates and reduced crown damage. Observations revealed that clones with earlier bud burst showed a 30% higher survival rate and up to 40% less crown damage compared to clones with later phenology. The timing of bud burst was strongly correlated with susceptibility to ash dieback (R2 = 0.37, p < 0.001). Statistical analyses, including ANOVA and mixed models, revealed significant differences in susceptibility to infection among clones from different bioclimatic regions. These findings underscore the importance of biological timing as a key factor in selecting genotypes resilient to ash dieback. The study highlights the potential of breeding approaches that focus on early bud burst traits to enhance the survival and vitality of ash populations. The results provide essential insights for developing adaptive forest management practices aimed at conserving ash resources and maintaining biodiversity in the face of climate change and the ongoing spread of the pathogen.

Host plant phenology drives risky larval dispersal in an outbreaking insect defoliator

Abstract Dispersal away from natal sites allows individuals to find suitable foraging sites to complete their development and successfully reproduce. Drivers of risky dispersal behaviour in forest landscapes by young larvae of outbreaking defoliators are not well understood. We assessed dispersal behaviour of young spruce budworm larvae in relation to spring budburst phenology of primary and secondary hosts, balsam fir and black spruce, respectively. We tested whether tree species and presence of suitable feeding sites influenced dispersal away from source branches and subsequent redistribution of insects. Laboratory experiments showed that dispersal is an active behaviour during which larvae disperse away from source trees without open buds, regardless of species. Establishment on sink branches was highest when they possessed open buds and the source did not. In the field, larval dispersal was higher from black spruce than from balsam fir and larval establishment was more persistent on balsam fir. The decision to disperse occurs before budburst of either host species. Larvae disperse preferentially away from black spruce whose old needles are too tough for larval mining, compared to balsam fir that can be mined for sustenance and refuge while larvae await budburst. While black spruce is a suitable host species after its buds expand, phenological defences drive larval dispersal away from this host plant. These findings are the first to show how risky dispersal behaviour in larval Lepidoptera is facultative and is determined by local food availability.

Response of Sunmuscat (Vitis vinifera L.) to Varying Cane Numbers When Managed on a Shaw Swing-Arm Trellis for Dried Grape Production

Background and Aims. Dried grapes from Sunmuscat compose more than 50% of Australia’s production. Sunmuscat is late ripening which can lead to suboptimal drying conditions and darkening of the final product. The response of Sunmuscat to varying cane number per vine was studied with the aim to promote earlier ripening and optimise berry size and yield, without detrimental effects on dried product quality. Methods and Results. The study was conducted in a trellis dried, commercial vineyard with pruning level treatments of 6, 9, 12, and 15 canes per vine over 3 seasons. It included assessment of budburst and fruitfulness in spring; monitoring of grape ripening; measurement of yield, bunch number, and moisture content at harvest; and post-harvest assessment of dry berry mass and fruit colour. Traits strongly affected by season were fruitfulness, yield, berry development, juice composition (TSS, pH, and TA), and dried grape quality (colour, dry berry mass, and sugar per berry). Retention of high cane numbers produced a slight delay in ripening (i.e., a mean of 1.1°Brix), small berries, and an asymptotic yield response without an effect on dried fruit colour or moisture. A linear response for bunch loss between spring and harvest was found with increasing cane number. Conclusions. Retention of fewer canes increased berry size and promoted earlier ripening, but at the expense of yield. Significance of the Study. Bunch loss between spring and harvest was the major yield determinant being more important than budburst, shoot fruitfulness, or berries per bunch.

Late autumn warming can both delay and advance spring budburst through contrasting effects on bud dormancy depth in Fagus sylvatica L.

