Plants in the UK flower a month earlier under recent warming.

Global temperatures are rising at an unprecedented rate, but environmental responses are often difficult to recognize and quantify. Long-term observations of plant phenology, the annually recurring sequence of plant developmental stages, can provide sensitive measures of climate change and important information for ecosystem services. Here, we present 419 354 recordings of the first flowering date from 406 plant species in the UK between 1753 and 2019 CE. Community-wide first flowering advanced by almost one month on average when comparing all observations before and after 1986 (p < 0.0001). The mean first flowering time is 6 days earlier in southern than northern sites, 5 days earlier under urban than rural settings, and 1 day earlier at lower than higher elevations. Compared to trees and shrubs, the largest lifeform-specific phenological shift of 32 days is found in herbs, which are generally characterized by fast turnover rates and potentially high levels of genetic adaptation. Correlated with January-April maximum temperatures at -0.81 from 1952-2019 (p < 0.0001), the observed trends (5.4 days per decade) and extremes (66 days between the earliest and latest annual mean) in the UK's first flowering dataset can affect the functioning and productivity of ecosystems and agriculture

Intra-annual density fluctuations (IADFs) in Pinus nigra (J. F. Arnold) at high-elevation in the central Apennines (Italy)

Abstract: Although wood anatomical features can provide yearly resolved climatic information at sub-seasonal resolution, the occurrence of intra-annual density fluctuations (IADFs) might be triggered by several abiotic factors under different ecological settings. Here, we use information on cambial age and tree-ring width to standardize the frequency of IADFs in European black pines from three different mountain slopes in the central Apennines (Italy). At each site, we sampled isolated 15–30-year pioneer pines above the forest limit, as well as close-grown 40–60-year planted pines at the forest limit. Mainly restricted to the latewood of both pioneer and planted trees, the occurrence of IADFs reveals a significant positive relationship with cambial age and ring width. Although the standardized IADFs are well synchronized between the planted and pioneer pines, the frequency of IADFs in narrow rings was higher in the pioneer pines. Drought conditions in July and August are responsible for the highest IADFs frequency in planted and pioneer pines, respectively. Our study underlines the value of IADFs to obtain a more nuanced understanding of the climatic drivers of wood formation at the intra-annual scale

Author Correction: Limited capacity of tree growth to mitigate the global greenhouse effect under predicted warming.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Functional Relationships of Wood Anatomical Traits in Norway Spruce

The quantitative assessment of wood anatomical traits offers important insights into those factors that shape tree growth. While it is known that conduit diameter, cell wall thickness, and wood density vary substantially between and within species, the interconnection between wood anatomical traits, tree-ring width, tree height and age, as well as environment effects on wood anatomy remain unclear. Here, we measure and derived 65 wood anatomical traits in cross-sections of the five outermost tree rings (2008–2012) of 30 Norway spruce [Picea abies (L.) H. Karst.] trees growing along an altitudinal gradient (1,400–1,750 m a.s.l.) in the northern Apennines (Italy). We assess the relationship among each anatomical trait and between anatomical trait groups according to their function for (i) tree-ring growth, (ii) cell growth, (iii) hydraulic traits, and (iv) mechanical traits. The results show that tree height significantly affects wood hydraulic traits, as well as number and tangential diameter of tracheids, and ultimately the total ring width. Moreover, the amount of earlywood and latewood percentage influence wood hydraulic safety and efficiency, as well as mechanical traits. Mechanically relevant wood anatomical traits are mainly influenced by tree age, not necessarily correlated with tree height. An additional level of complexity is also indicated by some anatomical traits, such as latewood lumen diameter and the cell wall reinforcement index, showing large inter-annual variation as a proxy of phenotypic plasticity. This study unravels the complex interconnection of tree-ring tracheid structure and identifies anatomical traits showing a large inter-individual variation and a strong interannual coherency. Knowing and quantifying anatomical variation in cells of plant stem is crucial in ecological and biological studies for an appropriate interpretation of abiotic drivers of wood formation often related to tree height and/or tree age

