Short term grass bud response to high and low energy fires

Increasingly, land managers have attempted to use extreme prescribed fire
as a method to address woody plant encroachment in savanna ecosystems. The
effect that these fires have on herbaceous vegetation is poorly
understood. We experimentally examined immediate (<24hr) bud
response of two dominant graminoids, a C3 caespitose grass, Nassella
leucotricha, and a C4 stoloniferous grass, Hilaria belangeri, following
fires of varying energy (J/m2) in a semi-arid savanna in the Edwards
Plateau ecoregion of Texas. Treatments included high- and low-energy fires
determined by contrasting fuel loading and a no burn (control) treatment.
Belowground axillary buds were counted and their activities classified to
determine immediate effects of fire energy on bud activity, dormancy, and
mortality. High-energy burns resulted in immediate mortality of N.
leucotricha and H. belangeri buds (P < 0.05). Active buds decreased
following high-energy and low-energy burns for both species (P <
0.05). In contrast, bud activity, dormancy, and mortality remained
constant in the control. In the high-energy treatment, 100% (n=24) of N.
leucotricha individuals resprouted while only 25% (n=24) of H. belangeri
individuals resprouted (P < 0.0001) three weeks following treatment
application. Bud depths differed between species and may account for this
divergence, with average bud depths for N. leucotricha 1.3 cm deeper than
H. belangeri (P < 0.0001). Synthesis and applications: Our results
suggest that fire energy directly affects bud activity and mortality
through soil heating for these two species. It is imperative to understand
how fire energy impacts the bud banks of grasses to better predict grass
response to increased use of extreme prescribed fire in land management.