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1. Understanding tropical forest abiotic response to hurricanes using experimental manipulations, field observations, and satellite data

   https://doi.org/10.5194/bg-17-3149-2020  

   Van Beusekom, Ashley E. ; González, Grizelle ; Stankavich, Sarah ; Zimmerman, Jess K. ; Ramírez, Alonso ( January 2020 , Biogeosciences)

   null (Ed.)

   Abstract. With projected increasing intensity of hurricanes and largeuncertainty in the path of forest recovery from hurricanes, studies areneeded to understand the fundamental response of forests to canopy openingand debris deposition: the response of the abiotic factors underneath thecanopy. Through two manipulative experiments and instrumenting prior toHurricane Maria (2017) in the Luquillo Experimental Forest (LEF) ofPuerto Rico, this study found a long recovery time of primary abioticfactors (beneath canopy light, throughfall, and temperature) influenced bythe disturbance of canopy opening, as well as complex responses by the secondaryabiotic factors (relative humidity, soil moisture, and leaf saturation)influenced by the disturbance of the primary factors. Recovery took 4–5 years for beneath canopy light, while throughfall recovery took 4–9 yearsand neither had recovered when Hurricane Maria passed 3 years after thesecond experiment. Air and soil temperature seemingly recovered quickly fromeach disturbance (<2.5 years in two experiments for ∼+1 ∘C of change); however, temperature was the most importantmodulator of secondary factors, which followed the long-term patterns of thethroughfall. While the soil remained wetter and relative humidity in the airstayed lower until recovery, leaves in the litter and canopy were wetter anddrier, with evidence that leaves dry out faster in low rainfall and saturatefaster in high rainfall after disturbance. Comparison of satellite and fielddata before and after the 2017 hurricanes showed the utility of satellitesin expanding the data coverage, but the muted response of the satellite datasuggests they measure dense forest as well as thin forest that is not asdisturbed by hurricanes. Thus, quick recovery times recorded by satellitesshould not be assumed representative of all the forest. Data recordsspanning the multiple manipulative experiments followed by HurricaneMaria in the LEF provide evidence that intermediate hurricane frequencyhas the most extreme abiotic response (with evidence on almost all abioticfactors tested) versus infrequent or frequent hurricanes. 

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2. Long‐term trends in gastropod abundance and biodiversity: Disentangling effects of press versus pulse disturbances

   https://doi.org/10.1111/geb.13425  

   Willig, Michael R. ; Presley, Steven J. ( November 2021 , Global Ecology and Biogeography)

   Climate‐induced pulse (e.g., hurricanes) and press (e.g., global warming) disturbances represent threats to populations, communities, and the ecosystem services that they provide. We leveraged three decades of annual data on tropical gastropods to quantify the effects of major hurricanes, associated secondary succession, and global warming on abundance, biodiversity, and species composition.

   Luquillo Mountains, Puerto Rico.

   Gastropod abundance, biodiversity, and composition were estimated annually for each of 27 years in a tropical montane forest that experienced three major hurricanes (Hugo, Georges, and Maria). Generalized linear mixed‐effects, linear mixed‐effects, and linear models evaluated population‐ and community‐level responses to year, ambient temperature, understorey temperature, hurricane, and time since hurricane. Variation partitioning determined the unique and shared variation in biotic responses associated with temperature, disturbance, and succession.

   Rather than declining, gastropod abundances generally increased through time, whereas the responses of biodiversity were weak and scale dependent. Hurricanes and associated secondary succession, rather than ambient atmospheric temperature, moulded long‐term trends in abundances and biodiversity.

   Global warming over the past 30 years has not progressed sufficiently to elicit significant responses by gastropods in the Luquillo Mountains. Rather, effects from pulse disturbances (i.e., hurricanes) and secondary succession currently drive long‐term variation in abundance and biodiversity. Gastropods evince high resilience in this tropical ecosystem. Historical exposure to recurrent hurricanes likely imbued the fauna with broad niches that make them resistant to current levels of global warming. We predict that biotic resiliency will be challenged once changes in temperature exceed interannual and inter‐habitat differences that typify this hurricane‐mediated system, or combine with an increased frequency of hurricanes and droughts to alter associations among environmental characteristics that define the fundamental niches of species. Only then might significant declines in abundance or the appearance of novel communities characterize the gastropod fauna in the Luquillo Mountains.

    

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3. Developing a more complete understanding of tropical montane forest disturbance ecology through landslide research

   https://doi.org/10.3389/ffgc.2023.1091387  

   Freund, Cathryn A. ; Silman, Miles R. ( May 2023 , Frontiers in Forests and Global Change)

