COS 258-3 - What are the impacts of varying fuel loads on air and soil temperatures in grassland systems?

Thursday, August 18, 2022

2:00 PM – 2:15 PM EDT

Location: 516B

Presenting Author(s)

SB

Seton Bachle

Postdoctoral Fellow
(1) Colorado State University Department of Forest and Rangeland Stewardship, (2) US Forest Service
Fort Collins, Colorado, United States

Coauthor(s)

TO

Troy Ocheltree

Assistant Professor
Department of Forest and Rangeland Stewardship, Colorado State University
Fort Collins, Colorado, United States
LP

Lauren M. Porensky

USDA-ARS
Fort Collins, CO, United States
DS

Derek Scasta

University of Wyoming, United States
JR

Jim Reardon

Forester
Fire Sciences Laboratory, Rocky Mountain Research Station
Missoula, Montana, United States
AS

Amy Symstad

Research Ecologist
U.S. Geological Survey, Northern Prairie Wildlife Research Center
Hot Springs, South Dakota, United States
CE

Catherine Estep

Crops Research Laboratory, USDA ARS–Rangeland Resources and Systems Research Unit
Fort Collins, Colorado, United States
BD

Brian Dickerson

Wildlife Biologist
Forest and Grassland Research Laboratory, Rocky Mountain Research Station
Rapid City, South Dakota, United States
SK

Shannon Kay

Statistician
USDA/FS Rocky Mountain Research Station
Fort Collins, Colorado, United States
JO

Jacqueline Ott

Research Ecologist
Forest and Grassland Research Laboratory, Rocky Mountain Research Station
Rapid City, South Dakota, United States

Background/Question/Methods

Fire is a primary driver for the maintenance and restoration of rangeland systems, and belowground plant tissues are responsible for aboveground regeneration following such disturbances (i.e., fire and grazing). However, varying management strategies in rangeland systems have led to variable fuel loads resulting in a wide range of fire intensities (Wm^-2). Although high fuel loads with greater energy release lead to increased air temperatures, the effects on soil heating and subsequent impact on belowground tissues of native species has received less study in grassland and shrubland systems than forested systems.

To examine the amount of heating exposure on belowground plant tissues, soil cores (12 in diameter) with intact native species were extracted from both Thunder Basin National Grassland (WY) and Buffalo Gap National Grassland (SD) during the spring of 2018. To simulate a range of fuel loads, cores were heated in a kiln to one of three experimental temperatures simulating 0.25, 1, and 3 tons of fuel per acre. Using thermocouples and a flux meter, we measured the following: soil surface heat flux, above ground temperature measurements within the fire environment (e.g., air, soil surface, etc), and temperatures at multiple soil depths (1 cm, 2 cm, and 5 cm).

Results/Conclusions

While air temperatures may be extremely high during a fire, temperatures precipitously decline at the soil surface and with increasing soil depth, reflecting minimal soil heating even at high fuel loadings. Future analyses will focus on: 1) considering how well grassland soil heating matches Campbell’s soil heating model designed in forested systems; and 2) examining how perennial grassland species respond to varying fuel loads. The small amount of soil heating, regardless of treatment, suggest a low likelihood of soil sterilization and also that differences in post-fire responses of grassland and shrubland vegetation with different fuel loads is due more to the biology of the plants rather than differences in soil heating.