Daniel M. Buonaiuto

Phenology, the timing of recurring life history events, can vary substantially in different environments and for different species. While climate change has shifted phenology by altering its environmental triggers, such as temperature, changes in the drivers that select for species‐level variation remain poorly explained. Theory suggests that species‐level variation in phenology can result from shifting environmental pressures that favour different strategies across the spring growing season: from the early season, where higher abiotic risks and greater availability of nutrients and light favour cheaper leaves and acquisitive growth strategies, to later, when a more benign environment and lower levels of light and nutrients favour conservative growth strategies. This framework predicts a suite of traits that may covary with species phenologies, but the high variability in phenology across environments has made testing its role within a trait framework challenging. Using a modelling framework that accommodates this variability, with phenological data from a database of controlled environment experiments and tree trait data from two major databases we tested for relationships between traits and spring phenology in trees. Specifically, we examined the cues that drive early to late budburst: spring temperatures (forcing), winter temperatures (chilling) and daylength (photoperiod). We found mixed support for our predictions for how traits relate to budburst timing and phenology. Species with cues that lead to earlier budburst (small responses to experimental chilling and photoperiod) were shorter with higher leaf nitrogen content, both traits related to acquisitive strategies and thus are in line with our predictions. However, our one reproductive trait of seed mass showed no relationship with phenology, and other traits (e.g. specific leaf area) showed relationships in the opposite direction to our predictions. Synthesis : Our findings show how spring budburst phenology partially fits within a functional trait framework of acquisitive to conservative growth strategies. Leveraging these relationships could improve predictions of how communities shift in their growth strategies alongside changing phenology with future warming.

Summary: Climate change could reduce dioecious plant fitness if the phenology of males and females responds differently to temperature. However, the extent to which spring phenological responses to climate differ between sexes in wind‐pollinated dioecious trees remains poorly understood. Here, we combined ground observations with climate‐controlled experiments to investigate sexual differences in spring budburst in Ginkgo biloba, Fraxinus chinensis, and Eucommia ulmoides. In 96% of in situ cases, male trees initiated budburst earlier than females, on average by 3.0 ± 0.4 d. This disparity was more pronounced in warmer regions. The experiment indicated that background climate is a key predictor of sexual disparity in budburst, with the largest differences observed in twigs originating from regions with higher mean annual temperatures and precipitation. However, these disparities declined in areas where mean annual temperatures exceeded 17.1°C, indicating nonlinear trends. This pattern aligns with the warming treatments, where sexual disparities decreased under spring warming of 2–10°C. These results suggest that while sexual disparities can be larger in warmer climates, dioecious trees possess stabilizing mechanisms, including photoperiod and chilling requirements, to maintain synchrony under warming conditions. Our findings enhance understanding of sex‐specific phenological responses to climate change, with important implications for future species conservation and ecosystem management.

Aim: Beta diversity quantifies the similarity of ecological assemblages. Its increase, known as biotic homogenisation, can be a consequence of biological invasions. However, species occurrence (presence/absence) and abundance‐based analyses can produce contradictory assessments of the magnitude and direction of changes in beta diversity. Previous work indicates these contradictions should be less frequent in nature than in theory, but a growing number of empirical studies report discrepancies between occurrence‐ and abundance‐based approaches. Understanding if these discrepancies represent a few isolated cases or are systematic across a diversity of ecosystems would allow us to better understand the general patterns, mechanisms and impacts of biotic homogenisation.Location: United States.Time Period: 1963–2020.Major Taxa Studied: Vascular plants.Methods: We used a dataset of more than 70,000 vegetation survey plots to assess differences in biotic homogenisation with and without invasion using both occurrence‐ and abundance‐based metrics of beta diversity. We estimated taxonomic biotic homogenisation by comparing beta diversity of invaded and uninvaded plots with both classes of metrics and investigated the characteristics of the non‐native species pool that influenced the likelihood that these metrics disagree.Results: In 78% of plot comparisons, occurrence‐ and abundance‐based calculations agreed in direction, and the two metrics were generally well correlated. Our empirical results are consistent with previous theory. Discrepancies between the metrics were more likely when the same non‐native species was at high cover at both plots compared for beta diversity, and when these plots were spatially distant.Main Conclusions: In about 20% of cases, our calculations revealed differences in direction (homogenisation vs. differentiation) when comparing occurrence‐ and abundance‐based metrics, indicating that the metrics are not interchangeable, especially when distances between plots are high and invader diversity is low. When data permit, combining the two approaches can offer insights into the role of invasions and extirpations in driving biotic homogenisation/differentiation.

