In 2023, more than half of olive harvests ( Olea europaea ) across Spain, Greece, and Türkiye were lost to drought. The same year late freeze destroyed 90% of the peach crop ( Prunus persica ) on the Georgia Piedmont and the apple crop ( Malus domestica ) in central New York, Vermont, and southern Quebec. Climate extremes now rank with the costliest threats to agriculture, but their role in forest recovery from diebacks that are happening globally is unknown for lack of tree fecundity estimates in forests. Tolerance of climate extremes could depend on past exposure but constrained by phylogenetic conservatism. We report a continental scale analysis of climate extremes and forest fecundity across North America and Europe showing that responses to late freeze and drought are happening now. Species differences are not explained by the traits typically included in ecological studies and they are weakly associated with phylogeny. Late freeze, that is, freezing temperatures that follow the onset of flower development in spring, is shown to be “normal” in North America, but not Europe, potentially explaining failed seed production due to delayed onset and the resultant shorter growing period by North American transplants dating back at least to the 18th century. Drought has thus far had the greatest impacts in dry forested regions, but here too, species differences are not explained by traditional trait values. If responses have been buffered from drought and late freeze by past exposure, acclimation and local adaptation prove inadequate as extremes intensify.

Climate change is intensifying drought stress in temperate forests, but its effects on tree reproduction, central to forest regeneration and migration capability, remain poorly understood. Here, we analyze 221 time series of beech (Fagus sylvatica) seed production across Europe to test whether drought reduces seed output. We isolate drought exposure during the flowering, pollination, and seed maturation phases of reproduction, and test for legacy effects on future reproduction. Seed production was not impaired by summer drought, and dry spring conditions were associated with increased output, likely via enhanced pollen dispersal. Thus, once initiated, beech reproduction is not reduced by drought, with no suppression of reproduction the following year. Reproduction was not reduced at the driest sites during exceptional European summer droughts in 2003, 2018, and 2022. Considered alongside prior evidence that drought suppresses forest growth and elevates mortality, these findings indicate that vital rates can respond in opposite directions to the same stressor. Such contrasts may sustain forest reproduction during heat-drought events yet shift demographic balance toward higher mortality and turnover as climatic extremes intensify.

Pine mistletoe (Viscum album subsp. austriacum) is increasingly recognized as a significant threat to Scots pine (Pinus sylvestris L.) forests across Europe. However, the factors driving the spread of mistletoe and its colonization of pine forests remain poorly understood. In this study, we applied species distribution modelling using MaxEnt to estimate the potential distribution of pine mistletoe across Poland. The model incorporated bioclimatic, environmental, and forest structure variables, sourced from national Polish datasets and a comprehensive survey conducted in 403 forest districts representing 93.7% of all such districts in the country, allowing for high-resolution predictions of mistletoe habitat suitability. Area under the curve of the model was 0.811, whereas true skill statistic was 0.62. The results indicated that mean summer temperature (48.1% of contribution), species richness in the upper forest layer (18.6%), and potential evapotranspiration (8.4%) were the most influential variables shaping mistletoe distribution. Furthermore, the analysis identified a pronounced spatial correlation between mistletoe presence and major river valleys, suggesting that certain riparian zones may act as key dispersal corridors with frugivorous birds responsible for seed transport. While climatic conditions remain a dominant factor, nonclimatic elements such as stand composition and habitat characteristics also play a significant role in mistletoe spread. Our transferable approach is suitable for assessing and predicting the spread of mistletoe in other regions and ecological contexts. Our results provide insights into the factors controlling the current and potential spread of pine mistletoe in Scots pine stands, highlighting the combined role of climatic, environmental, and forest structure variables. The strength of the approach applied in this study lies in the availability of an extensive, nation-wide field dataset, which enabled robust modelling of mistletoe distribution and the identification of key areas with elevated infestation risk that are relevant for forest management.

Background and Aims Both plants and animals display considerable variation in their phenotypic traits as they grow. This variation helps organisms to adapt to specific challenges at different stages of development. Masting, the variable and synchronized seed production across years by a population of plants, is a common reproductive strategy in perennial plants that can enhance reproductive efficiency through increasing pollination efficiency and decreasing seed predation. Masting represents a population-level phenomenon generated from individual plant behaviours. While the developmental trajectory of individual plants influences their masting behaviour, the translation of such changes into benefits derived from masting remains unexplored. Methods and Key Results We used 43 years of seed production monitoring in European beech (Fagus sylvatica) to address that gap. The largest improvements in reproductive efficiency from masting happen in the largest trees. Masting leads to a 48-fold reduction in seed predation in large trees compared with 28-fold in small trees. Masting yields a 6-fold increase in pollination efficiency in large trees compared with 2.5-fold in small trees. Paradoxically, although the largest trees show the biggest reproductive efficiency benefits from masting, large trees mast less strongly than small trees. Conclusions Apparently suboptimal allocation of effort across years by large plants may be a consequence of anatomical constraints or bet-hedging. Ontogenetic shifts in individual masting behaviour and associated variable benefits have implications for the reproductive potential of plant populations as their age distribution changes, with applications in plant conservation and management.

