What’s an inland, arid region tree doing hundreds of kilometres south of its native range? How did it end up here?
Along the Rowsley escarpment and nearby at Melton*, there are a couple of isolated populations of ancient White Cypress-pine, Callitris glaucophylla. The next nearest (isolated) report of this arid-zone, inland species is from over 100km north, at the Whipstick state park just north of Bendigo (according to the Atlas of Living Australia). A “disjunct population” like this raises interesting questions of history. Were these Callitris once widespread until changes like wetter times at the end of the last ice age led to most of them being overrun by wet forests? Did wet times bring greater vegetation growth and more fires, to burn them out (and promote the fire-loving Eucalypts)?
The most likely explanation seems to be something like the above, but the possibility of people or animals carrying the seed is also interesting to contemplate. The seed is a favourite food source for many parrots and cockatoos, or at least was until introduced pine species became widespread. I don’t know the history of Indigenous use of the tree, but such a widespread species inland would have undoubtedly been well known if not well used. How they survived here is another question. They are a slow-growing, tough and long lived tree, with a lifespan of at least 250 years(1). But they are vulnerable to fires, and seedlings are vulnerable to herbivores. The timber is strong and durable, resistant to termites, and prized for building. Useful trees don’t last in our culture! Perhaps there were once many such remnant populations in dry corners of southern Victoria, until the arrival of rabbits and pastoralists in the 1800s. A 1985 article on the genus in Victoria in the Victorian Naturalist, reported of our local stands:
“The stands of C. collumellaris are mostly on steep slopes subject to erosion and grazing. Grazing by domestic stock, and rabbits in particular, is responsible for the overall lack of regeneration in these populations…” (2)
A letter to his department from ranger David Munday detailed one small stand which is now right on the outskirts of Bacchus Marsh:
“This small stand…. is completely inside private property, the stands consists of approximately 20 individuals, at present the area is heavily grazed and there are no signs of regrowth. The trees are extremely old and some have already died and fallen over. “Immediately outside the fenceline, and growing on the road easement are quite a number of healthy seedlings, ranging in size from less than 15cm to almost 1 metre. These seedlings have no protection at all from roadside grazing, roadside spraying by Council employees, burning or slashing.” (3)
I had already found some of the remnant population in Werribee Gorge, where the volunteer group Friends of Werribee Gorge and Long Forest Mallee planted a stand at Picnic Point in 1985. Downhill from the planted grove, I found a couple of trees on the rocky spur descending to the river. These are probably from the older population in the Gorge, or maybe even individuals seeded from the replanted stand. I decided to find the stand mentioned by David Munday. It wasn’t hard; it’s just on the edge of town, now. It appeared to me maybe in better health than in 1985, with two trees several metres high by the roadside (see first picture above), and apparently a few more young trees growing up among the ancients. You can see in the pictures, the harsh conditions in this steep north-facing gully where they have been hanging on for who knows how many millenia.
The Picnic Point grove is still going strong, too.
Bacchus Marsh is in a dry, rainshadow region (annual rainfall averages 510mm, or 20 inches in the old measurements). There’s a few other dry-adapted inland species with disjunct populations in the area. Fragrant saltbush Rhagodia parabolica, Bull Mallee Eucalyptus behriana, White Box Eucalyptus albens, and Buloke Allocasuarina luehmannii are noteworthy in this respect. Maybe I’ll be able to cover them in future blog posts.
The Melton population were described in (2) as being at “Exford Weir”. I have since learned they are to be found along the Werribee River escarpment at Parwan/Exford.
Edit (16 October 2016): there’s more at Keilor and west of the Brisbane Ranges, if you count other Callitris species; see comments below & later post here)
References 1. Cohn, J. S., Lunt, I. D., Bradstock, R. A., Hua, Q., & McDonald, S. (2013). Demographic patterns of a widespread long-lived tree are associated with rainfall and disturbances along rainfall gradients in SE Australia. Ecology and Evolution, 3(7), 2169–2182. doi:10.1002/ece3.626
2. Adams, R. (1985). Distribution of Callitris in Victoira and Some Relic Populations Close to Melbourne. Victorian Naturalist 102(2). Reproduced in (3).
3. Reproduced in Douglas, J. and Reid, B. (eds) (2010). Exploring Werribee Gorge 1836-2010. Friends of Werribee Gorge & Long Forest Mallee Inc, Bacchus Marsh.