The current state of knowledge on bud dormancy is limited. However, expanding such knowledge is crucial in order to properly model forest responses and feedback to future climate. Recent studies have shown that warming can decrease chilling accumulation and increase dormancy depth, thereby inducing delayed budburst in European beech (Fagus sylvatica L). Whether fall warming can advance spring phenology is unclear. To investigate the effect of warming on endodormancy of deciduous trees, we tested the impact of mild elevated temperature (+ 2.5-3.5°C; temperature on average kept at 10°C) in mid- and late autumn on bud dormancy depth and spring phenology of beech. We studied saplings by inducing periods of warming in greenhouses during two years. Even though warming reduced chilling in both years, we observed that the response of dormancy depth and spring budburst were year-specific. We found that warming during endodormancy peak could decrease bud dormancy depth and therefore advance spring budburst. This effect appears to be modulated by factors such as the date of senescence onset and forcing intensity during endodormancy. Results from this study suggest that not only chilling, but also forcing controls bud development during endodormancy, and that extra forcing in autumn can offset reduced chilling.

气候变化对北京常见树种春季萌芽的影响——基于控制实验研究

PDF HTML阅读 XML下载 导出引用 引用提醒 气候变化对北京常见树种春季萌芽的影响——基于控制实验研究 DOI: 10.5846/stxb202112183591 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家杰出青年基金项目（42025101）；高等学校学科创新引智计划项目（B18006） Effects of climate change on spring budburst of typical tree species in Beijing based on manipulative experiments Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:气候变化对植物物候产生了重要影响，春季萌芽时间的变化不仅会通过改变植物的光合作用影响碳汇能力，还会通过改变群落内的种间关系影响生态系统结构和功能。因此，掌握群落内不同树种春季萌芽对气候变化的响应对于深刻理解物候时间位分化、认识陆地生态系统碳水循环和能量平衡具有重要意义。为提高春季物候模型的预测精度，阐明气候变化对不同树种春季萌芽的影响，以鹅耳枥（Carpinus turczaninowii）、黑桦（Betula dahurica）、华北落叶松（Larix principis-rupprechtii）、糠椴（Tilia mandshurica）和元宝枫（Acer truncatum）5个温带森林的典型树种为研究对象，通过剪枝实验分析了冬季冷激、春季温度和光周期对枝条春季萌芽时间的影响。结果表明，温度升高和冷激增加显著提前了所有树种的春季萌芽时间，从5℃到20℃，春季萌芽时间平均提前了54.5 d；在较高的冷激条件下，春季萌芽时间平均缩短了17.8 d；光周期对各树种春季萌芽时间均没有显著影响，8 h和16 h光周期条件下各树种平均萌芽时间分别为30.3和30.5 d。此外，随着温度升高，5个树种萌芽时间间隔显著缩短，这主要是由于温度升高萌芽热量需求降低导致的，冷激对树种间萌芽时间间隔无显著影响。在气候变暖背景下，森林群落中不同树种萌芽时间间隔将显著缩短，进而影响物候时间生态位分化，导致种间竞争加剧。研究阐明了气候变化对温带阔叶树种春季萌芽及其时间间隔的影响，为气候变化条件下森林生态系统群落动态及森林可持续经营与管理策略的制定提供了理论支撑。 Abstract:Climate change has caused substantial effects on plant phenology over the past decades. Shifts in spring budburst not only affect carbon sink capacity by changing plants' photosynthesis but also influence the structure and function of the ecosystem by altering the relationship between species within the forest community. Understanding how spring budburst of different species respond to climate change is thus essential to improve our knowledge of phenological temporal niche differentiation, carbon and water cycles, as well as the energy balance of terrestrial ecosystems. In order to improve the ability of the spring phenology model and the influence underlying the responses of spring budburst to climate change, we selected five typical temperate tree species in Beijing, i.e. Carpinus turczaninowii, Betula dahurica, Larix principis-rupprechtii, Tilia mandshurica, and Acer truncatum, to test the effects of winter chilling, spring temperature and photoperiod on spring budburst by using twig cutting experiment. We found that photoperiod had no significant effect on spring budburst while increasing spring temperature and winter chilling significantly advanced budburst date. From 5℃ to 20℃, the budburst was advanced by 54.5 days on average, and it was shortened under high chilling conditions by about 17.8 days. The photoperiod had no significant effect on the budburst of each tree species. The average budburst of tree species was 30.3 and 30.5 days under the condition of 8 hours and 16 hours of photoperiod, respectively. In addition, the time interval of budburst between the five tree species was significantly shortened with the spring warming, which might be caused by the heating requirements of budburst under different temperature treatments, which was mainly caused by the decrease of heat requirement for budburst with the increase of temperature, and the chilling had no significant effect on their time interval. Under the background of climate change, the budburst and time interval of budburst between tree species is likely to largely shorten, which would change the differentiation of temporal niche, leading to the increased inter-species competition. This study clarifies the impact of climate change on the budburst and time interval of temperate broad-leaved tree species and provides theoretical support for the formulation of forest ecosystem community dynamics and forest sustainable operation and management strategies under the condition of climate change. 参考文献 相似文献 引证文献

