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1. Intermediate-severity disturbance impacts in a mixedwood forest: A multi-scale analysis

   https://doi.org/10.1016/j.foreco.2022.120582  

   Davis Goode, J. ; Narayanan, Anuska ; Phillips, David L. ; Hart, Justin L. ; Torreano, Scott J. ; Dey, Daniel C. ( December 2022 , Forest Ecology and Management)
2. 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)

   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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3. Disturbance impacts on porosity and hydraulic properties of vesicular horizons

   https://doi.org/10.1002/saj2.20055  

   Turk, Judith K. ; Graham, Robert C. ( April 2020 , Soil Science Society of America Journal)

   Rapid formation of vesicular pores has been observed following disturbance of vesicular (V) horizons. This study investigates the post‐disturbance recovery of V horizons and the impact on hydraulic properties. At nine study sites, infiltration rates were measured using a tension disk infiltrometer, and intact samples were collected for analysis using high‐resolution x‐ray computed tomography (CT). The V horizon material was then removed, crushed, replaced, and left to recover for 1 yr before repeating the infiltration measurement and CT analysis. Some recovery of vesicular and vugh porosity was observed at all of the study sites. However, the V horizons formed in the first year after disturbance were thinner, with smaller pores, and with a reduction in vesicle and vugh porosity from an average of 2.9% before disturbance to 0.4% after disturbance. The saturated hydraulic conductivity of the V horizons was also significantly lowered, from an average of 20 cm d⁻¹prior to disturbance to 6.6 cm d⁻¹at 1 yr after disturbance. Vesicle and vugh porosity formed 1 yr after disturbance was positively correlated with predisturbance vesicle and vugh porosity (R² = .57;P = 0.02) and sand percentage (R² = .51;P = .03) and negatively correlated with silt percentage (R² = .51;P = .03). No relationship was observed between post‐disturbance formation of vesicle and vugh porosity and precipitation events during the recovery period, clay percentage, CaCO₃percentage, or saline‐sodic classification. V horizons show incipient development at 1 yr after disturbance, but porosity and hydraulic properties are significantly altered from their undisturbed state.

    

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4. Non-target impacts of fungicide disturbance on phyllosphere yeasts in conventional and no-till management

   https://doi.org/10.1038/s43705-022-00103-w  

   Noel, Zachary A. ; Longley, Reid ; Benucci, Gian Maria Niccolò ; Trail, Frances ; Chilvers, Martin I. ; Bonito, Gregory ( February 2022 , ISME Communications)

   Fungicides reduce fungal pathogen populations and are essential to food security. Understanding the impacts of fungicides on crop microbiomes is vital to minimizing unintended consequences while maintaining their use for plant protection. However, fungicide disturbance of plant microbiomes has received limited attention, and has not been examined in different agricultural management systems. We used amplicon sequencing of fungi and prokaryotes in maize and soybean microbiomes before and after foliar fungicide application in leaves and roots from plots under long-term no-till and conventional tillage management. We examined fungicide disturbance and resilience, which revealed consistent non-target effects and greater resiliency under no-till management. Fungicides lowered pathogen abundance in maize and soybean and decreased the abundance of Tremellomycetes yeasts, especially Bulleribasidiaceae, including core microbiome members. Fungicide application reduced network complexity in the soybean phyllosphere, which revealed altered co-occurrence patterns between yeast species of Bulleribasidiaceae, and Sphingomonas and Hymenobacter in fungicide treated plots. Results indicate that foliar fungicides lower pathogen and non-target fungal abundance and may impact prokaryotes indirectly. Treatment effects were confined to the phyllosphere and did not impact belowground microbial communities. Overall, these results demonstrate the resilience of no-till management to fungicide disturbance, a potential novel ecosystem service provided by no-till agriculture.

    

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5. Disturbance decreases genotypic diversity by reducing colonization: Implications for disturbance–diversity feedbacks

   https://doi.org/10.1002/ecy.3710  

   Kollars, Nicole M. ; Stachowicz, John J. ( July 2022 , Ecology)

   One objective of eco‐evolutionary dynamics is to understand how the interplay between ecology and evolution on contemporary timescales contributes to the maintenance of biodiversity. Disturbance is an ecological process that can alter species diversity through both ecological and evolutionary effects on colonization and extinction dynamics. While analogous mechanisms likely operate among genotypes within a population, empirical evidence demonstrating the relationship between disturbance and genotypic diversity remains limited. We experimentally tested how disturbance altered the colonization (gain) and extinction (loss) of genets within a population of the marine angiospermZostera marina(eelgrass). In a 2‐year field experiment conducted in northern California, we mimicked grazing disturbance by migratory geese by clipping leaves at varying frequencies during the winter months. Surprisingly, we found the greatest rates of new colonization in the absence of disturbance and that clipping had negligible effects on extinction. We hypothesize that genet extinction was not driven by selective mortality from clipping or from any stochastic loss resulting from the reduced shoot densities in clipped plots. We also hypothesize that increased flowering effort and facilitation within and among clones drove the increased colonization of new genets in the undisturbed treatment. This balance between colonization and extinction resulted in a negative relationship between clipping frequency and net changes in genotypic richness. We interpret our results in light of prior work showing that genotypic diversity increased resistance to grazing disturbance. We suggest that both directions of a feedback between disturbance and diversity occur in this system with consequences for the maintenance of eelgrass genotypic diversity.

    

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