The Yarra Gum
This is the story of a gum tree

I would venture to guess that many of you who read Tree Talk would have seen this gum tree in your travels, possibly on your own property. It tends to blend in with the other gums- just another tree in the bush. However, this tree is special. Not only for it's rarity but for the fact that one of it's main strongholds is right here in our own backyard, the Upper Barwon River Catchment.

The tree in question is the Yarra Gum (Eucalyptus yarraensis) and is endemic to Victoria. It grows nowhere else in Australia. The name obviously comes from the river of the same name where the species was first described, and is now very rare due to the suburban sprawl heading east out of Melbourne. According to Pryor (1981) the species was "probably never numerous and there are now mere remnants of the species in scattered localities throughout its original range." Those other localities include Gippsland (where populations only exist in unreserved remnants), Ballarat and the East Otways. On a positive note, the Ballarat population and our own East Otway population are more secure due to some stands growing in reserves.

Let's have a look at the ecology of the plant and how it is shaping up in our own area. Most of the trees found in the Upper Barwon Region are very large, isolated and tend to be on their last legs due to a number of reasons:
1. They are usually found as single trees growing in paddocks where stock camping, mistletoe, extreme winds, and increased salinity has taken their toll;
2. Because of the agricultural value of the land where it grows, very few of today's isolated remnants are fenced out, leaving little chance of seedling regeneration;
3. Due to the isolation, there maining trees tend to be in bred and can struggle to produce healthy seedlings.

Pryor (1981) states the yarra gum is "in a highly precarious position and one of the most threatened of the eucalypt species". Then, in 1992 the yarra gum was recommended for listing under the Flora and Fauna Guarantee Act (FFG) as under threat of extinction. This was, however, turned down by the scientific advisory committee doing the investigation. They stated the species was reproducing adequately on a statewide basis and the populations around Ballarat and the East Otways were secure. They also said that the species has been confused with other swamp gums and may be more abundant than was originally assumed. In the Angahook-Otway plant study (2003), DSE listed the yarra gum as "poorly known" (as opposed to rare or threatened, etc) and it also noted its rejection for listing under the FFG.

There are healthy reserves in our region, albeit fairly small reserves. Populations at Wensleydale, Bambra, Ricketts Marsh, Pennyroyal, Murroon and Yeodene are on road or rail reserves (and unofficially reserved), and one population is included in the Otway Forest Management Plan (in need of protection). I am personally not sure if the Forest Management Plan is still relevant with all the changes from DSE to Parks, etc. A beautiful stand of Yarra gum is situated on the old Birre-Forrest railway (now private land) at Murroon just north of Creamery Lane. The trees are very old and many are still healthy but with very little regeneration.
Over the years, the identification of the Yarra gum was often mistaken for a swamp gum (E. ovata).

There are a number of "swamp gums" in Victoria, all closely related and resembling one another. To make this story even more complicated, there is another "swamp gum" growing in our own region- Brookers Gum (E. brookerana) which tends to grow in the higher rainfall wet sclerophyll forests of the Otways. If you were trying to work out the identification of a eucalypt, nine times out of ten you would use the buds and fruit to help with that identification. However, if buds and fruit were collected from all three species and displayed on the bar at Martians Café, even Leon Costermans may have trouble distinguishing between the three! It is really the subtle differences that may help the layperson distinguish the Yarra Gum from the other two species:
1. Yarra gum has a rough, almost flaky bark up to the small branches. Swamp gum has a thick rough stocking about a third of the way up the trunk revealing a mostly smooth white/grey bark at the top. Brookers gum is mostly smooth with a relatively short rough stocking.
2. The best way to tell the difference between Yarra and Swamp is the mature leaves. Yarra has quite short (50-100mm) leaves and are oval in appearance. Swamp has "typical" gum leaves ie., sickle shaped- long (100mm-150mm) and narrow and tend to be somewhat crinkly (a scientific term for a leaf not laying flat when placed on a surface). Brookers gum has crenulated juvenile leaves (the leaf edge is minutely serrated). The other two species have no serrated juvenile leaves. There are only a handful of gums across Australia with this feature.
3. And as to those woody seed capsules, all three species have "megaphone" shaped gumnuts. The swamp gum and brookers gum have larger gumnuts than yarra gum, but only marginally.
4. Guess what, the buds are usually found in groups of seven... on all three species!
5. If you're really keen to identify a yarra gum, grab some leaves and boil them in water for two minutes. If it is a yarra, a volatile oil called benzaldehyde will be given off by the process. And according to Simmons (1986) it smells of a cross between bitter almonds and fish oil! So if you're really not sure what tree is out in the back paddock....

We have been growing the local yarra gum since 1995 and according to our records, over 20,000 have gone out to customers and landcare recipients in the region. If you have been one of those customers, you might just want to start looking out for it. It is a beautiful tree. It grows quickly and some customers have been pruning some for agroforestry due to the fine form they have experienced. The timber is dense and hard and when finished has a dark orange/brown appearance.

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