Fire effects on invasive and native warm‐season grass species in a North American grassland at a time of extreme drought

Abstract

Question: Can the timing of cutting or burning be used to selectively damage an invasive C 4 grass species while limiting collateral damage to dominant native C 4 grass species in a grassland community? Location: A medium to short grass prairie in central Texas, US.Methods: We conducted six cut and burn trials between June 2011 and January 2012 during an exceptional drought year. Target species were the native, perennial, C 4 grass Schizachyrium scoparium (little bluestem) and the introduced, perennial, C 4 grass Bothriochloa ischaemum (yellow bluestem). Burn trials were conducted inside a steel barrel using standardized fuel loads. To assess recovery, we counted the first cohort of new tillers that emerged after treatment and tillers that grew in the subsequent spring. We also recorded phenological status, meteorological variables and burn temperatures to determine if tiller recovery was predictable.Results: Bothriochloa ischaemum responded more negatively to burning than to cutting, but these treatments were no different for S. scoparium. Both species produced the smallest number of tillers after the summer burns, and the burn date 9 species interaction was insignificant. On average, peak fire temperature inside tussocks was 100°C higher in B. ischaemum than in S. scoparium. Judging from the reduction in tiller densities in undisturbed plots from spring 2011 to spring 2012, B. ischaemum was also more sensitive to drought. Multivariate models were significant and related burn recovery to peak fire temperature, among other factors, and recovery from cutting to ambient temperature on the day of cutting. In B. ischaemum, plants with higher investment in early reproductive growth suffered more burn damage.Conclusions: We identified no optimal burn time that maximized discrimination between the two species. Nonetheless, the invasive species was more sensitive to both drought and fire, possibly due to higher heat exposure of growing points. Thus, burning during the summer of a drought year may constitute the sought-after treatment that selectively favours native species. Ultimately, successful management will involve fuel and temperature management combined with assessment of the relative phenologies of the target species prior to burning. This study suggests that a hot fire at a time when the invasive species has a larger investment in early reproductive growth will provide the best control.

Attacking invasive grasses

“…Havill et al. () address the issue of how to target invasive species without causing collateral damage to native species in the fire‐prone shortgrass prairies of central Texas, by comparing the impacts of different burning and cutting treatments on the response of an introduced grass and a native grass.…”

“…In the recent study of Havill et al. () they took into account Pyke et al. 's () framework and focused on two C 4 perennial grasses, one introduced and the other native.…”

Knocking back invasions: variable resistance and resilience to multiple cold spells in native vs. nonnative fishes

“…There are not many applications of this approach, but a study by Havill et al. () showed that a nonnative C 4 grass species was more sensitive to burning during a drought than its native counterpart, supporting the notion that nonnative management should be poised for opportunities arising from a combination of disturbances, including extreme events.…”

“…), because native species are often competitively superior under resource limitation (e.g., lower water demands, Cavaleri and Sack , and lower sensitivity to burning, Havill et al. ).…”

Long‐term monitoring of a highly invaded annual grassland community through drought, before and after an unintentional fire

“…Previous grassland studies do not show enhanced effects of burning during drought, but in those cases dry years occurred immediately before (Larios et al, ) or at the same time (Arterburn et al, ) as fire, rather than during post‐fire succession. Other work suggests that water availability after prescribed fire can alter succession, although the direction of effects on exotic grasses is inconsistent for reasons that remain unclear (Davy & Dykier, ; Havill, Schwinning, & Lyons, ; Kimball, Goulden, Suding, & Parker, ; Villarreal, Norman, Buckley, Wallace, & Coe, ). At least one manipulative, factorial experiment supports stronger effects of water availability than burning on annual grass biomass (Potts, Suding, Winston, Rocha, & Goulden, ).…”