Higher spring phenological sensitivity to forcing temperatures of Asian compared to European tree species under low and high pre-chilling conditions

Winter chilling, spring forcing temperature and photoperiod are the most important drivers explaining the spatial and temporal variability of spring phenology in temperate trees. However, how these factors interact with each other on dormancy release and spring budburst date remains unclear and varies greatly depending on species. Our knowledge is also limited as to whether heat accumulation of forcing temperatures that trigger bud break in spring is a linear or non-linear process. Here, we aimed at experimentally quantifying the effect of chilling, forcing, photoperiod and their interactions on the budburst dates of nine different temperate tree species from East Asia (near Beijing, China) and Central Europe (near Zurich, Switzerland), including six phylogenetically related species (same genus). We conducted a full factorial experiment in climate chambers using two chilling (low and high, i.e., 0 vs. 56 days at 2°C after sampling at the end of December), four forcing (5, 10, 15, and 20°C), and two photoperiod (8 vs. 16 h) treatments simultaneously in Beijing and Zurich. We found that species growing near Beijing responded more readily to forcing conditions than species of the same genus growing near Zurich regardless of chilling treatment. Budburst timing of most species but European beech was marginally, if at all, affected by photoperiod. Furthermore, our results suggest that linear heat accumulation, as commonly used with the growing degree hours (GDH) model, could result in accurate prediction of budburst date depending on the temperature threshold used as a basis for heat accumulation. Our results also demonstrate the important role of chilling in shaping the sensitivity and rate of forcing accumulation to trigger budburst and suggest that species-specific sigmoid relationship for accumulating heat that accounts for prior chilling exposure may yield better predictions of budburst dates. Our results suggest that deciduous trees may have adapted their chilling and forcing requirements in regards to the predictability of winter-spring transition and late spring frosts. A less predictable winter-spring transition, as observed in Central Europe, could have driven species evolution towards higher chilling and forcing requirements compared to species growing in a more predictable climate of Northeastern Asia. Our cross-continental experiment therefore suggests that the spring phenology of East Asian species is tighter coupled to spring forcing temperature than Central European forests.

Inter-Individual Budburst Variation in Fagus sylvatica Is Driven by Warming Rate.

The onset of the growing season in temperate forests is relevant for forest ecology and biogeochemistry and is known to occur earlier with climate change. Variation in tree phenology among individual trees of the same stand and species, however, is not well understood. Yet, natural selection acts on this inter-individual variation, which consequently affects the adaptive potential to ongoing environmental changes. Budburst dates of 146 mature individuals of Fagus sylvatica, the dominant natural forest tree of central Europe, were recorded over 12 years in one forest stand of 1 ha in the Müritz National Park, Germany. The tree-specific location, topographical differences, as well as social status, were measured to explain the inter-individual variation in budburst. Furthermore, inter-individual differences in bud dormancy were quantified. Additional phenology and weather data across Germany from 405 sites over a 25-year period was used to put the insights from the single stand into perspective. Consistent phenological ranking over the years with respect to early and late flushing trees was observed within the single forest stand, with 23 trees consistently flushing 3–6 days earlier and 22 trees consistently flushing 3–10 days later than the median. Trees flushing consistently early varied most in their spring budburst dates and were less dormant than late-flushing trees already in mid-winter. The higher variation in earlier flushing trees was best explained by a slower warming rate during their budburst period in the observed stand as well as across Germany. Likewise, years with a lower warming rate during the budburst period were more variable in budburst dates. The rate of warming during spring time is crucial to accurately project future within-species variation and the resulting adaptive potential in spring phenology of dominant forest tree species.

