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.

For silver fir (Abies alba), a species expected to play an important role in climate-change adaptation of Central European forests, seed viability in Austria appears to be declining. Therefore, it is crucial to examine the constraints on seed viability and to identify ways to counteract the observed trend. In this study, we investigated factors associated with silver fir seed viability in seed stands and seed orchards in Austria. We hypothesized that seedling emergence is affected by endogenous (tree age, species abundance) and exogenous (climatic) conditions of seed stands, and that differences in emergence occur among seed production unit types, with higher success expected in seed orchards. We conducted a common garden experiment using seed lots from 63 seed stands and 6 seed orchards across Austria to investigate the likelihood of seedling emergence as a function of the proportion of silver fir-associated forest cover in seed stands, tree age, climate parameters and seed weight. Our results show a positive relationship between seedling emergence and the proportion of silver fir-associated forest cover, as well as between seedling emergence and the maximum age of the silver trees in stands. The effect of mean annual temperature on seedling emergence depended on annual precipitation levels: seeds from stands in warmer conditions had a higher probability of emergence, but only under sufficient precipitation. Synthesis and applications. As climate change, habitat loss and fragmentation intensify, seed-sourcing strategies should explicitly incorporate ecological filters when selecting stands for seed harvest to safeguard seed viability and genetic diversity for nursery production. Seed stand management should be refocused on promoting structural conditions that enhance reproductive success, while seed orchards should continue to serve as essential sources of quality and genetically diverse reproductive material.

Ecological forecasting is essential for climate change adaptation and mitigation. In reforestation and restoration, seed production forecasting has the potential to support planning and resource allocation, while providing benefits for wildlife management and public health. We hind- and forecast seed production using statistical models based on weekly weather and high-resolution seed data of six tree species recorded in two Austrian old-growth forest sites. Using a sliding-window approach and model selection, we model annual reproduction for three coniferous (Silver fir, European larch, Norway spruce) and three broad-leaved species (Sycamore maple, European beech, European ash). We investigate changes in explained variance with decreasing time before seed rain and evaluate hindcasting proficiency and the potential forecast horizon using quantitative and categorical measures useful to practitioners. Furthermore, we compare the performance of local models with a general forecasting model for seed production in European beech. Most local models show unbiased but partly imprecise predictions with a broad range in explained variance (0.15-0.93) in the year prior to seed rain. Nonetheless, within this timeframe, hindcasting seed rain above 10% of the long-term maximum, a threshold relevant to practitioners, works well for all species. Previous seed rain explains a considerable proportion of the variation in seed rain of fir, ash, and maple. We forecast seed rain for 2022 to 2025, with mixed results for 2022 and 2023. Overall, categorical year out predictions seem feasible for most studied species, but model refinement is required. Local models for beech outperformed the general model in predicting crop failures and bumper crops. Synthesis and applications: Seed production can be predictable with a promising degree of accuracy for six European tree species in the year prior to seed rain, if combined with on-site monitoring of seeds, phenology, and weather. This holds value for seed harvesters, nurseries and forest managers, and may inform orchard management and public health risk anticipation. Seed forecasts will help address seed scarcity and support climate change adaptation and mitigation. Future efforts should prioritise species based on rarity and seed storability, as well as forming stronger partnerships with potential forecast users.

Mast-seeding trees can vary seed output by orders of magnitude among years, but it remains unclear whether high seed production reduces per-seed investment, as predicted by fixed-budget allocation models. We quantified individual seed production with seed mass in European beech across 2792 trees and 123 populations spanning the species' range and quantified seed protein and lipid content in 35 populations. Seed mass increased with seed production, with seeds from high-seeding years being 14% heavier than those from low-seeding years, providing no evidence for a seed size-number trade-off and instead supporting variable reproductive allocation. By contrast, protein content decreased by 31% with increasing seed production, whereas lipid content increased (by 14%), indicating that nitrogen becomes constraining at high reproductive output while carbon-based provisioning is maintained. Climate further structured provisioning: seed mass and protein content were the lowest at climatic range margins, being 28% and 32% lower, respectively, than at the center of the climatic range. European beech can increase seed output without reducing per-seed biomass, but that nitrogen limitation and climatic constraints may strengthen regeneration bottlenecks at both trailing and leading margins, especially as climate warming intensifies.

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.

