Environmental variation drives continental-scale synchrony of European beech reproduction

Continental-scale evaluation of downy birch pollen production: Estimating the impacts of global change

The high prevalence of hay fever in Europe has raised concerns about the implications of climate change-induced higher temperatures on pollen production. Our study focuses on downy birch pollen production across Europe by analyzing 456 catkins during 2019-2021 in 37 International Phenological Gardens (IPG) spanning a large geographic gradient. As IPGs rely on genetically identical plants, we were able to reduce the effects of genetic variability. We studied the potential association with masting behavior and three model specifications based on mean and quantile regression to assess the impact of meteorology (e.g., temperature and precipitation) and atmospheric gases (e.g., ozone (O3) and carbon-dioxide (CO2)) on pollen and catkin production, while controlling for tree age approximated by stem circumference. The results revealed a substantial geographic variability in mean pollen production, ranging from 1.9 to 2.5 million pollen grains per catkin. Regression analyses indicated that elevated average temperatures of the previous summer corresponded to increased pollen production, while higher O3 levels led to a reduction. Additionally, catkins number was positively influenced by preceding summer's temperature and precipitation but negatively by O3 levels. The investigation of quantile effects revealed that the impacts of mean temperature and O3 levels from the previous summer varied throughout the conditional response distribution. We found that temperature predominantly affected trees characterized by a high pollen production. We therefore suggest that birches modulate their physiological processes to optimize pollen production under varying temperature regimes. In turn, O3 levels negatively affected trees with pollen production levels exceeding the conditional median. We conclude that future temperature increase might exacerbate pollen production while other factors may modify (decrease in the case of O3 and amplify for precipitation) this effect. Our comprehensive study sheds light on potential impacts of climate change on downy birch pollen production, which is crucial for birch reproduction and human health.

Tail-dependence of masting synchrony results in continent-wide seed scarcity

Spatial synchrony may be tail-dependent, meaning it is stronger for peaks rather than troughs, or vice versa. High interannual variation in seed production in perennial plants, called masting, can be synchronized at subcontinental scales, triggering extensive resource pulses or famines. We used data from 99 populations of European beech (Fagus sylvatica) to examine whether masting synchrony differs between mast peaks and years of seed scarcity. Our results revealed that seed scarcity occurs simultaneously across the majority of the species range, extending to populations separated by distances up to 1800 km. Mast peaks were spatially synchronized at distances up to 1000 km and synchrony was geographically concentrated in northeastern Europe. Extensive synchrony in the masting lower tail means that famines caused by beech seed scarcity are amplified by their extensive spatial synchrony, with diverse consequences for food web functioning and climate change biology.

Dispersal synchronizes giant kelp forests

Spatial synchrony is the tendency for population fluctuations to be correlated among different locations. This phenomenon is a ubiquitous feature of population dynamics and is important for ecosystem stability, but several aspects of synchrony remain unresolved. In particular, the extent to which any particular mechanism, such as dispersal, contributes to observed synchrony in natural populations has been difficult to determine. To address this gap, we leveraged recent methodological improvements to determine how dispersal structures synchrony in giant kelp (Macrocystis pyrifera), a global marine foundation species that has served as a useful system for understanding synchrony. We quantified population synchrony and fecundity with satellite imagery across 11 years and 880 km of coastline in southern California, USA, and estimated propagule dispersal probabilities using a high-resolution ocean circulation model. Using matrix regression models that control for the influence of geographic distance, resources (seawater nitrate), and disturbance (destructive waves), we discovered that dispersal was an important driver of synchrony. Our findings were robust to assumptions about propagule mortality during dispersal and consistent between two metrics of dispersal: (1) the individual probability of dispersal and (2) estimates of demographic connectivity that incorporate fecundity (the number of propagules dispersing). We also found that dispersal and environmental conditions resulted in geographic clusters with distinct patterns of synchrony. This study is among the few to statistically associate synchrony with dispersal in a natural population and the first to do so in a marine organism. The synchronizing effects of dispersal and environmental conditions on foundation species, such as giant kelp, likely have cascading effects on the spatial stability of biodiversity and ecosystem function.

Summer solstice orchestrates the subcontinental-scale synchrony of mast seeding

High interannual variation in seed production in perennial plants can be synchronized at subcontinental scales with wide consequences for ecosystem functioning, but how such synchrony is generated is unclear1-3. We investigated the factors contributing to masting synchrony in European beech (Fagus sylvatica), which extends to a geographic range of 2,000 km. Maximizing masting synchrony via spatial weather coordination, known as the Moran effect, requires a simultaneous response to weather conditions across distant populations. A celestial cue that occurs simultaneously across the entire hemisphere is the longest day (the summer solstice). We show that European beech abruptly opens its temperature-sensing window on the solstice, and hence widely separated populations all start responding to weather signals in the same week. This celestial 'starting gun' generates ecological events with high spatial synchrony across the continent.