Time-Resolved Analysis of Candidate Gene Expression and Ambient Temperature During Bud Dormancy in Apple.

Winter dormancy – a period of low metabolic activity and no visible growth – appears as an adaptation to harsh winter conditions and can be divided into different phases. It is tightly controlled by environmental cues, with ambient temperature playing a major role. During endodormancy, a cultivar-specific amount of cold needs to be perceived, and during ecodormancy, heat hours accumulate before bud burst and anthesis in spring. Expression analysis, performed in several key fruit tree species, proved to be very useful in elucidating the molecular control of onset and release of dormancy. However, the time resolution of these experiments has been limited. Therefore, in this study, dense time-series expression analysis was conducted for 40 candidate genes involved in dormancy control, under the cool-temperate climate conditions in Dresden. Samples were taken from the cultivars ‘Pinova’ and ‘Gala,’ which differ in flowering time. The set of candidate genes included well-established dormancy genes such as DAM genes, MdFLC-like, MdICE1, MdPRE 1, and MdPIF4. Furthermore, we tested genes from dormancy-associated pathways including the brassinosteroid, gibberellic acid, abscisic acid (ABA), cytokinin response, and respiratory stress pathways. The expression patterns of well-established dormancy genes were confirmed and could be associated with specific dormancy phases. In addition, less well-known transcription factors and genes of the ABA signaling pathway showed associations with dormancy progression. The three ABA signaling genes HAB1_chr15, HAI3, and ABF2 showed a local minimum of gene expression in proximity of the endodormancy to ecodormancy transition. The number of sampling points allowed us to correlate expression values with temperature data, which revealed significant correlations of ambient temperature with the expression of the Malus domestica genes MdICE1, MdPIF4, MdFLC-like, HAB1chr15, and the type-B cytokinin response regulator BRR9. Interestingly, the slope of the linear correlation of temperature with the expression of MdPIF4 differed between cultivars. Whether the strength of inducibility of MdPIF4 expression by low temperature differs between the ‘Pinova’ and ‘Gala’ alleles needs to be tested further.

The bud dormancy disconnect: latent buds of grapevine are dormant during summer despite a high metabolic rate.

Grapevine (Vitis vinifera L.) displays wide plasticity to climate; however, the physiology of dormancy along a seasonal continuum is poorly understood. Here we investigated the apparent disconnect between dormancy and the underlying respiratory physiology and transcriptome of grapevine buds, from bud set in summer to bud burst in spring. The establishment of dormancy in summer was pronounced and reproducible; however, this was coupled with little or no change in physiology, indicated by respiration, hydration, and tissue oxygen tension. The release of dormancy was biphasic; the depth of dormancy declined substantially by mid-autumn, while the subsequent decline towards spring was moderate. Observed changes in physiology failed to explain the first phase of dormancy decline, in particular. Transcriptome data contrasting development from summer through to spring also indicated that dormancy was poorly reflected by metabolic quiescence during summer and autumn. Gene Ontology and enrichment data revealed the prevailing influence of abscisic acid (ABA)-related gene expression during the transition from summer to autumn, and promoter motif analysis suggested that photoperiod may play an important role in regulating ABA functions during the establishment of dormancy. Transcriptomic data from later transitions reinforced the importance of oxidation and hypoxia as physiological cues to regulate the maintenance of quiescence and resumption of growth. Collectively these data reveal a novel disconnect between growth and metabolic quiescence in grapevine following bud set, which requires further experimentation to explain the phenology and dormancy relationships.

