Fire Effects on Resprouting of Shrubs in Headwaters of Southeastern Longleaf Pine Savannas

Abstract

Woody plants in fire-frequented ecosystems commonly resprout from underground organs after fires. Responses to variation in characteristics of fire regimes may be a function of plant physiological status or fire intensity. Although these hypotheses have been explored for trees in southeastern longleaf pine (Pinus palustris) savannas, responses of other life forms and stages have not been studied. We examined effects of fire season and frequency, geography, habitat, and underground organ morphology on resprouting of shrubs. In 1994, we located replicated sites, each containing two habitats, upslope savannas and downslope seepages, in Louisiana and Florida. Each site, which contained quadrats located along transects within a 30 ϫ 60 m plot, was burned either during the dormant or growing season and then reburned similarly two years later. Maximum fire temperatures were measured, and densities of shrub stems were censused in quadrats before and after fires.Shrubs collectively resprouted more following dormant than growing-season fires, regardless of habitat or geographic region. After repeated dormant-season fires, collective densities in seepages of both regions and densities of root-crown-bearing shrubs in Florida seepages were greater than those initially and after repeated growing-season fires. Shrub responses were generally unrelated to fire temperatures, supporting the hypothesis that resprouting of shrubs may be more dependent on their physiological status at the time of fires. There was, nonetheless, an inverse relationship between collective and root-crownbearing shrub densities following repeated fires and maximum fire temperatures in Florida seepages. Anthropogenic dormant-season fires over many decades may have resulted in increases in shrub densities in longleaf pine savannas, especially seepages. Repeated growing-season fires, however, neither increased nor reduced densities of established shrubs. Long-term shifts in characteristics of fire regimes, even in fire-frequented habitats, may produce effects that are not reversible in the short term (Ͻ10 yr) by simply reintroducing prescribed fires that resemble those that occurred naturally during the growing season.

Are vegetation—environment relationships different between herbaceous and woody groundcover plants in barrens with shallow soils?

“…During periods of fire suppression, woody plants are more likely to invade (Rykiel & Cook, 1986), accumulate aboveground biomass, and form well developed root structures (Taft, 1997). In addition, associated carbohydrate reserves in underground organs will likely ensure that almost all woody plants vigorously resprout and thus persist following the re-introduction of single (Olson & Platt, 1995;Taft, 1997) and even repeated fires (Peterson & Reich, 2001;Drewa, Platt & Moser, 2002b). This is especially the case in tallgrass prairie, where intermediate fire frequencies (every 3-4 y) accelerated the spread of shrubs more than extremely frequent or infrequent fire, suggesting, in part, that prescribed fires are not conducted at high enough frequencies (Heisler, Briggs, & Knapp, 2003;Briggs et al, 2005).…”

“…In our study sites, many root crown-bearing shrubs (e.g., Corylus americana, Zanthoxylem americanum, and Physocarpus opulifolius) and young life history stages of trees (e.g., Cercis canadensis, Ostrya virginiana, and Carpinus caroliniana) formed dense clusters of resprouts that entirely covered some quadrats. In contrast, growingseason fires remove aboveground biomass along with remobilized carbohydrates and have been more effective in deterring recovery of woody groundcover vegetation in southeastern savannas (Drewa, Platt & Moser, 2002b), Chihuahuan desert grasslands (Drewa, 2003), and Sierra Nevada conifer forests (Kauffman & Martin, 1990). Based on climatic data, growing season fires, initiated by light-ning, likely once characterized our barrens prior to Euro-American settlement (Petersen & Drewa, 2006).…”

Chaparral shrub recovery after fuel reduction: a comparison of prescribed fire and mastication techniques

“…Shrub growth patterns can be altered due to different physiological activity during the burn time (Drewa et al 2002;Radosevich and Conard 1980;Bond and van Wilgen 1996). Lower resprouting shrub cover after spring treatments would be expected because carbohydrate and water reserves have already been partially expended.…”

Fire Effects on Demography of the Invasive Shrub Brazilian Pepper (Schinus terebinthifolius) in Florida Pine Savannas

“…All individuals in our study populations that survived the 2006 fire did so by resprouting (Figure 2). Therefore, observed plant size was effectively reduced to the seedling class post-fire, but belowground biomass (and energy reserves) would be expected to be greater than for true seedlings (Snyder 1999; Drewa et al 2002) plants < 1.0 cm diameter and to all unburned plants of any diameter. The mean growth increment was higher among plants recovering from fire (0.69 cm/yr) than it was among unburned plants less than 1 cm diameter (0.42 cm/yr) and among unburned plants of any size (0.33 cm/yr).…”