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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. 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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3. 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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4. Recovery of soil microbial diversity and functions along a tropical montane forest disturbance gradient

   https://doi.org/10.3389/fenvs.2022.853686  

   Sniegocki, Renee ; Moon, Jessica B. ; Rutrough, Abigail L. ; Gireneus, Jude ; Seelan, Jaya Seelan ; Farmer, Michael C. ; Weindorf, David C. ; Naithani, Kusum ( September 2022 , Frontiers in Environmental Science)

   Logging and forest conversion are occurring at alarming rates in tropical forests. These disturbances alter soil microbial community structure and functions. While direct links between changes in soil properties, such as pH and microbial community structure are well established, the indirect effects of logging and forest conversion on soil microbial community structure and functions are poorly understood. We used a space-for-time substitution to investigate the changes in soil microbial diversity and functions across a forest recovery gradient in the tropical montane forests of northern Borneo. We used surface (top 5 cm) soil to assess soil physicochemical and microbial (next-generation DNA sequencing) properties, and standardized litterbags (Tea Bag Index) to assess litter decomposition and stabilization. Our results show that bacterial and fungal diversity increases with recovery time and reaches pre-disturbance levels between 60- and 80-years post-disturbance. Litter decomposition rate constants increased linearly with increasing bacterial and fungal diversity. Litter stabilization also increased linearly with fungal diversity, but was highest at intermediate levels of bacterial diversity. Our results provide insights on the effects of forest logging and conversion on soils and highlight the tight coupling between soil microbial diversity and soil functions in tropical montane forests. 

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5. Modeling the Effects of Increased Hurricane Frequency on the Tropical Forest Carbon Cycle

   https://doi.org/10.1007/s10021-024-00937-6  

   Gutiérrez_del_Arroyo, Omar ; Hartman, Melannie_D ; Silver, Whendee_L ( October 2024 , Ecosystems)

   Models project that climate change is increasing the frequency of severe storm events such as hurricanes. Hurricanes are an important driver of ecosystem structure and function in tropical coastal and island regions and thus impact tropical forest carbon (C) cycling. We used the DayCent model to explore the effects of increased hurricane frequency on humid tropical forest C stocks and fluxes at decadal and centennial timescales. The model was parameterized with empirical data from the Luquillo Experimental Forest (LEF), Puerto Rico. The DayCent model replicated the well-documented cyclical pattern of forest biomass fluctuations in hurricane-impacted forests such as the LEF. At the historical hurricane frequency (60 years), the dynamic steady state mean forest biomass was 80.9 ± 0.8 Mg C/ha during the 500-year study period. Increasing hurricane frequency to 30 and 10 years did not significantly affect net primary productivity but resulted in a significant decrease in mean forest biomass to 61.1 ± 0.6 and 33.2 ± 0.2 Mg C/ha, respectively (p < 0.001). Hurricane events at all intervals had a positive effect on soil C stocks, although the magnitude and rate of change of soil C varied with hurricane frequency. However, the gain in soil C stocks was insufficient to offset the larger losses from aboveground biomass C over the time period. Heterotrophic respiration increased with hurricane frequency by 1.6 to 4.8%. Overall, we found that an increasing frequency of tropical hurricanes led to a decrease in net ecosystem production by − 0.2 ± 0.08 Mg C/ha/y to − 0.4 ± 0.04 Mg C/ha/y for 30–10-year hurricane intervals, respectively, significantly increasing the C source strength of this forest. These results demonstrate how changes in hurricane frequency can have major implications for the tropical forest C cycle and limit the potential for this ecosystem to serve as a net C sink.

    

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