TIMING OF BUD BURST IS ASSOCIATED WITH CLIMATE OF MATERNAL ORIGIN IN QUERCUS LOBATA PROGENY IN A COMMON GARDEN

Deciduous trees leaf out in the spring beginning with bud burst. Proximally, the timing of that process is triggered by temperature, but natural selection on bud burst timing may have acted in local populations through additional factors, such as frost damage, insect herbivores and fungal pathogens. Valley Oak, Quercus lobata Née, is a deciduous California endemic tree species that shapes the ecosystems where it is found. We examined the phenology of spring bud burst in trees collected from 674 maternal families across the species range, grown in two replicate common gardens. We found significant differences among the families for timing of bud burst, and also found that onset of bud burst differed between gardens, presumably due to climate. The differences among families were associated with the climate of origin where the trees were collected suggesting that some extent of genetic differentiation in bud burst is due to local adaptation. Given predicted changes in climate in California for the future, understanding patterns of bud burst will help inform the selection of seed sources for reforestation efforts.

Night interruption provides evidence for photoperiodic regulation of bud burst in Japanese beech, Fagus crenata

ABSTRACT Some of trees in cool and temperate regions regulate bud burst by perceiving photoperiod. However, it is not clear whether the difference in bud burst timing between the two photoperiod conditions is due to differences in perception of day length or the daily light integral (DLI) because majority of studies concerning the photoperiodic regulation of bud burst make use of an experimental design that compares the differential timing of bud burst between long and shortday length. We conducted night and day interrupt experiments using twig cuttings of Japanese beech, Fagus crenata, to investigate the effect of photoperiod on bud burst. Twigs with leaf buds were collected in winter (February 2020) and maintained in four conditions: 1) long day length (16L8D; LD), 2) short day length (8L16D; SD), 3) day interruption for 2-h in the middle of the 16-h light period and a 6-h dark period (DI; total time of light period is the same as LD), and 4) night interruption with 2-h of light in the middle of the dark period and a 6-h light period (NI; total time of light period is the same as SD) for a duration of 40 d. We then measured the number of days until burst for each bud. Timing of bud burst was delayed in the SD treatment compared to the LD, DI, and NI treatments. These results demonstrate that the difference in bud burst phenology observed between SD and LD conditions is mainly due to day length perception rather than DLI, and an uninterrupted night period plays a major role in the perception of photoperiod. Our results provide the experimental evidence of perception of photoperiod regulating bud burst in spring.

Potential of C-band Synthetic Aperture Radar Sentinel-1 time-series for the monitoring of phenological cycles in a deciduous forest

Annual time-series of the two satellites C-band SAR (Synthetic Aperture Radar) Sentinel-1A and 1B data over five years were used to characterize the phenological cycle of a temperate deciduous forest. Six phenological metrics of the start (SOS), middle (MOS) and end (EOS) of budburst and leaf expansion stage in spring, and the start (SOF), middle (MOF) and end (EOF) of leaf senescence in autumn were extracted using an asymmetric double sigmoid function (ADS) fitted to the time-series of the ratio (VV/VH) of backscattering at co-polarization VV (vertical–vertical) and at cross polarization VH (vertical-horizontal). Phenological metrics were also derived from other four vegetation proxies (Normalized Difference Vegetation Index NDVI time-series from Sentinel-2A and 2B images, and in situ measurements of NDVI measurements, Leaf Area Index LAI and litterfall temporal dynamics). These estimated phenological metrics were compared to phenological observations obtained by visual observations from the ground, achieved using binoculars by three inter-calibrated observers, on a bi-weekly basis during the budburst and weekly during the senescence. We observe a decrease in the backscattering coefficient (σ0) at VH cross polarization during the leaf development and the expansion phase in spring and an increase during the senescence phase, contrary to what is usually observed on various types of crops. In vertical polarization, σ0VV shows very little variation throughout the year. S-1 time-series of VV/VH ratio provide a good description of the seasonal vegetation cycle allowing the estimation of spring and autumn phenological metrics. Estimates provided by VV/VH of budburst dates using MOS criterion differ by approximately 8 days on average (mean average deviation) from phenological observations. During senescence phase, estimates using MOF criterion are later and deviate by about 20 days from phenological observations of leaf senescence while the differences are of the order of 2 to 4 days between the phenological observations and estimates based on in situ NDVI and LAI time-series, respectively. A deviation of about 7 days, comparable to that observed during budburst, is obtained between the estimates of senescence (MOF) from S-1 and those determined from the in situ monitoring of litterfall. While in spring, leaf emergence and expansion described by LAI or NDVI explain the increase of VV/VH (or the decrease of σ0VH), during senescence, S-1 VV/VH is decorrelated from LAI or NDVI and is better explained by litterfall temporal dynamics. This behavior resulted in a hysteresis phenomenon observed on the relationships between VV/VH and NDVI or LAI. For the same LAI or NDVI, the response of VV/VH is different depending on the phenological phase considered. This study shows the high potential offered by Sentinel-1 SAR C-band time-series for the detection of forest phenology, thus overcoming the limitations caused by cloud cover in optical remote sensing of vegetation phenology.

