Temperature-dependent shifts in phenology contribute to the success of exotic species with climate change

High preseason temperature variability drives convergence of xylem phenology in the Northern Hemisphere conifers

Wood growth is key to understanding the feedback of forest ecosystems to the ongoing climate warming. An increase in spatial synchrony (i.e., coincident changes in distant populations) of spring phenology is one of the most prominent climate responses of forest trees. However, whether temperature variability contributes to an increase in the spatial synchrony of spring phenology and its underlying mechanisms remains largely unknown. Here, we analyzed an extensive dataset of xylem phenology observations of 20 conifer species from 75 sites over the Northern Hemisphere. Along the gradient of increase in temperature variability in the 75 sites, we observed a convergence in the onset of cell enlargement roughly toward the 5th of June, with a convergence in the onset of cell wall thickening toward the summer solstice. The increase in rainfall since the 5th of June is favorable for cell division and expansion, and as the most hours of sunlight are received around the summer solstice, it allows the optimization of carbon assimilation for cell wall thickening. Hence, the convergences can be considered as the result of matching xylem phenological activities to favorable conditions in regions with high temperature variability. Yet, forest trees relying on such consistent seasonal cues for xylem growth could constrain their ability to respond to climate warming, with consequences for the potential growing season length and, ultimately, forest productivity and survival in the future.

Chronosequence of invasion reveals minimal losses of population genomic diversity, niche expansion, and trait divergence in the polyploid, leafy spurge

Rapid evolution may play an important role in the range expansion of invasive species and modify forecasts of invasion, which are the backbone of land management strategies. However, losses of genetic variation associated with colonization bottlenecks may constrain trait and niche divergence at leading range edges, thereby impacting management decisions that anticipate future range expansion. The spatial and temporal scales over which adaptation contributes to invasion dynamics remain unresolved. We leveraged detailed records of the ~130-year invasion history of the invasive polyploid plant, leafy spurge (Euphorbia virgata), across ~500 km in Minnesota, U.S.A. We examined the consequences of range expansion for population genomic diversity, niche breadth, and the evolution of germination behavior. Using genotyping-by-sequencing, we found some population structure in the range core, where introduction occurred, but panmixia among all other populations. Range expansion was accompanied by only modest losses in sequence diversity, with small, isolated populations at the leading edge harboring similar levels of diversity to those in the range core. The climatic niche expanded during most of the range expansion, and the niche of the range core was largely non-overlapping with the invasion front. Ecological niche models indicated that mean temperature of the warmest quarter was the strongest determinant of habitat suitability and that populations at the leading edge had the lowest habitat suitability. Guided by these findings, we tested for rapid evolution in germination behavior over the time course of range expansion using a common garden experiment and temperature manipulations. Germination behavior diverged from the early to late phases of the invasion, with populations from later phases having higher dormancy at lower temperatures. Our results suggest that trait evolution may have contributed to niche expansion during invasion and that distribution models, which inform future management planning, may underestimate invasion potential without accounting for evolution.

Complex climate-mediated effects of urbanization on plant reproductive phenology and frost risk

Urbanization can affect the timing of plant reproduction (i.e. flowering and fruiting) and associated ecosystem processes. However, our knowledge of how plant phenology responds to urbanization and its associated environmental changes is limited. Herbaria represent an important, but underutilized source of data for investigating this question. We harnessed phenological data from herbarium specimens representing 200 plant species collected across 120 yr from the eastern US to investigate the spatiotemporal effects of urbanization on flowering and fruiting phenology and frost risk (i.e. time between the last frost date and flowering). Effects of urbanization on plant reproductive phenology varied significantly in direction and magnitude across species ranges. Increased urbanization led to earlier flowering in colder and wetter regions and delayed fruiting in regions with wetter spring conditions. Frost risk was elevated with increased urbanization in regions with colder and wetter spring conditions. Our study demonstrates that predictions of phenological change and its associated impacts must account for both climatic and human effects, which are context dependent and do not necessarily coincide. We must move beyond phenological models that only incorporate temperature variables and consider multiple environmental factors and their interactions when estimating plant phenology, especially at larger spatial and taxonomic scales.

Climate drivers of seed rain phenology of subtropical forest communities along an elevational gradient

Seed rain phenology (the start and end date of seed rain) is an essential component of plant phenology, critical for understanding population regeneration and community dynamics. However, intra- and inter-annual changes of seed rain phenology along environmental gradients have rarely been studied and the responses of seed rain phenology to climate variations are unclear. We monitored seed rain phenology of four forest communities in four years at different elevations (900 m, 1450 m, 1650 m, 1900 m a.s.l.) of a subtropical mountain in Central China. We analyzed the spatiotemporal patterns of seed rain phenology of 29 common woody plant species (total observed species in the seed rain), and related the phenological variations to seed number and climatic variables using mixed-effect models with the correlation matrix of phylogeny. We found that changes in the period length were mainly driven by the end rather than the start date. The end date and the period length of seed rain were significantly different between the mast and non-mast seeding years, while no significant elevation-related trend was detected in seed rain phenology variation. Seed number, mean temperature in spring (T_spr), and winter (T_win), summer precipitation (P_sum) had significant effects on seed rain phenology. When T_spr increased, the start date of seed rain advanced, while the end date was delayed and the seed rain period length was mainly prolonged by a higher seed number, T_win and P_sum. Forest canopy might have a buffering effect on understory climatic conditions, especially in precipitation that lead to difference in seed rain phenology between canopy and shrub species. Our novel evidence of seed rain phenology can improve prediction of community regeneration dynamics in responding to climate changes.

