On the steep hillside near the western boundary of my property, and visible from the highway as you travel south from Oatlands, is a village of small plastic domes. When they first went up, I used to think they looked like extra-terrestrial vehicles just the right size for a baby Yoda.
In fact, they are part of an international research program looking at the effects of climate change on native pastures in many locations around the world. The Tasmanian component of the program is run by Prof Mark Hovenden and his team from the University of Tasmania.
The domes are open at the top, and cleverly designed to maintain the temperature within the dome at 3°C above the ambient temperature, mimicking the long-term temperature rise predicted to occur as a result of human-induced climate change. Several times a year, Mark and Co. take precise measurements of species composition and other variables, including seed set and soil moisture, both inside and outside the spaceships. The experiment has been running since 2015.
Initially, the dominant species in half of the plots were removed, in order to study the ecosystem’s response to human-induced global warming in terms of the type and variety of species in the native grasslands. This has particular interest to me because of the importance of biodiversity in sheep nutrition as well as the resilience of the ecosystem to naturally occurring variability in weather patterns.
I asked Mark if he would be able to share any initial results from the first five years with us, and the following are his comments. “First off, warming in such a dry system as at White Gum has led to a reduction in soil water content, as the plants release more water in an effort to stay cool. The chambers warm the plants by 3°C and that extra few degrees on a hot day, or even a warm one, is enough to make the plants use considerably more water to cool their leaves. Plants cool their leaves using evaporative cooling, just like people do when they sweat.” (We’ll come back to the issue of evaporation and evapotranspiration in another Yarn—Nan.)
"This extra water use means that the soil becomes drier in the warmed plots than in the plots without the chambers. It also means that plants compete more with each other for the water in the soil. The outcome of this is that plants in the warmed plots produce fewer seeds than those in the unwarmed plots, and this is entirely due to increased competition from their neighbours.”
“Unfortunately, this means that the prospects for the future of water-limited environments such as at White Gum are not great if we cannot halt global warming. Seeds are very important for , recruiting seedlings and new plants into the community following dry times. There has been reduced recruitment in our warmed plots, meaning that over the five year period, the number of species has declined in the warmed plots.”
“There are, however, a few winners. One such winner is the dominant grass, the (native) spear grass, and another is the native morning glory, Convolvulus. Both of these species do well out of the harsher conditions as they are basically tougher and do better when there are fewer other species around. Luckily, they are both natives.”
It’s worth noting that Mark’s results are independent of changes in rainfall, since the rain falls equally on the plots with and without domes. Drying occurs because of the temperature rise. The effects will be more pronounced if reduced rainfall in the long-range forecast for SE Australia from climate change models is correct. In a future Yarn I’ll return to rainfall issues, as well as evaporation, in the context of historical meteorological data.
As sobering as Mark’s results are, though, there was a hopeful coda the other day. The day after reading Mark’s comments, I took the flock into a fresh paddock with a lovely collection of native morning glory, one of his climate change “winners”. While I often see it on the property, I’ve never been sure the sheep eat it.
The flock pretty much stalled, all 550 heads down and grazing, and soon I saw head after head come up with pink morning glory flowers hanging out the sides of their mouths. Yep, they certainly do eat it, with great relish. After waiting an hour or so for them to finish up and move on, Pearl and I eventually gave up, left them to their feast, and went home to our own lunch.