Marshalla and Fraterrigo 2026 (Journal of Applied Ecology)
RESEARCH BRIEF #56
A summary based on the following publication:
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MANAGEMENT IMPLICATIONS
Increased fire frequency promoted oak regeneration while mitigating expected invasive grass–fire feedbacks.
Higher Microstegium vimineum cover was associated with lower fire intensity and showed no direct effect on oak seedling survival.
More frequent fire reduced M. vimineum cover over time.
Increased fire frequency was associated with enhanced understory light availability and lower fire intensity; together, these conditions led to improved oak seedling survival and resprouting.
The goal of this study was to determine how fire frequency and non-native grass invasion interact to affect survival and resprouting of oak seedlings and saplings in the U.S. central hardwood region. Better understanding of this interaction can lead to more effective use of prescribed fire to promote oak regeneration and reduce invasive grass impacts. This is especially important given the potential for the occurrence of an invasive grass-fire feedback cycle, in which invading grasses increase fire intensity, thus promoting further invasion of fire-adapted grasses, to the detriment of native trees including oaks.
Research was conducted at Shawnee National Forest and Dixon Springs State Park in southern Illinois, where oak and hickory trees dominate the overstory, with maple, ash, elm, eastern redcedar, and tulip poplar trees also common. In recent decades, low-intensity prescribed burns have been used to restore and maintain upland forests to promote oak regeneration. In the same period, Microstegium vimineum (M.), a non-native grass, has spread across the region complicating the efficacy of prescribed fire.
Study sites were identified based on recent fire history information, including fire frequencies, total number of burns, years since last fire, and the length of fire-management periods. Twenty-six research sites averaging 100 ha (247 acres), with similar slopes and aspects, were selected to represent a range of historical fire occurrences.
At each site, paired plots were established, consisting of an M.‑invaded plot and an uninvaded plot. Within each plot, four black oak (Quercus velutina) and four white oak (Q. alba) 1‑year‑old, nursery‑grown, bare‑root seedlings were planted one year prior to burning to ensure root establishment. Up to eight naturally colonized oak saplings were selected in each plot to assess effects on natural oak regeneration. Pre‑ and post‑burn data were collected, including amount of M. cover around each planted oak, oak seedling height and diameter, availability of resources (e.g., light, soil inorganic N, and soil moisture), and fuel availability. Fire intensities were quantified by measuring maximum fire temperature and fire residence time. Plots were experimentally burned in February and March.
Fire treatments supported higher post‑fire planted oak survival, with the total number of prior burns emerging as the strongest predictor of seedling survival (see figure below). Increased fire frequency enhanced understory light availability by reducing midstory stem density, which was associated with higher planted oak seedling survival. Sites with more frequent burns experienced lower fire intensity due to reduced fuel loads, and planted oaks showed greater survival where maximum fire temperatures were lower. Over 90% of naturally colonized oak saplings also survived burns, but fire and resource availability variables were not found to be significantly related.
For planted seedlings that were top-killed, resprouting was more vigorous (assessed considering the height and diameter of the tallest individual sprout per seedling) in plots with more burns. Resprout height and diameter were 35% and 47% greater, respectively, in plots with five prior burns compared to those with only one. Naturally occurring oak saplings showed a similar pattern, with resprouting vigor increasing with the number of burns and decreasing with time since the last fire.
M. cover was not associated with increased fire intensity, showing no relationship with maximum fire temperature and only a marginal negative relationship with fire residence time; overall, fire intensity was negatively related to M. cover. No direct effects of M. cover on oak seedling survival or resprouting vigor were detected, although M. cover was positively associated with light availability, soil moisture, and inorganic N—conditions potentially favorable to oak seedling establishment. M. cover declined as fire occurrence increased, indicating that repeated prescribed fire can help suppress this invasive grass.
An important finding from this study is that, in temperate deciduous forests, recurring prescribed fire can remain an effective tool for promoting early oak regeneration in the presence of invasive grasses such as M. Repeated fire enhances oak seedling survival and resprouting by increasing understory light availability and reducing fire intensity through lower fuel loads. These effects may also indirectly improve resprouting vigor by enhancing understory vegetation cover and associated soil moisture conditions. M. invasion does not appear to negate the benefits of recurring fire for oak regeneration, although its effects on fire behavior may vary with location, season, and burn conditions. Overall, repeated burning may help disrupt grass-fire feedbacks, reduce fire intensity, and increase resource availability for oak regeneration in grass‑invaded forests.
