Conservation of Carnivorous Plants and Bog Communities at Atlanta Botanical Garden, Georgia, U.S.A.
Volume 2 Number 10 - June 1998
Ron Determann and Madeleine Groves
Officially incorporated in 1976 on land belonging to the City of Atlanta in Piedmont Park (the city's largest communal park), the Garden's mission is to develop and maintain plant collections for the purposes of display, education, conservation, research and enjoyment. The Atlanta Botanical Garden (ABG) is a private, non-profit botanic garden overseen by a Board of Trustees, with over 40 staff, upward of 300 volunteers, and a 10,000-strong membership base.
Like many urban botanic gardens, ABG makes the most of the 30 acres it occupies within a busy metropolis. The outdoor collections offer botanists, horticulturists, and the general public a series of different landscapes to explore. These range from the traditional, such as the Japanese and Rose Gardens, to the more informal, such as the Woodland Garden and Storza Woods. The latter is an example of the few remaining acres of mature hardwood forest found within the metropolitan area. Plants native to the southeastern USA, in particular carnivorous plants, are well represented within the collections with many species found within the outdoor bog area and surrounding educational planters. ABG's Sheffield Botanical Library, Plant Hotline and Plant Mobile provide the public with access to botanical and horticultural information and allows the Garden to reach a wider audience.
The centerpiece of the Garden is the Dorothy Fuqua Chapman Conservatory. Opened to the public in 1989, and voted one of the three most significant conservatories in the USA (Garden Design Magazine, 1997). The Conservatory covers 16,000 sq. feet including a tropical Rotunda, desert house, special exhibit area and Orangery. Serviced by backup greenhouses covering 10,000 sq. feet, the collections focus on under-represented and endangered plant groups. They include Old World desert collections, Old World island palms that follow an island biogeographical theme, and other conservation collections including tropical conifers, orchids, cycads and carnivorous plants. ABG also houses a collection of poison dart frogs that are on public display, with interpretive signage, in the Conservatory lobby.
ABG's Conservation Program encompasses a number of regional and international projects and has a hands-on and project-driven approach. The key to this Program has been to work directly with local landowners, to bring as many of the relevant agencies, botanical institutes and organizations into collaboration, and to disseminate the staff's horticultural and botanical expertise to as wide a field as possible. One of its major goals is to use low-cost restoration and recovery techniques.
ABG has one of the world's most comprehensive and stunning collections of native and non-native carnivorous plants. As part of its Conservation Program, ABG is active in the monitoring, restoration and conservation of their habitats, especially the unique and species-rich bog communities that are found throughout the Coastal Plain and Southern Appalachian Mountains of the south eastern USA. Impacted by agricultural runoff, land conversion, soil erosion, drainage, herbicide use, invasive exotic species and the exclusion of many processes, such as fire, many of these plant communities have been reduced to small, fragmented plots of land. With little or no buffer to offset continual encroachment from human activities, species diversity is in steady decline. The carnivorous pitcher plants (Sarracenia spp.), endemic to the eastern and Gulf Coast States of the USA, are often cited as an example of this decline. It has been estimated that only 2.5% of Sarracenia habitat remains in the southeastern USA (Groves, M., 1993, Sarracenia A Review of Trade & Conservation in the Southeastern USA. Fauna and Flora International. Proceedings of a meeting held on 22-23 September, 1993 at the Atlanta Botanical Garden, Georgia, USA).
Succession by invasive woody species, both native and non-native, is a major problem facing degraded bog communities, especially when favorable growing conditions arise. These can occur when the hydrology of the site is tampered with and the water table is lowered, and when processes, such as fire, which normally would keep woody species in check, are suppressed. This eventually leads to the herbaceous layer being shaded out. It is, however, this herbaceous layer that provides the fuel to 'carry' the fires that are associated with maintaining these open, nutrient-poor, and species diverse habitats.