Return of the moth: rethinking the effect of climate on insect outbreaks

Abstract: The sudden interruption of recurring larch budmoth (LBM; Zeiraphera diniana or griseana Gn.) outbreaks across the European Alps after 1982 was surprising, because populations had regularly oscillated every 8–9 years for the past 1200 years or more. Although ecophysiological evidence was limited and underlying processes remained uncertain, climate change has been indicated as a possible driver of this disruption. An unexpected, recent return of LBM population peaks in 2017 and 2018 provides insight into this insect’s climate sensitivity. Here, we combine meteorological and dendrochronological data to explore the influence of temperature variation and atmospheric circulation on cyclic LBM outbreaks since the early 1950s. Anomalous cold European winters, associated with a persistent negative phase of the North Atlantic Oscillation, coincide with four consecutive epidemics between 1953 and 1982, and any of three warming-induced mechanisms could explain the system’s failure thereafter: (1) high egg mortality, (2) asynchrony between egg hatch and foliage growth, and (3) upward shifts of outbreak epicentres. In demonstrating that LBM populations continued to oscillate every 8–9 years at sub-outbreak levels, this study emphasizes the relevance of winter temperatures on trophic interactions between insects and their host trees, as well as the importance of separating natural from anthropogenic climate forcing on population behaviour

Prominent role of volcanism in Common Era climate variability and human history

Climate reconstructions for the Common Era are compromised by the paucity of annually-resolved and absolutely-dated proxy records prior to medieval times. Where reconstructions are based on combinations of different climate archive types (of varying spatiotemporal resolution, dating uncertainty, record length and predictive skill), it is challenging to estimate past amplitude ranges, disentangle the relative roles of natural and anthropogenic forcing, or probe deeper interrelationships between climate variability and human history. Here, we compile and analyse updated versions of all the existing summer temperature sensitive tree-ring width chronologies from the Northern Hemisphere that span the entire Common Era. We apply a novel ensemble approach to reconstruct extra-tropical summer temperatures from 1 to 2010 CE, and calculate uncertainties at continental to hemispheric scales. Peak warming in the 280s, 990s and 1020s, when volcanic forcing was low, was comparable to modern conditions until 2010 CE. The lowest June–August temperature anomaly in 536 not only marks the beginning of the coldest decade, but also defines the onset of the Late Antique Little Ice Age (LALIA). While prolonged warmth during Roman and medieval times roughly coincides with the tendency towards societal prosperity across much of the North Atlantic/European sector and East Asia, major episodes of volcanically-forced summer cooling often presaged widespread famines, plague outbreaks and political upheavals. Our study reveals a larger amplitude of spatially synchronized summer temperature variation during the first millennium of the Common Era than previously recognised

European black pine recolonization at high altitude in the central Apennines (Italy). Spatial and Temporal Patterns

