LOVE them or loathe them, jacarandas, with their brilliant purple petals, have an important story to reveal about the effects of climate change.
The familiar Sydney trees are part of a new ''citizen scientist'' project in which visitors to the Royal Botanic Gardens can observe a selection of plants and animals and record information such as whether they are in bloom, nesting, or flying about.
Other ''indicator'' species on the ClimateWatch trail - the first in an Australian botanic garden - include English oaks, firewheel trees, cabbage white butterflies, cotton harlequin bugs, black flying-foxes, common koels and St Andrew's Cross spiders.
Brett Summerell, director of science and public programs for the gardens, said all the data would be made freely available to researchers studying the biological impacts of a changing environment.
It was hoped visitors would go back to their own backyard, park or local bushland and continue to observe indicator species, for years if possible, uploading their reports onto the ClimateWatch website.
Scientists on their own could not gather the vast amount of national data needed on species distribution or breeding cycles to detect any subtle shifts due to a warming world.
Community assistance was vital. ''ClimateWatch empowers every Australian to become a citizen scientist [and] help shape the country's scientific response to climate change,'' Dr Summerell, a scientific adviser to the national program, said.
Criteria for choosing the indicator plants included ease of identification, broad geographical range and characteristics that changed abruptly with temperature and rainfall, he said.
Because jacarandas are natives of South America, Herald readers have recently hotly debated the virtues of Sydney's annual purple haze on the letters page.
The trees were certainly very easy to identify, said Andy Donnelly, science director of Earthwatch, which co-established ClimateWatch.
And it was important to include non-natives on the list, he said. ''Then we can compare what is happening here with other parts of the world.''
Jim Nicol, head volunteer guide at the gardens, said plant lovers and amateur botanists had a long history of contributing to scientific knowledge. The new trail provided a timely opportunity to help answer questions about climate change.
''Getting this sort of data is very valuable,'' he said. The guides will start leading free training walks on the ClimateWatch trail from Wednesday, November 23. Mr Donnelly said as technology developed, people would be able to upload photographs and GPS locations from anywhere, to improve the accuracy of the data.
They could also create their own local trails to monitor and get community groups, schools or workplaces involved.
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