Comparative Seed Heat Tolerances Among Native and Non-indigenous Invasive Grassland Species

Prescribed burning is a popular method for the control of invasive species; however, research is lacking on the application of fire in a species-specific manner. We assess whether heat sensitivity differences among seeds of Texas grassland species can be used to target invasive species in prescribed burns. We conducted heat treatments on the invasive yellow bluestem (Bothriochloa ischaemum), and 5 native species, little bluestem (Schizachyrium scoparium), silver beardgrass (Bothriochloa laguroides), sideoats grama (Bouteloua curtipendula), Indiangrass (Sorghastrum nutans), and Texas bluebonnets (Lupinus texensis) at 125, 175, 225, and 250°C and at durations of 30, 60, 120 and 240 s. Temperature affected percent germination of yellow bluestem, while duration affected all species except Texas bluebonnet. A temperature*duration interaction affected sideoats grama. We also calculated a native species:yellow bluestem index of germination response which provided a measure of the responses of the native species relative to yellow bluestem. Little bluestem was the only species that germinated at higher percentages than yellow bluestem across all treatments, although, at the highest temperature Indiangrass outperformed yellow bluestem. Among native species, intermediate temperatures and exposure times had the least damaging effects on germination. Burning during the non-growing season will result in little damage to grass tissue and greater damage to the seeds of native species, while active-season burns applied at an optimal time are likely to have greater consequences for the target invasive. The use of invasive-species-targeted prescribed fire will require careful planning to maximize damage to the invasive while minimizing damage to the native seed bank.