Woody species composition following a wildfire in the Dugger Mountain Wilderness, Talladega National Forest, al.
A point-centered quarter survey was conducted within the Dugger Mountain Wilderness in the Talladega National Forest eighteen months after a March 2007 wildfire to determine tree and sapling species composition. In the tree stratum, dominant species were Quercus prinus, Pinus echinata, Pinus virginiana, Quercus velutina, and Oxydendrum arboreum. The summed importance value of Quercus species in the tree stratum was 53.99. Dominant species in the sapling stratum included Acer rubrum, Nyssa sylvatica, and Prunus alabamensis. The importance value of sapling A. rubrum (23.62) and N. sylvatica (25.73) exceeded that of all oaks combined (16.26). A. rubrum, N. sylvatica, and P. alabamensis were observed to be prolific sprouters following the fire. Unless a pre-Colonial fire regime is restored with the possibility of more intense fires, the high importance value of A. rubrum and N sylvatica in the sapling stratum may prevail over Quercus species resulting in an overstory dominated by shade-tolerant species with low fire resistance. Due to restrictions on management mandated by the Wilderness Act of 1964, it is not likely that fires of the needed intensity to maintain the current Quercus dominated overstory will be possible.
Lightning-caused and Native American set fires historically were a major force in shaping ecosystems of the eastern US (Van Lear and Waldrop 1989, Frost 1998, Abrams 2006). Frequent, low intensity fires created conditions favorable for the establishment and dominance of Quercus (Abrams 2000, Van Lear et al. 2000) and other fire tolerant species (Wade et al. 2000). Quercus species have an ecological advantage under a regime of frequent fires due to their thick bark, sprouting ability, and resistance to decay when damaged (Lorimer 1985). In addition, fire reduces soil moisture that would favor mesophytic species, prepares a seedbed by reducing litter thickness, and reduces competition from fire-intolerant species (Barnes and Van Lear 1998, Darley-Hill and Johnson 1981, Van Lear and Watt 1993).
Since the early 1900's, the understory of Quercus dominated forests has been invaded by shade-tolerant later successional species, such as Acer rubrum (Abrams 2000), that may eventually replace Quercus dominance in the overstory (Abrams 2000, Lorimer 1985, McGee 1984, Wade et all 2000). A. rubrum and other mesophytic species can become so dense that the shade reduces Quercus seedling and forb abundance. The long-term effect is a reduction in species richness as fire adapted species are replaced by more fire-sensitive species (Nowacki and Abrams 2008). Thus, fire exclusion can be a major disruption in Quercus dominated ecosystems (Packard 1993). When fire does return to fire suppressed sites, the mesophytic species are often top-killed but resprout and may dominate the site (Wade et al. 2000). Such is the case in Tennessee where repeated low intensity fires reduced A. rubrum seedling density, but the surviving A. rubrum grew at a faster rate than the Quercus seedlings present (Green et at 2010).
The absence of fire in the Dugger Mountain Wilderness could result in unnatural conditions such as the intrusion of mesophytic species into the landscape (Lorimer 1985, McGee 1984, Wade et at 2000), but the use of prescribed fire could result in a less self-willed landscape (Parsons et at 1986) in violation of the Wilderness Act. According to section 2 (a) of the Wilderness Act of 1964, designated Wilderness Areas are to be untrammeled by humans and retain a primeval character that is protected and managed to preserve its natural conditions. The human imprint should be substantially unnoticeable (Hendee et at 1990). The use of prescribed fire in wilderness areas managed by the Forest Service is permitted to reduce fuel loadings but not to restore natural processes (Parsons et at 1986). This study sought to assess the species composition of saplings and trees following a wildfire in the Dugger Mountain Wilderness to determine post-fire regeneration and the potential future overstory.
