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1. Chilling consequences: Herbarium records reveal earlier reproductive phenology of winter annual gladecress in a wetter, cooler climate

   https://doi.org/10.1002/ppp3.10095  

   Banaszak, Caitlin ; Grinath, Joshua B. ; Herlihy, Christopher R. ( January 2020 , PLANTS, PEOPLE, PLANET)

   Networks of digitized herbarium records are rich resources for understanding plant responses to climate change. While the climate is warming globally, some localities are experiencing climate cooling, the effects of which are poorly understood. Our herbarium‐based study of a geographically restricted species shows that the timing of reproduction can shift earlier as the climate becomes cooler and wetter. Local variation in climate change may be a key factor driving the high variability of changes observed in plant reproduction and climate cooling should be considered along with other global change drivers. This will help enable accurate predictions for the successful management of climate change effects.

   Summary

   Plant phenological responses to global warming are well studied. However, while many locations are experiencing increased temperatures, some locations are experiencing climate cooling. Little work has been conducted to understand plant phenological responses to cooling trends, much less the combined effects of cooling and other factors, such as changing precipitation. Furthermore, studies based on herbarium specimens have been instrumental in demonstrating plant responses to global warming; but to our knowledge, herbarium records have not been used to investigate responses to cooling.

   We collected data from 98 years of herbarium records to evaluate whether the reproductive phenology (flowering/fruiting) of an annual mustard, cedar gladecress (Leavenworthia stylosa), has changed as the climate has become cooler and wetter in central Tennessee, USA. Additionally, we conducted two field experiments to assess reproductive consequences of different flowering times.

   Over the last century, gladecress reproductive phenology has shifted 2.1 days earlier per decade, concurrent with wetter conditions during germination and cooler conditions during reproduction. Field experiments showed that plants with extremely early and moderately early flowering had equivalent reproduction, but these plants had greater reproduction than intermediate‐ and late‐flowering plants.

   Counter to expectations from global warming studies, our work demonstrates that climate cooling and greater rainfall can result in earlier plant reproductive phenology, potentially due to asymmetric selection for early flowering. Future studies may need to consider climate cooling along with other global change factors to fully explain changes in plant phenology. Our understanding of plant responses to climate cooling can be enhanced through additional herbarium‐based research.

    

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2. Where should they come from? Where should they go? Several measures of seed source locality fail to predict plant establishment in early prairie restorations

   https://doi.org/10.1002/2688-8319.12223  

   Pizza, Riley B. ; Foster, Jared ; Brudvig, Lars A. ( April 2023 , Ecological Solutions and Evidence)

   During the “decade on restoration,” we must understand how to reliably re‐establish native plant populations. When establishing populations through seed addition, practitioners often prioritize obtaining seed from locations geographically near the restoration site (i.e. “local seed sourcing”). They are assumed to be under similar environmental conditions to the restoration site and should establish more robust plant populations and preserve local biotic interactions better than seeds sourced from further away. However, this assumption remains virtually untested in realistic restoration settings and the importance of seed sourcing, relative to other factors such as seeding rate and management regimes, is unclear.

   To determine if seed sourcing decision impacts plant establishment, abundance and phenology, we developed a partnership between university‐researchers and a native seed producer that kept records on where their seed was sourced from and where it was planted. At each site, we recorded the abundance and phenological stage of five commonly used tallgrass prairie restoration species seeded at 24 sites undergoing restoration across Michigan. We considered two measures of seed source locality: geographic distance (seeds were sourced from locations 6–750 km away from their respective restoration sites) and environmental distance. We also obtained data on the seeding rate and post‐seeding management at each site.

   We found that no measure of seed source locality predicted the likelihood of plant establishment or abundance at restoration sites. However, sites sown with seed from further away, or from cooler and wetter climates, had a greater proportion of flowering individuals earlier in the season. Finally, sites with higher seeding rates had greater plant abundance, and post‐seeding management of the restoration site increased the likelihood a species would establish by 36%.

   Overall, these results support that seed sourcing decisions did not impact plant establishment or abundance in our system. However, using less‐local seed sources may alter flowering phenology.

   Our results suggest that tallgrass prairie restoration efforts should prioritize higher seeding rates, post‐seeding management, and might expand the region seed sources are considered “local”, though this may impact flowering phenology. Future research leveraging native seed producer records can help answer critical questions about restoration seed sourcing.

    

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3. The individual and combined effects of snowmelt timing and frost exposure on the reproductive success of montane forbs

   https://doi.org/10.1111/1365-2745.13152  

   Pardee, Gabriella L. ; Jensen, Isaac O. ; Inouye, David W. ; Irwin, Rebecca E. ; Satake, ed., Akiko ( March 2019 , Journal of Ecology)

   Changes from historic weather patterns have affected the phenology of many organisms world‐wide. Altered phenology can introduce organisms to novel abiotic conditions during growth and modify species interactions, both of which could drive changes in reproduction.

