More Like this

1. Seasonal patterns of increases in stem girth, vessel development, and hydraulic function in deciduous tree species

   https://doi.org/10.1093/aob/mcac032  

   Valdovinos-Ayala, Jessica ; Robles, Catherine ; Fickle, Jaycie C. ; Pérez-de-Lis, Gonzalo ; Pratt, R. Brandon ; Jacobsen, Anna L. ( March 2022 , Annals of Botany)

   The onset of spring growth and vessel formation were examined within three deciduous woody plant species, Acer rubrum, Populus balsamifera ssp. trichocarpa and Quercus rubra. We were broadly interested in the lag between the onset of girth expansion and the formation of mature and hydraulically conductive vessels within the new xylem.

   Dendrometers were installed on 20 trees (6–7 per species), and expansion of both bole and distal stems was monitored throughout the growing season in a common garden. For each species, four to six distal stems were harvested every other week for anatomical examination of vessel formation. Additionally, for Populus and Quercus, hydraulic conductivity measurements and active xylem staining were completed on all stem samples.

   For all three species, the timing of girth expansion was similar. Expansion of distal branches occurred 12–37 d earlier than that of the bole. Vessel formation initiated several weeks prior to leaf-out, but no new earlywood vessels were mature at the time of bud break for Acer and Populus and only a few were present in Quercus. Initial stem girth expansion occurred 2 to >6 weeks before the maturation of the first current-year vessels, and there was an additional delay of up to 4 weeks before mature vessels became hydraulically functional. Hydraulic conductivity was strongly correlated with the number and diameter of stained vessels.

   Bud break and leaf expansion relied predominantly on water supplied by vessels formed during prior seasons. Early-season activity is likely affected by the function of older xylem vessels and the environmental factors that influence their structure and function. Understanding the functional lifespan of vessels and the varying contributions of new and older vessels to conductivity are critical to understanding of the phenology and vascular function of long-lived woody plants in response to changing climates.

    

   more » « less
2. Coordination of spring vascular and organ phenology in deciduous angiosperms growing in seasonally cold climates

   https://doi.org/10.1111/nph.17289  

   Savage, Jessica A. ; Chuine, Isabelle ( March 2021 , New Phytologist)

   In seasonally cold climates, many woody plants tolerate chilling and freezing temperatures by ceasing growth, shedding leaves and entering dormancy. At the same time, transport within these plants often decreases as the vascular system exhibits reduced functionality. As spring growth requires water and nutrients, we ask the question: how much does bud, leaf and flower development depend on the vasculature in spring? In this review, we present what is known about leaf, flower and vascular phenology to sort out this question. In early stages of bud development, buds rely on internal resources and do not appear to require vascular support. The situation changes during organ expansion, after leaves and flowers reconnect to the stem vascular system. However, there are major gaps in our understanding of the timing of vascular development, especially regarding the phloem, as well as the synchronization among leaves, flowers, stem and root vasculature. We believe these gaps are mainly the outcome of research completed in silo and urge future work to take a more integrative approach. We highlight current challenges and propose future directions to make rapid progress on this important topic in upcoming years.

    

   more » « less
3. Co‐occurrence patterns at four spatial scales implicate reproductive processes in shaping community assembly in clovers

   https://doi.org/10.1111/1365-2745.13776  

   Christie, Kyle ; Harrison, Susan P. ; Friesen, Maren L. ; Strauss, Sharon Y. ( October 2021 , Journal of Ecology)

   Competition, niche differences and chance all contribute to community assembly; yet, the role of reproductive interactions between species is often less appreciated. Closely related plant species that share floral form, phenology and habitat often interact through pollination. They potentially facilitate pollinator attraction, compete for pollination services and/or exchange pollen. If reproductive processes are important to co‐occurrence, we predicted that fitness costs of heterospecific pollen transfer or pollen limitation should result in lower rates of co‐occurrence among outcrossing congeners. In contrast, selfers, which may be less exposed to heterospecific pollen, and/or less negatively affected by it, should co‐occur more frequently.

   Flower size is an excellent proxy for mating system in clovers. Using herbarium records and three independent field datasets, we documented co‐occurrence patterns ofTrifoliumat 1 m²–1 km²scales in California. Using a randomization procedure to reshuffle matrices of community membership, we generated null hypotheses for the expected composition of large‐ and small‐flowered species inTrifoliumcommunities of different sizes.

   Across all spatial scales, large‐flowered outcrossers were over‐represented at sites lacking congeners, but under‐represented in communities with multiple congeners. Conversely, small‐flowered selfers often occupied sites with multiple otherTrifoliumspecies. Patterns for plant height and leaf size, which are weakly or strongly correlated with flower size, did not explain co‐occurrence patterns as robustly. Regression analysis and model selection corroborated the null model analyses, indicating that the likelihood of co‐occurrence decreased as flower size, and thus reliance on outcrossing, increased.

   Synthesis. This study suggests that reproductive traits and processes may be significant contributors to community assembly and co‐occurrence in flowering plants.

    

   more » « less
4. Trails‐as‐transects: phenology monitoring across heterogeneous microclimates in Acadia National Park, Maine

   https://doi.org/10.1002/ecs2.2626  

   McDonough MacKenzie, Caitlin ; Primack, Richard B. ; Miller‐Rushing, Abraham J. ( March 2019 , Ecosphere)

   Climate‐driven shifts in phenology, which are being observed worldwide, affect ecosystem services, trophic interactions, and community composition, presenting challenges to managers in protected areas. Resource management benefits from local, species‐specific phenology information. However, phenology monitoring programs in heterogeneous landscapes typically require serendipitous historical records or many years of contemporary data before trends in phenological responses to changes in climate can be analyzed. Here, we used a trails‐as‐transects approach to rapidly accumulate monitoring data across environmental gradients on three mountains in Acadia National Park, Maine,USA, and compared our results to phenological changes observed in Concord, Massachusetts,USA. In four years of intensive monitoring of transects on three mountains, we found large variability in spring temperatures across the mountains, but consistent patterns of advancing flower and leaf phenology in warmer microclimates. Reduced sampling intensity would have yielded similar results, but a shorter duration would not have revealed these patterns. The plants in Acadia responded to warming spring temperatures by shifting leaf and flower phenology in the same direction (earlier), but at a reduced rate (as measured in d/°C), in comparison with plants in southern New England (e.g., Concord, Massachusetts,USA). Our approach takes advantage of topographical complexity and associated microclimate gradients to substitute for long time series, allowing for rapid assessment of phenological response to climate. Other climate gradients (e.g., urban‐to‐rural, latitudinal, or coastal‐to‐inland) could work similarly. This intensive monitoring over a short time period quickly builds a robust dataset and can inform management decisions regarding future monitoring strategies, including sampling designs for citizen science‐based phenology monitoring programs.

    

   more » « less
5. 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.

    

   more » « less