MATERIALS AND METHODS
The study area was within the Dugger Mountain Wilderness located on the Shoal Creek Ranger District of the Talladega National Forest, Calhoun County, Alabama. This area is in the Southern Ridge and Valley Section and is characterized by low mountains with steep slopes and shallow excessively drained soils. The elevation ranges from 244 to 640 meters above sea level (Soil Conservation Service 1958). A low intensity human caused wildfire burned 267 hectares in the northern end of the wilderness area from February 27-March 4 2007. The surface fire with 0.5 to 1.8m flame lengths consumed primarily hardwood leaf litter and downed hardwood and pine trees.
In September of 2008, 18 months following the fire, a point-center quarter survey (Cottam and Curtis 1956) of trees and saplings was conducted on a 200 X 200 meter grid throughout the burned area. At each point, four quarters were established (northeast, southeast, northwest, southwest). Within each quarter, the diameter at breast height (dbh) and distance to the center of each sapling and tree closest to the center point were measured Saplings were defined as manifesting woody sterns at least 1.4 m tall but less than 11.4 cm dbh. Woody stems greater than 11.4 cm dbh were considered trees. The tree density, basal area, relative frequency, relative density, relative basal area, importance value, and density were calculated for each species in the tree and sapling strata. A pine plantation established before the creation of the wilderness area was excluded from sampling.
Calculations were performed utilizing with the following formulae:
Frequency = number of points containing a species
Relative frequency = frequency/sum of frequencies for all species * 100
Density = number of sterns per species
Relative density = density/total number of sterns * 100
Basal area = sum of dbh by species/2 * [pi]
Relative basal area = basal area per species/sum of basal area * 100
Importance value = Relative frequency + relative density + relative basal area/3
Area of tree coverage = [[(total distance for all species/number of stems)/2].sup.2] * [pi]
Total stems/ha = 10,000m/area of tree coverage
Stems/ha by species = total stems/ha * relative density
In the tree stratum, dominant species based on importance values were Quercus prinus, Pinus echinata, P. virginiana, and Oxydendrum arboreum (Table 1). Q. prinus dominated in terms of importance value and density (Table 1). The importance value of Quercus species summed to 53.99, while the importance value sum for Pinus species was only 22.30, half that of Q. prinus (44.23) alone (Table 1). Acer rubrum and Nyssa sylvatica had importance values of 3.81 and 2.97, respectively.
Table 1. Relative frequency, relative density, relative abundance, importance value, basal area, and density of trees following a wildfire in the Dugger Mountain Wilderness, Talladega National Forest, Alabama. Tree Species Relative Relative Relative Importance Density Density (stems/ha) Frequency Density Abundance Value Acer rubrum 5.44 4.56 1.42 3.81 21.12 Carya alba 0.68 0.42 0.09 0.40 1.92 Carya glabra 4.76 5.39 3.79 4.65 24.96 Carya 2.04 2.49 1.81 2.11 11.52 pallida Cornus 1.36 0.83 0.20 0.80 3.84 florida Liriodendron 0.68 0.42 0.25 0.45 1.92 tulipifera Nyssa 4.08 2.90 1.97 2.97 13.44 sylvatica Oxydendrum 9.52 8.30 2.95 6.93 38.40 arboreum Pinus 10.88 10.37 8.51 9.92 48.00 echinata Pinus taeda 4.08 2.90 2.64 321 13.44 Pinus 9.52 9.54 8.45 9.17 44.16 virginiana Prunus 2.04 1.24 0.34 1.21 5.76 alabamensis Quercus 0.68 0.42 0.64 0.58 1.92 coccinea Quercus 2.04 1.55 0.42 1.38 