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

   https://doi.org/10.1002/ajb2.1684  

   Zettlemoyer, Meredith A. ; Renaldi, Katarina ; Muzyka, Michael D. ; Lau, Jennifer A. ( June 2021 , American Journal of Botany)

   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.

   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.

   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.

   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.

    

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2. 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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3. Herbarium records provide reliable phenology estimates in the understudied tropics

   https://doi.org/10.1101/2022.08.19.504574  

   Park, D. S. ; Lyra, G.M. ; Ellison, A.M. ; Maruyama, R.K.B. ; Torquato, D. ; Asprino, R.C. ; Cook, B.I. ; Davis, C.C. ( August 2022 , bioRxiv)

   Plant phenology has been shifting dramatically in response to climate change, a shift that may have significant and widespread ecological consequences. Of particular concern are tropical biomes, which represent the most biodiverse and imperiled regions of the world. However, compared to temperate floras, we know little about phenological responses of tropical plants because long-term observational datasets from the tropics are sparse. Herbarium specimens have greatly increased our phenological knowledge in temperate regions, but similar data have been underutilized in the tropics and their suitability for this purpose has not been broadly validated. Here, we compare phenological estimates derived from field observational data (i.e., plot surveys) and herbarium specimens at various spatial and taxonomic scales to determine whether specimens can provide accurate estimations of reproductive timing and its spatial variation. Here we demonstrate that phenological estimates from field observations and herbarium specimens coincide well. Fewer than 5% of the species exhibited significant differences between flowering periods inferred from field observations versus specimens regardless of spatial aggregation. In contrast to studies based on field records, herbarium specimens sampled much larger geographic and climatic ranges, as has been documented previously for temperate plants, and effectively captured phenological responses across varied environments. Herbarium specimens are verified to be a vital resource for closing the gap in our phenological knowledge of tropical systems. Tropical plant reproductive phenology inferred from herbarium records are widely congruent with field observations, suggesting that they can (and should) be used to investigate phenological variation and their associated environmental cues more broadly across tropical biomes. 

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4. Prairie plant phenology driven more by temperature than moisture in climate manipulations across a latitudinal gradient in the Pacific Northwest, USA

   https://doi.org/10.1002/ece3.4995  

   Reed, Paul B. ; Pfeifer‐Meister, Laurel E. ; Roy, Bitty A. ; Johnson, Bart R. ; Bailes, Graham T. ; Nelson, Aaron A. ; Boulay, Margaret C. ; Hamman, Sarah T. ; Bridgham, Scott D. ( February 2019 , Ecology and Evolution)

   Plant phenology will likely shift with climate change, but how temperature and/or moisture regimes will control phenological responses is not well understood. This is particularly true in Mediterranean climate ecosystems where the warmest temperatures and greatest moisture availability are seasonally asynchronous. We examined plant phenological responses at both the population and community levels to four climate treatments (control, warming, drought, and warming plus additional precipitation) embedded within three prairies across a 520 km latitudinal Mediterranean climate gradient within the Pacific Northwest, USA. At the population level, we monitored flowering and abundances in spring 2017 of eight range‐restricted focal species planted both within and north of their current ranges. At the community level, we used normalized difference vegetation index (NDVI) measured from fall 2016 to summer 2018 to estimate peak live biomass, senescence, seasonal patterns, and growing season length. We found that warming exerted a stronger control than our moisture manipulations on phenology at both the population and community levels. Warming advanced flowering regardless of whether a species was within or beyond its current range. Importantly, many of our focal species had low abundances, particularly in the south, suggesting that establishment, in addition to phenological shifts, may be a strong constraint on their future viability. At the community level, warming advanced the date of peak biomass regardless of site or year. The date of senescence advanced regardless of year for the southern and central sites but only in 2018 for the northern site. Growing season length contracted due to warming at the southern and central sites (~3 weeks) but was unaffected at the northern site. Our results emphasize that future temperature changes may exert strong influence on the timing of a variety of plant phenological events, especially those events that occur when temperature is most limiting, even in seasonally water‐limited Mediterranean ecosystems.

    

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5. Fine‐scale environmental heterogeneity and spatial niche partitioning among spring‐flowering forest herbs

   https://doi.org/10.1002/ajb2.1593  

   Beck, Jared J. ; Givnish, Thomas J. ( January 2021 , American Journal of Botany)

   Environmental heterogeneity influences plant distributions and diversity at several spatial scales. In temperate forests, fine‐scale environmental variation may promote local coexistence among herbaceous species by allowing plants to spatially partition microsites within forest stands. Here we argue that shallow soils, low soil water‐holding capacity and fertility, and reduced light near tree boles should favor short, shallow‐rooted, evergreen species likeAnemone acutilobawith low moisture, nutrient, and light requirements. Farther from trees, richer, deeper soils should favor taller, deeper‐rooted herbs with greater moisture and nutrient demands, such asSanguinaria canadensisandTrillium flexipes.

   We tested these hypotheses by mapping the fine‐scale distributions ofAnemone,Sanguinaria, andTrilliumindividuals within a 50 × 50 m plot, comparing local species’ distributions with respect to soil depth and proximity to neighboring trees, and characterizing intraspecific and interspecific spatial associations.

   Local plant distributions were consistent with our predictions based on leaf height, physiology, and phenology.Anemonewas found in microsites on shallower soils and closer to trees than eitherSanguinariaorTrillium. In all three species, individual plants were spatially aggregated within 2 m, but spatially segregated from individuals of the other species beyond 2 m.

   Differential plant responses to fine‐scale environmental heterogeneity and observed spatial associations suggest that local species‐environment associations could facilitate coexistence. These findings illustrate how fine‐scale environmental heterogeneity coupled with phenological and physiological differences likely contribute to spatial niche partitioning among spring‐flowering forest herbs and maintain high local plant diversity within temperate forests.

    

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