COS 237-4 - Assessing the effects of prescribed fire energy on soils and the persistence of resprouting shrubs and grasses in a semi-arid savanna

Thursday, August 18, 2022

10:45 AM – 11:00 AM EDT

Location: 516B

Presenting Author(s)

WR

William E. Rogers, Ph.D.

Professor of Ecology
Texas A&M University
College Station, Texas, United States

Coauthor(s)

LC

Lela S. Culpepper, M.S.

Texas A&M University
College Station, Texas, United States
QH

Quinn A. Hiers, M.S.

Texas A&M University
College Station, Texas, United States
VP

Virginia D. Preiss, M.S.

Texas A&M University
College Station, Texas, United States
MD

Matthew B. Dickinson, Ph.D.

USDA-USFS
Delaware, Ohio, United States
KK

Kathleen L. Kavanagh, Ph.D.

Oregon State University
Corvallis, Oregon, United States
AL

Alexandra G. Lodge, Ph.D.

Minnesota Department of Natural Resources
Saint Paul, Minnesota, United States
AS

A. Peyton Smith, Ph.D.

Texas A&M University
College Station, Texas, United States
HS

Heath D. Starns, Ph.D.

Texas A&M University
College Station, Texas, United States
DT

Douglas R. Tolleson, Ph.D.

Texas A&M University
College Station, Texas, United States
MT

Morgan L. Treadwell, Ph.D.

Texas A&M University
College Station, Texas, United States
DT

Dirac Twidwell, Ph.D.

University of Nebraska
Lincoln, Nebraska, United States
CW

Carissa L. Wonkka, Ph.D.

USDA-ARS
Sidney, Montana, United States

Background/Question/Methods

Savannas worldwide are experiencing increases in woody-shrub densities and concomitant decreases in the abundance of graminoids thereby threatening biodiversity and numerous goods and services these ecosystems provide. Conventional management has dismissed the potential for fire to reduce resprouting woody-shrub densities; however, previous research showed that high-energy prescribed fires during drought could cause resprouting shrub mortality. The consequences of these high-energy fires on soils and native herbaceous vegetation is uncertain. In August 2018, we manipulated fire-energy (J/m²) via supplemental fuel loads in 72 completely randomized 100m² plots centered on a mature Prosopis glandulosa in a semiarid Texas savanna ecosystem. We experimentally exposed the belowground root collar on half of the shrubs. We also examined fire treatment effects on tiller density, bud bank dynamics, and resprouting potential of two abundant grass species, Nassella leucotricha (C₃-caespitose) and Hilaria belangeri (C₄-stoloniferous). Wildlife herbivory exclosures in the different fire treatments were established. Finally, we assessed the physical, chemical, and biological properties of the soils before and after fire treatments.

Results/Conclusions

All Prosopis shrubs resprouted in low-energy prescribed fire treatments, whereas only 25% of shrubs resprouted when exposed to high-energy fire. Shrubs exposed to low-energy fires had 30x more resprouts compared to shrubs exposed to high-energy fires. Graminoids were differentially affected by fire likely due to varied phenology and morphology. For both species, dead buds significantly increased and bud-activity significantly decreased within 24hr post-fire treatments. Despite early bud deaths, all Nassella individuals exposed to high-energy fire resprouted, whereas only 25% of Hilaria did. After 8-months, Nassella bud numbers and activity in high-energy treatments were equal to unburned controls whereas Hilaria buds did not recover. Significant effects of wildlife herbivory were observed, but these did not manifest in response to fire treatments. Although physical properties of soil were not significantly affected by fire treatments, high-energy fires altered chemical and biological properties. Soil pH decreased one-year post-fire while total organic carbon and nitrogen marginally increased. Extracellular enzyme activities decreased in response to high-energy fires compared to low-energy fires and unburned soil. These experimental assessments demonstrate the resilience of herbaceous vegetation and soils in this semiarid ecosystem to extreme disturbance events and the potential effectiveness of high-energy prescribed burning for managing woody-shrub encroachment.