7.68 marilandica Quercus 31.97 41.08 59.62 44.23 190.08 prinus Quercus 0.68 0.42 1.55 0.88 1.92 rubra Quercus 2.72 1.66 0.74 1.71 7.68 stellata Quercus 6.12 4.98 4.53 5.21 23.04 velutina Vaccinium 0.68 0.42 0.08 0.39 1.92 arboreum Tree Species Basal Area ([m.sup.2] /ha) Acer rubrum 0.08403 Carya alba 0.00664 Carya glabra 0.14977 Carya 0.07088 pallida Cornus 0.01403 florida Liriodendron 0.02113 tulipifera Nyssa 0.07639 sylvatica Oxydendrum 0.16943 arboreum Pinus 0.30793 echinata Pinus taeda 0.09179 Pinus 0.29504 virginiana Prunus 0.02196 alabamensis Quercus 0.01802 coccinea Quercus 0.02880 marilandica Quercus 1.56035 prinus Quercus 0.02805 rubra Quercus 0.03794 stellata Quercus 0.16066 velutina Vaccinium 0.00639 arboreum
Dominant species in the sapling stratum included Acer rubrum, Nyssa sylvatica, and Prunus alabamensis (Table 2). A. rubrum and N. sylvatica both exceeded 20% of relative frequency, density, and abundance. Combined the importance value of A. rubrum and N. sylvatica was 49.35 and the density was 53.46%. Even when the importance values of Quercus saplings was summed (16.26), it did not exceed that of Acer rubrum or Nyssa sylvatica (Table 2). When considering just saplings [less than or equal to] 2.54 cm in diameter at breast height, Q. prinus was the fourth most abundant species following A. rubrum, N. sylvatica, and P. alabamensis (Table 3).
Table 2. Relative frequency, relative density, relative abundance, importance value, basal area, and density of saplings following a wildfire in the Dugger Mountain Wilderness, Talladega National Forest, Alabama Sapling Relative Relative Relative Importance Density species Acer rubrum 23.46 26.44 20.95 23.62 160.18 Carya glabra 1.24 0.77 2.21 1.41 4.64 Carya 1.85 0.77 1.27 1.30 4.64 pallida Cornus 5.56 4.21 7.60 5.79 25.54 florida Liquidambar 0.62 0.38 0.01 0.34 2.32 styraciflua Liriodendron 0.62 0.38 0.08 0.36 2.32 tulipifera Nyssa 22.84 27.20 27.14 25.73 164.83 sylvatica Oxydendrum 5.56 3.84 3.24 4.21 23.22 arboreum Pinus 1.23 1.15 1.89 1.42 6.97 echinata Pinus 0.62 0.38 0.99 0.66 2.32 palustris Pinus 0.62 0.38 0.93 0.64 2.32 virginiana Prunus 14.82 13.80 14.14 14.25 83.57 alabamensis Primus 1.85 1.50 0.22 1.07 6.96 serotina Quercus 1.23 1.15 0.88 1.09 6.96 marilandica Quercus 9.88 9.58 10.59 10.01 58.04 prinus Quercus 1.85 1.53 3.73 2.37 9.29 stellata Quercus 3.09 3.45 1.84 2.79 20.90 velutina Rhus 0.62 0.38 0.01 0.34 2.32 copallinum Sassafras 0.62 1.15 1.51 1.09 6.97 albidum Vaccinium 1.85 1.92 0.78 1.52 11.61 arboreum Sapling Basal species Area Acer rubrum 0.10099 Carya glabra 0.00839 Carya 0.00501 pallida Cornus 0.03481 florida Liquidambar 0.00038 styraciflua Liriodendron 0.00113 tulipifera Nyssa 0.13899 sylvatica Oxydendrum 0.01565 arboreum Pinus 0.00902 echinata Pinus 0.00401 palustris Pinus 0.00388 virginiana Prunus 0.06437 alabamensis Primus 0.00276 serotina Quercus 0.00576 marilandica Quercus 0.04746 prinus Quercus 0.01440 stellata Quercus 0.00889 velutina Rhus 0.00038 copallinum Sassafras 0.00589 albidum Vaccinium 0.00738 arboreum Table 3. Stems/ha for saplings [less than or equal to] 2.54 cm dbh following a wildfire in the Dugger Mountain Wilderness, Talladega National Forest, Alabama Sapling Species Density (Stems/ha) Acer rubrum 106.79 Carya pallida 2.32 Cornus florida 2.32 Liquidambar styraciflua 2.32 Liriodendron tulipifera 2.32 Nyssa sylvatica 78.93 Oxydendrum arboreum 16.25 Pinus echinata 2.32 Prunus alabamensis 55.72 Prunus serotina 18.57 Quercus marilandica 2.32 Quercus prinus 34.82 Quercus stellata 2.32 Quercus velutina 6.96 Rhus copallinum 2.32 Sassafras albidum 4.64 Vaccinium arboreum 6.96