Climatic effects on the synchrony and stability of temperate headwater invertebrates over four decades

Important clues about the ecological effects of climate change can arise from understanding the influence of other Earth-system processes on ecosystem dynamics but few studies span the inter-decadal timescales required. We, therefore, examined how variation in annual weather patterns associated with the North Atlantic Oscillation (NAO) over four decades was linked to synchrony and stability in a metacommunity of stream invertebrates across multiple, contrasting headwaters in central Wales (UK). Prolonged warmer and wetter conditions during positive NAO winters appeared to synchronize variations in population and community composition among and within streams thereby reducing stability across levels of ecological organization. This climatically mediated synchronization occurred in all streams irrespective of acid-base status and land use, but was weaker where invertebrate communities were more functionally diverse. Wavelet linear models indicated that variation in the NAO explained up to 50% of overall synchrony in species abundances at a timescale of 4-6 years. The NAO appeared to affect ecological dynamics through local variations in temperature, precipitation and discharge, but increasing hydrochemical variability within sites during wetter winters might have contributed. Our findings illustrate how large-scale climatic fluctuations generated over the North Atlantic can affect population persistence and dynamics in inland freshwater ecosystems in ways that transcend local catchment character. Protecting and restoring functional diversity in stream communities might increase their stability against warmer, wetter conditions that are analogues of ongoing climate change. Catchment management could also dampen impacts and provide options for climate change adaptation.

Mechanisms driving interspecific variation in regional synchrony of trees reproduction

Seed production in many plants is characterized by large interannual variation, which is synchronized at subcontinental scales in some species but local in others. The reproductive synchrony affects animal migrations, trophic responses to resource pulses and the planning of management and conservation. Spatial synchrony of reproduction is typically attributed to the Moran effect, but this alone is unable to explain interspecific differences in synchrony. We show that interspecific differences in the conservation of seed production-weather relationships combine with the Moran effect to explain variation in reproductive synchrony. Conservative timing of weather cues that trigger masting allows populations to be synchronized at distances >1000 km. Conversely, if populations respond to variable weather signals, synchrony cannot be achieved. Our study shows that species vary in the extent to which their weather cueing is spatiotemporally conserved, with important consequences, including an interspecific variation of masting vulnerability to climate change.

Identification of DNA Methylation Changes in European Beech Seeds during Desiccation and Storage

Ageing and deterioration of seeds is a major problem for the maintenance of seed quality and viability during long-term storage. Prediction of early stages of seed deterioration in order to point out the plantlets' regeneration time is a major challenge of successful storage. In preserved seeds, damages accumulate within cells at the rate mainly related to their moisture content and temperature of storage. Current research reveals global alterations in DNA methylation in lipid-rich intermediate seeds during desiccation and storage at various regimes covering nonoptimal and optimal conditions. We show for the first time that monitoring of 5-methylcytosine (m⁵C) level in seeds can be used as a truly universal viability marker regardless of postharvest category of seeds and their composition. For seeds stored up to three years, in varied conditions, moisture content, temperature, and time of storage had significant influence on seedling emergence and DNA methylation (p < 0.05). Similarities among lipid-rich intermediate and orthodox seeds regarding different reactions of embryonic axes and cotyledons to desiccation are newly revealed. Along with previous studies on seeds dramatically different in desiccation tolerance (recalcitrant vs. orthodox), results regarding lipid-rich seeds positioned in-between (intermediate) prove that maintaining global DNA methylation status is crucial for maintaining seed viability.

From pattern to process? Dual travelling waves, with contrasting propagation speeds, best describe a self-organised spatio-temporal pattern in population growth of a cyclic rodent

The dynamics of cyclic populations distributed in space result from the relative strength of synchronising influences and the limited dispersal of destabilising factors (activators and inhibitors), known to cause multi‐annual population cycles. However, while each of these have been well studied in isolation, there is limited empirical evidence of how the processes of synchronisation and activation–inhibition act together, largely owing to the scarcity of datasets with sufficient spatial and temporal scale and resolution. We assessed a variety of models that could be underlying the spatio‐temporal pattern, designed to capture both theoretical and empirical understandings of travelling waves using large‐scale (>35,000 km²), multi‐year (2011–2017) field monitoring data on abundances of common vole (Microtus arvalis), a cyclic agricultural rodent pest. We found most support for a pattern formed from the summation of two radial travelling waves with contrasting speeds that together describe population growth rates across the region.

MASTREE+: Time-series of plant reproductive effort from six continents

Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long-lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time-series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population-level time-series from 974 species in 66 countries. The mean and median time-series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well-studied species, MASTREE+ includes extensive replication of time-series across geographical and climatic gradients. Here we describe the open-access data set, available as a.csv file, and we introduce an associated web-based app for data exploration. MASTREE+ will provide the basis for improved understanding of the response of long-lived plant reproduction to environmental change. Additionally, MASTREE+ will enable investigation of the ecology and evolution of reproductive strategies in perennial plants, and the role of plant reproduction as a driver of ecosystem dynamics.

