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1. Increased mortality of tropical tree seedlings during the extreme 2015–16 El Niño

   https://doi.org/10.1111/gcb.15809  

   Browne, Luke; Markesteijn, Lars; Engelbrecht, Bettina M. J.; Jones, F. Andrew; Lewis, Owen T.; Manzané‐Pinzón, Eric; Wright, S. Joseph; Comita, Liza S. (July 2021, Global Change Biology)

   Abstract As extreme climate events are predicted to become more frequent because of global climate change, understanding their impacts on natural systems is crucial. Tropical forests are vulnerable to droughts associated with extreme El Niño events. However, little is known about how tropical seedling communities respond to El Niño–related droughts, even though patterns of seedling survival shape future forest structure and diversity. Using long‐term data from eight tropical moist forests spanning a rainfall gradient in central Panama, we show that community‐wide seedling mortality increased by 11% during the extreme 2015–16 El Niño, with mortality increasing most in drought‐sensitive species and in wetter forests. These results indicate that severe El Niño–related droughts influence understory dynamics in tropical forests, with effects varying both within and across sites. Our findings suggest that predicted increases in the frequency of extreme El Niño events will alter tropical plant communities through their effects on early life stages. 

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2. Liana versus tree seedling responses to spatial and temporal variation in dry season severity

   https://doi.org/10.1002/ecs2.70058  

   Estrada‐Villegas, Sergio; Browne, Luke; Manzané‐Pinzón, Eric; Comita, Liza S (November 2024, Ecosphere)

   Abstract Lianas are key components of tropical forests, particularly at sites with more severe dry seasons. In contrast, trees are more abundant and speciose in wetter areas. The seasonal growth advantage (SGA) hypothesis postulates that such contrasting distributions are produced by higher liana growth relative to trees during seasonal droughts. The SGA has been investigated for larger size classes (e.g., ≥5 cm diameter at 1.3 m, dbh), but rarely for seedlings. Using eight annual censuses of >12,000 seedlings of 483 tree and liana species conducted at eight 1‐ha plots spanning a strong rainfall gradient in central Panama, we evaluated whether liana seedlings had higher growth and/or survival rates than tree seedlings at sites with stronger droughts. We also tested whether an extreme El Niño drought during the study period had a more negative effect on tree compared to liana seedlings. The absolute density of liana seedlings was similar across the rainfall gradient, ranging from 0.32 individuals/m²(0.20–0.49, 95% credible interval [CI]) at the driest end of the gradient and 0.27 individuals/m²(0.13–0.51 95% CI) at the wettest end of the gradient. The relative density of liana seedlings compared to tree seedlings was higher at sites with stronger dry seasons (0.27, 0.21–0.33, 95% CI), compared to wetter sites (0.12, 0.04–0.20 95% CI), due to lower tree seedling densities at drier sites. However, liana seedlings did not grow or survive better than tree seedlings in drier sites compared to wetter sites. Tree seedlings were more negatively impacted in terms of mortality by the extreme El Niño drought than liana seedlings, with an increase in annual mortality rate of 0.013 (0.003–0.025 95% CI) compared to lianas of −0.009 (−0.028 to 0.008 95% CI), but not growth. Our results indicate that lianas do not have a SGA over trees at the seedling stage. Instead, higher survival of liana versus tree seedlings during severe droughts or differences in liana versus tree fecundity or germination across the rainfall gradient likely explain why liana seedlings have higher relative densities at drier sites. 

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3. Data for "Effects of Azteca trigona alarm pheromones on heterospecific ant behavior"

   https://doi.org/10.25422/azu.data.13963886  

   Frost, Christopher; Yanoviak, Stephen; Wells, Rachel (January 2021, University of Arizona Research Data Repository)

   Data and video files of behavioral responses of Canopy ant species individuals to volatile odors of Azteca trigona ants or control ambient air collected at Barro Colorado Island in Panama. Two videos provide a general examples of the experimental arena and protocol, and the difference between responses to control air and A. trigona headspace air. The single .csv file provides the specific behavioral responses of the individual ants observed and recorded during the behavioral trials.</div></div></div></div>For inquiries regarding the contents of this dataset, please contact the Corresponding Author listed in the README.txt file. Administrative inquiries (e.g., removal requests, trouble downloading, etc.) can be directed to data-management@arizona.edu</i></div></div> 

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4. Droughts, Wildfires, and Forest Carbon Cycling: A Pantropical Synthesis

   https://doi.org/10.1146/annurev-earth-082517-010235  

   Brando, Paulo M.; Paolucci, Lucas; Ummenhofer, Caroline C.; Ordway, Elsa M.; Hartmann, Henrik; Cattau, Megan E.; Rattis, Ludmila; Medjibe, Vincent; Coe, Michael T.; Balch, Jennifer (May 2019, Annual Review of Earth and Planetary Sciences)

   Tropical woody plants store ∼230 petagrams of carbon (PgC) in their aboveground living biomass. This review suggests that these stocks are currently growing in primary forests at rates that have decreased in recent decades. Droughts are an important mechanism in reducing forest C uptake and stocks by decreasing photosynthesis, elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. Tropical forests were a C source to the atmosphere during the 2015–2016 El Niño–related drought, with some estimates suggesting that up to 2.3 PgC were released. With continued climate change, the intensity and frequency of droughts and fires will likely increase. It is unclear at what point the impacts of severe, repeated disturbances by drought and fires could exceed tropical forests’ capacity to recover. Although specific threshold conditions beyond which ecosystem properties could lead to alternative stable states are largely unknown, the growing body of scientific evidence points to such threshold conditions becoming more likely as climate and land use change across the tropics. ▪ Droughts have reduced forest carbon uptake and stocks by elevating tree mortality, increasing autotrophic respiration, and promoting wildfires. ▪ Threshold conditions beyond which tropical forests are pushed into alternative stable states are becoming more likely as effects of droughts intensify. 

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5. Data and Workshop Spreadsheet for "A Visual Technique Used by Citizen Scientists Shows Higher Herbivory in Understory vs Canopy Leaves of a Tropical Forest"

   https://doi.org/10.25422/azu.data.14192885  

   Frost, Christopher (January 2021, University of Arizona Research Data Repository)

   These files are an accompaniment to the manuscript describing nine years of collections with citizen scientists using a visual estimation technique to record herbivory in a neo-tropical forest in the Peruvian Amazon.</div></div></div>For inquiries regarding the contents of this dataset, please contact the Corresponding Author listed in the README.txt file. Administrative inquiries (e.g., removal requests, trouble downloading, etc.) can be directed to data-management@arizona.edu</i></div></div> 

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