DOI: 10.25338/b8n626
title: Wildfire alters the disturbance impacts of an emerging infectious disease via changes to host occurrence and demographic structure

description: 1. 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. 2.
 The disease “sudden oak death” (SOD), associated with the introduced
 pathogen Phytophthora 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 and P. ramorum dynamics across the Big Sur region, we
 modeled the influence of recent and historical fires on epidemiological
 parameters, including pathogen presence, infestation intensity,
 reinvasion, and host mortality. 3. 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 by P. 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 of P.
 ramorum infestation and reinvasion, but younger, rapidly regenerating host
 vegetation capable of sporulation did not measurably influence disease
 dynamics. Notably, the effect of P. ramorum infection on host mortality
 was reduced in recently-burned areas, indicating that the loss of mature
 host canopies may temporarily dampen pathogen transmission and “release”
 susceptible species from significant inoculum pressure. 4.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 outbreaks, and driving biotic disturbance regimes.
description: This dataset is a subset of a long-term forest monitoring study
 to examine the impacts of <em>Phytopthora ramorum </em>on the
 coast redwood and mixed evergreen forests of Big Sur, California. The data
 was collected over 3 field survey periods, from 2006-7, 2010-11, and
 2013-14, and a subset of the included survey plots were impacted by the
 2008 Basin Complex and Chalk fires. More detailed information about the
 variables collected and the field and laboratory methods used to collect
 these variables can be found in the associated manuscript. The plot-level
 variables included in this dataset have been aggregated from measurements
 collected at the stem and tree level from individual tagged trees. The
 included tree and stem measurements have been subsetted to include only
 tanoak and oak trees, which are the focus of the associated
 manuscript.
description: <strong>Metadata, variable
 descriptions</strong> Relevant
 abbreviations:<br> ## UMCA = bay laurel, Umbellularia
 californica<br> ## LIDE = tanoak, Notholithocarpus densiflorus
 (previous genus = Lithocarpus)<br> ## QUAG = coast live oak, Quercus
 agrifolia<br> ## 06/2006 = data collected in the 2006-07
 surveys<br> ## 2010/10 = data collected in the 2010-11
 surveys<br> ## 2013/14 = data collected in the 2013-14
 surveys Variable descriptions:<br> # Big Sur Plot
 = plot identification number<br> # Forest Alliance Type = index for
 Redwood forest (2) or Mixed Evergreen forest (1)<br> ## tmax = mean
 30 year dry-season maximum temperature, derived from PRISM<br> ##
 totalfire.nb = # of fires experienced since 1950, excluding the Basin
 complex fire (which occurred before 2006-2007 sampling points)<br>
 ## burned1950 = whether or not a plot has burned since 1950<br> ##
 LiveBA0607 = total live woody plant basal area in cm^2 (for stems
 &gt;1cm dbh) in 2006-2007 samples<br> ## Hosts06 = total host
 tree basal area in cm^2 (LIDE, Quercus sp, and UMCA stems &gt;1cm dbh)
 in 2006-2007<br> ## UMCAnonzero = presence/absence of bay laurel at
 plot level in 2006-2007 samples<br> ## LIDEnonzero =
 presence/absence of tanoak at plot level in 2006-2007 samples<br> ##
 UMCA.BA.LIVE.0607 = total bay laurel basal area in cm^2 in 2006-07
 samples<br> ## LIDE.BA.LIVE.0607 = total tanoak basal area in cm^2
 in 2006-07 samples  
 <strong>Github repository for analysis described
 in manuscript: </strong> https://github.com/absimler/postfireepidemiology