|Scientific Name:||Quercus georgiana|
|Taxonomic Source(s):||Trehane, P. 2007-2015. The Oak Names Checklist. Available at: http://oaknames.org/search/goodnames.asp. (Accessed: 2 February 2016).|
|Red List Category & Criteria:||Endangered B2ab(i,ii,iii,iv,v) ver 3.1|
|Assessor(s):||Wenzell , K. & Kenny, L.|
Abundant at only a few localities, Georgia Oak (Quercus georgiana) is restricted to small occurrences on isolated granite outcrops in the Piedmont Plateau of the southeastern United States. This species is believed to occupy an are of occupancy (AOO) of 72-272 km2. Extant occurrences are known from three counties in Alabama and 14 counties in Georgia. Historic occurrences in South Carolina are now considered extirpated, and a single occurrence in North Carolina is considered eradicated due to heavy introgression and non-viable subpopulation size. Additional threats to Georgia Oak include drought, climate change, as well as soil compaction and trampling from tourism and recreation, particularly at Stone Mountain, a popular recreation site where the plant was first discovered. Recent and ongoing declines in occurrences, habitat quality, and number of individuals, along with its highly restricted area of occupancy, indicate that Q. georgiana is Endangered.
|Previously published Red List assessments:|
|Range Description:||Georgia Oak (Quercus georgiana) is restricted to isolated granite outcrops and flat-rocks in the Piedmont Plateau of the southeastern United States (Georgia, Alabama, North Carolina and South Carolina, historically). Even within this narrow habitat, however, this species is uncommon, considered abundant at a few localities only. This species' extent of occurrence (EOO) is between 16,570 km2 and 21,600 km2, and its area of occupancy (AOO) is believed to be about 72 km2, possibly up to 272 km2 (well within the threshold for listing as Endangered under AOO).|
Native:United States (Alabama, Georgia, North Carolina - Possibly Extinct, South Carolina - Possibly Extinct)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Quercus georgiana is documented from 14 counties in Georgia, three in Alabama and historically from South Carolina and North Carolina. |
The type locality of this species, located at Stone Mountain, DeKalb County, Georgia, is the best-documented and probably the largest occurrence. Another well-documented occurrence, located on Pine Mountain, Harris Co., Georgia, was observed to be relatively large and healthy in the late 1980s (R. Lance and M. Westwood pers. comm. 2015). Houle and Delwaide (1991) observed that Q. georgiana was often the second most frequent and abundant woody species on soil islands on Arabia Mountain, DeKalb Co., Georgia, in addition to noting a high proportion of juvenile trees (seedlings and saplings), suggesting successful reproduction was occurring at that time.
Occurrences in South Carolina are believed to be extirpated, and the single known occurrence in North Carolina, first documented in 2011, is reported to contain too few individuals to be considered viable (i.e., fewer than ten). Additionally, the North Carolina stand shows a high level of putative hybridization, likely due to introgression by other, more common Red Oak species in the vicinity. Therefore, for the purposes of maintaining the true genetic identity of the species, this subpopulation should be considered eradicated (R. Lance and M. Westwood pers. comm. 2015).
Throughout its restricted range, occurrences of Q. georgiana are small and geographically isolated. However, despite the geographic distance between occurrences, a recent molecular analysis of the species' genetic diversity revealed evidence of gene flow and low genetic isolation between subpopulations, suggesting these occurrences are not genetically isolated enough to be considered severely fragmented (Toppila 2012). The report did note, though, that this apparent gene flow could be a relict of past interconnectedness, and negative consequences of fragmentation may still remain to be seen. This study sampled approximately 25 individual trees each from nine occurrences in Georgia and Alabama (suggesting the population size is at least greater than 225 individuals). Notably, two subpopulations in Georgia were not sampled because trees were infrequent or not positively identifiable, indicating that these occurrences may be declining and/or suffering from introgression.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Quercus georgiana is a small, often multi-stemmed tree, typically growing eight to 15 metres tall. This species is restricted to intermittent granite outcrops and shallow soils overlying granite in the Piedmont Plateau. These discontinuous pockets of soil, sometimes referred to as "soil islands," have been reported to have a soil depth of only 50-100 cm at Arabia Mountain. Georgia Oak is associated with the oak-pine forests of dry slopes of the southeastern US. Its acorns provide an important food source for numerous bird and mammal species, while Luna Moth and Red-spotted Purple larvae feed on its leaves.|
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Use and Trade:||Quercus georgiana has potential for commercial use in the horticulture trade, for propagation as an ornamental plant due to its glossy leaves and vibrant fall colour.|
Threats to Georgia Oak include erosion, poor regeneration and compacted soils resulting from foot and vehicle traffic on granite outcrops. Impacts of tourism and recreation are of concern, given that many occurrences lie within state parks and nature preserves, particularly at Stone Mountain where plants grow alongside popular hiking trails.
For occurrences with especially small numbers of individuals, genetic swamping and introgression from surrounding Red Oak species threaten the genetic identity of Quercus georgiana (R. Russell pers. comm. 2015, R. Lance and M. Westwood pers. comm. 2015).
Climate change may prove a serious threat to this species as well, given that Q. georgiana is confined to intermittent "soil islands" on granite outcrops, which have little or no connectivity to allow migration. Additionally, Q. georgiana displays many of the life history traits associated with vulnerability to climate change: limited dispersal ability, slow reproductive rates, specialized habitat requirements, and restricted distribution and rarity (Pacifici et al. 2015).
Drought also poses a considerable threat to Georgia Oak, given its restriction to very thin soils (50-100 cm in depth at some sites) on granite flat-rocks which provide little or no access to groundwater. Severe drought has been reported as an inciting factor in the phenomenon of oak decline, occurring when typically non-lethal stresses, such as drought, defoliating pests or fungal pathogens, are combined under certain conditions and effectively overwhelm oaks' defences, resulting in potentially widespread mortality (Bendixsen et al. 2015, Thomas et al. 2002). Additionally, many climate models project that climate change will contribute to dramatic increases in drought conditions in much of the United States, including the Southeast (Aiguo 2011). Recent severe drought events are already taking place, such as the drought that reached its peak in 2012, during which the entire extent of occupancy was considered to be affected, with much of this area experiencing Extreme or Exceptional drought intensity in late summer 2012 (Svoboda and the National Drought Mitigation Center 2012).
Quercus georgiana is considered Vulnerable (G3) by NatureServe, and is a focus of ongoing research and ex situ conservation efforts.
Kramer and Pence (2012) highlighted the successful in vitro propagation of Q. georgiana and the potential of cryopreservation as a conservation option for recalcitrant species, which cannot be stored in seed banks, such as oaks.
A recent study found that living collections of Georgia Oak exist in 30 institutions around the world, with 50% of accessions from known wild provenance (Toppila 2012). However, these accessions were found to be collected from only two subpopulations (Stone Mountain and Pine Mountain), indicating that future efforts should focus on collecting from other, more distant subpopulations in order to capture genetic diversity from across the species' range.
A research project is currently underway by scientists at The Morton Arboretum and Chicago Botanic Garden to further examine the genetic diversity of Q. georgiana trees, both in its natural stands and those in cultivated collections, which will help inform and guide future conservation efforts.
|Citation:||Wenzell , K. & Kenny, L. 2015. Quercus georgiana. The IUCN Red List of Threatened Species 2015: e.T34011A2840268.Downloaded on 26 August 2016.|
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