DOI: 10.5061/dryad.kprr4xh48
title: Short term grass bud response to high and low energy fires

description: 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 (&lt;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 &lt; 0.05). Active buds decreased
 following high-energy and low-energy burns for both species (P &lt;
 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 &lt; 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 &lt; 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.
description: Location:<br> Sonora Texas A&M Agrilife Research
 Station (SARS)<br> Western edge of the Edwards Plateau ecoregion in
 Texas (-100.574°, 30.251°)<br> Semiarid savanna ecosystem encroached
 by Prosopis glandulosa and Juniperus spp. Experimental
 Design:<br> Fire treatments arranged in a randomized design with
 three treatments (no burn, low fire energy, and high fire energy)
 replicated 12 times for a total of 36 experimental plots. Each plot was 10
 x 10 m and centered on a mature mesquite shrub (Prosopis
 glandulosa). Two grass species were selected for this
 study: Nassella leucotricha and Hilaria belangeri.<br>     Nassella
 leucotricha: C3 bunchgrass<br>     Hilaria belangeri: C4
 stoloniferous grass Within each 100
 m<sup>2</sup> plot, two 1 m<sup>2</sup> subplots
 were demarcated with steel posts. One of these subplots was created around
 a patch of N. leucotricha, and the other around a patch of H. belangeri,
 and both served as a reference group for tiller collections described in
 the next section.  Reemergence:<br> Within each
 of these subplots, two individuals of the focal species were marked and
 monitored for regrowth of tillers three weeks following fire
 application. Bud Activity:<br> Tillers were
 harvested 24hrs before and after fires from three randomly determined
 individuals of each grass species inside each plot. These tillers were
 collected from individuals in similar phenological stages as the
 permanently marked individuals using the classification system of Moore et
 al. (1991). All collected tillers were from current year growth and all
 vegetative. Plants visibly damaged by herbivores, insects, or pathogens
 were excluded. The buds associated with these tillers were counted and
 their activity classified as either active, dormant, or dead using the
 Tetrazolium and Evans Blue staining procedures established by Busso
 (1989). Bud Depth:<br> The day before the fire
 treatments were applied, bud depth was measured. Two random individuals of
 each species from each large plot were selected based on similar size and
 phenological stage as our permanently marked individuals. A hole dug at
 the base of each individual grass exposed the deepest buds. Bud depth was
 recorded as the distance between the mineral soil surface and the base of
 each tiller (approximately at the beginning of the root system).