This account presents information on all aspects of the biology of Cytisus scoparius (L.) Link (Broom or Scotch Broom) ( Sarothamnus scoparius (L.) W.D.J. Koch) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles : distribution, habitat, communities, responses to biotic factors, responses to the environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation. Broom is shade‐intolerant and drought‐tolerant, aided by c . 40% of net carbon fixation coming from stem photosynthesis and an ability to shed leaves in inclement periods. It is at its best in lowland, open, disturbed habitats but also open woodland; widespread across Britain, Ireland and much of Europe. It has been widely introduced to all continents (except Antarctica) where due to its prolific seeding and rapid spread it is often an invasive shrub. Broom thrives in an oceanic climate on a range of moist soils but is capable of invading arid and poor soils, helped by its ability to acquire 50% of its nitrogen from bacteria in root nodules. Broom is an obligate seeder, pollinated by a limited range of insects, primarily bees large enough to trip the explosive pollination mechanism. Seeds are dispersed explosively from the fruit and secondarily moved by ants attracted to the elaiosome. The water impermeable seed coat results in high dormancy, and so broom forms a significant seed bank. In Britain and Ireland, populations are showing little decline and broom is not considered to be at threat of extinction. In introduced areas, broom can rapidly spread despite browsing by native species and livestock. Biological control using a range of insects introduced from native areas, particularly seed eaters, together with mechanical and possibly chemical treatment, is showing some promise in its control.

Masting, i.e. interannually variable and synchronized seed production, plays a crucial role in forest ecosystems, influencing wildlife dynamics, pathogen prevalence, and forest regeneration. Accurately capturing masting variability is important for effective forest management, conservation efforts, and predicting ecosystem responses to environmental changes. The adoption of low-cost methods facilitates the large-scale data acquisition needed in this time of unprecedented environmental upheaval, but it is important to understand the reliability of such methods. We investigated the relationship between the timed count method and the quadrat-based method for monitoring seed production in European beech (Fagus sylvatica). The timed count method is fast, cost-effective, and suitable for areas with public access. These characteristics make time counts a practical choice for large-scale seed monitoring. However, the method has not been cross-calibrated with more traditional ground-based methods like quadrat sampling, which involves exhaustive seed collection from designated plots under tree canopies. Our research reveals a loglinear relationship between seed counts obtained by the two methods, and shows that the timed count is an effective method of estimating seed production. We also found that seed production exhibits greater dispersion in patchiness at lower levels of seed fall, which explains why the timed count method, covering a larger area, captures greater variability in seed fall compared to the quadrat method in such contexts. This highlights the importance of choosing an appropriate sampling strategy to accurately assess seed fall. The differences between the two methods introduce variability into derived masting metrics, such as the coefficient of variation and synchrony, with individual-level seed production variability metrics being more affected than population-level ones. The findings underscore the importance of understanding how different sampling methods can impact long-term ecological studies, particularly those focused on masting behaviour.

Climate change is impacting forests in complex ways, with indirect effects arising from interactions between tree growth and reproduction often overlooked. Our 43- y study of European beech (Fagus sylvatica) showed that rising summer temperatures since 2005 have led to more frequent seed production events. This shift increases reproductive effort but depletes the trees' stored resources due to insufficient recovery periods between seed crops. Consequently, annual tree ring increments have declined by 28%, dropping from a stable average of 1.60 mm y-1 between 1980 and 2005 to 1.16 mm y-1 thereafter. Importantly, this growth decline occurred without an accompanying trend in summer drought, indicating that altered reproductive patterns-not moisture stress-are driving the reduction. This creates a "perfect storm": Increased reproductive effort drains resources, viable seed output falls due to the loss of mast- seeding benefits via pollination and lower seed predation, and the ongoing growth decline reduces current carbon uptake and future reproductive potential. These compounding factors threaten the sustainability of Europe's most widespread forest tree. Our findings unveil a critical yet underrecognized indirect mechanism by which climate change endangers forest ecosystems, emphasizing the need to consider interactions between demographic processes when assessing species vulnerability to climate change.

