Forest Biology Center

Our new study, published in Global Change Biology, shows that climate warming is reducing seed mass in European beech. Using long-term records from the UK and the Netherlands (1976–2024), we found that beech seeds have become 13% lighter, with the decline beginning around the mid-2000s.

The main driver was a decline in estimated stored resources, with increasing drought during seed development contributing further. Warmer conditions trigger more frequent reproductive events, leaving trees less time to replenish resources between seed crops. As a result, trees invest less in individual seeds.

Because larger seeds generally produce stronger seedlings with better survival prospects, this decline may further weaken the ability of European forests to regenerate under climate change.
Read the paper: https://doi.org/10.1111/gcb.71196

Mast seeding—the intermittent production of large, synchronized seed crops—can help trees achieve successful pollination and escape seed predators. Our new study shows that these benefits can extend beyond germination, influencing the survival of seedlings in subsequent years.

Using 15 years of monitoring of over 4,500 individually marked rowan seedlings in a natural subalpine forest in the Western Carpathians, we examined how survival depended on the size of the seed crop from which seedlings originated and the trees growing above them. Rowan seedlings generally survived better beneath spruce trees than beneath adult rowans, in line with Janzen-Conell effects. However, seedlings originating from high-crop years survived better beneath adult rowans than those from low-crop years.

The difference was substantial: beneath rowans, predicted annual survival increased from 44% for seedlings originating from low-crop years to 55% for those from high-crop years. Beneath spruces, survival changed little with crop size. Even modest improvements in annual survival can accumulate over several years, potentially producing large differences in the number of seedlings that persist.

These findings suggest that the demographic benefits of masting extend beyond producing more seeds. High-crop years may also produce offspring better able to survive challenging neighbourhood conditions. Whether this reflects better seed provisioning or other differences among cohorts remains to be tested.

How does drought affect tree reproduction? In our new study published in Proceedings of the National Academy of Sciences (PNAS), led by Jakub Szymkowiak, we show a surprising result: European beech continues to produce seeds even during severe drought.

We analysed 221 long-term time series of European beech reproduction across Europe, comprising 5,362 annual population-level observations. The analysis separated drought exposure during flowering and pollination in spring, seed maturation in summer, and potential effects carried over to reproduction in the following year.

After accounting for the temperature cues that trigger mast reproduction, we found that summer drought did not reduce seed production. Dry spring conditions were actually associated with higher seed output, likely because dry weather improves airborne pollen dispersal and pollination efficiency. We also found no evidence that summer drought suppressed reproduction in the following year.
We then focused on three exceptional European droughts: 2003, 2018, and 2022. Even at the sites experiencing the strongest water deficits, seed production was not lower than expected. Once beech trees are committed to reproduction, they appear to maintain seed production even under extreme short-term water stress.

This creates an important contrast in how trees respond to drought. The same drought events that suppress tree growth and increase mortality can leave reproductive output largely intact. Different components of tree demography can therefore respond very differently to the same climatic stress, with consequences for how we predict forest regeneration, turnover, and resilience under a warmer and drier climate.

The finding should not be interpreted as broad resilience of beech reproduction to climate change. Climate warming can disrupt masting dynamics, while drought may still affect seed viability, seedling establishment, and survival. Understanding how seed production connects to successful recruitment is therefore the next major challenge.

Read the full paper here!

How birds learn that specific sounds are cues of a threat, such as predator vocalizations or heterospecific alarm calls? A new study led by Jakub Szymkowiak and published in Behavioral Ecology and Sociobiology reveals that birds can learn to recognize novel, previously unfamiliar sounds (samples of punk rock songs) as acoustic risk cues socially, by associating them with conspecific alarm calls. Moreover, social learning is threat-sensitive, with naïve individuals acquiring anti-predator responses to novel sounds depending on the strength of the anti-predator responses of conspecifics to these sounds.

The study provides experimental evidence that even though during the breeding season individual birds occupy distinct territories that are spaced apart each other, they are still inter-connected via information sharing and, at the population level, form a kind of “information network”. In such networks, novel anti-predator responses can be socially acquired and transmitted among the individuals across territory borders. Under natural conditions, the threat-sensitive social transmission likely allows individuals to minimize the costs of incorrectly associating neutral sounds as cues of a threat when learning via indirect risk cues.

Such social transmission of risk recognition among territorial conspecifics can have important eco-evolutionary consequences. Traditionally, co-occurring conspecifics have been considered as putative competitors and the negative impacts of competitive interactions on individuals’ fitness and higher order ecological phenomena have been emphasized. However, the results of this study show that apart from being competitors, conspecifics are also the repositories of vital, fitness-enhancing information, which they can transfer to other individuals.

Read the full paper here: https://doi.org/10.1007/s00265-026-03751-3

Seeds start forest renewal, allowing forests to regenerate, expand and adapt to changing conditions. But our new study, published in Nature Climate Change, shows that climate change may be weakening tree fecundity in Europe’s trees.

We analysed 34 years of Polish forest seed-harvest records, covering 40,530 annual observations from 438 forest districts between 1988 and 2021. The dataset included five major forest-forming species: European beech, silver fir, Scots pine, pedunculate oak and sessile oak.

