Cave fern drawing: Margaret Saul
Scientific name: Tectaria devexa var. devexa
Conservation status: Tectaria devexa is listed as Endangered in Australia (Environment Protection and Biodiversity Conservation Act 1999) with two varieties of this species occuring in Australia (Tectaria devexa var devexa and Tectaria devexa var. minor). Tectaria devexa var. devexa is the variety that occurs in Queensland, Sri Lanka to Thailand, south China and Taiwan, the Philippines, and Malesia to Vanuatu. This variety is listed as Endangered in Queensland (Nature Conservation Act 1992) and is considered a low priority for conservation under the Department of Environment and Heritage Protection Back on Track species prioritisation framework.
Tectaria devexa var. devexa (T.devexa var. devexa) is a small, tufted, terrestrial fern with pale green fronds.
Habitat and distribution
T. devexa var. devexa typically grows in thin pockets of soil on the walls and floor near the entrance to limestone caves. It can occur deeper within the cave in situations where sufficient natural light and moisture are available to support plant growth. Mature plants produce microscopic spores that spread over the surrounding cave surface and which germinate during moist conditions. The moisture required to sustain these ferns is largely from seepage that occurs after periods of heavy rainfall.
T.devexa var. devexa is widely distributed on limestone in Sri Lanka, parts of Southeast Asia and Vanuatu. Within Australia, the cave fern is known from just two places in The Caves district, 25 km north of the central Queensland city of Rockhampton. Thousands of kilometres separate the ferns of central Queensland from other populations of this variety in the Pacific and Asia. This may indicate that the Queensland varietie is a relict population from a time when the distribution of the fern was more continuous across the land masses that now make up these Asia-Pacific countries. For this to be the case, the ancestors of the Queensland population may have survived in isolated pockets of suitable habitat for in Australia hundreds of thousands of years.
Alternately, the ancestors of the Queensland cave ferns may be more recent colonisers, whose tiny spores were carried to Australia on the wind, or even on the body of a bat or bird. The colonisers may have initially thrived and expanded in range if they arrived when conditions were wetter. Recent changes in climate and habitat since that time may have caused the cave fern population to contract, leaving the two disjunct populations of the cave fern which persist today in central Queensland.
The cave fern was first collected by botanists from Capricorn Caves, one of the two known Australian sites, in 1945 where plants reportedly covered large sections of the cavern walls. A small second population was discovered at a cave entrance at nearby Mt Etna National Park in 2001.
There is anecdotal information that around the time of European settlement the cave fern may have been more widespread around the caves.
The limestone caves and associated vine thickets north of Rockhampton support a number of species of special conservation interest in addition to cave fern. Examples are the ghost bat Macrcodema gigas and the shrub scarlet fuchsia Graptophyllum excelsum.
A survey in the mid-1990’s highlighted that the cave fern population at Capricorn Caves was in decline. A total of just 39 adult and sub-adult plants were observed. Ten years later, the number of plants had dwindled further to 21 at six different locations within the cave system.
When discovered in 2001, the nearby population at Mt Etna Caves comprised just four adult plants and 5-6 juveniles. The health of these ferns was also observed to decline over time.
The reduction in the number of cave ferns at both sites has been largely attributed to prolonged dry periods associated with drought.
A national recovery plan for Tectaria devexa has been developed and outlines conservation management actions to help recovery of the species. An innovative project to recover T.devexa var. devexa was commenced in 2006 by Greening Australia in partnership with Capricorn Caves, the Queensland Herbarium, Heaton’s Fern Nursery, Griffith University and The Society for Growing Australian Plants. The project was funded through the WWF Threatened Species Network.
The project pioneered the propagation of T.devexa var. devexa, with hundreds of young plants successfully raised from spores collected from mature surviving plants. Ferns which were hand-raised in a controlled environment have been planted out into suitable micro-sites at Capricorn Caves. Many of the ferns have survived, however they are vulnerable to changes in weather and will wilt in prolonged periods of hot weather. While the fronds may appear dead, it has been found that the rhizome (roots) can remain dormant for 6-8 weeks. They recover after rain and soon grow new fronds. A watering system has been installed to help the ferns survive dry periods.
The excessive rainfall in 2011 created a population explosion on the cave wall which was sustained until December 2012, when the ferns showed signs of stress due to the prolonged dry and increasingly hot weather. Rainfall in January 2013 revitalised the population.
Prolonged dry weather isn’t the only obstacle that cave fern endures. It is also eaten by native rock wallabies, and scrub turkeys will uproot the fern as they search for bugs among the rhizomes. Covering the ferns with wire mesh helped to protect them from marauding wallabies and turkeys.
Butz M. 2004. National Recovery Plan for Tectaria devexa. Department of the Environment and Heritage, Canberra.
Department of Sustainability, Environment, Water, Population and Communties. 2012. Tectari devexa Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra.