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1. Wildfire alters the disturbance impacts of an emerging forest disease via changes to host occurrence and demographic structure

   https://doi.org/10.1111/1365-2745.13495  

   Simler‐Williamson, Allison B.; Metz, Margaret R.; Frangioso, Kerri M.; Rizzo, David M.; Thrall, ed., Peter (September 2020, Journal of Ecology)

   Abstract Anthropogenic activities have altered historical disturbance regimes, and understanding the mechanisms by which these shifting perturbations interact is essential to predicting where they may erode ecosystem resilience. Emerging infectious plant diseases, caused by human translocation of nonnative pathogens, can generate ecologically damaging forms of novel biotic disturbance. Further, abiotic disturbances, such as wildfire, may influence the severity and extent of disease‐related perturbations via their effects on the occurrence of hosts, pathogens and microclimates; however, these interactions have rarely been examined.The disease ‘sudden oak death’ (SOD), associated with the introduced pathogenPhytophthora ramorum, causes acute, landscape‐scale tree mortality in California's fire‐prone coastal forests. Here, we examined interactions between wildfire and the biotic disturbance impacts of this emerging infectious disease. Leveraging long‐term datasets that describe wildfire occurrence andP. ramorumdynamics across the Big Sur region, we modelled the influence of recent and historical fires on epidemiological parameters, including pathogen presence, infestation intensity, reinvasion, and host mortality.Past wildfire altered disease dynamics and reduced SOD‐related mortality, indicating a negative interaction between these abiotic and biotic disturbances. Frequently burned forests were less likely to be invaded byP. ramorum, had lower incidence of host infection, and exhibited decreased disease‐related biotic disturbance, which was associated with reduced occurrence and density of epidemiologically significant hosts. Following a recent wildfire, survival of mature bay laurel, a key sporulating host, was the primary driver ofP. ramoruminfestation and reinvasion, but younger, rapidly regenerating host vegetation capable of sporulation did not measurably influence disease dynamics. Notably, the effect ofP. ramoruminfection on host mortality was reduced in recently burned areas, indicating that the loss of tall, mature host canopies may temporarily dampen pathogen transmission and ‘release’ susceptible species from significant inoculum pressure.Synthesis. Cumulatively, our findings indicate that fire history has contributed to heterogeneous patterns of biotic disturbance and disease‐related decline across this landscape, via changes to the both the occurrence of available hosts and the demography of epidemiologically important host populations. These results highlight that human‐altered abiotic disturbances may play a foundational role in structuring infectious disease dynamics, contributing to future outbreak emergence and driving biotic disturbance regimes. 

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2. On the Shoulders of Giants: Continuing the Legacy of Large-Scale Ecosystem Manipulation Experiments in Puerto Rico

   https://doi.org/10.3390/f10030210  

   Wood, Tana; González, Grizelle; Silver, Whendee; Reed, Sasha; Cavaleri, Molly (March 2019, Forests)

   There is a long history of experimental research in the Luquillo Experimental Forest in Puerto Rico. These experiments have addressed questions about biotic thresholds, assessed why communities vary along natural gradients, and have explored forest responses to a range of both anthropogenic and non-anthropogenic disturbances. Combined, these studies cover many of the major disturbances that affect tropical forests around the world and span a wide range of topics, including the effects of forest thinning, ionizing radiation, hurricane disturbance, nitrogen deposition, drought, and global warming. These invaluable studies have greatly enhanced our understanding of tropical forest function under different disturbance regimes and informed the development of management strategies. Here we summarize the major field experiments that have occurred within the Luquillo Experimental Forest. Taken together, results from the major experiments conducted in the Luquillo Experimental Forest demonstrate a high resilience of Puerto Rico’s tropical forests to a variety of stressors. 

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3. Soil microbiome feedbacks during disturbance-driven forest ecosystem conversion

   https://doi.org/10.1093/ismejo/wrae047  

   Nelson, Amelia R.; Fegel, Timothy S.; Danczak, Robert E.; Caiafa, Marcos V.; Roth, Holly K.; Dunn, Oliver I.; Turvold, Cosette A.; Borch, Thomas; Glassman, Sydney I.; Barnes, Rebecca T.; et al (March 2024, The ISME Journal)

   Abstract Disturbances cause rapid changes to forests, with different disturbance types and severities creating unique ecosystem trajectories that can impact the underlying soil microbiome. Pile burning—the combustion of logging residue on the forest floor—is a common fuel reduction practice that can have impacts on forest soils analogous to those following high-severity wildfire. Further, pile burning following clear-cut harvesting can create persistent openings dominated by nonwoody plants surrounded by dense regenerating conifer forest. A paired 60-year chronosequence of burn scar openings and surrounding regenerating forest after clear-cut harvesting provides a unique opportunity to assess whether belowground microbial processes mirror aboveground vegetation during disturbance-induced ecosystem shifts. Soil ectomycorrhizal fungal diversity was reduced the first decade after pile burning, which could explain poor tree seedling establishment and subsequent persistence of herbaceous species within the openings. Fine-scale changes in the soil microbiome mirrored aboveground shifts in vegetation, with short-term changes to microbial carbon cycling functions resembling a postfire microbiome (e.g. enrichment of aromatic degradation genes) and respiration in burn scars decoupled from substrate quantity and quality. Broadly, however, soil microbiome composition and function within burn scar soils converged with that of the surrounding regenerating forest six decades after the disturbances, indicating potential microbial resilience that was disconnected from aboveground vegetation shifts. This work begins to unravel the belowground microbial processes that underlie disturbance-induced ecosystem changes, which are increasing in frequency tied to climate change. 

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4. Mapping primary forest loss using dense time series and resilience metrics

   Suh, J; Hong, F; Zhu, Z; Hedges, S; Yang, Z (December 2024, AGU Fall Meeting 2024, Session: Global Environmental Change, 2024AGUFMGC51O0157S)

   Primary forests play a crucial role in providing essential ecosystem services and supporting biodiversity compared to secondary forests. With increasing threats from extreme climate events and human activities, monitoring primary forest loss is critical for understanding the impact of these threats on ecosystems and biodiversity. Dense time series data from remotely sensed satellite imagery allow us to track historical disturbances, making it an effective source for mapping primary forests over time. However, distinguishing between primary and secondary forests based on spectral-temporal information remains challenging as primary forests can show high resilience to certain natural disturbances (e.g., drought), and secondary forests may not have experienced any disturbance during the satellite observation period. In this context, this study aims to map primary forests on the Caribbean island of Hispaniola using the time series approach and resilience metrics given that primary forests tend to be more resilient than secondary forests. To achieve this, we used spectral-temporal features from COntinuous monitoring of Land Disturbance (COLD) algorithm based on all available Landsat data between 1984 and 2023. Additionally, a resilience map is generated from deseasonalized and detrended spectral observations using the lag-1 autocorrelation method. Then, a Random Forest model was employed to generate an annual primary forest map. 

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5. Disease and fire interact to influence transitions between savanna–forest ecosystems over a multi‐decadal experiment

   https://doi.org/10.1111/ele.13719  

   Pellegrini, Adam F. A.; Hein, Andrew M.; Cavender‐Bares, Jeannine; Montgomery, Rebecca A.; Staver, A. Carla; Silla, Fernando; Hobbie, Sarah E.; Reich, Peter B.; Williams, ed., John (March 2021, Ecology Letters)

   Abstract Global change is shifting disturbance regimes that may rapidly change ecosystems, sometimes causing ecosystems to shift between states. Interactions between disturbances such as fire and disease could have especially severe effects, but experimental tests of multi‐decadal changes in disturbance regimes are rare. Here, we surveyed vegetation for 35 years in a 54‐year fire frequency experiment in a temperate oak savanna–forest ecotone that experienced a recent outbreak of oak wilt. Different fire regimes determined whether plots were savanna or forest by regulating tree abundance (r² = 0.70), but disease rapidly reversed the effect of fire exclusion, increasing mortality by 765% in unburned forests, but causing relatively minor changes in frequently burned savannas. Model simulations demonstrated that disease caused unburned forests to transition towards a unique woodland that was prone to transition to savanna if fire was reintroduced. Consequently, disease–fire interactions could shift ecosystem resilience and biome boundaries as pathogen distributions change. 

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