Controlling woody species can be achieved through full-scale and/or selective burning which can be carried out at different times of the year depending on the type and status of the habitat and species diversity involved. When restoring degraded habitat (e.g. removing woody species and restoring the fuel layer) winter burns are effective. When maintaining and/or manipulating it after restoration (e.g. controlling resprouting woody species) summer burns are effective. ABG now uses a combination of the two with severely degraded habitats. Summer fires can, however, occur naturally with lightening strikes. Winter burns, which historically were the result of Native Americans burning for game food plots, are often still favoured by landowners. Winter burns are effective in controlling the build-up of sedge and grass species that can choke out many less vigorous herbaceous species, and, when carried out earlier in the year, do not damage emerging flower buds. The leaching of nutrients released by burning is also far greater at this time of year as it occurs before they can be taken up by new vegetation. This favours plants, such as Sarracenia species, that prefer the low nutrient bog soils.
Controlling woody species involves cutting back shrubs and trees in the winter or summer and scorching the resprouting stems with a simple, clean and highly effective propane-fuelled flame thrower developed by a pitcher plant connoisseur from Mississippi. This technique damages or kills the cambium layer, making the plants susceptible to disease and decay, especially in the summer months when pathogens are active and the plants are in full growth.
However, this work is being compromised at present due to the difficulty in getting smoke easements for burns. Years of anti-fire/anti-smoke propaganda, symbolized by 'Smokey the Bear', has produced a fear and intolerance of fire and smoke. In solving this problem close community relations and education programs are needed to demonstrate the benefits of such restoration work to the community and biodiversity. It is ironic that the burning of these habitats, given their small size, would produce no more smoke then the average large trash pile that can often be seen burning in this region.
The restoration and maintenance of the site's hydrology and soil structure are equally important. Many bogs, especially low-lying sites suitable for conversion to agriculture, have had drainage ditches or drainage tiles installed to lower the water table. Given the complex hydrology of these wetland habitats, it is vital not to break through the hard pan when restoring the hydrology. Also, any restoration work must be carried out with the minimum of human traffic and machinery to minimize soil disturbance and the creation of ruderal sites where more opportunistic plants (e.g. briars and exotic species) can take hold. Again, a simple, but effective method is to dam up ditches using the organic debris accumulated from clearing the site. This slows the entry of water into the bog, reducing the erosion and widening of any ponds and ditches. The debris also acts as a sieve, reducing the amount of silt deposited over the bog that can eventually choke out the majority of the plant species adapted to growing in bog soils. Creating these organic dams also maintains or restores a high water table, an intrinsic element to these habitats and one that would, historically, have been maintained through beaver activity. The motto at ABG is 'think like a beaver!'
ABG conducts many projects in collaboration with The Nature Conservancy, other Georgia Plant Conservation Alliance members (see news item), and is under contract to the US Fish & Wildlife Service (USFWS) to assist in the recovery of several endangered carnivorous plant species. ABG is, at present, focusing on the recovery of the three Federally Endangered pitcher plant species, Sarracenia rubra spp. jonesii (Mountain Sweet pitcher plant) in North and South Carolina, S. oreophila (Green pitcher plant) in Georgia and Alabama, and S. alabamensis (Alabama Canebrake pitcher plant) in Alabama.
ABG also encourages many of the different organizations and individuals involved in the trade, conservation and propagation of carnivorous plants to collaborate, and is an active member of the IUCN Species Survival Commission's Carnivorous Plant Specialist Group (CPSG). In September 1993, ABG hosted an innovative meeting to discuss carnivorous plant conservation in the south eastern USA. Participants included the USFWS, US Office of Scientific Authority, paper companies, taxonomists, botanists, ecologists and private landowners. A number of collaborative projects arose from this meeting and, as a follow up, ABG hosted the first International Conference of the International Carnivorous Plant Society at the Garden in May 1997. There were over 100 participants and 20 speakers from the UK, USA, Sabah (Malaysia), Japan and France.
ABG's tissue culture laboratory propagates rare and endangered native and non-native species. It also raises funds for the Conservation Program through the development and propagation of unusual and horticulturally interesting plant forms and cultivars. These include an all red form of the Venus flytrap (Akai Ryu - Red Dragon developed by ABG staff member, Ron Gagliardo) and an all green form of the Gulf Coast purple pitcher plant (Sarracenia purpurea subsp. venosa var. burkii).
ABG's expertise in carnivorous plant habitats is based on over 15 years experience in the field and from working with landowners and conservation organizations who have managed such sites for over 40 years. Although the main goal is to conserve primary habitat with a surrounding buffer zone, ABG has developed restoration, management and propagation techniques to augment these communities and re-establish certain processes crucial to the maintenance of species diversity.