In Italia gran parte degli studi sulle dinamiche della treeline è stata condotta in ambiente alpino. Pochi sono invece quelli sulle cenosi appenniniche, dove la sinergia tra disturbi naturali e antropici è decisamente più accentuata. Negli Appennini la treeline attuale è caratterizzata in grande prevalenza da cenosi di faggio, situate tra 1500 m e 1900 m di quota. Alcuni studi hanno evidenziato una notevole stazionarietà spazio-temporale di tali cenosi forestali nel settore centrale ed un maggiore dinamismo di formazioni arbustive. Nell’Appennino centro-meridionale le cenosi naturaliformi con Pinus mugo, Pinus laricio, Pinus leucodermis appaiono più dinamiche. Tale fenomeno trova analogie nelle zone calcaree dell’Appennino centrale con la diffusione spontanea di individui di Pinus nigra sopra l’attuale limite superiore del bosco, spesso ma non solo a partire da rimboschimenti di protezione. La ricolonizzazione di pino nero in ecotoni di treeline è stata analizzata in 5 siti dell’Appennino centrale lungo un gradiente Nord-Sud di circa 170 km compreso fra Marche e Abruzzo. Obiettivi dello studio erano: i) individuare possibili pattern comuni nell’assetto fisionomico - strutturale e nei dinamismi di diffusione del pino nero; ii) datare accuratamente l’insediamento degli individui arborei; iii) determinare l’influenza dei principali fattori climatici nel processo di ricolonizzazione. Globalmente sono stati censiti oltre 900 individui arborei di pino nero, tutti localizzati al di sopra della treeline attuale fino alla massima altitudine possibile. E’ stata rilevata la loro posizione mediante GPS, determinato l'habitat di crescita e misurati il diametro del fusto, l’altezza totale, gli accrescimenti longitudinali ed altri caratteri fisionomici e strutturali. Da ogni fusto è stata anche prelevata una carota basale per la determinazione dell’età cambiale, accrescimento radiale e individuazione di fluttuazioni intra-annuali di densità (IADF). Carote legnose sono state estratte anche da 20 individui arborei adulti, per ogni sito, al limite esterno dei rimboschimenti di pino nero presenti, per verificare la sensitività climatica del pino nero. Con l’analisi univariata (regressione) e multivariata (PCA) e con l'analisi dendroecologica sono state esplorate le correlazioni fra i diversi attributi strutturali degli alberi, una possibile influenza delle variabili ambientali, e le analogie o differenze tra i diversi siti, le relazioni fra incrementi radiali e longitudinali e l’influenza di temperature e precipitazioni mensili sull’accrescimento e la formazione delle IADF. Gran parte dei pini sono ubicati ad altitudini elevate e i loro caratteri fisionomico-strutturali sono molto simili nei cinque siti, dove il processo ricolonizzativo è iniziato circa 30-40 anni fa con picchi di frequenza e dinamismi di accrescimento sincroni. Il pino nero è particolarmente sensibile alle temperature massime estive periodo in cui si formano preferenzialmente anche le IADF il cui acme di frequenza è nel 2003 e 2004. La diffusione del pino nero, sebbene vi siano differenze nei caratteri ambientali e nell’uso del suolo pregresso dei cinque siti, appare sincronica e spazialmente dispersa. Simili dinamismi di accrescimento e adattamento della specie al riscaldamento climatico sono segnali che potrebbero preludere ad un futuro innalzamento del limite superiore del bosco.Most of the studies on treeline dynamics in Italy have been conducted in the Alps. Only a few ones concern the Apennines where stronger is the synergic influence of natural and anthropic disturbance. In the Apennines the current treeline is mainly formed by beech forests located between 1500 and 1900 m a.s.l. In the central Apennines some studies have proved that these forests feature a spatio-temporal stationarity, whereas shrubs community are more dynamic, as well as treeline ecotones with conifer species such as Pinus mugo, Pinus laricio, Pinus leucodermis, especially on the southern Apennines. Similarly, in several limestone slopes of central Apennines a natural encroachment of Pinus nigra trees was observed above the current treeline, especially where pine stands were planted for soil erosion control. This process occurred at increasing elevation and was analysed at five treeline ecotones in the central Apennines. The study sites are located along a 170 km North-South gradient across Marche and Abruzzo regions in the Central Italy. The aims of this study were: i) to detect possible common patterns of structural attributes of black pine regeneration at the treeline ecotones; ii) to date the seedlings germination; iii) to assess the climate influence on the pine upward encroachment process also using intra-annual density fluctuations (IADFs) in tree-rings. We sampled over 900 encroached black pine trees above the current treeline to the mountain tops. All individuals were mapped and their basal stem diameter, total height, annual height increments and other structural attributes measured. One increment core was extracted from stem base of most samples for cambial age determination and detection of intra-annual density fluctuations (IADFs). We also extracted cores at DBH from pine plantations to assess climate-growth relationships. We used multivariate analyses (PCA) to explore the correlation structure of the main tree attributes, regression analyses to relate radial and height increment, and dendroclimatic analyses to assess the influence of climate on tree growth and IADF formation. Most black pine trees were located at high altitude and their structural attributes were similar at the five sites where the pine encroachment process started between 30 and 40 years ago, featuring similar germination peaks and growth patterns. Black pine is particularly sensitive to maximum temperatures, and IADF occurred in mid-late summer with highest frequency peaks between 2003 and 2004. The pine encroachment process, besides the differences of environmental features and land use histories of the five study sites, appears synchronic and spatially diffused. The consistent tree-growth dynamics and the species adaptation to a warming climate are signals envisaging a possible treeline upward shift