These long-term records are particularly valuable because they report sorted seed lots. In other words, they reflect seeds that pass quality control, with empty, damaged or infested seeds largely removed. This means the data provide insight into viable seed production, not just the total number of seeds produced.

The results were striking. Viable seed production declined across all studied taxa: by around 65% in oaks, 64% in Scots pine, 44% in silver fir and 32% in European beech.

One important challenge was that seed harvest records reflect both biological seed availability and ‘human’ demand for seeds. Foresters collect seed when they are needed, and demand for seed also declined over time. To address this, we accounted for seed collection effort in our analyses. Even after doing so, the decline in viable seed production remained, suggesting that the pattern cannot solely be explained by people collecting fewer seeds.

Summer warming emerged as the strongest driver of the decline. Across species, hotter summers were linked to lower viable seed output. Spring temperatures and growing-season moisture also affected reproduction, but they explained less of the long-term decline than summer warming.

We also found that climate effects differed among local populations. A warm or dry year could have different consequences depending on the long-term climate of a site. This points to a possible role for local adaptation or acclimation.

A second line of evidence of fecundity decline came from the MASTREE+ database, an independent open-access dataset of plant reproduction. For the same period and species, we found declines in masting: the boom-and-bust pattern of seed production that many trees rely on to produce viable seeds.

Our findings suggest that climate change is reducing the reproductive capacity of important European forest trees. This has direct implications for forest regeneration and seed supply. If viable seed crops continue to decline, nurseries may face shortages of provenance-appropriate seed, and forests may have less capacity to recover after disturbance.

The next step is to connect these fecundity trends with long-term regeneration data. Are declining seed crops already translating into fewer young trees, or are other ecological processes of greater influence?

Read the paper here:
https://rdcu.be/figE9

Foest J.J., Szymkowiak J., Dyderski M.K., Kelly D., Kunstler G., Jastrzębowski S., Bogdziewicz M. 2026. Forest fecundity declines as climate shifts. Nature Climate Change.

How do trees balance the number and quality of seeds during mast years? In our new paper in New Phytologist, led by Kasia Kondrat, we tested this question in European beech using data from 2,792 trees across 123 populations. Contrary to the expectation that producing more seeds should reduce investment per seed, high-seeding years produced heavier seeds. However, seed chemistry changed: protein content declined with increasing seed production, while lipid content increased. We also found that seed mass and protein content were lowest toward the climatic margins of the species’ range. Read the paper here!

This paper is a product of the European Beech Reproduction Network, a collaborative initiative coordinated by our lab to monitor beech reproduction across Europe using a standardized, lightweight field protocol. The network was established to understand how seed production, pollination, seed predation, tree size, and climate interact across the species’ range. This study shows the value of coordinated continental-scale sampling for answering questions that cannot be addressed from single sites or regions alone.

We are continuing to expand the network and welcome new collaborators with access to European beech populations! Please, get in touch if interested.

European Beech Reproduction Network – Forest Biology Center

Sebastian joined our team in January 2026, working on the climate change biology of trees reproduction, which will include climate gradients in fecundity, seed traits, local adaptations, and more. Stay tuned for outcomes!
Godspeed Sebastian 🙂

In a new study published in Proceedings of the National Academy of Sciences, we show that in temperate European forests, years of seed failure are more strongly synchronized over space than mast years with high seed production. Using 36 years of data from over 400 sites and seven dominant tree species, we demonstrate that regional coherence in tree reproduction is driven primarily by synchronized seed scarcity, not abundance. Among-species synchrony was largely local, suggesting that forest diversity buffers food webs against continent-scale boom–bust dynamics. Our findings highlight the ecological importance of widespread reproductive failure and have implications for wildlife dynamics, forest regeneration, and seed sourcing under climate change. Read the paper here!

Reproduction is essential for forests to recover from disturbance and adapt to climate change, yet it is often overlooked in climate impact assessments. Our new study, published in Ecology Letters, shows that climate warming has likely already reduced the natural year-to-year variation in seed production of European beech (‘masting’), with declines of up to ~54% under current conditions. Looking ahead, these losses could become even more severe, reaching up to ~83% under moderate future warming scenarios. This matters because strong fluctuations in seed production help trees pollinate successfully and overwhelm seed predators, ensuring enough viable seeds are produced. Importantly, the strongest effects are expected at the colder edges of the species’ range. Thus, contrary to common assumptions, cooler regions and high elevations appear to offer no safe haven: reduced seed production is likely to limit forest regeneration, species movement, and long-term forest resilience as the climate continues to warm.
Read the paper here!

Our new study, published in Oikos, shows how flexible pollinator communities sustain reproduction in the mast-seeding tree Sorbus aucuparia. Despite large year-to-year swings in flowering intensity, pollination efficiency remained high, driven by dynamic shifts in pollinator composition. Bumblebees dominated during abundant flowering, while solitary bees became proportionally more important when flowers were scarce. These results reveal that pollinator life histories and network flexibility buffer animal-pollinated trees from pollination failure, helping explain why strong masting can evolve even in insect-pollinated species.
👉 Read the paper in Oikos.