Chilling rather than photoperiod controls budburst for gymnosperm species in subtropical China

AbstractThe mechanisms regulating spring phenology have been extensively studied in angiosperm species. However, given that gymnosperms and angiosperms diverged 300 million years ago, phenology may be triggered by different cues in gymnosperm species. The regulatory mechanisms of phenology in subtropical regions remain largely unknown. In combination, it remains untested whether subtropical gymnosperm species have chilling requirements and are photosensitive. We conducted a climate chamber experiment with three chilling and three photoperiod treatments to investigate budburst during an 8-week forcing period. We tested whether budburst of eight gymnosperms species (Cryptomeria japonica, Cunninghamia lanceolata, Cupressus funebris, Ginkgo biloba, Metasequoia glyptostroboides, Pinus massoniana, Pseudolarix amabilis and Podocarpus macrophyllus) was photoperiod sensitive or has strong chilling requirements and whether photoperiod or chilling was more important for advancing budburst. Chilling advanced budburst and increased the percentage of budburst for gymnosperm species. Gymnosperm species required moderate chilling days to advance budburst. Interestingly, the forcing requirement for gymnosperm species was higher than that for angiosperms in the same forest, suggesting that gymnosperms may need more cumulative forcing to initiate budburst than do angiosperms. Compared with temperate gymnosperm species in Germany (194–600 °C days), the subtropical species studied here had a much higher forcing requirement (814–1150 °C days). The effects of photoperiod were minor, suggesting that chilling outweighs photoperiod in advancing budburst of gymnosperm species in this subtropical region. These results reveal that increased winter temperatures with continued global warming may impact not only angiosperms but also gymnosperms, leading to their delayed spring budburst.

Warming Events Advance or Delay Spring Phenology by Affecting Bud Dormancy Depth in Trees.

The frequency of sudden, strong warming events is projected to increase in the future. The effects of such events on spring phenology of trees might depend on their timing because spring warming has generally been shown to advance spring budburst while fall and winter warming have been shown to delay spring phenology. To understand the mechanism behind timing-specific warming effects on spring phenology, I simulated warming events during fall, mid-winter and at the end of winter and quantified their effects on bud dormancy depth and subsequently on spring leaf out. The warming events were carried out in climate chambers on tree seedlings of Betula pendula and Fagus sylvatica in October, January, and February. Control seedlings were kept at photoperiod and temperature matching the daily fluctuating field conditions. Warmed seedlings were kept 10°C warmer than the control seedlings for 10 days during the respective warming periods. Warming in October increased bud dormancy depth and decreased spring leaf-out rate only for F. sylvatica, whereas warming in February reduced bud dormancy depth and advanced spring leaf-out rate only for B. pendula. Neither bud dormancy depth nor spring leaf out rate were affected by January warming. The results indicate that warming-induced changes in bud dormancy depth may explain species- and timing-specific warming effects on spring phenology. The extent to which the timing of bud dormancy phases is species-specific will influence among-species variation in future spring leaf out times.

