Understory response to varying fire frequencies after 20 years of prescribed burning in an upland oak forest

Abstract

Ecosystems in the eastern United States that were shaped by fire over thousands of years of anthropogenic burning recently have been subjected to fire suppression resulting in significant changes in vegetation composition and structure and encroachment by invasive species. Renewed interest in use of fire to manage such ecosystems will require knowledge of effects of fire regime on vegetation. We studied the effects of one aspect of the fire regime, fire frequency, on biomass, cover and diversity of understory vegetation in upland oak forests prescribeburned for 20 years at different frequencies ranging from zero to five fires per decade. Overstory canopy closure ranged from 88 to 96% and was not affected by fire frequency indicating high tolerance of large trees for even the most frequent burning. Understory species richness and cover was dominated by woody reproduction followed in descending order by forbs, C3 graminoids, C4 grasses, and legumes. Woody plant understory cover did not change with fire frequency and increased 30% from one to three years after a burn. Both forbs and C3 graminoids showed a linear increase in species richness and cover as fire frequency increased. In contrast, C4 grasses and legumes did not show a response to fire frequency. The reduction of litter by fire may have encouraged regeneration of herbaceous plants and helped explain the positive response of forbs and C3 graminoids to increasing fire frequency. Our results showed that herbaceous biomass, cover, and diversity can be managed with long-term prescribed fire under the closed canopy of upland oak forests.

Frequency of prescribed burning in an upland oak forest determines soil and litter properties and alters the soil microbial community

“…It has been suggested that fire only causes short term changes in soil microbial communities while larger changes may be driven by vegetation dynamics (Hart et al, 2005). Therefore, differences in soil microbial communities were presumably indirectly related to burning through changes to nutrient and substrate availability via changes in aboveground vegetation observed at the same site (Burton et al, 2010(Burton et al, , 2011. There were no correlations between soil nutrients or soil physical properties measured in our study with the abundance of Gram negative bacterial PLFAs (data not shown).…”

“…Lignin:N ratio under 5 FPD was not significantly different from 0 FPD. One explanation for this may due to the greater abundance of forbs and legumes in the more frequently burned site (Burton et al, 2011). It has been reported that burning in oak savannas can lead to an ecosystem-level N limitation due to volatilization of N. Loss of N through volatilization can result in low plant tissue quality, which in turn may lead to slower decomposition rates (Reich et al, 2001).…”

“…Recent research found prescribed burning of upland oak forests over a 20-year period can have large effects on understory shrubs, saplings and herbaceous vegetation depending on the fire frequency. As fire frequency increased from 0 to 5 fires per decade (FPD), herbaceous species diversity and cover increased while woody shrub and sapling species diversity and density decreased (Burton et al, 2010(Burton et al, , 2011. Our study was conducted in the same forest systems as Burton et al (2010Burton et al ( , 2011, allowing us to expand on their findings and determine the effects of long-term prescribed burning and fire frequency on litter, and soil physical, chemical and biological properties.…”

“…In addition, earlier studies provided abundant information about the forests and effects of burning on aboveground vegetation (Burton et al, 2010(Burton et al, , 2011. Combining both above-and belowground influences of prescribed fire frequencies will improve the practical value of the research findings to forest land managers.…”

Effect of repeated fire on understory plant species diversity in Saravan forests, northern Iran

“…According to our study, fire can increase richness and diversity of species, however, such an increase is different with respect to repetition and number of fire incidents. Burton et al (2011) found that species overall diversity, coverage and richness in oak forests could significantly increase from zero to five by repetition of fire incidence during a decade.…”