PARENT SESSION
Oral Session #48: Vegetation Change and Response.
Presiding: D. Zobel
Tuesday, August 6. 1:00 PM to 4:45 PM. Mesquite Room, Radisson.
The interaction of woody vegetation and fire in a C4 grassland: mechanisms driving shrub expansion.
HEISLER, JANA*,1, BRIGGS, JOHN1, 1 ARIZONA STATE UNIVERSITY, TEMPE, ARIZONA
ABSTRACT- The interaction of fire and woody vegetation within grasslands is a function of the direct effects associated with the destruction of aboveground tissues and indirect effects related to changes in resource availability such as N and light and soil temperature. In 2001, fire was re-introduced into a transitional landscape within the tallgrass prairie and the following experimental manipulations were imposed in order to quantify the relative impacts of the direct and indirect effects of fire on individual shrub patches: (1) protected (from fire), (2) protected with N supplementation, (3) unprotected (from fire), (4) unprotected with N supplementation, and (5) unprotected with litter addition. In shrub patches exposed to fire, 100% mortality of aboveground stems was observed while all stems protected from fire survived. Over 4000 stems within 40 shrub patches (8 patches/treatment) of the species Cornus dummondii were tagged upon emergence and monitored throughout the duration of this first growing season. At 30 days post-fire, unprotected shrubs had initiated new sprouts and stem density of all treatments was similar; however, by day 60, stem density of unprotected shrubs had increased by 320% and was significantly greater than protected shrubs (62%). There was no significant effect of N supplementation at any of the 5 census periods from May-August. Comparatively, greater availability of light and warmer soils appear to stimulate the production of new sprouts within a given shrub patch.
KEY WORDS: C4 grassland, woody expansion, fire, resource availability