COS 223-1 - The physiological response of sweetgum (Liquidambar styraciflua) to fire restoration management efforts in Central Arkansas

Abstract: Largely due to fire suppression, grasslands and savannahs are facing woody encroachment from species that were previously controlled by recurrent fires. In response, land managers utilize prescribed fire to re-establish pre-suppression conditions and promote fire-tolerant species. Sweetgum (Liquidambar styraciflua) is a common species invading southeastern grassland habitats, and its ability to vigorously resprout has made it difficult to eradicate. It is unclear how best to apply prescribed fire to control this encroachment. Specifically, it is not well understood if the timing of fire might impact the ability of species to resprout or recover long term. However, fires that coincide with periods of seasonally lower root NSC concentrations and higher metabolic requirements – late spring through summer – could be more effective at reducing resprouting growth. The goal of this study was therefore to investigate how the timing of prescribed fire impacts the resprouting vigor and carbohydrate storage of sweetgum.

In this study, we monitored the recovery of top-killed sweetgum trees at two similar prairie sites in Central Arkansas with different disturbance histories – one burned in August 2021 and one burned in March 2022. Resprouting trees were harvested on four dates to compare NSC concentrations, resprout growth, and water relations over time and to determine if initial tree size affected resprouting response. Measurements of the herbaceous vegetation were also made to investigate how differences in the competing vegetation at each site might impact the recovery of sweetgum.

Generally, initial tree size prior to the fire disturbance strongly influenced resprout mass and height. In June, summer-burn site trees had greater resprout mass than winter-burned trees; however by August, this difference in resprouting was only seen among large trees (significant site x size interaction). By the end of the growing season, there was no longer any difference in resprout mass or height between sites. While root NSC concentrations didn’t initially differ between the sites, by December the winter-burned trees had significantly higher root starch concentrations. Lower water potentials and stomatal conductance of summer-burned trees during late summer indicate these trees suffered greater water stress than winter-burned trees. Summer prescribed fire may be more impactful than dormant season fire for sweetgum trees, especially if followed by drought making these trees more susceptible to future disturbance.