Radical shift in the genetic composition of New England chicory populations

Human activities have been altering the flora and fauna across the planet. Distributions and the diversity of species, and the phenotypes of individuals in those species are changing. New England with its rapidly changing human demographics is an ideal place to investigate these temporal changes in the habitat. The flora of New England consists of both native and nonnative species. Non-indigenous plant species have been introduced since the first Europeans arrived in North America in the 15th century. Cichorium intybus (chicory), native to Eurasia, was first recorded in North America in 1774. Subsequently, chicory spread and became naturalized throughout much of the continent.In this study, we used chloroplast DNA sequences and 12 microsatellite nuclear markers to assess the temporal genetic changes in New England populations of chicory. We analysed 84 herbarium specimens and 18 contemporary extant populations (228 individuals in total).Three chloroplast DNA haplotypes were detected and all were present in New England prior to 1890; however, Hap3 was rare prior to the 1950s. The nuclear DNA markers showed a major shift in the genetic diversity and composition, with all historical herbarium collections belonging to a single genetic cluster and 16 out of 18 contemporary chicory populations belonging to different genetic clusters. This change occurred regionally and also on a local scale with contemporary populations being very different from herbarium specimens collected previously in the corresponding localities. Synthesis. Our results indicate that the genetic diversity and structure of Cichorium intybus populations have changed substantially since the founding populations in New England. These changes may have contributed to the success of this nonnative species and helped to fuel its rapid expansion and adaptation to the changing landscapes in both New England and the rest of North America.

The influence of climate warming on flowering phenology in relation to historical annual and seasonal temperatures and plant functional traits

Climate warming has the potential to influence plant flowering phenology which in turn can have broader ecological consequences. Herbarium collections offer a source of historical plant data that makes possible the ability to document and better understand how warming climate can influence long-term shifts in flowering phenology. We examined the influence of annual, winter, and spring temperatures on the flowering phenology of herbarium specimens for 36 species collected from 1884-2015. We then compared the response to warming between native and non-native, woody and herbaceous, dry and fleshy fruit, and spring vs summer blooming species. Across all species, plants flowered 2.26 days earlier per 1 °C increase in annual average temperatures and 2.93 days earlier per 1 °C increase in spring onset average temperatures. Winter temperatures did not significantly influence flowering phenology. The relationship of temperature and flowering phenology was not significantly different between native and non-native species. Woody species flowered earlier than herbaceous species only in response to increasing annual temperatures. There was no difference in the phenological response between species with dry fruits and those fleshy fruits for any of the temperature periods. Spring blooming species exhibited a significantly greater phenological response to warming yearly average temperatures than summer blooming species. Although herbarium specimens can reveal climate change impacts on phenology, it is also evident that the phenological responses to warming vary greatly among species due to differences in functional traits such as those considered here, as well as other factors.

Are really Nature-Based Solutions sustainable solutions to design future cities in a context of global change? Discussion about the vulnerability of these new solutions and their probable unsustainable implementation

The urban ecosystem is a very challenging environment that faces many problems such as various pollutions, higher temperatures than its surroundings or flooding risks due to soil sealing. Nature-based solutions (NBS) seem to be good option to address these problems, while simultaneously offering benefits for facing climate change and the biodiversity crisis. Despite their potential, NBS can be threatened by various urban disturbance, namely: land use change, pollution, or invasive species. These disturbances can have multiple consequences on urban NBS, such as causing changes in plant characteristics/traits, altering the services they provide, and even make certain plant populations disappear, etc. In turn, these consequences may even jeopardize the solutions themselves, which then may no longer solve the problems they originally targeted. To avoid this, NBS should be eco-designed, i.e. designed in function of their environment. Their management should be adaptive and should also take into consideration the evolution of climatic and anthropogenic factors. The choice of species should not be left to chance or random: In this sense, is it better to plant native species for biodiversity conservation or exotic species that are more likely to resist global changes? Is it better to find resistant or ruderal species that have proven themselves in the face of certain disturbances? In any case, it would be good to diversify any NBS to have a better chance of survival in the face of global changes.

Phenology and morphology of the invasive legume Lupinus polyphyllus along a latitudinal gradient in Europe

Plant phenology, i. e. the timing of life cycle events, is related to individual fitness and species distribution ranges. Temperature is one of the most important drivers of plant phenology together with day length. The adaptation of their phenology may be important for the success of invasive plant species. The present study aims at understanding how the performance and the phenology of the invasive legume Lupinus polyphyllus vary with latitude. We sampled data across a >2000 km latitudinal gradient from Central to Northern Europe. We quantified variation in phenology of flowering and fruiting of L. polyphyllus using >1600 digital photos of inflorescences from 220 individual plants observed weekly at 22 sites. The day of the year at which different phenological phases were reached, increased 1.3–1.8 days per degree latitude, whereas the growing degree days (gdd) required for these phenological phases decreased 5–16 gdd per degree latitude. However, this difference disappeared, when the day length of each day included in the calculation of gdd was considered. The day of the year of the earliest and the latest climatic zone to reach any of the three studied phenological phases differed by 23–30 days and temperature requirements to reach these stages differed between 62 and 236 gdd. Probably, the invasion of this species will further increase in the northern part of Europe over the next decades due to climate warming. For invasive species control, our results suggest that in countries with a large latitudinal extent, the mowing date should shift by ca. one week per 500 km at sites with similar elevations.

Invasive species do not exploit early growing seasons in burned tallgrass prairies

Invasive species management is key to conserving critically threatened native prairie ecosystems. While prescribed burning is widely demonstrated to increase native diversity and suppress invasive species, elucidating the conditions under which burning is most effective remains an ongoing focus of applied prairie ecology research. Understanding how conservation management interacts with climate is increasingly pressing, because climate change is altering weather conditions and seasonal timing around the world. Increasingly early growing seasons due to climate change are shifting the timing and availability of resources and niche space, which may disproportionately advantage invasive species and influence the outcome of burning. We estimated the effects of burning, start time of the growing season, and their interaction on invasive species relative cover and frequency, two metrics for species abundance and dominance. We used 25 observed prairie sites and 853 observations of 267 transects spread throughout Minnesota, USA from 2010 to 2019 to conduct our analysis. Here, we show that burning reduced the abundance of invasive cool-season grasses, leading to reduced abundance of invasive species as a whole. This reduction persisted over time for invasive cover but quickly waned for their frequency of occurrence. Additionally, and contrary to expectations that early growing season starts benefit invasive species, we found evidence that later growing season starts increased the abundance of some invasive species. However, the effects of burning on plant communities were largely unaltered by the timing of the growing season, although earlier growing season starts weakened the effectiveness of burning on Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), two of the most dominant invasive species in the region. Our results suggest that prescribed burning will likely continue to be a useful conservation tool in the context of earlier growing season starts, and that changes to growing season timing will not be a primary mechanism driving increased invasion due to climate change in these ecosystems. We propose that future research seek to better understand abiotic controls on invasive species phenology in managed systems and how burning intensity and timing interact with spring conditions.

