Fire and non‐native grass invasion interact to suppress tree regeneration in temperate deciduous forests

Abstract

Summary1. While many ecosystems depend on fire to maintain biodiversity, non-native plant invasions can enhance fire intensity, suppressing native species and generating a fire-invasion feedback. These dynamics have been observed in arid and semi-arid ecosystems, but fire-invasion interactions in temperate deciduous forests, where prescribed fires are often used as management tools to enhance native diversity, have rarely been investigated. 2. Here we evaluated the effects of a widespread invasive grass on fire behaviour in eastern deciduous forests in the USA and the potential effects of fire and invasions on tree regeneration. We planted native trees into invaded and uninvaded forests, quantified fuel loads, then applied landscape-scale prescribed fires and no-burn controls, and measured fire behaviour and tree seedling and invasive plant performance. 3. Our results show that fires in invaded habitats were significantly more intense, including higher fire temperatures, longer duration and higher flame heights, even though invasions did not alter total fuel loads. The invasion plus fire treatment suppressed native tree seedling survival by 54% compared to invasions without fire, and invasions reduced natural tree recruitment by 66%. 4. We also show that invasive plant biomass did not change from one season to the next in plots where fire was applied, but invader biomass declined significantly in unburned reference plots, suggesting a positive invasive grass-fire feedback. 5. Synthesis and applications. These findings demonstrate that fire-invasion interactions can have significant consequences for invaded temperate forest ecosystems by increasing fire intensity and reducing tree establishment while promoting invasive plant persistence. To encourage tree regeneration and slow invasive spread, we recommend that forest managers remove invasions prior to applying prescribed fires or avoid the use of fire in habitats invaded by non-native grasses.

Effects of a non‐native grass invasion decline over time

“…fire temperatures or flame height), native seed survival, tree survival and growth, or invader populations (Flory et al . ). In addition, the fires were conducted in one quadrant of the plots, which were already limited in size, and fire behaviour and effects may vary based on the spatial scale of fires.…”

“…Microstegium can have direct effects during the growing season via competition and indirect effects through dense litter accumulation, which can hinder native seedling recruitment (Flory & Clay ), and cause more intense fires and exacerbate fire effects on native species (Flory et al . ).…”

Microstegium vimineum (Trin.) A. Camus

“…Flory et al . () showed that maximum fire temperatures were on average 57% greater in sites invaded by M. vimineum than in uninvaded control areas. In addition, fires burned at temperatures of over 300 ° C for nearly twice as long and flame heights were 98% higher in invaded compared with uninvaded habitats.…”

Changing Fire Regimes in Tropical and Subtropical Australia

“…Conclusion cycle" (Setterfield et al 2010;van Klinken et al 2013;Wagner and Fraterrigo 2015) due to the increases in the abundance of fine fuels. With increases in fire frequency and intensity (D'Antonio and Vitousek 1992), a decrease in native tree and shrub cover and abundance can result, which will further facilitate more grass invasion, further increasing the risk of higher intensity and more frequent fires resulting in an ever increasing self-perpetuating fire cycle (Flory et al 2015). Introduced grass invasion is likely to result in substantial changes to fire regimes in invaded ecosystems, as these fire promoting grasses are ecosystem transformers that have the potential to alter the community structure (RossiterRachor et al 2016 Ecosystem transformation can also occur with a reduction in fire frequency and intensity, where fire is or has been withheld and there is a change in fire management, as Chapter 5…”

“…The grass-fire cycle occurs when alien grass invades an area and increases the abundance of fine fuels, which increases fire frequency and intensity (D'Antonio and Vitousek 1992). This can result in a decrease in native tree and shrub cover and abundance, which further facilitates more grass invasion, which in turn increases the risk of future higher intensity and frequency of wildfires in an ever increasing self-perpetuating fire cycle (Flory et al 2015). found that Mission grass fuel loads were approximately five times greater than that of native grasses.…”