   Landslides are a central component of tropical montane forest disturbance regimes, including in the tropical Andes biodiversity hotspot, one of the most biodiverse ecosystems in the world. Technological developments in remote sensing have made landscape-scale landslide studies possible, unlocking new avenues for understanding montane biodiversity, ecosystem functioning, and the future effects of climate change. Here, we outline three axes of inquiry for future landslide ecology research in Andean tropical montane forest. We focus exclusively on the Andes due to the vast floral diversity and high endemicity of the tropical Andes biodiversity hotspot, and its importance for global biodiversity and regional ecosystem service provisioning; the broad elevational, latitudinal, and topographic gradients across which landslide dynamics play out; and the existence of long-term plot networks that provide the necessary baseline data on mature forest structure, composition, and functioning to contextualize disturbance impacts. The three lines of study we outline, which draw heavily on remote sensing data and techniques, will deepen scientific understanding of tropical montane forest biodiversity and ecosystem functioning, and the potential impacts of climate change on both. They are: (1) tracking landslide biodiversity dynamics across time and space with high spatial and temporal resolution satellite and unoccupied aerial vehicle imagery; (2) assessing the ecological influence of landslides through the lens of plant functional diversity with imaging spectroscopy; and (3) understanding current and predicting future landslide regimes at scale by building a living landslide inventory spanning the tropical Andes. The research findings from these three axes of inquiry will shed light on the role of landslides and the process of forest recovery from them in both the Andes and worldwide.

    

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4. Arthropods are not declining but are responsive to disturbance in the Luquillo Experimental Forest, Puerto Rico

   https://doi.org/10.1073/pnas.2002556117  

   Schowalter, Timothy D. ; Pandey, Manoj ; Presley, Steven J. ; Willig, Michael R. ; Zimmerman, Jess K. ( January 2021 , Proceedings of the National Academy of Sciences)

   A number of recent studies have documented long-term declines in abundances of important arthropod groups, primarily in Europe and North America. These declines are generally attributed to habitat loss, but a recent study [B.C. Lister, A. Garcia,Proc. Natl. Acad. Sci. USA115, E10397–E10406 (2018)] from the Luquillo Experimental Forest (LEF) in Puerto Rico attributed declines to global warming. We analyze arthropod data from the LEF to evaluate long-term trends within the context of hurricane-induced disturbance, secondary succession, and temporal variation in temperature. Our analyses demonstrate that responses to hurricane-induced disturbance and ensuing succession were the primary factors that affected total canopy arthropod abundances on host trees, as well as walkingstick abundance on understory shrubs. Ambient and understory temperatures played secondary roles for particular arthropod species, but populations were just as likely to increase as they were to decrease in abundance with increasing temperature. The LEF is a hurricane-mediated system, with major hurricanes effecting changes in temperature that are larger than those induced thus far by global climate change. To persist, arthropods in the LEF must contend with the considerable variation in abiotic conditions associated with repeated, large-scale, and increasingly frequent pulse disturbances. Consequently, they are likely to be well-adapted to the effects of climate change, at least over the short term. Total abundance of canopy arthropods after Hurricane Maria has risen to levels comparable to the peak after Hurricane Hugo. Although the abundances of some taxa have declined over the 29-y period, others have increased, reflecting species turnover in response to disturbance and secondary succession.

    

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5. Bloom succession and nitrogen dynamics during snowmelt in a mid-order montane river

   https://doi.org/10.1007/s10533-023-01080-5  

   Valett, H. Maurice ; de Lima, Rafael Feijó ; Peipoch, Marc ; Engstrom, Royce C. ( September 2023 , Biogeochemistry)

   The Upper Clark Fork River (UCFR), Montana, a mid-order well-lit system with contemporary anthropogenic nitrogen (N) enrichment and natural geogenic sources of phosphorus (P), experiences annual algal blooms that influence ecosystem structure and function. This study was designed to assess the occurrence of riverine algal blooms (RABs) in the UCFR by characterizing the succession of periphyton and biogeochemical conditions following annual snowmelt runoff through autumnal baseflow conditions, and to provide a framework for assessing RAB progression in montane mid-order rivers more broadly. Using a 21-year database (2000–2020) collected over the growing season at three sites, historical assessment of the persistent and recurrent character of RABs in the UCFR showed that the magnitude of the summer bloom was, in part, moderated by snowmelt disturbance. Abundance and growth forms of benthic algae, along with river physicochemistry (e.g., temperature) and water chemistry (N and P concentration), were measured over the course of snowmelt recession for three years (2018–2020) at the same three sites. Results documented the onset of major blooms of the filamentous green algaeCladophoraacross all sites, commensurate with declines in dissolved inorganic N. Atomic N:P ratios of river water suggest successional transitions from P- to N-limitation associated with mid-season senescence ofCladophoraand development of a secondary bloom of N-fixing cyanobacteria, dominated byNostoc cf. pruniforme. Rates of N-fixation, addressed at one of the sites during the 2020 snowmelt recession, increased uponCladophorasenescence to a maximal value among the highest reported for lotic systems (5.80 mg N/m²/h) before decreasing again to background levels at the end of the growing season. Based on these data, a heuristic model for mid-order rivers responding to snowmelt disturbance suggests progression from phases of physical stress (snowmelt) to optimal growth conditions, to conditions of biotic stress later in the growing season. Optimal growth is observed as green algal blooms that form shortly after peak snowmelt, then transition to stages dominated by cyanobacteria and autochthonous N production later in the growing season. Accordingly, interactions among algal composition, reactive N abundance, and autochthonous N production, suggest successional progression from reliance on external nutrient sources to increased importance of autochthony, including N-fixation that sustains riverine productivity during late stages of snowmelt recession.

    

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