The ecological implications of intra- and inter-species variation in phenological sensitivity

Plant-pollinator mutualisms rely upon the synchrony of interacting taxa. Climate change can disrupt this synchrony as phenological responses to climate vary within and across species. However, intra- and interspecific variation in phenological responses is seldom considered simultaneously, limiting our understanding of climate change impacts on interactions among taxa across their ranges. We investigated how variation in phenological sensitivity to climate can alter ecological interactions simultaneously within and among species using natural history collections and citizen science data. We focus on a unique system, comprising a wide-ranged spring ephemeral with varying color morphs (Claytonia virginica) and its specialist bee pollinator (Andrena erigeniae). We found strongly opposing trends in the phenological sensitivities of plants vs their pollinators. Flowering phenology was more sensitive to temperature in warmer regions, whereas bee phenology was more responsive in colder regions. Phenological sensitivity varied across flower color morphs. Temporal synchrony between flowering and pollinator activity was predicted to change heterogeneously across the species' ranges in the future. Our work demonstrates the complexity and fragility of ecological interactions in time and the necessity of incorporating variation in phenological responses across multiple axes to understand how such interactions will change in the future.

Limited evidence for phenological differences between non-native and native species

Although many species shift their phenology with climate change, species vary significantly in the direction and magnitude of these responses (i.e., phenological sensitivity). Studies increasingly detect early phenology or high phenological sensitivity to climate in non-native species, which may favor non-native species over natives in warming climates. Yet relatively few studies explicitly compare phenological responses to climate between native vs. non-native species or between non-native populations in the native vs. introduced range, limiting our ability to quantify the role of phenology in invasion success. Here, we review the empirical evidence for and against differences in phenology and phenological sensitivity to climate in both native vs. non-native species and native and introduced populations of non-native species. Contrary to common assumptions, native and non-native plant species did not consistently differ in mean phenology or phenological sensitivity. However, non-native plant species were often either just as or more sensitive, but rarely less sensitive, to climate as natives. Introduced populations of non-native plant species often show earlier reproduction than native populations of the same species, but there was mixed evidence for differences in phenological sensitivity between introduced and native plant populations. We found very few studies comparing native vs. invasive animal phenology. Future work should characterize phenological sensitivity to climate in native vs. non-native plant and animal species, in native vs. introduced populations of non-native species, and across different stages of invasion, and should carefully consider how differences in phenology might promote invasion success or disadvantage native species under climate change.

New directions in tropical phenology

Earth's most speciose biomes are in the tropics, yet tropical plant phenology remains poorly understood. Tropical phenological data are comparatively scarce and viewed through the lens of a 'temperate phenological paradigm' expecting phenological traits to respond to strong, predictably annual shifts in climate (e.g., between subfreezing and frost-free periods). Digitized herbarium data greatly expand existing phenological data for tropical plants; and circular data, statistics, and models are more appropriate for analyzing tropical (and temperate) phenological datasets. Phylogenetic information, which remains seldom applied in phenological investigations, provides new insights into phenological responses of large groups of related species to climate. Consistent combined use of herbarium data, circular statistical distributions, and robust phylogenies will rapidly advance our understanding of tropical - and temperate - phenology.

Fast but steady: An integrated leaf-stem-root trait syndrome for woody forest invaders

Successful control and prevention of biological invasions depend on identifying traits of non-native species that promote fitness advantages in competition with native species. Here, we show that, among 76 native and non-native woody plants of deciduous forests of North America, invaders express a unique functional syndrome that combines high metabolic rate with robust leaves of longer lifespan and a greater duration of annual carbon gain, behaviours enabled by seasonally plastic xylem structure and rapid production of thin roots. This trait combination was absent in all native species examined and suggests the success of forest invaders is driven by a novel resource-use strategy. Furthermore, two traits alone-annual leaf duration and nuclear DNA content-separated native and invasive species with 93% accuracy, supporting the use of functional traits in invader risk assessments. A trait syndrome reflecting both fast growth capacity and understorey persistence may be a key driver of forest invasions.

Machine Learning Undercounts Reproductive Organs on Herbarium Specimens but Accurately Derives Their Quantitative Phenological Status: A Case Study of Streptanthus tortuosus

Machine learning (ML) can accelerate the extraction of phenological data from herbarium specimens; however, no studies have assessed whether ML-derived phenological data can be used reliably to evaluate ecological patterns. In this study, 709 herbarium specimens representing a widespread annual herb, Streptanthus tortuosus, were scored both manually by human observers and by a mask R-CNN object detection model to (1) evaluate the concordance between ML and manually-derived phenological data and (2) determine whether ML-derived data can be used to reliably assess phenological patterns. The ML model generally underestimated the number of reproductive structures present on each specimen; however, when these counts were used to provide a quantitative estimate of the phenological stage of plants on a given sheet (i.e., the phenological index or PI), the ML and manually-derived PI's were highly concordant. Moreover, herbarium specimen age had no effect on the estimated PI of a given sheet. Finally, including ML-derived PIs as predictor variables in phenological models produced estimates of the phenological sensitivity of this species to climate, temporal shifts in flowering time, and the rate of phenological progression that are indistinguishable from those produced by models based on data provided by human observers. This study demonstrates that phenological data extracted using machine learning can be used reliably to estimate the phenological stage of herbarium specimens and to detect phenological patterns.

Dissecting impacts of phenological shifts for performance across biological scales

Although phenological shifts in response to climate are often assumed to benefit species' performance and viability, phenology's role in allowing population persistence and mediating species-level responses in the face of climate change remain unclear. Here, we develop a framework to understand when and why phenological shifts at three biological scales will influence performance: individuals, populations, and macroecological patterns. Specifically, we highlight three underexplored assumptions: (i) individual variability in phenology does not affect population fitness; (ii) population growth rates are sensitive to vital rates affected by phenology; and (iii) phenology mediates species-level responses to climate change including patterns of extinction, invasion, and range shifts. We outline promising methods for understanding how phenological shifts will influence performance within and across biological scales.

