Water and the frequent lack of it could be the key that allows such a surprising mix of plants to grow in the Burren - and a new study hopes toprove this. Dick Ahlstrom reports
The Burren is famous for its unusual plant life, but what is it about the Burren that makes this happen? A researcher at University College Dublin believes the answer might be as simple as water.
The rough, wind-swept limestone landscape of north Clare supports a surprising range of plants, from sun-loving Mediterranean varieties to alpine species normally found high up on mountain slopes. "It has been a puzzle to explain the unusual distribution of plants in the area," explains Dr Bruce Osborne of UCD's botany department.
Osborne has begun a three-year €220,000 study to help explain this, with funding from Enterprise Ireland and from the Environmental Protection Agency. "The idea is to look at the role of water availability and its effect on the plant community in the area," he says. It will involve post-doctoral researcher, Dr Deirdre Lynn, and post-grad student, Ms Sarah Ryan.
The western seaboard hardly seems like a place where water would be in short supply, but the unique Burren habitat helps to create this situation, says Osborne. "It may be associated with the nature of the substrate," limestone rock underneath and precious little soil above. "There is actually very little storage availability in the limestone aquifer," he says, so the plants are forced to endure "episodic drought" between rainfalls as the thin soil quickly dries out.Osborne has already conducted experiments showing that plants growing in the Burren respond to water supply in an unusual way. They could be adjusting to the unique conditions, causing them to respond to rainfall in a different way to plants in less extreme conditions.
"The plants seem to be very susceptible to differences in rainfall," says Osborne. Just two hours after rainfall many begin to batten down the hatches as if preparing for drought. Photosynthesis is reduced and pores in the leaves, known as stomata, start to close.
The stomata are crucial for plant survival, says Osborne. They open to allow in carbon dioxide for photosynthesis, but they also regulate water loss. "These control the loss of water to the atmosphere," he says. They close down to retain moisture, but in doing so reduce carbon dioxide intake and so photosynthesis.
These unexpected characteristics may be caused by the quick dry-out experienced in the Burren. "It could be the shift from one extreme to the other. We are going to test this in laboratory experiments," says Osborne.
Central to the work will be the use of natural leaf fluorescence as a way to measure photosynthetic activity. After exposure to strong light, leaves fluoresce for a time and then the effect declines. "It is an indirect assessment of photosynthesis," says Osborne.
It is easier and faster to measure, but also means that communities of plants can be tested together, an approach that he describes as "very important". The team can measure 50 or 60 plants over an area in a few hours, giving a better impression of how water availability is affecting plant activity.
Field work will be matched in the lab with structured experiments giving a measurable connection between levels of fluorescence and known water deficits. Plants of a single species from the Burren will also be compared to the same species taken from places where water availability is more stable.
It could be that evolutionary selection pressure exerted by the Burren is influencing plant response. "If the water supply is the main ecological factor, then there should be selection," he says. They will also try to transplant matching species into the Burren to see how they cope with the tougher conditions.
No rare plants are being used and the team is licensed to pursue this work, explains Osborne. The main species under study is Teucrium scorodonia or "wood sage", an abundant nettle-like plant that thrives where drought conditions are worst. Others include the hazel, a grass species called sesleria and a small shrub, Mycelis muralis.
The work involves more than Burren conservation, says Osborne. Climate change and local water extraction could tip the balance against these plants. "If there are plants only just able to survive then if that \ should increase we don't know what will happen," he says.
Osborne is editing a special Proceedings of the Royal Irish Academy related to the Burren which should be out next year.