Effects of habitat and growing season fires on resprouting of shrubs in longleaf pine savannas
Published source details
Olson M.S. & Platt W.J. (1995) Effects of habitat and growing season fires on resprouting of shrubs in longleaf pine savannas. Plant Ecology (formerly Vegetatio 1948-1996), 101-118.
Published source details Olson M.S. & Platt W.J. (1995) Effects of habitat and growing season fires on resprouting of shrubs in longleaf pine savannas. Plant Ecology (formerly Vegetatio 1948-1996), 101-118.
Prior to European settlement, longleaf pine Pinus palustris savannas were a widespread habitat in the west Gulf of Mexico coastal plain of southeast USA. These savannas were maintained as generally open, wooded habitats by periodic (once every 10 years or so) lightening-induced fires. Although pre-settlement densities and distributions are not well known, trees and shrubs are integral habitat components. Alterations of fire regimes, especially those resulting from anthropogenic changes, have been shown to influence the woody vegetation; woody species increase when fire frequencies decrease and when fire timing change from the lightning season (the growing season) to the non-lightning season. Overtime this leads to loss of open savanna and succession to more closed, hardwood-dominated woodland. This study examined differences in resprouting of shrubs (the primary mechanism resulting in persistence of perennial shrubs in longleaf pine savannas) following single prescribed fires early (June) or late (August) in the growing season; effects of shrub size and fire intensity on mortality and vigor of resprouting were monitored.
Study areas: This study was conducted in the Vernon District of the Kisatchie National Forest, southwestern Louisiana (31ºN, 93ºW), USA.
Within the headwaters of three different drainages of the Calcasieu River, replicated permanent transects were established that extended from upland (dry) longleaf pine savannas (dominated by longleaf pine) into downslope seepage savannas; seepage savannas (also known as pitcher plant bogs, wetland pine savannas, and hillside seepage herb bogs) tend to have few trees and are important for forbs and shrubs, including many endemic and carnivorous plants.
Prescribed burns and shrub monitoring: All shrubs were mapped and tagged, and numbers of stems were counted prior to the prescribed fires. Replicated prescribed fires were set June and August during the 1990 growing season; maximum fire temperatures were measured within each transect. The tagged shrubs were revisited; stems were recensused 2- and 12-months after the fires; mortality was recorded.
Within the burned areas, at least some shrubs of all species resprouted from underground organs, whilst none regenerated solely from soil seed banks. At least some shrubs of all species present resprouted from underground organs, none regenerated solely from the soil seed bank. One year subsequent to fires, an initial reduction in stems due to burning was no longer evident in either of the habitats due to resprouting; there was no reduction in total numbers of stems one year after early or late growing season fires. Resprouting occurred more rapidly in seepage than upland savannas, but more resprouts were produced in upland savannas within 12 months after burning.
The rate of resprouting varied among species and between habitats. In contrast to other upland species, farkleberry Vaccinium arboretum and Elliott's blueberry V.elliottii did not produce new shoots for more than two months following fire. Stems of winged sumac Rhus copallina and red chokeberry Pyrus arbutifolia, species with long rhizomes, increased more after fires in June than fires in August. Only smaller shrubs (< 18 stems) were killed by fire, and mortality was not correlated with high fire temperatures.
The authors suggest that whilst growing season fires may prevent further recruitment of shrubs into longleaf pine savanna habitats, a reduction in numbers of established large shrubs (if considered desirable) may require alternative management.
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