Plant phenological responses to experimental warming-A synthesis

Although there is abundant evidence that plant phenology is shifting with climatic warming, the magnitude and direction of these shifts can depend on the environmental context, plant species, and even the specific phenophase of study. These disparities have resulted in difficulties predicting future phenological shifts, detecting phenological mismatches and identifying other ecological consequences. Experimental warming studies are uniquely poised to help us understand how climate warming will impact plant phenology, and meta-analyses allow us to expose broader trends from individual studies. Here, we review 70 studies comprised 1226 observations of plant phenology under experimental warming. We find that plants are advancing their early-season phenophases (bud break, leaf-out, and flowering) in response to warming while marginally delaying their late-season phenophases (leaf coloration, leaf fall, and senescence). We find consistency in the magnitude of phenological shifts across latitude, elevation, and habitat types, whereas the effect of warming on nonnative annual plants is two times larger than the effect of warming on native perennial plants. Encouragingly for researchers, plant phenological responses were generally consistent across a variety of experimental warming methods. However, we found numerous gaps in the experimental warming literature, limiting our ability to predict the effects of warming on phenological shifts. In particular, studies outside of temperate ecosystems in the Northern Hemisphere, or those that focused on late-season phenophases, annual plants, nonnative plants, or woody plants and grasses, were underrepresented in our data set. Future experimental warming studies could further refine our understanding of phenological responses to warming by setting up experiments outside of traditionally studied biogeographic zones and measuring multiple plant phenophases (especially late-season phenophases) across species of varying origin, growth form, and life cycle.

How phenological tracking shapes species and communities in non-stationary environments

Climate change alters the environments of all species. Predicting species responses requires understanding how species track environmental change, and how such tracking shapes communities. Growing empirical evidence suggests that how species track phenologically - how an organism shifts the timing of major biological events in response to the environment - is linked to species performance and community structure. Such research tantalizingly suggests a potential framework to predict the winners and losers of climate change, and the future communities we can expect. But developing this framework requires far greater efforts to ground empirical studies of phenological tracking in relevant ecological theory. Here we review the concept of phenological tracking in empirical studies and through the lens of coexistence theory to show why a community-level perspective is critical to accurate predictions with climate change. While much current theory for tracking ignores the importance of a multi-species context, basic community assembly theory predicts that competition will drive variation in tracking and trade-offs with other traits. We highlight how existing community assembly theory can help understand tracking in stationary and non-stationary systems. But major advances in predicting the species- and community-level consequences of climate change will require advances in theoretical and empirical studies. We outline a path forward built on greater efforts to integrate priority effects into modern coexistence theory, improved empirical estimates of multivariate environmental change, and clearly defined estimates of phenological tracking and its underlying environmental cues.

Phenological sensitivity to temperature mediates herbivory

Species interactions drive ecosystem processes and are a major focus of global change research. Among the most consequential interactions expected to shift with climate change are those between insect herbivores and plants, both of which are highly sensitive to temperature. Insect herbivores and their host plants display varying levels of synchrony that could be disrupted or enhanced by climate change, yet empirical data on changes in synchrony are lacking. Using evidence of herbivory on herbarium specimens collected from the northeastern United States and France from 1900 to 2015, we provide evidence that plant species with temperature-sensitive phenologies experience higher levels of insect damage in warmer years, while less temperature-sensitive, co-occurring species do not. While herbivory might be mediated by interactions between warming and phenology through multiple pathways, we suggest that warming might lengthen growing seasons for phenologically sensitive plant species, exposing their leaves to herbivores for longer periods of time in warm years. We propose that elevated herbivory in warm years may represent a previously underappreciated cost to phenological tracking of climate change over longer timescales.

Extirpated prairie species demonstrate more variable phenological responses to warming than extant congeners

PREMISE

Shifting phenology in response to climate is one mechanism that can promote population persistence and geographic spread; therefore, species with limited ability to phenologically track changing environmental conditions may be more susceptible to population declines. Alternatively, apparently nonresponding species may demonstrate divergent responses to multiple environmental conditions experienced across seasons.

METHODS

Capitalizing on herbarium records from across the midwestern United States and on detailed botanical surveys documenting local extinctions over the past century, we investigated whether extirpated and extant taxa differ in their phenological responses to temperature and precipitation during winter and spring (during flowering and the growing season before flowering) or in the magnitude of their flowering time shift over the past century.

RESULTS

Although warmer temperatures across seasons advanced flowering, extirpated and extant species differed in the magnitude of their phenological responses to winter and spring warming. Extirpated species demonstrated inconsistent phenological responses to warmer spring temperatures, whereas extant species consistently advanced flowering in response to warmer spring temperatures. In contrast, extirpated species advanced flowering more than extant species in response to warmer winter temperatures. Greater spring precipitation tended to delay flowering for both extirpated and extant taxa. Finally, both extirpated and extant taxa delayed flowering over time.

CONCLUSIONS

This study highlights the importance of understanding phenological responses to seasonal warming and indicates that extirpated species may demonstrate more variable phenological responses to temperature than extant congeners, a finding consistent with the hypothesis that appropriate phenological responses may reduce species' likelihood of extinction.

Anthropogenic alteration of flow, temperature, and light as life-history cues in stream ecosystems

Life history events, from mating and voltinism to migration and emergence, are governed by external and historically predictable environmental factors. The ways humans have altered natural environments during the Anthropocene have created myriad and compounding changes to these historically predictable environmental cues. Over the past few decades, there has been an increased interest in the control temperature exerts on life history events as concern over climate change has increased. However, temperature is not the only life history cue that humans have altered. In stream ecosystems, flow and light serve as important life history cues in addition to temperature. The timing and magnitude of peak flows can trigger migrations, decreases in stream temperature may cause a stream insect to enter diapause, and photoperiod appears to prompt spawning in some species of fish. Two or more of these cues may interact with one another in complex and sometimes unpredictable ways. Large dams and increasing impervious cover in urban ecosystems have modified flows and altered the timing of spawning and migration in fish. Precipitation draining hot impervious surfaces increases stream temperature and adds variability to the general pattern of stream warming from climate change. The addition of artificial light in urban and suburban areas is bright enough to eliminate or dampen the photoperiod signal and has resulted in caddisfly emergence becoming acyclical. The resulting changes in the timing of life history events also have the potential to influence the evolutionary trajectory of an organism and its interactions with other species. This paper offers a review and conceptual framework for future research into how flow, temperature, and light interact to drive life history events of stream organisms and how humans have changed these cues. We then present some of the potential evolutionary and ecological consequences of altered life history events, and conclude by highlighting what we perceive to be the most pressing research needs.