The temporal separation of male and female flowering—known as dichogamy—is a widespread adaptation across the plant kingdom that increases reproductive success and enhances plant fitness. Differences in timing between male and female flowering can be highly sensitive to environmental variation—and with widespread evidence of shifts in seasonal timing of flowering (i.e., phenology) due to anthropogenic warming—climate change may alter the sequences of male and female flowering for a diversity of taxa around the globe. However, we currently lack a broad understanding of both the extent to which climate change may alter patterns of dichogamy and the potential implications of these shifts for plant reproduction. Here I present evidence that links variation in dichogamy to variation in temperature for a variety of plant taxa. I synthesize the limited number of studies that have investigated shifts in dichogamy specifically in the context of climate change, and detail the physiological, genetic, and developmental factors that control the relative timing of male and female flowering. The literature indicates that dichogamy is highly plastic and sensitive to temperature variation. Plasticity in dichogamy is observed across species with different sexual systems and growth habits, and in both female‐first and male‐first flowering taxa, but at present, no clear patterns of dichogamy shifts related to these associated traits are discernible. Together, these lines of evidence suggest that sequences of male and female flowering are likely to shift with climate change. However, more research is needed to better understand and predict the ecological consequences of shifting patterns of dichogamy in the context of global change.

Despite decades of research documenting the consequences of naturalized and invasive plant species on ecosystem functions, our understanding of the functional underpinnings of these changes remains rudimentary. This is partially due to ineffective scaling of trait differences between native and naturalized species to whole plant communities. Working with data from over 75,000 plots and over 5,500 species from across the United States, we show that changes in the functional composition of communities associated with increasing abundance of naturalized species mirror the differences in traits between native and naturalized plants. We find that communities with greater abundance of naturalized species are more resource acquisitive aboveground and belowground, shorter, more shallowly rooted, and increasingly aligned with an independent strategy for belowground resource acquisition via thin fine roots with high specific root length. We observe shifts toward herbaceous-dominated communities but shifts within both woody and herbaceous functional groups follow community-level patterns for most traits. Patterns are remarkably similar across desert, grassland, and forest ecosystems. Our results demonstrate that the establishment and spread of naturalized species, likely in combination with underlying environmental shifts, leads to predictable and consistent changes in community-level traits that can alter ecosystem functions.

Summary: Across temperate forests, many tree species produce flowers before their leaves emerge. This flower–leaf phenological sequence, known as hysteranthy, is generally described as an adaptation for wind pollination. However, this explanation does not address why hysteranthy is also common in biotically pollinated taxa. We quantified flower–leaf sequence variation in the American plums ( Prunus , subg. Prunus sect. Prunocerasus ), a clade of insect‐pollinated trees, using herbaria specimens and Bayesian hierarchical modeling. We tested two common, but rarely interrogated hypotheses – that hysteranthy confers aridity tolerance and/or pollinator visibility – by modeling the associations between hysteranthy and related traits. To understand how these phenology–trait associations were sensitive to taxonomic scale and flower–leaf sequence classification, we then extended these analyses to all Prunus species in North America. Our findings across two taxonomic levels support the hypotheses that hysteranthy may help temporally partition hydraulic demand to reduce water stress and increase pollinator visibility – thereby reducing selective pressure on inflorescence size. Our results provide foundational insights into the evolution of flower–leaf sequences in the genus Prunus , with implications for understanding these patterns in biotically pollinated plants in general. Our approach suggests a path to advance these hypotheses to other clades, but teasing out drivers fully will require new experiments.