AimThe well-proven positive correlation between the increased proportion of entire-leaved woody dicotyledonous species and increased mean annual temperature has been commonly used to estimate temperature in the past. However, in regions of colder climates, this relationship is not straightforward, questioning the accuracy of temperature estimation.LocationFinland, Poland, Germany.TaxonDicotyledons.MethodsThe floristic composition of 10 x 10 km squares in 20 km wide transects through Finland, Poland and Germany was analysed.ResultsAt higher temperatures, deciduous woody plants appeared to show the expected positive relationship between mean annual temperature and the proportion of entire leaf margins. However, we found a negative correlation within woody deciduous plants at higher latitudes with mean annual temperature values from approximately -2.5 degrees C to +2-4 degrees C and at all temperatures when all woody plants were included. Herbaceous species showed a weak relationship between morphology and temperature.Main ConclusionsThe hypothesis that the phenomenon was caused by a large percentage of entire-leaved evergreen species that winter under snow cover was rejected. These results indicate that using the leaf margin analysis method for past temperature estimation is increasingly inaccurate at colder temperatures. Consequently, we recommend avoiding this method at locations where the mean annual temperature falls below 5 degrees C.

The fundamental trade-off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade-off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non-proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.

1. This account presents information on all aspects of the biology of Ceratonia siliqua L. (Carob) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the International Biological Flora: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. 2. Ceratonia siliqua is a lowland evergreen shrub or tree, native around the Mediterranean basin and widely cultivated in areas with a warm temperate and subtropical climate, with more than 100 named cultivars. Carob grows on a wide range of soils including nutrient-poor and strongly calcareous, dry soils. 3. Carob is dioecious or rarely hermaphrodite although females dominate in cultivation due to their fruit. Pollination is primarily by insects and the relatively large seeds are spread mainly by ingestion of fruits by mammals. Seed dormancy is imposed by a hard seed coat and seeds germinate readily after natural or artificial scarification. 4. Drought tolerance is very high, acting as a drought avoiding water spender. Carob is also very tolerant of saline conditions and tolerant of fire and can act to restrict wildfire spread by generating fuel discontinuity. It shows high post-fire regrowth. Old individuals house a diversity of associated fauna and are comparatively unaffected by serious pests and diseases. 5. Carob has a long cultural history around the Mediterranean as a food source for humans and domesticated animals, in herbal and modern medicine and, more recently, for the carob bean gum used in a variety of domestic products and foods. Commercial production of fruits has declined over past decades but the low cultural care needed in growing orchards, potential new markets for fruit and seeds, and growing use of the tree to prevent soil erosion and sequester carbon gives carob a brighter future.

Abstract Masting, variable and synchronized seed production across years by a population of perennial plants, enhances reproductive efficiency through increasing pollination efficiency and decreasing seed predation. Masting represents a population-level phenomenon generated from individual plant behaviors. While the developmental trajectory of individual plants influences their masting behavior, the translation of such changes into benefits derived from masting remains unexplored. We used 43 years of seed production monitoring in European beech (Fagus sylvatica) to address that gap. The largest improvements in reproductive efficiency from masting happen in the largest trees. Masting leads to a 49-fold reduction in seed predation in large, compared to 20-fold in small trees. Masting yields an 8-fold increase in pollination efficiency in large, compared to 1.8-fold in small trees. Paradoxically, although the largest trees show the biggest reproductive efficiency benefits from masting, large trees mast less strongly than small trees. That apparently suboptimal allocation of effort across years by large plants may be a consequence of anatomical constraints or bet-hedging. Ontogenetic shifts in individual masting behavior and associated variable benefits have implications for the reproductive potential of plant populations as their age distribution changes, with applications in plant conservation and management.

The benefits of masting (volatile, quasi-synchronous seed production at lagged intervals) include satiation of seed predators, but these benefits come with a cost to mutualist pollen and seed dispersers. If the evolution of masting represents a balance between these benefits and costs, we expect mast avoidance in species that are heavily reliant on mutualist dispersers. These effects play out in the context of variable climate and site fertility among species that vary widely in nutrient demand. Meta-analyses of published data have focused on variation at the population scale, thus omitting periodicity within trees and synchronicity between trees. From raw data on 12 million tree-years worldwide, we quantified three components of masting that have not previously been analysed together: (i) volatility, defined as the frequency-weighted year-to-year variation; (ii) periodicity, representing the lag between high-seed years; and (iii) synchronicity, indicating the tree-to-tree correlation. Results show that mast avoidance (low volatility and low synchronicity) by species dependent on mutualist dispersers explains more variation than any other effect. Nutrient-demanding species have low volatility, and species that are most common on nutrient-rich and warm/wet sites exhibit short periods. The prevalence of masting in cold/dry sites coincides with climatic conditions where dependence on vertebrate dispersers is less common than in the wet tropics. Mutualist dispersers neutralize the benefits of masting for predator satiation, further balancing the effects of climate, site fertility and nutrient demands. A new method to quantify three masting components from individual tree-years has revealed that globally, masting is uncommon in tree species that depend on mutualist dispersers, with its distribution further mediated by climate and nutrient availability.

