Abstract: Climate change is leading to species redistributions. In the tundra biome, shrubs are generally expanding, but not all tundra shrub species will benefit from warming. Winner and loser species, and the characteristics that may determine success or failure, have not yet been fully identified. Here, we investigate whether past abundance changes, current range sizes and projected range shifts derived from species distribution models are related to plant trait values and intraspecific trait variation. We combined 17,921 trait records with observed past and modelled future distributions from 62 tundra shrub species across three continents. We found that species with greater variation in seed mass and specific leaf area had larger projected range shifts, and projected winner species had greater seed mass values. However, trait values and variation were not consistently related to current and projected ranges, nor to past abundance change. Overall, our findings indicate that abundance change and range shifts will not lead to directional modifications in shrub trait composition, since winner and loser species share relatively similar trait spaces.

Abstract: The Arctic is warming twice as fast as the rest of the globe. Graminoid, deciduous shrub, and evergreen shrub cover has increased in some regions, but not others. To better understand why plant responses vary across regions, we compared change in plant cover over time with nine functional traits of 12 dominant species in three regions of northern Alaska (Utqiaġvik, Atqasuk, and Toolik Lake). Cover was measured three times from 2008 to 2018. Repeated-measures analysis of variance (ANOVA) found that one species — Carex aquatilis — showed significant change in cover over time, increasing by 12.7% at Atqasuk. Canonical correspondence analysis suggested a relationship between shifts in species cover and traits, but Pearson and Spearman rank correlations did not find a significant trend for any trait when analyzed individually. Investigation of community-weighted means (CWMs) for each trait revealed no significant changes over time for any trait in any region. By comparison, estimated ecosystem values for several traits important to ecosystem functioning showed consistent increases over time in two regions (Utqiaġvik and Atqasuk). Our results indicate that vascular plant community composition and function have remained consistent over time; however, documented increases in total plant cover have important implications for ecosystem functioning.

Abstract: The Arctic is experiencing rapid climate change. This research documents changes to tundra vegetation near Atqasuk and Utqiaġvik, Alaska. At each location, 30 plots were sampled annually from 2010 to 2019 using a point frame. For every encounter, we recorded the height and classified it into eight groupings (deciduous shrubs, evergreen shrubs, forbs, graminoids, bryophytes, lichens, litter, and standing dead vegetation); for vascular plants we also identified the species. We found an increase in plant stature and cover over time, consistent with regional warming. Graminoid cover and height increased at both sites, with a 5-fold increase in cover in Atqasuk. At Atqasuk, the cover and height of shrubs and forbs increased. Species diversity decreased at both the sites. Year was generally the strongest predictor of vegetation change, suggesting a cumulative change over time; however, soil moisture and soil temperature were also predictors of vegetation change. We anticipate that plants in the region will continue to grow taller as the region warms, resulting in greater plant cover, especially of graminoids and shrubs. The increase in plant cover and accumulation of litter may negatively impact non-vascular plants. Continued changes in community structure will impact energy balance and carbon cycling and may have regional and global consequences.

Abstract: Increases in shrub growth and canopy cover are well documented community responses to climate warming in the Arctic. An important consequence of larger deciduous shrubs is shading of prostrate plant species, many of which are important sources of nectar and berries. Here, we present the impact of a shading experiment on two prostrate shrubs, Vaccinium vitis-idaea L. and Arctous alpina L., in northern Alaska over two growing seasons. We implemented three levels of shading (no shade, 40% shade, and 80% shade) in dry heath and moist acidic tundra. Plots were monitored for soil moisture content, surface temperature, normalized difference vegetation index (NDVI), and flowering. Shading was shown to, on average, lower surface temperature (0.7 °C to 5.3 °C) and increase soil moisture content (0.5% to 5.6%) in both communities. Both species- and plot-level NDVI values were delayed in timing of peak values (7 to 13 days) and decreased at the highest shading. Flower abundance of both species was lower in shaded plots and peak flowering was delayed (3 to 8 days) compared with controls. Changes in timing may result in phenological mismatches and can impact other trophic levels in the Arctic as both the flowers and resulting berries are important food sources for animals.