Exposure to cold temperature affects the spring phenology of Alaskan deciduous vegetation types

Temperature is a dominant factor driving arctic and boreal ecosystem phenology, including leaf budburst and gross primary production (GPP) onset in Alaskan spring. Previous studies hypothesized that both accumulated growing degree day (GDD) and cold temperature (chilling) exposure are important to leaf budburst. We test this hypothesis by combining both satellite and aircraft vegetation measurements with the Community Land Model Version 4.5 (CLM), in which the end of plant dormancy depends on thermal conditions (i.e. GDD). We study the sensitivity of GPP onset of different Alaskan deciduous vegetation types to a GDD model with chilling requirement (GC model) included. The default CLM simulations have a 1–12 d earlier day of year GPP onset over Alaska vegetated regions compared to satellite constrained estimates from the Polar Vegetation Photosynthesis and Respiration Model. Integrating a GC model into CLM shifts the phase and amplitude of GPP. During 2007–2016, mean GPP onset is postponed by 5 ± 7, 4 ± 8, and 1 ± 6 d over Alaskan northern tundra, shrub, and forest, respectively. The GC model has the greatest impact during warm springs, which is critical for predicting phenology response to future warming. Overall, spring GPP high bias is reduced by 10%. Thus, including chilling requirement in thermal forcing models improves northern high-latitude phenology, but leads to other impacts during the growing season which require further investigation.

Greater capacity to exploit warming temperatures in northern populations of European beech is partly driven by delayed leaf senescence

One of the most widespread consequences of climate change is the disruption of trees’ phenological cycles. The extent to which tree phenology varies with local climate is largely genetically determined, and while a combination of temperature and photoperiodic cues are typically found to trigger bud burst (BB) in spring, it has proven harder to identify the main cues driving leaf senescence (LS) in autumn. We used 905 individual field-observations of BB and LS from six Fagus sylvatica populations, covering the range of environmental conditions found across the species distribution, to: (i) estimate the dates of BB and LS of these populations; (ii) assess the main drivers of LS; and (iii) predict the likely variation in growing season length (GSL; defined as the period from BB to LS timing) across populations under current and future climate scenarios. To this end, we first calibrated linear mixed-effects models for LS as a function of temperature, insolation and BB date. Secondly, we calculated GSL for each population as the number of days between BB and LS. We found that: i) there were larger differences among populations in the date of BB than in the date of LS; ii) the temperature through September, October and November was the main determinant of LS, although covariation of temperature with daily insolation and precipitation-related variables suggests that all three variables may affect LS timing; and iii) GSL was predicted to increase in northern populations and to shrink in central and southern populations under climate change. Consequently, the large present-day differences in GSL across the range of beech are likely to decrease under future climates where rising temperatures will alter the relationship between BB and LS. Northern populations are likely to increase their productivity as warmer conditions will enable them to extend their growing season.

Freeze-thaw events delay spring budburst and leaf expansion while longer photoperiods have opposite effect under different [CO2] in white birch: Advance it under elevated but delay it under ambient [CO2

