DOI: 10.5061/dryad.47d7wm3c6
title: Wildfire impacts on forest microclimate vary with biophysical context

description: Increasing wildfire activity in western North America has the potential to
 remove forest canopy cover over large areas, increasing the vulnerability
 of understory plants and juvenile trees to microclimatic extremes. To
 understand the impacts of wildfire on forest microclimatic buffering, we
 monitored daily temperature and vapor pressure deficit (VPD) in 33 plots
 over the first two growing seasons following two wildfires from 2017. The
 Lolo Peak and Sunrise fires occurred during a regionally extensive fire
 season, burning mixed-conifer and subalpine forests across complex
 mountainous topography in western Montana. Sensors were deployed from June
 to September in 2018 and 2019 in plots stratified by aspect, elevation,
 and fire severity (unburned, moderate, high) to capture a range of forest
 types, biophysical contexts, and fire effects. Loss of canopy and
 understory vegetation had marked effects on microclimate: on average,
 plots burned at high severity had 3.7 °C higher daily maximum temperatures
 and 0.81 kPa higher daily maximum VPD relative to paired unburned plots.
 Differences between burned and unburned plots were most pronounced when
 ambient temperatures were high, across diurnal and seasonal time scales.
 Differences were also more pronounced at sites with less canopy cover,
 more bare ground post-fire, and greater long-term water availability
 (i.e., low climatic water deficit). Our results reveal fire-caused changes
 in microclimate extremes that are biologically meaningful for the
 post-fire establishment of tree seedlings and understory vegetation. These
 effects depend strongly on biophysical context, with cool-wet forest more
 vulnerable to fire-caused changes in microclimate compared to warm-dry
 setting. Our results further highlight the functional importance of
 standing dead trees for moderating surface temperature in post-fire
 environments. Anticipating forest ecosystem responses to increased warming
 and wildfire activity, and the potential for fire to catalyze vegetation
 changes, thus requires considering the substantial impacts of fire on
 microclimate.
description: Near-ground microclimate conditions (temperature and relative
 humidity) were monitored in two wildfires which burned in 2017 in northern
 Rocky Mountain conifer forests. Microclimate was monitored over June-Sept.
 2018 and 2019 at 33 sites spanning gradients in local water balance (via
 elevation and aspect) and fire severity, including 11 unburned sites.
 Field data describing site characteristics and fire severity were also
 collected, including ground cover of bare ground, litter, and understory
 vegetation; scorch height; distance to seed source; tree mortality; live
 and dead canopy cover; and live and dead basal area. Site climate
 information derived from gridded datasets are also reported.
 Microclimate data were quality-checked by visually examining
 values with &gt;5 degrees Celsius change within a half-hour timestep,
 with less than 0.02% of data excluded from analysis. Microclimate data
 were collected using two sensor models, and a laboratory calibration was
 conducted to ensure comparability among measurements. Microclimate data
 were used to calculate vapor pressure deficit (VPD) and aggregated to
 daily maximum temperature and VPD. See Wolf et al.
 (2020) <em>Ecosphere</em> for detailed methods. 
description: Please reference the following files:
 README_for_Wolf_et_al_2020_Ecosphere_Data
 README_for_Wolf_et_al_2020_Ecosphere_Code