Warming and shifting phenology accelerate an invasive plant life cycle

Numerous studies have documented changes in the seasonal timing of organisms' growth and reproduction in response to climate warming. These changes correlate with documented changes in species' abundance, but mechanisms linking these trends remain elusive. We investigated the joint demographic effects of advanced reproductive phenology and warming on a globally invasive plant (Carduus nutans) in a field experiment, documenting a substantial shift toward completion of the life cycle at younger ages. Demographic modeling projected 71% of warmed individuals flower as annuals, compared to 61% under current conditions. As this species only reproduces once, this represents a major acceleration of the life cycle. We project a 15% increase in this invader's population growth rate. We show that rising temperatures accelerate this invasive species' population growth by increasing the average size of reproducing individuals; increasing the proportion of individuals that survive to reproduce; and increasing the fraction that reproduce as annuals. Major increases in population growth in this, and potentially many other, invasive species will threaten food security and require careful planning to avoid significant environmental and economic impacts.

Plant traits and vegetation data from climate warming experiments along an 1100 m elevation gradient in Gongga Mountains, China

Functional trait data enhance climate change research by linking climate change, biodiversity response, and ecosystem functioning, and by enabling comparison between systems sharing few taxa. Across four sites along a 3000–4130 m a.s.l. gradient spanning 5.3 °C in growing season temperature in Mt. Gongga, Sichuan, China, we collected plant functional trait and vegetation data from control plots, open top chambers (OTCs), and reciprocally transplanted vegetation turfs. Over five years, we recorded vascular plant composition in 140 experimental treatment and control plots. We collected trait data associated with plant resource use, growth, and life history strategies (leaf area, leaf thickness, specific leaf area, leaf dry matter content, leaf C, N and P content and C and N isotopes) from local populations and from experimental treatments. The database consists of 6,671 plant records and 36,743 trait measurements (increasing the trait data coverage of the regional flora by 500%) covering 11 traits and 193 plant taxa (ca. 50% of which have no previous published trait data) across 37 families.

Measurement(s)	leaf growth and development trait • Abundance • leaf area trait • leaf composition trait • leaf morphology trait • Vascular Plant • total biomass yield • climate
Technology Type(s)	balance • visual observation method • Scanner Device • leaf stoichiometry and isotope assays • weather station
Factor Type(s)	plants • temperature • plant functional traits (specific leaf area, leaf dry matter content, leaf carbon content, leaf nitrogen content, leaf size, leaf thickness) • type of treatment (e.g in situ warming experiments using an Open Top Chamber)
Sample Characteristic - Organism	Tracheophyta
Sample Characteristic - Environment	area of sedge- and forb-dominated herbaceous vegetation
Sample Characteristic - Location	Ganzi Tibetan Autonomous Prefecture

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12033786

A review of the challenges and opportunities for restoring animal-mediated pollination of native plants

Ecological restoration is increasingly implemented to reverse habitat loss and concomitant declines in biological diversity. Typically, restoration success is evaluated by measuring the abundance and/or diversity of a single taxon. However, for a restoration to be successful and persistent, critical ecosystem functions such as animal-mediated pollination must be maintained. In this review, we focus on three aspects of pollination within ecological restorations. First, we address the need to measure pollination directly in restored habitats. Proxies such as pollinator abundance and richness do not always accurately assess pollination function. Pollen supplementation experiments, pollen deposition studies, and pollen transport networks are more robust methods for assessing pollination function within restorations. Second, we highlight how local-scale management and landscape-level factors may influence pollination within restorations. Local-scale management actions such as prescribed fire and removal of non-native species can have large impacts on pollinator communities and ultimately on pollination services. In addition, landscape context including proximity and connectivity to natural habitats may be an important factor for land managers and conservation practitioners to consider to maximize restoration success. Third, as climate change is predicted to be a primary driver of future loss in biodiversity, we discuss the potential effects climate change may have on animal-mediated pollination within restorations. An increased mechanistic understanding of how climate change affects pollination and incorporation of climate change predictions will help practitioners design stable, functioning restorations into the future.

Spring wildflower phenology and pollinator activity respond similarly to climatic variation in an eastern hardwood forest

Climate warming could disrupt species interactions if organisms' phenologies respond to climate change at different rates. Phenologies of plants and insects can be sensitive to temperature and timing of snowmelt; however, many important pollinators including ground-nesting bees have been little studied in this context. Without knowledge of the environmental cues affecting phenologies of co-occurring species, we have little ability to predict how species assemblages, and species interactions, will be affected by climate change. Here, we studied a hardwood forest understory over six years, to determine how spring temperatures, snowmelt timing, and photoperiod influence the phenology of two spring wildflowers (Anemone spp. and Trillium grandiflorum), activity of ground-nesting bees, and their temporal overlap. Surface degree-day accumulation was a better predictor of phenology for Anemone spp. (plant) and Nomada (bees) than were day of year (a proxy for photoperiod) or snowmelt date, whereas Trillium flowering appeared most sensitive to photoperiodic cues. Activity periods of Andrena and Lasioglossum bees were equally well described by degree-day accumulation and day of year. No taxon's phenology was best predicted by snowmelt date. Despite these differences among taxa in their phenological responses, timing of bee activity and flowering responded similarly to variation in snowmelt date and early spring temperatures. Furthermore, temporal overlap between flowering and bee activity was similar over the years of this study and was unaffected by variability in snowmelt date or temperature. Nevertheless, the differences among some taxa in their phenological responses suggests that diverging temporal shifts are a possibility for the future.

Seed source regions drive fitness differences in invasive macrophytes

PREMISE

Worldwide, ecosystems are threatened by global changes, including biological invasions. Invasive species arriving in novel environments experience new climatic conditions that can affect their successful establishment. Determining the response of functional traits and fitness components of invasive populations from contrasting environments can provide a useful framework to assess species responses to climate change and the variability of these responses among source populations. Much research on macrophytes has focused on establishment from clonal fragments; however, colonization from sexual propagules has rarely been studied. Our objective was to compare trait responses of plants generated from sexual propagules sourced from three climatic regions but grown under common environmental conditions, using L. peploides subsp. montevidensis as a model taxon.