Past studies indicate that narrower conduits such as those in diffuse-porous species are less vulnerable to freeze-thaw (FT) induced embolism and also facilitate the refilling of embolized xylem conduits early in the spring, resulting in an earlier bud break. In this study, we investigated if a novel environmental condition associated with climate change-induced northward migration will affect the vulnerability to FT-induced embolism and spring phenology in white birch. Seedlings were grown under ambient (400 μmol mol−1) or elevated CO2 concentration (1000 μmol mol−1), and four photoperiod regimes corresponding to 48 (seed origin), 52, 55, and 58 °N latitude. We found that the longest photoperiod (corresponding to 58 °N latitude) significantly increased the maximum specific hydraulic conductivity of the stem. CO2 concentration ([CO2]) and photoperiod had no significant impact on the vulnerability to FT-induced embolism. The treatment of 5 freeze-thaw cycles (+5 to −20 °C) led to an 11 % loss of hydraulic conductivity in dormant seedlings that had been stored at −4 °C for 3 months while the effect of such a treatment in the fall was much smaller. This result suggests that freeze-thaw events in late winter or spring can impair the hydraulic conductivity of the xylem which in turn may negatively affect the physiology of the trees. Indeed, the FT treatment in this study delayed budburst and leaf expansion in the spring. It is interesting to note that photoperiods had the opposite effect on budburst under different [CO2]: longer photoperiods led to earlier budburst in the spring under elevated [CO2], but delayed budburst under ambient [CO2]. The synergistic effect of longer photoperiods and CO2 elevation suggests that the growing season for white birch may be longer than what we predict from either factor alone at a migration site in the future when [CO2] will be much higher.

Climate and host genotype jointly shape tree phenology, disease levels and insect attacks

One of the best known ecological consequences of climate change is the advancement of spring phenology. Yet, we lack insights into how changes in climate interact with intraspecific genetic variation in shaping spring and autumn phenology, and how such changes in phenology will translate into seasonal dynamics of tree‐associated organisms. To elucidate the impact of warming and tree genotype on spring and autumn phenology, as well as the consequences for the population dynamics of a fungal pathogen Erysiphe alphitoides and plant‐feeding insect Tuberculatus annulatus, we conducted an active field heating experiment using grafts of five oak genotypes Quercus robur. We found that experimental warming generally advanced oak bud burst in spring and delayed leaf senescence in autumn, while additional variation was explained by tree genotype and warming‐by‐genotype interactions. Warming or tree genotype did not affect disease levels at the beginning of the season, but shaped both disease levels and aphid density during the latter part of the season. Overall, our findings demonstrate that elevated temperature and genetic variation affect spring and autumn phenology, as well as the seasonal dynamics of higher trophic levels. Such effects may be either direct (i.e. temperature affecting tree phenology and attack independently) or indirect (as due to climate‐induced changes in plant traits or the synchrony between trees and their attackers). To achieve a predictive understanding of the ecological responses and potential evolutionary changes of natural food webs in response to climate warming, we should merge the frameworks of global warming and community genetics.

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.

Recovery of Abies alba and Picea abies saplings to browsing and frost damage depends on seed source.

The density of wild ungulates has increased in the last century, and browsing has become a major driver of forest succession in the northern hemisphere. In addition, tree species are expected to respond differently to future climate conditions, especially an increased frequency of late frost events. The aim of this study was to analyze the influence of intraspecific genetic variation on the recovery of two tree species to frost and browsing. An experiment with saplings from 90 Abies alba and 72 Picea abies seed sources was conducted. Five‐year‐old saplings were clipped at three intensities before budburst in spring. Growth (height, diameter, leader shoot length, and biomass) and quality (e.g. stem form, multistemming, reaction type) were assessed before and 1–2 years after clipping or 3–4 years after natural frost events, and provenance differences were related to environmental differences at the seed source. For Abies, frost and clipping resulted in reduced height growth in the first year after the stress and reduced height for two (clipping) to four (frost) vegetation periods. Sapling biomass, diameter increment, and quality decreased after heavy clipping. For Picea, which grew twice as fast as Abies, such effects were only found after frost damage. Population differences were significant for both species for all investigated growth traits and for Picea also for some quality variables. The “reaction type” after browsing (e.g. new shoot, existing twig bending upward) seems to be species specific and independent of seed source. In contrast, the time lag between clipping and formation of a clear new leader shoot increased for Abieswith lower temperatures at the seed source. Lowland populations with warmer climates grew faster, and for Picea also qualitatively better, and recovered faster from leader shoot loss (Abies) or reacted at the uppermost meristem (Picea). Thus, the investigated stressors increased the existing differences among populations.