Quantitative Analysis of Methodological and Environmental Influences on Survival of Planted Mangroves in Restoration and Afforestation

Mangrove planting has been employed for decades to achieve aims associated with restoration and afforestation. Often, survival of planted mangroves is low. Improving survival might be aided by augmenting the understanding of which planting methods and environmental variables most influence plant survival across a range of contexts. The aim of this study was to provide a global synthesis of the influence of planting methods and background environment on mangrove survival. This was achieved through a global meta-analysis, which compiled published survival rates for the period 1979–2021 and analyzed the influence of decisions about minimum spacing and which life stage to plant, and environmental contexts such as climate, tidal range and coastal setting on the reported survival of planted individuals, classified by species and root morphology. Generalized Additive Mixed Modeling (GAMM) revealed that planting larger mangrove saplings was associated with increased survival for pencil-rooted species such as Avicennia spp. and Sonneratia spp. (17% increase cf. seedlings), while greater plant spacing was associated with higher survival of stilt-rooted species in the family Rhizophoraceae (39% increase when doubling plant spacing from 1.5 to 3.0 m). Tidal range showed a nonlinear positive correlation with survival for pencil-rooted species, and the coastal environmental setting was associated with significant variation in survival for both pencil- and stilt-rooted species. The results suggest that improving decisions about which species to plant in different contexts, and intensive care after planting, is likely to improve the survival of planted mangroves.

Modes of climate variability bridge proximate and evolutionary mechanisms of masting

There is evidence that variable and synchronous reproduction in seed plants (masting) correlates to modes of climate variability, e.g. El Niño Southern Oscillation and North Atlantic Oscillation. In this perspective, we explore the breadth of knowledge on how climate modes control reproduction in major masting species throughout Earth's biomes. We posit that intrinsic properties of climate modes (periodicity, persistence and trends) drive interannual and decadal variability of plant reproduction, as well as the spatial extent of its synchrony, aligning multiple proximate causes of masting through space and time. Moreover, climate modes force lagged but in-phase ecological processes that interact synergistically with multiple stages of plant reproductive cycles. This sets up adaptive benefits by increasing offspring fitness through either economies of scale or environmental prediction. Community-wide links between climate modes and masting across plant taxa suggest an evolutionary role of climate variability. We argue that climate modes may 'bridge' proximate and ultimate causes of masting selecting for variable and synchronous reproduction. The future of such interaction is uncertain: processes that improve reproductive fitness may remain coupled with climate modes even under changing climates, but chances are that abrupt global warming will affect Earth's climate modes so rapidly as to alter ecological and evolutionary links. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Climate change and plant reproduction: trends and drivers of mast seeding change

Climate change is reshaping global vegetation through its impacts on plant mortality, but recruitment creates the next generation of plants and will determine the structure and composition of future communities. Recruitment depends on mean seed production, but also on the interannual variability and among-plant synchrony in seed production, the phenomenon known as mast seeding. Thus, predicting the long-term response of global vegetation dynamics to climate change requires understanding the response of masting to changing climate. Recently, data and methods have become available allowing the first assessments of long-term changes in masting. Reviewing the literature, we evaluate evidence for a fingerprint of climate change on mast seeding and discuss the drivers and impacts of these changes. We divide our discussion into the main characteristics of mast seeding: interannual variation, synchrony, temporal autocorrelation and mast frequency. Data indicate that masting patterns are changing but the direction of that change varies, likely reflecting the diversity of proximate factors underlying masting across taxa. Experiments to understand the proximate mechanisms underlying masting, in combination with the analysis of long-term datasets, will enable us to understand this observed variability in the response of masting. This will allow us to predict future shifts in masting patterns, and consequently ecosystem impacts of climate change via its impacts on masting. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Tree hazards compounded by successive climate extremes after masting in a small endemic tree, Distylium lepidotum, on subtropical islands in Japan

Ongoing global warming increases the frequency and severity of tropical typhoons and prolonged drought, leading to forest degradation. Simultaneous and/or successive masting events and climatic extremes may thus occur frequently in the near future. If these climatic extremes occur immediately after mass seed reproduction, their effects on individual trees are expected to be very severe because mass reproduction decreases carbohydrate reserves. While the effects of either a single climate extreme or masting alone on tree resilience/growth have received past research attention, understanding the cumulative effects of such multiple events remains challenging and is crucial for predicting future forest changes. Here, we report tree hazards compound by two successive climate extremes, a tropical typhoon and prolonged drought, after mass reproduction in an endemic tree species (Distylium lepidotum Nakai) on oceanic islands. Across individual trees, the starch stored within the sapwood of branchlets significantly decreased with reproductive efforts (fruit mass/shoot mass ratio). Typhoon damage significantly decreased not only the total leaf area of apical shoots but also the maximum photosynthetic rates. During the 5-month period after the typhoon, the mortality of large branchlets (8-10-mm diameter) increased with decreasing stored starch when the typhoon hit. During the prolonged summer drought in the next year, the recovery of total leaf area, stored starch, and hydraulic conductivity was negatively correlated with the stored starch at the typhoon. These data indicate that the level of stored starch within branchlets is the driving factor determining tree regrowth or dieback, and the restoration of carbohydrates after mass reproduction is synergistically delayed by such climate extremes. Stored carbohydrates are the major cumulative factor affecting individual tree resilience, resulting in their historical effects. Because of highly variable carbohydrate levels among individual trees, the resultant impacts of such successive events on forest dieback will be fundamentally different among trees.