METHODS

We grew seedlings to reproductive stage in experimental mesocosms under a mediterranean California (MCA) climate from seeds collected in oceanic France (OFR), mediterranean France (MFR), and MCA.

RESULTS

Seed source region was a major factor influencing differences among invasive plants recruiting from sexual propagules of L. peploides subsp. montevidensis. Trait responses of young individual recruits from MCA and OFR, sourced from geographically distant and climatically distinct source regions, were the most different. The MCA individuals accumulated more biomass, flowered earlier, and had higher leaf N concentrations than the OFR plants. Those from MFR had intermediate profiles.

CONCLUSIONS

By showing that the closer a seedling is from its parental climate, the better it performs, this study provides new insights to the understanding of colonization of invasive plant species and informs its management under novel and changing environmental conditions.

Evolutionary genomics can improve prediction of species' responses to climate change

Global climate change (GCC) increasingly threatens biodiversity through the loss of species, and the transformation of entire ecosystems. Many species are challenged by the pace of GCC because they might not be able to respond fast enough to changing biotic and abiotic conditions. Species can respond either by shifting their range, or by persisting in their local habitat. If populations persist, they can tolerate climatic changes through phenotypic plasticity, or genetically adapt to changing conditions depending on their genetic variability and census population size to allow for de novo mutations. Otherwise, populations will experience demographic collapses and species may go extinct. Current approaches to predicting species responses to GCC begin to combine ecological and evolutionary information for species distribution modelling. Including an evolutionary dimension will substantially improve species distribution projections which have not accounted for key processes such as dispersal, adaptive genetic change, demography, or species interactions. However, eco-evolutionary models require new data and methods for the estimation of a species' adaptive potential, which have so far only been available for a small number of model species. To represent global biodiversity, we need to devise large-scale data collection strategies to define the ecology and evolutionary potential of a broad range of species, especially of keystone species of ecosystems. We also need standardized and replicable modelling approaches that integrate these new data to account for eco-evolutionary processes when predicting the impact of GCC on species' survival. Here, we discuss different genomic approaches that can be used to investigate and predict species responses to GCC. This can serve as guidance for researchers looking for the appropriate experimental setup for their particular system. We furthermore highlight future directions for moving forward in the field and allocating available resources more effectively, to implement mitigation measures before species go extinct and ecosystems lose important functions.

Transgenerational Plasticity in Human-Altered Environments

Our ability to predict how species will respond to human-induced rapid environmental change (HIREC) may depend upon our understanding of transgenerational plasticity (TGP), which occurs when environments experienced by previous generations influence phenotypes of subsequent generations. TGP evolved to help organisms cope with environmental stressors when parental environments are highly predictive of offspring environments. HIREC can alter conditions that favored TGP in historical environments by reducing parents' ability to detect environmental conditions, disrupting previous correlations between parental and offspring environments, and interfering with the transmission of parental cues to offspring. Because of the propensity to produce errors in these processes, TGP will likely generate negative fitness outcomes in response to HIREC, though beneficial fitness outcomes may occur in some cases.

Pleiotropy in developmental regulation by flowering-pathway genes: is it an evolutionary constraint?

Pleiotropy occurs when one gene influences more than one trait, contributing to genetic correlations among traits. Consequently, it is considered a constraint on the evolution of adaptive phenotypes because of potential antagonistic selection on correlated traits, or, alternatively, preservation of functional trait combinations. Such evolutionary constraints may be mitigated by the evolution of different functions of pleiotropic genes in their regulation of different traits. Arabidopsis thaliana flowering-time genes, and the pathways in which they operate, are among the most thoroughly studied regarding molecular functions, phenotypic effects, and adaptive significance. Many of them show strong pleiotropic effects. Here, we review examples of pleiotropy of flowering-time genes and highlight those that also influence seed germination. Some genes appear to operate in the same genetic pathways when regulating both traits, whereas others show diversity of function in their regulation, either interacting with the same genetic partners but in different ways or potentially interacting with different partners. We discuss how functional diversification of pleiotropic genes in the regulation of different traits across the life cycle may mitigate evolutionary constraints of pleiotropy, permitting traits to respond more independently to environmental cues, and how it may even contribute to the evolutionary divergence of gene function across taxa.

Phenology in a warming world: differences between native and non-native plant species

Phenology is a harbinger of climate change, with many species advancing flowering in response to rising temperatures. However, there is tremendous variation among species in phenological response to warming, and any phenological differences between native and non-native species may influence invasion outcomes under global warming. We simulated global warming in the field and found that non-native species flowered earlier and were more phenologically plastic to temperature than natives, which did not accelerate flowering in response to warming. Non-native species' flowering also became more synchronous with other community members under warming. Earlier flowering was associated with greater geographic spread of non-native species, implicating phenology as a potential trait associated with the successful establishment of non-native species across large geographic regions. Such phenological differences in both timing and plasticity between native and non-natives are hypothesised to promote invasion success and population persistence, potentially benefiting non-native over native species under climate change.

Species characteristics affect local extinctions

PREMISE OF THE STUDY

Human activities threaten thousands of species with extinction. However, it remains difficult to predict extinction risk for many vulnerable species. Species traits, species characteristics such as rarity or habitat use, and phylogenetic patterns are associated with responses to anthropogenic environmental change and may help predict likelihood of extinction.

METHODS

We used historical botanical data from Kalamazoo County, Michigan, USA, to examine whether species traits (growth form, life history, nitrogen-fixation, photosynthetic pathway), species characteristics (community association, species origin, range edge, habitat specialization, rarity), or phylogenetic relatedness explain local species loss at the county level.

KEY RESULTS

Across Kalamazoo County, prairie species, species at the edge of their native range, regionally rare species, and habitat specialists were most likely to become locally extinct. Prairie species experienced the highest local extinction rates of any habitat type, and among prairie species, regionally rare and specialist species were most vulnerable to loss. We found no evidence for a phylogenetic pattern in plant extinctions.