Risk assessments are conservation tools used to prevent the introduction of invasive species. Many assessments ask whether a taxon has invasive close relatives, but it is unclear whether this phylogenetic information is useful, and which taxonomic scales (e.g., genus, family) are most predictive of risk. Combining phylogenetic clustering analyses with models predicting invasion risk, we found invasive plants were clustered within nonnative flora of the conterminous United States. Taxonomic information in models improved their predictive capacity; invasion risk for taxa with invasive confamilials, congeners, or sister taxa increased by 9%, 16%, and 19% respectively. Phylogenetic information did not improve inference for species without any congeners, or those from large genera. The most common approach—assessing congeners—is well suited to identify invaders, particularly for genera with 2–10 established species. While existing phylogenetic information can enhance assessments of invasion risk, biologists and regulators should collaborate to improve nonnative species phylogenies.

Invasive plants are often characterized by rapid germination and precocious phenology. Theory suggests that early germination may provide invaders with a competitive advantage over slower germinating natives, but the relative contribution of rapid germination versus other intrinsic competitive traits (e.g. rapid growth, high fecundity, broad environmental tolerance) to the success of invaders is poorly understood. Depending on the relationship between germination and competition, shifts in germination phenology due to climate change may increase the dominance of invaders or buffer communities against their impacts. We investigated the link between temperature variation, germination phenology and competitive interactions with a sequence of controlled environment experiments. First, we evaluated the relationships between temperature variation and germination phenology for two herbaceous species found in North American woodlands, the non‐native Hesperis matronalis and native Cryptotaenia canadensis. We then leveraged temperature‐response differences to manipulate the relative germination phenology of these taxa and quantified the effects of their phenological differences on competition. Seeds of the invasive H. matronalis germinated rapidly, reaching 50% germination in under 10 days in all treatment combinations. C. canadensis did not reach 50% germination with less than 7 weeks of cold stratification. However, with more than 10 weeks of cold stratification and low (20/10°C) incubation temperatures, the germination phenology of C. canadensis was well‐matched to that of H. matronalis. When grown together, we found that precocious germination phenology doubled the competitive impact of H. matronalis relative to its other intrinsic competitive traits. Phenological advantage of just 2–3 days relative to C. canadensis was enough to secure competitive dominance at the seedling stage. Synthesis. This study revealed that the mechanistic link between the germination phenology and competitive success of an invasive plant can be strongly mediated by climate sensitivity differences between introduced and native species. Climate change will likely exacerbate these differences, especially in regions where warming reduces cold stratification. Our findings suggest that phenological diversity in native plant communities is an important property of invasion resistance. The relationship between environmental variation, germination dynamics and competition provides a path forward for forecasting climate change impacts on seasonal community assembly and highlights the need to incorporate phenological diversity in restorations.

Temperature and light cues interact to control many biological processes. Experiments give researchers the ability to manipulate these environmental cues independently and can be designed to robustly quantify their individual and interactive effects on any particular biological activity. Such experiments have produced important insights into the environmental controls on numerous biological processes in both plant and animal taxa across terrestrial and aquatic environments. Testing the interactive effects of multiple environmental cues, however, requires experimental treatments to be fully independent; any unmeasured experimental covariation among treatments can result in incorrect conclusions. Using a database of controlled environment experiments on the spring phenology of woody plants as a case study, we highlight how a common experimental set‐up, designed to parse the interactive effects of temperature and photoperiod on time to budburst, introduces a latent experimental covariation of these treatments by coupling photo‐ and thermoperiodicity. Using data simulations, algebraic corrections and a comparative analysis of published experiments, we demonstrate how this unmeasured experimental covariation biases statistical inference regarding the relative contribution of light and temperature cues to phenological variation. We identify this experimental covariation in more than 40% of published phenology studies that manipulate photoperiod. Our analyses demonstrate that the coupling of thermo‐ and photoperiodicity results in the overestimation of the effect of photoperiod, the underestimation of forcing effects, and misleading conclusions about their interactions on phenology. This may, in part, explain why the significance of photoperiod cues for spring phenology is currently debated in the literature. Accurate forecasting of how varying environmental conditions will impact the dynamics of biological events requires accurately quantifying cue responses. To this end, we present several options for statistical corrections and alternative experimental designs that can provide more robust estimates of the relative effects of temperature and photoperiod on phenology and many other biological processes controlled by temperature and light. Read the freePlain Language Summaryfor this article on the Journal blog.