The timing of prescribed burns is critical to the development of effective invasive species management programs.  The widespread introduction of KR Bluestem (Bothriochloa ischaemum), an invasive, non-indigenous, C4 grass, threatens the biodiversity of grasslands and rights-of-ways of the Edwards Plateau, TX, U.S.A.  To date, approaches to control the species have included dormant-season prescribed burns, growing-season prescribed burns as well as more traditional approaches such as grazing, herbicides, and mowing.  Previous results with prescribed burns suggest that dormant-season fire may select for KR Bluestem growth over the native species while growing-season fire has the opposite effect.  The goal of this study was to determine the comparative effects of convective heat on the germination of five native, C4, herbaceous species and KR Bluestem.  In a two-way factorial experiment, replicates of seeds of each species were heated at five temperature levels (25 (control), 125, 175, 225, 275°C) and four durations (15 secs., 30 secs., 1 min., 2 min.) to simulate field conditions in which seeds are exposed in a prescribed burn.   

Results/Conclusions

We found that, with the exception of 25°C, heat treatments at all temperatures and durations negatively affected germination of three of the five natives species.  Two of the five natives were relatively tolerant of heat treatment, particularly at 125°C across all durations.  Significantly, KR Bluestem germination was enhanced, relative to the control, at 125°C across all durations and at 175°C for 1 minute.  Thus, burning, in general, may enhance germination of KR Bluestem while negatively affecting the native grass species.  These results may explain observations that active-season burns reduce KR Bluestem abundance while dormant-season burns increase its abundance.  In both seasons germination of KR Bluestem is enhanced; however, only in the active season burn is above ground growth negatively affected.  Results of this study suggest that prescribed burns used to control KR Bluestem should be restricted to the fall growing season in the Edwards Plateau ecosystem.