Abstract: Introduction: Toxoplasmosis is a rare complication of allogeneic hematopoietic stem cell transplantation (AlloHSCT) usually through reactivation in a previously seropositive recipient, and is associated with mortality as high as 60% (Paccoud et al. BMT 2020). Seroprevalence in the population varies ranging from 5% or lower in North America to over 50% in France. Risk factors for reactivation include immune suppression, seronegative donors, cord blood grafts, and lack of adequate antimicrobial prophylaxis (Robin et al. BBMT 2019). We sought to evaluate the outcomes of patients with toxoplasma reactivation after undergoing AlloHSCT in the modern era. Methods: This study was a retrospective single center analysis of all patients who underwent AlloHSCT between January 2012 and June 2021 at our center. Primary objectives were to assess the incidence of toxoplasma reactivation and the effects of reactivation on survival. Patients were identified in the department database and relevant demographic and clinical data were extracted. Results of toxoplasma testing [IgG serology and polymerase chain reaction (PCR)] were collected and verified by manual chart review. Patients with negative toxoplasma serology and/or missing serology or PCR data were excluded from analysis. Reactivation was defined as positive PCR in a seropositive patient. Toxoplasma reactivation associations were assessed by logistic regression models. Overall Survival (OS) was estimated using the Kaplan-Meier method and differences compared using the log-rank test. Cox proportional hazards models were used for survival associations. Cumulative incidence of non-relapse mortality (NRM) was determined using competing risks method. This study was approved by the institutional board review (IRB) committee at our center. Results: A total of 370 patients who received AlloHSCT and had a positive toxoplasma IgG were identified. Fifty-two patients had missing toxoplasma PCR and 4 did not meet eligibility criteria and were excluded. Twenty-two (7%) out of the remaining 314 seropositive patients experienced toxoplasma reactivation as confirmed by positive PCR. Median age in the reactivation group was 55 years, and patients were mostly white males with myeloid neoplasms who underwent AlloHSCT in first complete remission using nonmyeloablative conditioning and a matched unrelated donor (table 1). No significant differences in baseline characteristics were seen between the seropositive only and the reactivation groups, except for antimicrobial prophylaxis use (P & lt;0.001). Fifty-nine percent of patients (13 out of 22) in the reactivation group were on toxoplasma prophylaxis compared to 93% (273 out of 292) in the seropositive patients without reactivation. Sixteen out of the 22 (73%) patients with reactivation developed clinical symptoms while 6 (27%) had asymptomatic reactivation. Antimicrobial prophylaxis only with either pentamidine, atovaquone, trimethoprim/sulfamethoxazole but not dapsone, was associated with lower risk of developing reactivation (table 2). With a median follow up of 15.4 months (0.3-98.9), the median OS was 9.6 months in patients with reactivation versus 58.5 months in seropositive patients without reactivation [HR, 2.06; (95% CI, 1.21 to 3.52); P=0.008] (figure 1). NRM was also higher in the reactivation group [HR, 2.61; (95% CI, 1.34 to 5.11); P=0.005] (figure 2). Specifically, day 100, 1-year and 2-year NRM were higher in the reactivation group versus (vs) seropositive patients (36% vs 10%, 41% vs 18%, and 47% vs 20% respectively). Toxoplasma reactivation was associated with worse OS and increased NRM in univariable analysis however this did not reach statistical significance in multivariable analysis. Conclusion: Toxoplasma reactivation in seropositive AlloSCT patients remains low at our center at around 7%. Toxoplasma reactivation is associated with worse outcomes after AlloHSCT and reactivation could be mitigated by improved compliance with antimicrobial prophylaxis. Figure 1 Figure 1. Disclosures Mehta: Kadmon: Research Funding; Incyte: Research Funding; CSLBehring: Research Funding; Syndax: Research Funding. Shah: Amgen: Consultancy; Bluebird Bio: Research Funding; BMS/Celgene: Research Funding; CareDx: Consultancy; CSL Behring: Consultancy; GSK: Consultancy; Indapta Therapeutics: Consultancy; Janssen: Research Funding; Karyopharm: Consultancy; Kite: Consultancy; Nektar: Research Funding; Oncopeptides: Consultancy; Poseida: Research Funding; Precision Biosciences: Research Funding; Sanofi: Consultancy; Sutro Biopharma: Research Funding; Teneobio: Research Funding. Hosing: Nkarta Therapeutics: Membership on an entity's Board of Directors or advisory committees. Rezvani: Pharmacyclics: Other: Educational grant, Research Funding; Affimed: Other: License agreement and research agreement; education grant, Patents & Royalties, Research Funding; Takeda: Other: License agreement and research agreement, Patents & Royalties; GSK: Other: Scientific Advisory Board ; Caribou: Other: Scientific Advisory Board; GemoAb: Other: Scientific Advisory Board ; AvengeBio: Other: Scientific Advisory Board ; Virogin: Other: Scientific Advisory Board ; Navan Technologies: Other: Scientific Advisory Board; Bayer: Other: Scientific Advisory Board . Qazilbash: Janssen: Research Funding; Bristol-Myers Squibb: Other: Advisory Board; Angiocrine: Research Funding; Amgen: Research Funding; Oncopeptides: Other: Advisory Board; Biolline: Research Funding; NexImmune: Research Funding. Popat: Bayer: Research Funding; Abbvie: Research Funding; Novartis: Research Funding; Incyte: Research Funding. Shpall: Takeda: Patents & Royalties; Navan: Consultancy; Novartis: Honoraria; Magenta: Honoraria; Affimed: Patents & Royalties; Novartis: Consultancy; Magenta: Consultancy; Adaptimmune: Consultancy; Axio: Consultancy; Bayer HealthCare Pharmaceuticals: Honoraria. Ahmed: Seagen: Research Funding; Xencor: Research Funding; Tessa Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Research Funding.