CONCLUSIONS

Our study illustrates the value of historical datasets for understanding and potentially predicting biodiversity loss. Not surprisingly, rare, specialist species occupying threatened habitats are most at risk of local extinction. As a result, identifying mechanisms to conserve or restore rare or declining species and preventing further habitat destruction may be the most effective strategies for reducing future extinction.

Biological collections for understanding biodiversity in the Anthropocene

Global change has become a central focus of modern biology. Yet, our knowledge of how anthropogenic drivers affect biodiversity and natural resources is limited by a lack of biological data spanning the Anthropocene. We propose that the hundreds of millions of plant, fungal and animal specimens deposited in natural history museums have the potential to transform the field of global change biology. We suggest that museum specimens are underused, particularly in ecological studies, given their capacity to reveal patterns that are not observable from other data sources. Increasingly, museum specimens are becoming mobilized online, providing unparalleled access to physiological, ecological and evolutionary data spanning decades and sometimes centuries. Here, we describe the diversity of collections data archived in museums and provide an overview of the diverse uses and applications of these data as discussed in the accompanying collection of papers within this theme issue. As these unparalleled resources are under threat owing to budget cuts and other institutional pressures, we aim to shed light on the unique discoveries that are possible in museums and, thus, the singular value of natural history collections in a period of rapid change.This article is part of the theme issue 'Biological collections for understanding biodiversity in the Anthropocene'.

Herbarium specimens reveal substantial and unexpected variation in phenological sensitivity across the eastern United States

Phenology is a key biological trait that can determine an organism's survival and provides one of the clearest indicators of the effects of recent climatic change. Long time-series observations of plant phenology collected at continental scales could clarify latitudinal and regional patterns of plant responses and illuminate drivers of that variation, but few such datasets exist. Here, we use the web tool CrowdCurio to crowdsource phenological data from over 7000 herbarium specimens representing 30 diverse flowering plant species distributed across the eastern United States. Our results, spanning 120 years and generated from over 2000 crowdsourcers, illustrate numerous aspects of continental-scale plant reproductive phenology. First, they support prior studies that found plant reproductive phenology significantly advances in response to warming, especially for early-flowering species. Second, they reveal that fruiting in populations from warmer, lower latitudes is significantly more phenologically sensitive to temperature than that for populations from colder, higher-latitude regions. Last, we found that variation in phenological sensitivities to climate within species between regions was of similar magnitude to variation between species. Overall, our results suggest that phenological responses to anthropogenic climate change will be heterogeneous within communities and across regions, with large amounts of regional variability driven by local adaptation, phenotypic plasticity and differences in species assemblages. As millions of imaged herbarium specimens become available online, they will play an increasingly critical role in revealing large-scale patterns within assemblages and across continents that ultimately can improve forecasts of the impacts of climatic change on the structure and function of ecosystems.This article is part of the theme issue 'Biological collections for understanding biodiversity in the Anthropocene'.

Phylogenetically diverse native systems are more resistant to invasive plant species on Robben Island, South Africa 1

Alien invasive species are problematic both economically and ecologically, particularly on islands. As such, understanding how they interact with their environment is necessary to inform invasive species management. Here, we ask the following questions: What are the main functional traits that correlate with invasion success of alien plants on Robben Island? How does phylogenetic structure shape biotic interactions on the island? Using multiple approaches to explore these questions, we found that alien invasive species flower later during the year and for longer period, although flowering phenology was sensitive to alternative starting date. Additionally, we observed that alien invasive species are mostly abiotically pollinated and are generally hermaphroditic whilst their native counterparts rely on biotic pollinators, flower earlier, and are generally dioecious, suggesting that alien invasive and native species use different ecological niches. Furthermore, we found a facilitative interaction between an alien invasive legume and other invasive plants as predicted by the invasional meltdown hypothesis, but this does not influence the phylogenetic structure of plant communities. Finally, phylogenetically diverse set of native species are less receptive to alien invasive species. Collectively, our findings reveal how biotic interactions and phylogenetic relatedness structure alien invasive - native co-existence.

Temperature and photoperiod drive spring phenology across all species in a temperate forest community

Accurate predictions of spring plant phenology with climate change are critical for projections of growing seasons, plant communities and a number of ecosystem services, including carbon storage. Progress towards prediction, however, has been slow because the major cues known to drive phenology - temperature (including winter chilling and spring forcing) and photoperiod - generally covary in nature and may interact, making accurate predictions of plant responses to climate change complex and nonlinear. Alternatively, recent work suggests many species may be dominated by one cue, which would make predictions much simpler. Here, we manipulated all three cues across 28 woody species from two North American forests. All species responded to all cues examined. Chilling exerted a strong effect, especially on budburst (-15.8 d), with responses to forcing and photoperiod greatest for leafout (-19.1 and -11.2 d, respectively). Interactions between chilling and forcing suggest that each cue may compensate somewhat for the other. Cues varied across species, leading to staggered leafout within each community and supporting the idea that phenology is a critical aspect of species' temporal niches. Our results suggest that predicting the spring phenology of communities will be difficult, as all species we studied could have complex, nonlinear responses to future warming.

Rapid alignment of functional trait variation with locality across the invaded range of Sahara mustard (Brassica tournefortii)

PREMISE OF STUDY

Mechanisms by which invasive species succeed across multiple novel environmental contexts are poorly understood. Functional traits show promise for identifying such mechanisms, yet we lack knowledge of which functional traits are critical for success and how they vary across invaded ranges and with environmental features. We evaluated the widespread recent invasion of Sahara mustard (Brassica tournefortii) in the southwestern United States to understand the extent of functional trait variation across the invaded range and how such variation is related to spatial and climatic gradients.

METHODS

We used a common garden approach, growing two generations of plants in controlled conditions sourced from 10 locations across the invaded range. We measured variation within and among populations in phenological, morphological, and physiological traits, as well as performance.

KEY RESULTS

We found nine key traits that varied among populations. These traits were related to phenology and early growth strategies, such as the timing of germination and flowering, as well as relative allocation of biomass to reproduction and individual seed mass. Trait variation was related most strongly to variation in winter precipitation patterns across localities, though variations in temperature and latitude also had significant contributions.

CONCLUSIONS

Our results identify key functional traits of this invasive species that showed significant variation among introduced populations across a broad geographic and climatic range. Further, trait variation among populations was strongly related to key climatic variables, which suggests that population divergence in these traits may explain the successful colonization of Sahara mustard across its invaded US range.