The species dominating the sapling stratum, Acer rubrum, Nyssa sylvatica, and Prunus alabamensis, have low fire resistance but are prolific sprouters following fires (Hare 1965, Walters and Yawney 1990, Boyer 1990). A. rubrum has some characteristics of early successional species, such as rapid invasion of disturbed sites, and characteristics of late successional species, such as high tolerance of low light conditions in the understory (Abrams 1998). The reduction of fire frequency in the 20th century permitted A. rubrum to expand from moist areas with low fire frequency to dominate the understory of much of the current Quercus forests (Abrams 2006).
Acer rubrum (Scheiner et al. 1988, Walters and Yawney 1990, Elliott et al. 1999, Green et al. 2010) and Quercus prinus (Elliott et al. 1999) have been shown to increase in abundance following fires due to vigorous sprouting. In the Dugger Mountain Wilderness, Q. prinus saplings ([less than or equal to] 2.54 cm dbh) were relatively dense post-fire but were well below the density of A. rubrum, N. sylvatica, and P. alabamensis (Table 3). In Tennessee, Green et aL (2010) found that low intensity fires reduced A. rubrum seedling survival compared to unburned areas, but the low intensity fires did not provide a successional advantage for Q. prinus seedlings. The Q. prinus and A. rubrum seedling survival levels were nearly equal (Green et aL 2010). The single low intensity fire in the Dugger Mountain Wilderness may even cause increased sprouting of non-oak species (Arthur et aL 1998).
Although A. rubrum and N. sylvatica did not dominate the tree stratum (Table 1), their dominance in the sapling stratum indicates that the future forest without significant disturbances such as fire is likely to be dominated by these species (Arthur et al 1998). A. rubrum and N. sylvatica are prolific sprouters following low intensity fires, and low intensity fires may select for A. rubrum (Green et al 2010). If more shade-tolerant species become established, the understory microenvironment becomes cooler and moister (Nowacki and Abrams 2008) making the application of prescribed fires of acceptable intensity to favor Quercus species more difficult. Green et al. (2010) and Alexander et al. (2008) recommend more intense fires or mechanical canopy removal mixed with low intensity fire to reduce the canopy cover. This will reduce the density of A. rubrum and allow Quercus species with a mid-shade tolerance to receive the light necessary to compete.
Even if a pre-Colonial fire regime is restored to the Dugger Mountain Wilderness, a decline in Quercus species and increases in species with low fire tolerance and high shade tolerance are likely. More intense prescribed fire are not likely in a wilderness area where mechanized equipment is not permitted and mechanical treatment to reduce overstory density would be a violation of the Wilderness Act (Hendee et al. 1990). Thus, the forest within the wilderness area will likely proceed to a mesophytic species dominated forest.
This research was supported by a grant from the USDA Forest Service.
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Robert E. Carter and Grant C. Cobb
Department of Biology, Jacksonville State University, 700 Pelham Road North, Jacksonville, AL 36265
Correspondence Robert Carter (email@example.com)
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|Author:||Carter, Robert E.; Cobb, Grant C.|
|Publication:||Journal of the Alabama Academy of Science|
|Date:||Jan 1, 2012|
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