   We explored how climate change can alter plant reproduction using an experiment in which we manipulated the individual and combined effects of snowmelt timing and frost exposure, and measured subsequent effects on flowering phenology, peak flower density, frost damage, pollinator visitation and reproduction of four subalpine wildflowers. Additionally, we conducted a pollen‐supplementation experiment to test whether the plants in our snowmelt and frost treatments were pollen limited for reproduction. The four plants included species flowering in early spring to mid‐summer.

   The phenology of all four species was significantly advanced, and the bloom duration was longer in the plots from which we removed snow, but with species‐specific responses to snow removal and frost exposure in terms of frost damage, flower production, pollinator visitation and reproduction. The two early blooming species showed significant signs of frost damage in both early snowmelt and frost treatments, which negatively impacted reproduction for one of the species. Further, we recorded fewer pollinators during flowering for the earliest‐blooming species in the snow removal plots. We also found lower fruit and seed set for the early blooming species in the snow removal treatment, which could be attributed to the plants growing under unfavourable abiotic conditions. However, the later‐blooming species escaped frost damage even in the plots where snow was removed, and experienced increased pollinator visitation and reproduction.

   Synthesis.This study provides insight into how plant communities could become altered due to changes in abiotic conditions, and some of the mechanisms involved. While early blooming species may be at a disadvantage under climate change, species that bloom later in the season may benefit from early snowmelt, suggesting that climate change has the potential to reshape flowering communities.

    

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4. Reproductive losses due to climate change‐induced earlier flowering are not the primary threat to plant population viability in a perennial herb

   https://doi.org/10.1111/1365-2745.13146  

   Iler, Amy M. ; Compagnoni, Aldo ; Inouye, David W. ; Williams, Jennifer L. ; CaraDonna, Paul J. ; Anderson, Aaron ; Miller, Tom E. X. ; Catford, ed., Jane ( March 2019 , Journal of Ecology)

   Despite a global footprint of shifts in flowering phenology in response to climate change, the reproductive consequences of these shifts are poorly understood. Furthermore, it is unknown whether altered flowering times affect plant population viability.

   We examine whether climate change‐induced earlier flowering has consequences for population persistence by incorporating reproductive losses from frost damage (a risk of early flowering) into population models of a subalpine sunflower (Helianthella quinquenervis). Using long‐term demographic data for three populations that span the species’ elevation range (8–15 years, depending on the population), we first examine how snowmelt date affects plant vital rates. To verify vital rate responses to snowmelt date experimentally, we manipulate snowmelt date with a snow removal experiment at one population. Finally, we construct stochastic population projection models and Life Table Response Experiments for each population.

   We find that populations decline (λ_s < 1) as snowmelt dates become earlier. Frost damage to flower buds, a consequence of climate change‐induced earlier flowering, does not contribute strongly to population declines. Instead, we find evidence that negative effects on survival, likely due to increased drought risk during longer growing seasons, drive projected population declines under earlier snowmelt dates.

   Synthesis.Shifts in flowering phenology are a conspicuous and important aspect of biological responses to climate change, but here we show that the phenology of reproductive events can be unreliable measures of threats to population persistence, even when earlier flowering is associated with substantial reproductive losses. Evidence for shifts in reproductive phenology, along with scarcer evidence that these shifts actually influence reproductive success, are valuable but can paint an incomplete and even misleading picture of plant population responses to climate change.

    

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5. Warmer springs increase potential for temporal reproductive isolation among habitat patches in subalpine flowering plants

   https://doi.org/10.1111/1365-2745.14175  

   Rivest, Sébastien ; Inouye, Brian D. ; Forrest, Jessica R. K. ( August 2023 , Journal of Ecology)

   Flowering phenology can vary considerably even at fine spatial scales, potentially leading to temporal reproductive isolation among habitat patches. Climate change could alter flowering synchrony, and hence temporal isolation, if plants in different microhabitats vary in their phenological response to climate change. Despite the importance of temporal isolation in determining patterns of gene flow, and hence population genetic structure and local adaptation, little is known about how changes in climate affect temporal isolation within populations.

   Here, we use flowering phenology and floral abundance data of 50 subalpine plant species over 44 years to test whether temporal isolation between habitat patches is affected by spring temperature. For each species and year, we analysed temporal separation in peak flowering and flowering overlap between habitat patches separated by 5–950 m.

   Across our study species, warmer springs were associated with more temporal differentiation in flowering peaks among habitat patches, and less flowering overlap, increasing potential for temporal isolation within populations.

   Synthesis. By reducing opportunities for mating among plants in nearby habitat patches, our results suggest that warmer springs may reduce opportunities for gene flow within populations, and, consequently, the capacity of plant populations to adapt to environmental changes.

    

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