Forty years ago a young PhD student left a great legacy. She did all the things that PhD students are supposed to do. She wrote a great thesis, and put a copy in the library for others to read. Better still, she published five papers in scientific journals – a great outcome indeed. By publishing her work, she allowed others to answer the questions she had asked, without needing to repeat her experiments.
But she did more than that. She left a legacy that allowed others to answer, not just her old questions, but new questions, by building on her data.
She banged a stake into the ground. In fact she banged lots of them in the ground, one picket in the corner of each of her plots.
Forty years later, the student no longer does research, her papers aren’t read that often, and her questions aren’t that popular any more. But the stakes are still there. And they show us things we couldn’t otherwise see. That’s an amazing legacy for a student who abandoned research at the end of her PhD.
The student’s name was Jennifer Withers. Dr Withers did a series of fantastic experiments in the laboratory, glasshouse and field, to try to understand why some species were declining and others becoming dominant in an unburnt woodland. In the language of today’s ecology, she attempted to link plant traits and ecosystem assembly. In the language of her era, she investigated how the ecophysiology of dominant trees influenced vegetation succession. And fortunately, she left some stakes, fences and plastic tags that marked the seedlings she planted, many of which still survive today.
When Dr Withers set up her plots in the early 1970s, the Ocean Grove Nature Reserve contained an open grassy woodland that was beginning to be overtaken by dense shrubs and small trees, especially Golden Wattle (Acacia pycnantha) and two Allocasuarina species, Black She-oak (Allocasuarina littoralis) and Drooping She-oak (A. verticillata). At that time, many open gaps remained, but it seemed inevitable that the woodland would continue to thicken up if it remained unburnt.
Jennifer and her supervisor, David Ashton, did lots of experiments to work out why some species were regenerating while others didn’t. In the glasshouse, they measured how well seedlings grew in pots, some of which they left shaded or unshaded, while others were watered and left dry. In the field, they put seeds in trays and counted how quickly ants ate the seeds of different species. They sowed seeds and seedlings into plots that they burnt, to see if some species needed fire to promote their establishment. Plastic plant tags must have been a lot tougher in the 1970s than they are nowadays, because many of the tags they used still survive today.
I first visited the plots in the mid-1990s, 25 years after they were first surveyed. It was fascinating to see how the vegetation had changed in the interim. The density of trees had almost doubled and the large open gaps had almost completely disappeared. In 1996, there were over 5,600 trees and saplings per hectare, which is extremely dense! Surprisingly, many of the eucalypt seedlings that Dr Withers planted in her burnt plots were still alive 25 years later, even though they were less than knee-high and spindly, suppressed by tall she-oaks and wattles. Suppressed eucalypt seedlings just seem to hang in there forever.
Last weekend I re-visited the plots for the first time since 1996 – the first time in 15 years. It inspires a certain sense of awe to sit in a small fenced plot where someone counted plants 40 years ago, sowing seeds that would stimulate even more ecological inquiries 40 years later.
In the last decade we’ve had a long, severe drought, and there are many more dead trees now than there were in the 1990s. In the 1990s, hardly any She-oaks were dead (only about 1%), but many have since died. There don’t seem to be as many young saplings now either, whereas saplings were really common 15 years ago. These are impressionistic observations from a short visit, and I wouldn’t put much stock by them at this stage.
Fortunately, courtesy of the Withers Pickets, we can easily re-measure the plots, and see how one of the worst droughts of the last century has influenced the long-term process of vegetation encroachment (or ‘thickening’). In other regions, severe droughts have completely reversed the process of thickening that occurred during wet decades. The changes at Ocean Grove are not that dramatic, but it shall be interesting to see how many trees died during the drought , and how the relative abundance of different species has changed. Was tree mortality density dependent, with more deaths in areas that had more plants initially?
Quantitative ecology is a young profession. In Australia we have precious few data sets that extend longer than 40 years. The Ocean Grove plots are an important scientific resource for documenting how Australian ecosystems have changed over many decades. This legacy is solely due to a student who vanished from the research world soon after she finished her PhD.
Our new ways of storing information aren’t built to last. To view the data that I collected 15 years ago, I now need to find a computer that will read my old floppy discs. By contrast, a stake in the ground is immutable.
The Withers Pickets gave me an opportunity to act as a link in a longer chain, updating Withers and Ashton’s work for another generation of ecologists. The stakes I leave will let others answer new questions in the future.
To the class of 2011: Leave a legacy. If you seek immortality, hammer a stake through your plots. It’ll probably outlive everything else that seems important right now.
Lunt ID (1998a) Two hundred years of land use and vegetation change in a remnant coastal woodland in southern Australia. Australian Journal of Botany, 46, 629-647.
Lunt ID (1998b) Allocasuarina (Casuarinaceae) invasion of an unburnt coastal woodland at Ocean Grove, Victoria: structural changes 1971-1996. Australian Journal of Botany, 46, 649-656.
Withers JR & Ashton DH (1977) Studies on the status of unburnt Eucalyptus woodland at Ocean Grove, Victoria. I. The structure and regeneration. Australian Journal of Botany, 25, 623-637.