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. In mast-seeding species such as European beech (\textit{Fagus sylvatica}), reproduction is regulated by temperature cues rather than current-year resource availability, raising questions about drought sensitivity once reproduction is triggered. Here, we analyse 221 time series of beech seed production across Europe to test whether drought, after reproduction has been initiated, reduces seed output. We isolate drought exposure during pollination and seed maturation phases, including severe events in 2003, 2018, and 2022. Seed production was not impaired by summer drought, and dry spring conditions were associated with increased output, likely via enhanced pollen dispersal. Thus, once triggered, beech reproduction is not reduced by drought. Considered alongside prior evidence that drought suppresses growth and elevates mortality, these findings indicate that vital rates can respond in opposite directions to the same stressor—reproduction is buffered while growth and survival decline. Such contrasts may sustain short-term regeneration during heat–drought events yet shift demographic balance toward higher mortality and turnover as climatic extremes intensify.

Transdisciplinary, co-creative research deals with complex real-world problems, with complexity being a common denominator of sustainability issues. It is often understood as an interplay of two dimensions, collaboration and creativity, that facilitates the integration of different forms of knowledge and the creation of transformative outcomes. In the end, it aims to find more holistic and systemic solutions to complex real-world problems. Increasingly, Arts-Based Interventions (ABIs) are proposed to support sustainability-oriented transdisciplinary research. However, little research has been done so far to gauge the extent to which adding arts to the mix actually benefits the transdisciplinary research process and outcomes. In the research project reported on in this article, we took a first step into the realm of the arts by including ABIs into transdisciplinary brainstorming sessions. We investigated their influence on the research process and outcomes as perceived by the participants. We found ABIs to positively influence both dimensions of co-creativity—(1) collaboration, through enhancing the sense of togetherness in the group, and (2) creativity, directly and indirectly through a perceived emotionalization. ABIs were perceived to induce a change of perspective and a broadening of horizons that can facilitate the creation of transformative solutions. Moreover, their reported emotionalizing impact points toward an integration of tacit—in particular emotional—knowledge. This can lead to a more holistic view of the investigated problem. Altogether, the reported impacts of ABIs on transdisciplinary research can promote the creation of transformative and holistic solutions to sustainability issues in transdisciplinary sustainability research.

Food-hoarding granivores act as both predators and dispersers of plant seeds, resulting in facultative species interactions along a mutualism-antagonism continuum. The position along this continuum is determined by the positive and negative interactions that vary with the ratio between seed availability and animal abundance, particularly for mast-seeding species with interannual variation and spatial synchrony of seed production. Empirical data on the entire fate of seeds up to germination and the influence of rodents on seed survival is rare, resulting in a lack of consensus on their position along the mutualism-antagonism continuum. Here, we quantified annual seed rain and rodent abundance in an old-growth European beech forest and tracked 639 beechnuts to the seedling stage with 84% of seeds successfully located. Over 4 study years that covered the range of seed-to-rodent ratios, not a single seed successfully germinated after dispersal, illustrating a predominantly antagonistic interaction between rodents and seeds of European beech. Therefore, our findings do not support the predator dispersal hypothesis and partially contradict the predator satiation hypothesis, as the highest number of germinants and intact seeds were found in situ after an intermediate seed crop, not a bumper crop. Our results underline the necessity to track seeds up to germination.

Masting, the spatial synchronization of interannual variation in seed production, can enhance reproductive efficiency through positive density-dependent processes (DD) that result in economies of scale (EOS), such as decreased pollen limitation and predator satiation in years of high reproduction. While the general occurrence of such EOS effects has been documented for masting species, few studies simultaneously investigated how spatial and temporal variation in reproduction affects pollination and predation. Furthermore, it is unclear whether the same mechanisms apply to co-occurring species with different levels of conspecific density, pollen limitation, and seed defences. Here, we use a long-term dataset with high spatial resolution of seed production of European beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba) in a primeval montane forest to investigate the relationship between reproductive effort, pollination efficiency and predispersal predation by insects. We found that, along the temporal axis, the proportion of sound (fertilized and unpredated) seeds correlated positively with annual seed production over the 14-year study period in all three species, most strongly in beech and only weakly in silver fir. Moreover, the results show that in beech, spatial seed density interacts with plot-wide annual seed rain to enhance DD effects on seed predation, suggesting additive effects of synchronous reproduction on fitness benefits. Synthesis: For both pollination and predispersal predation in beech and spruce, the strongest DD effects occur at low levels of reproduction and quickly reach asymptotes at higher levels, suggesting the presence of thresholds in different EOS mechanisms. As variability and synchrony in mast-seeding are expected to decline with climate change, EOS effects driven by DD may remain stable until the threshold is reached, at which sudden declines would result in devastating effects on the availability of viable seeds for germination and recruitment. Evolutionary benefits of mast-seeding-the synchronized interannual variation in seed production of plant populations-are hypothesized to arise from economies of scale (EOS) in reproduction, so that pollination efficiency increases or insect predation decreases when population-wide reproduction is larger. Using high-resolution (81 traps/ha) seed trapping in an European montane old-growth forest over 15 years, the authors found that EOS mechanisms vary between species (strong in Fagus sylvatica, weaker in Picea abies, no effects in Abies alba), respond more strongly to temporal than spatial variation in reproductive effort, and generally show thresholds so that little EOS benefits accrue over 20% of observed population-wide reproductive effort. These results illustrate that spatiotemporal variation in tree reproductive effort results in sequential economy-of-scale effects on early seed fate, which, combined with post-dispersal benefits, result in selection for mast-seeding in tree populations.image

