At Boolcoomatta Reserve recently, under a brilliant blue sky with a hint of the summer to come, Glen Norris, Aaron Fenner and I went to check on a herbivore exclosure in a rocky badlands area. Here most of the mulga trees were dead and there had been no successful mulga recruitment for more than a century.
The exclosure had been built to find out what effect excluding kangaroos and goats, excluding rabbits, and excluding all of the above would have on recruitment by mulga and other plants. We were motivated by the research of Dr Fleur Tiver from the University of Adelaide in the north-east pastoral region, which had found mulga and many other tree species were on a slow road to local extinction.
On the way out we detoured to examine a bore in an area of the property none of us was familiar with, and spotted a distant tree that looked like a white cypress-pine - a species unknown on our reserve but recorded on several adjoining properties. Following a rocky walk we confirmed it as the first white cypress pine (Callitris glaucophylla) to be entered in the database for Boolcoomatta (although examination of some of the fence posts suggest there were more in times past).
This tree was just hanging onto life with half its trunk severely damaged as though it had been struck by lightning. As the tallest thing on a low ridge it was highly possible. After noting a few-full looking fruits but lack of mates we hugged the tree and decided Lone Pine Ridge was a good name for the locality.
From there we retraced our steps with Glen’s frustration building as orange chats sat photogenically and enticingly on top of saltbush and bluebush shrubs, only to fly off when he pointed the camera in their direction.
Nevertheless the plants were more co-operative and every time we crossed a gully with sandy soil we saw many Australian broomrape (Orobanche cernua) plants. A rare plant in South Australia, it’s a parasitic herb that looks like a large multi-flowered orchid with mauve flowers but as a root parasite it lacks green pigment, so the stems are white.
Soon we were at the site with a few mulga recruits we already knew of from our monitoring work a year ago. Some had grown considerably in the past year despite the generally average conditions on top of a dry year previously.
But even more exciting was when we looked further afield – there were a considerable number of Mulga recruits (up to 50) in the adjoining hectare. We surmise these seedlings had developed from seed set following two wet summers in 2010 and 2011 when the Mulgas had flowered well and set fruit. But this raises the question ‘What enabled the first recruitment in more than a century, and outside any herbivore exclosure?
There’s little doubt the goat culling program on Boolcoomatta as part of the South Australian Department of Environment Water and Natural Resources (DEWNR) ‘Bounceback’ program, (of which Boolcoomatta reserve is a participant) had a large part to play in it.
After a 1km walk to the exclosure we found one recruit that had developed to a size where it was obvious, since the exclosure was built 3 years ago.
But the afternoon of discovery hadn’t finished yet, with another exciting event on the way when we found a dispersed population of six slender bellfruit (Codonocarpus pyramidalis) trees - a short-lived species listed as ‘vulnerable’ under the Federal EPBC Act.
This species is thought to regenerate after fire, like its close relatives in mallee and heath communities. But fire isn’t a frequent event in these parts and it may be that the ongoing regeneration of seedlings had never had the chance to develop into the typically tall, narrow, leaning trees we were looking at until the goat browsing had been removed.
We inferred from their size and likely age that these quick-growing and short-lived trees would have also started their lives when the Bounceback goat control program began. In this way they’re like the mulgas, but unlike the long-lived but slow-growing mulga trees, which were still comparatively small, they have a quick component to their lifecycle as visible plants with an extended period as dormant seeds.
It was encouraging to see developing fruit on the bellfruit trees, which when they shed their seeds would then lie in the soil for a long time until some soil disturbance induced them to germinate.
A bit further downslope we found a horse mulga (Acacia ramulosa) the first of this species to be found on Boolcoomatta, and what may be an extension of range from the north and west of the state.
Since we were in tree hugging mode we spread our love around and hugged them all!