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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 micro- climatic 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 follow- ing 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 sites stratified by aspect, ele- vation, and fire severity (unburned, moderate, high) to capture a range of forest types, biophysical con- texts, and fire effects. Loss of canopy and understory vegetation had marked effects on microclimate: On average, sites burned at high severity had 3.7°C higher daily maximum temperatures and 0.81 kPa higher daily maximum VPD relative to paired unburned sites. Differences between burned and unburned sites 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 postfire, 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 postfire establishment of tree seedlings and understory vegetation. These effects depend strongly on biophysical context, with cool-wet forests more vulnerable to fire-caused changes in microclimate compared with warm-dry settings. Our results fur- ther highlight the functional importance of standing dead trees for moderating surface temperature in postfire 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.
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This content will become publicly available on May 1, 2027
Forest composition and diversity buffer microclimates and enhance productivity
Abstract Tree diversity may play a role in buffering forest ecosystems against climate extremes. We asked how diverse tree communities could (1) influence local atmospheric water demand, and (2) how changes in microclimate could be linked to the productivity of trees within forest communities.To assess forest canopy characteristics and calculate above‐ground productivity, we measured plant fractional cover using UAV‐LiDAR and conducted growth inventories in 148 forest plots of a young temperate tree diversity experiment. We monitored the microclimate and tracked soil moisture in a subset of forest plots to understand the relative influence of above‐ground and below‐ground water status on tree growth. Gas exchange, spectral reflectance and leaf mass per area were measured on four tree species distributed throughout the experiment to assess the influence of microclimate on tree physiology.We found that fast‐growing, early successional tree species increased forest cover, which was linked to buffered daily amplitudes of vapour pressure deficits (VPD) within forest plots and increases in the annual wood production of slower‐growing, shade‐tolerant tree species. In assemblages with more buffered microclimates, several slower‐growing tree species showed increased leaf water content and reduced physiological stress. Plots with reduced amplitude in VPD exhibited greater complementarity and productivity relative to those with higher variability.Synthesis. Our findings show that tree diversity and the proportion of fast‐growing, early successional tree species can increase canopy cover and buffer the microclimates of young forests, benefiting the physiology and productivity of slower‐growing, shade tolerant tree species. We reason that a self‐reinforcing dynamic of tree growth and microclimate buffering is likely at play. In the context of a rapidly changing climate, our findings suggest that diverse forest communities can shape local microenvironments to support sustainable ecosystem functioning.
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- Award ID(s):
- 2425352
- PAR ID:
- 10692420
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 114
- Issue:
- 5
- ISSN:
- 0022-0477
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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