Aim Our understanding of the mechanisms that maintain forest diversity under changing climate can benefit from knowledge about traits that are closely linked to fitness. We tested whether the link between traits and seed number and seed size is consistent with two hypotheses, termed the leaf economics spectrum and the plant size syndrome, or whether reproduction represents an independent dimension related to a seed size-seed number trade-off.Location Most of the data come from Europe, North and Central America and East Asia. A minority of the data come from South America, Africa and Australia.Time period 1960-2022.Major taxa studied Trees.Methods We gathered 12 million observations of the number of seeds produced in 784 tree species. We estimated the number of seeds produced by individual trees and scaled it up to the species level. Next, we used principal components analysis and generalized joint attribute modelling (GJAM) to map seed number and size on the tree traits spectrum.Results Incorporating seed size and number into trait analysis while controlling for environment and phylogeny with GJAM exposes relationships in trees that might otherwise remain hidden. Production of the large total biomass of seeds [product of seed number and seed size; hereafter, species seed productivity (SSP)] is associated with high leaf area, low foliar nitrogen, low specific leaf area (SLA) and dense wood. Production of high seed numbers is associated with small seeds produced by nutrient-demanding species with softwood, small leaves and high SLA. Trait covariation is consistent with opposing strategies: one fast-growing, early successional, with high dispersal, and the other slow-growing, stress-tolerant, that recruit in shaded conditions.Main conclusions Earth system models currently assume that reproductive allocation is indifferent among plant functional types. Easily measurable seed size is a strong predictor of the seed number and species seed productivity. The connection of SSP with the functional traits can form the first basis of improved fecundity prediction across global forests.

Due to global climate cooling and aridification since the Paleogene, the members of the Neogene flora were extirpated from the Northern Hemisphere or were confined to a few refugial areas. For some species, the final reduction/extinction came in the Pleistocene, but some others have survived climatic transformations up to the present. This has occurred in Castanea sativa , a species of high commercial value in Europe and a significant component of the Caucasian forests’ biodiversity. In contrast to the European range, neither the historical biogeography nor the population genetic structure of the species in the isolated Caucasian range has been clarified. Here, based on a survey of 21 natural populations from the Caucasus and a single one from Europe, we provide likely biogeographic reconstruction and genetic diversity details. By applying Bayesian inference, species distribution modelling, and fossil pollen data, we estimated (1) the time of the Caucasian - European divergence during the Middle Pleistocene (436.5 ka), (2) the time of divergence among Caucasian lineages, and (3) outlined the glacial refugia for species. The climate changes related to the Early Middle Pleistocene Transition and the alpine orogenic uplift in the region are proposed as the major drivers of the intraspecific divergence and European-Caucasian disjunction, while the impact of the last glacial cycle was of marginal importance.

The climate drives species distribution and genetic diversity; the latter defines the adaptability of populations and species. The ongoing climate crisis induces tree decline in many regions, compromising the mitigation potential of forests. Scientific-based strategies for prioritizing forest tree populations are critical to managing the impact of climate change. Identifying future climate refugia, which are locations naturally buffering the negative impact of climate change, may facilitate local conservation. In this work, we conducted the populations' prioritization for Castanea sativa (sweet chestnut), a Neogene relict growing in the Caucasus global biodiversity hotspot. We generated genetic and ecological metrics for 21 sites in Georgia and Azerbaijan, which cover the natural range of sweet chestnut across the region. We demonstrated that climate primarily drives the pattern of genetic diversity in C. sativa, proved with a significant isolation-by-environment model. In future, climate change may significantly reorganize the species' genetic diversity, inducing even some genetic loss, especially in the very distinct eastern fringe of the species range in Azerbaijan. Based on our combined approach, we mapped populations suitable for ex situ and in situ conservation, accounting for genetic variability and the location of future climate refugia.

Climate warming increases tree mortality which will require sufficient reproduction to ensure population viability. However, the response of tree reproduction to climate change remains poorly understood. Warming can reduce synchrony and interannual variability of seed production ("masting breakdown") which can increase seed predation and decrease pollination efficiency in trees. Here, using 40 years of observations of individual seed production in European beech (Fagus sylvatica), we showed that masting breakdown results in declining viable seed production over time, in contrast to the positive trend apparent in raw seed count data. Furthermore, tree size modulates the consequences of masting breakdown on viable seed production. While seed predation increased over time mainly in small trees, pollination efficiency disproportionately decreased in larger individuals. Consequently, fecundity declined over time across all size classes, but the overall effect was greatest in large trees. Our study showed that a fundamental biological relationship-correlation between tree size and viable seed production-has been reversed as the climate has warmed. That reversal has diverse consequences for forest dynamics; including for stand- and biogeographical-level dynamics of forest regeneration. The tree size effects suggest management options to increase forest resilience under changing climates.

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.