Zusammenfassung Die Technische Zusammenfassung des APCC-Sonderberichts ″Landnutzung und Klimawandel in Österreich″ umfasst die Kernbotschaften der Kapitel 1–9. In ihr sind die Hauptaussagen zu den sozioökonomischen und klimatischen Treibern der Landnutzungsänderungen, zu den Auswirkungen von Landnutzung und -bewirtschaftung auf den Klimawandel, zu Minderungs- und Anpassungsoptionen im Kontext nachhaltiger Entwicklungsziele sowie zu Synergien, Zielkonflikten und Umsetzungsbarrieren von Klimamaßnahmen enthalten.

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.

Zusammenfassung Dieses Kapitel präsentiert und bewertet den aktuellen Stand des Wissens zum Konnex Landnutzung und Klimawandel in Österreich aus dem systemischen Blickwinkel der UN Agenda 2030 für eine Nachhaltige Entwicklung. Dabei wird dem Thema entsprechend auf die Verflechtungen zwischen den lokalen, nationalen und internationalen Ebenen eingegangen. Die Menschheit befindet sich in kritischen, vielfältigen und vernetzten Krisen. Integrative und globale Lösungsansätze, wie sie in der Agenda 2030 festgeschrieben sind, haben für diese multiplen Krisen ein hohes Lösungspotenzial.

Climate change effects on tree reproduction are poorly understood, even though the resilience of populations relies on sufficient regeneration to balance increasing rates of mortality. Forest-forming tree species often mast, i.e. reproduce through synchronised year-to-year variation in seed production, which improves pollination and reduces seed predation. Recent observations in European beech show, however, that current climate change can dampen interannual variation and synchrony of seed production and that this masting breakdown drastically reduces the viability of seed crops. Importantly, it is unclear under which conditions masting breakdown occurs and how widespread breakdown is in this pan-European species. Here, we analysed 50 long-term datasets of population-level seed production, sampled across the distribution of European beech, and identified increasing summer temperatures as the general driver of masting breakdown. Specifically, increases in site-specific mean maximum temperatures during June and July were observed across most of the species range, while the interannual variability of population-level seed production (CVp) decreased. The declines in CVp were greatest, where temperatures increased most rapidly. Additionally, the occurrence of crop failures and low seed years has decreased during the last four decades, signalling altered starvation effects of masting on seed predators. Notably, CVp did not vary among sites according to site mean summer temperature. Instead, masting breakdown occurs in response to warming local temperatures (i.e. increasing relative temperatures), such that the risk is not restricted to populations growing in warm average conditions. As lowered CVp can reduce viable seed production despite the overall increase in seed count, our results warn that a covert mechanism is underway that may hinder the regeneration potential of European beech under climate change, with great potential to alter forest functioning and community dynamics.

Forests in the Himalayas are a major carbon store, but are under threat due to changes in precipitation regime. To simulate a precipitation decline, throughfall-exclusion (TFE) shelters were applied during three consecutive monsoon seasons in an oak forest (2.650 m a.s.l.) and a conifer-dominated forest (3.260 m a.s.l.) in central Bhutan. Leaf water potentials, tree mortality, stem increment, soil CO2 efflux, litterfall and fine root dynamics were assessed. TFE significantly and consistently decreased topsoil (0-30 cm) moisture and leaf water potentials of Quercus lanata and Quercus griffithii (lower elevation), and to a lesser extend those of Tsuga dumosa and Quercus semecarpifolia, (higher elevation). TFE did not impose tree mortality. Stem increment remained unaffected until the second TFE year, but showed reductions during the third year with Tsuga dumosa being most severely affected (-60%). Standing fine root biomass stocks were hardly affected by TFE. Increased root necromass and faster fine root growth in the lower elevation forest suggest that the oak trees increased C allocation below ground. Soil CO2 efflux sharply declined during all three TFE years in both forests. Above ground litter input was unaffected by TFE until the second treatment year. Overall, both forest ecosystems appeared highly resistant to the imposed soil drying, with no signs of tree mortality and stable living root biomass stocks.

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.

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.