Abstract: Few studies have clearly linked long‐term monitoring with in situ experiments to clarify potential drivers of observed change at a given site. This is especially necessary when findings from a site are applied to a much broader geographic area. Here, we document vegetation change at Barrow and Atqasuk, Alaska, occurring naturally and due to experimental warming over nearly two decades. An examination of plant cover, canopy height, and community indices showed more significant differences between years than due to experimental warming. However, changes with warming were more consistent than changes between years and were cumulative in many cases. Most cases of directional change observed in the control plots over time corresponded with a directional change in response to experimental warming. These included increases in canopy height and decreases in lichen cover. Experimental warming resulted in additional increases in evergreen shrub cover and decreases in diversity and bryophyte cover. This study suggests that the directional changes occurring at the sites are primarily due to warming and indicates that further changes are likely in the next two decades if the regional warming trend continues. These findings provide an example of the utility of coupling in situ experiments with long‐term monitoring to accurately document vegetation change in response to global change and to identify the underlying mechanisms driving observed changes.

Abstract: Wind damage from cyclones can devastate the forest canopy, altering environmental conditions in the understory that affect seedling growth and plant community regeneration. To investigate the impact of hurricane‐induced increases in light and soil nutrients as a result of canopy defoliation, we conducted a two‐way factorial light and nutrient manipulation in a shadehouse experiment. We measured seedling growth of the dominant canopy species in the four Everglades forest communities: pine rocklands ( Pinus elliottii var densa ), cypress domes ( Taxodium distichum ), hardwood hammocks, and tree islands ( Quercus virginiana and Bursera simaruba ). Light levels were full sun and 50% shade, and nutrient levels coupled with an additional set of individuals that were subjected to a treatment mimicking the sudden effects of canopy opening from hurricane‐induced defoliation and the corresponding nutrient pulse. Seedlings were measured weekly for height growth and photosynthesis, with seedlings being harvested after 16 weeks for biomass, leaf area, and leaf tissue N and 13 C isotope ratio. Growth rates and biomass accumulation responded more to differences in soil nutrients than differences in light availability, with largest individuals being in the high nutrient treatments. For B .  simaruba and P .  elliottii , the highest photosynthetic rates occurred in the high light, high nutrient treatment, while T .  distichum and Q .  virginiana photosynthetic rates were highest in low light, high nutrient treatment. Tissue biomass allocation patterns remained similar across treatments, except for Q .  virginiana , which altered above‐ and belowground biomass allocation to increase capture of limiting soil and light resources. In response to the hurricane simulation treatment, height growth increased rapidly for Q .  virginiana and B .  simaruba , with nonsignificant increases for the other two species. We show here that ultimately, hurricane‐adapted, tropical species may be more likely to recolonize the forest canopy following a large‐scale hurricane disturbance.

Abstract: Foundation species have disproportionately large impacts on ecosystem structure and function. As a result, future changes to their distribution may be important determinants of ecosystem carbon (C) cycling in a warmer world. We assessed the role of a foundation tussock sedge ( Eriophorum vaginatum ) as a climatically vulnerable C stock using field data, a machine learning ecological niche model, and an ensemble of terrestrial biosphere models (TBMs). Field data indicated that tussock density has decreased by ∼0.97 tussocks per m 2 over the past ∼38 years on Alaska’s North Slope from ∼1981 to 2019. This declining trend is concerning because tussocks are a large Arctic C stock, which enhances soil organic layer C stocks by 6.9% on average and represents 745 Tg C across our study area. By 2100, we project that changes in tussock density may decrease the tussock C stock by 41% in regions where tussocks are currently abundant (e.g. −0.8 tussocks per m 2 and −85 Tg C on the North Slope) and may increase the tussock C stock by 46% in regions where tussocks are currently scarce (e.g. +0.9 tussocks per m 2 and +81 Tg C on Victoria Island). These climate-induced changes to the tussock C stock were comparable to, but sometimes opposite in sign, to vegetation C stock changes predicted by an ensemble of TBMs. Our results illustrate the important role of tussocks as a foundation species in determining future Arctic C stocks and highlight the need for better representation of this species in TBMs.