How can an invasive grass affect fire behavior in a tropical savanna? A community and individual plant level approach

Abstract

Some invasive grasses have been reported to change fire behavior in invaded plant communities. Urochloa brizantha is an aggressive invasive grass in the Brazilian Cerrado, an ecosystem where fire is a common disturbance. We investigated the effects of U. brizantha on fire behavior in an open Cerrado physiognomy in Central Brazil. Using experimental burnings we compared fire behavior at both the community and the individual plant level in invaded (UJ) and non-invaded (NJ) areas burned in July. We also assessed the effect of fire season in invaded areas by comparing July (UJ) and October (UO) burnings. We evaluated the following variables: fuel load, fuel moisture, combustion efficiency, maximum fire temperature, flame height, and fire intensity. Additionally, we evaluated the temperatures reached under invasive and native grass tussocks in both seasons. Fuel load, combustion efficiency, and fire intensity were higher in NJ than in UJ, whilst flame height showed the opposite trend. Fuel amount and fire intensity were higher in October than in July. At the individual plant level, U. brizantha moisture was higher than that of native species, however, temperatures reaching C600°C at ground level were more frequent under U. brizantha tussocks than under native grasses. At the community level, the invasive grass modified fire behavior towards lower intensity, lower burning efficiency, and higher flame height. These results provide essential information for the planning of prescribed burnings in invaded Cerrado areas.

Abandoned pastures cannot spontaneously recover the attributes of old‐growth savannas

“…Monitoring natural regeneration until some of the secondary savanna characteristics reach old‐growth savanna values and subsequently removing trees to avoid the thickening of the vegetation (Brudvig, ) may be the most adequate restoration strategy because it has relatively low costs and at least maintains the old‐growth savanna structure and part of its animal and plant diversity, which requires an open habitat to survive (Abreu et al., ; Durigan & Ratter, ; Murphy, Andersen, & Parr, ; Veldman et al., ). The reintroduction of fire to secondary Neotropical savannas may be equally effective to avoid vegetation thickening, but further studies are needed to optimize this management practice because exotic grasses change fire behaviour (Gorgone‐Barbosa et al., ) and may have undesirable effects on secondary savannas.…”

Community‐level flammability declines over 25 years of plant invasion in grasslands

“…Exotic invasive species (hereafter exotic species) can alter community‐level flammability in two main ways. First, the exotic species may possess functional traits, such as substantially different moisture content, volatile organic compounds or retention of dead material, which make it either more or less flammable than the native species in the recipient community, therefore changing community‐level flammability (Brooks et al., ; Gorgone‐Barbosa et al., ; Livingston & Varner, ; McGranahan, Engle, Miller, & Debinski, ). Second, invaders can increase, decrease or change the distribution and continuity of fuel loads (Berry, Wevill, & Curran, ; Brooks, ; Gorgone‐Barbosa et al., ; McGranahan et al., ).…”

“…First, the exotic species may possess functional traits, such as substantially different moisture content, volatile organic compounds or retention of dead material, which make it either more or less flammable than the native species in the recipient community, therefore changing community-level flammability (Brooks et al, 2004;Gorgone-Barbosa et al, 2015;Livingston & Varner, 2016;McGranahan, Engle, Miller, & Debinski, 2013). Second, invaders can increase, decrease or change the distribution and continuity of fuel loads (Berry, Wevill, & Curran, 2011;Brooks, 2008;Gorgone-Barbosa et al, 2015;McGranahan et al, 2013). Most examples of invasion-induced changes to fire regimes have focussed on the effect of a single invading species and have shown that the invader has increased the flammability of the community (D'Antonio & Vitousek, 1992); but invaders can also reduce plant community flammability (Brooks et al, 2004;Gorgone-Barbosa et al, 2015;Livingston & Varner, 2016;McGranahan et al, 2013).…”

Disturbance as a factor in breaking dormancy and enhancing invasiveness of African grasses in a Neotropical Savanna

“…In addition, the presence of Urochloa spp. in Cerrado can change fire behavior by affecting fire intensity, maximum temperature and flame height (Gorgone-Barbosa et al 2015).…”