Genetic adaptation as a biological buffer against climate change: Potential and limitations

Climate change profoundly impacts ecosystems and their biota, resulting in range shifts, novel interactions, food web alterations, changed intensities of host-parasite interactions, and extinctions. An increasing number of studies have documented evolutionary changes in traits such as phenology and thermal tolerance. In this opinion paper, we argue that, while evolutionary responses have the potential to provide a buffer against extinctions or range shifts, a number of constraints and complexities blur this simple prediction. First, there are limits to evolutionary potential both in terms of genetic variation and demographic effects, and these limits differ strongly among taxa and populations. Second, there can be costs associated with genetic adaptation, such as a reduced evolutionary potential towards other (human-induced) environmental stressors or direct fitness costs due to tradeoffs. Third, the differential capacity of taxa to genetically respond to climate change results in novel interactions because different organism groups respond to a different degree with local compared to regional (dispersal and range shift) responses. These complexities result in additional changes in the selection pressures on populations. We conclude that evolution can provide an initial buffer against climate change for some taxa and populations but does not guarantee their survival. It does not necessarily result in reduced extinction risks across the range of taxa in a region or continent. Yet, considering evolution is crucial, as it is likely to strongly change how biota will respond to climate change and will impact which taxa will be the winners or losers at the local, metacommunity and regional scales.

Warming delays the phenological sequences of an autumn-flowering invader

Phenology can play an important role in driving plant invasions; however, little is known about how climate warming, nitrogen (N) deposition, and invasion stages influence the phenological sequences of autumn-flowering invaders in a subtropical climate. Accordingly, we conducted an experiment to address the effects of experimental warming, N-addition, and community types on the first inflorescence buds, flowering, seed-setting, and dieback of invasive Solidago canadensis. Warming delayed the onset of first inflorescence buds, flowering, seed-setting, and dieback; N-addition did not influence these four phenophases; community types influenced the onset of first seed-setting but not the other phenological phases. Seed-setting was more sensitive to experimental manipulations than the other phenophases. The onset of first inflorescence buds, flowering, and seed-setting was marginally or significantly correlated with ramet height but not ramet numbers. Our results suggest that future climate warming might delay the phenological sequences of autumn-flowering invaders and some phenophases can shift with invasion stages.

Experimental warming advances phenology of groundlayer plants at the boreal-temperate forest ecotone

PREMISE OF THE STUDY

Changes to plant phenology have been linked to warmer temperatures caused by climate change. Despite the importance of the groundlayer to community and forest dynamics, few warming experiments have focused on herbaceous plant and shrub phenology.

METHODS

Using a field study in Minnesota, United States, we investigated phenological responses of 16 species to warming over five growing seasons (2009-2013) at two sites, under two canopy covers, and in three levels of simultaneous above- and belowground warming: ambient temperature, ambient +1.7°C and ambient +3.4°C. We tested whether warming led to earlier phenology throughout the growing season and whether responses varied among species and years and depended on canopy cover.

KEY RESULTS

Warming extended the growing season between 11-30 days, primarily through earlier leaf unfolding. Leaf senescence was delayed for about half of the species. Warming advanced flowering across species, especially those flowering in August, with modest impacts on fruit maturation for two species. Importantly, warming caused more than half of the species to either converge or diverge phenologically in relation to each other, suggesting that future warmed climate conditions will alter phenological relationships of the groundlayer. Warm springs elicited a stronger advance of leaf unfolding compared to cool spring years. Several species advanced leaf unfolding (in response to warming) more in the closed canopy compared to the open.

CONCLUSIONS

Climate warming will extend the growing season of groundlayer species in the boreal-temperate forest ecotone and alter the synchrony of their phenology.

Short-term responses to warming vary between native vs. exotic species and with latitude in an early successional plant community

Climate change is expected to favor exotic plant species over native species, because exotics tend to have wider climatic tolerances and greater phenological plasticity, and also because climate change may intensify enemy release. Here, we examine direct effects of warming (+ 1.8 °C above ambient) on plant abundance and phenology, as well as indirect effects of warming propagated through herbivores, in two heavily invaded plant communities in Michigan, USA, separated by approximately three degrees latitude. At the northern site, warming increased exotic plant abundance by 19% but decreased native plant abundance by 31%, indicating that exotic species may be favored in a warmer world. Warming also resulted in earlier spring green-up (1.65 ± 0.77 days), earlier flowering (2.18 ± 0.92 days), and greater damage by herbivores (twofold increase), affecting exotic and native species equally. Contrary to expectations, native and exotic plants experienced similar amounts of herbivory. Warming did not have strong ecological effects at the southern site, only resulting in a delay of flowering time by 2.42 ± 0.83 days for both native and exotic species. Consistent with the enemy release hypothesis, exotic plants experienced less herbivory than native plants at the southern site. Herbivory was lower under warming for both exotic and native species at the southern site. Thus, climate warming may favor exotic over native plant species, but the response is likely to depend on additional environmental and individual species' traits.

Widespread sampling biases in herbaria revealed from large-scale digitization

Nonrandom collecting practices may bias conclusions drawn from analyses of herbarium records. Recent efforts to fully digitize and mobilize regional floras online offer a timely opportunity to assess commonalities and differences in herbarium sampling biases. We determined spatial, temporal, trait, phylogenetic, and collector biases in c. 5 million herbarium records, representing three of the most complete digitized floras of the world: Australia (AU), South Africa (SA), and New England, USA (NE). We identified numerous shared and unique biases among these regions. Shared biases included specimens collected close to roads and herbaria; specimens collected more frequently during biological spring and summer; specimens of threatened species collected less frequently; and specimens of close relatives collected in similar numbers. Regional differences included overrepresentation of graminoids in SA and AU and of annuals in AU; and peak collection during the 1910s in NE, 1980s in SA, and 1990s in AU. Finally, in all regions, a disproportionately large percentage of specimens were collected by very few individuals. We hypothesize that these mega-collectors, with their associated preferences and idiosyncrasies, shaped patterns of collection bias via 'founder effects'. Studies using herbarium collections should account for sampling biases, and future collecting efforts should avoid compounding these biases to the extent possible.