A Rare plant that is a long way from home

Eucalyptus aggregata is a medium-sized tree with a sparse canopy and fissured bark on the trunk and branches.  It is known in Victoria from a few locations near the central Victorian towns of Woodend and Daylesford.  Almost all of the known populations are on private property or public land that is not managed primarily for flora and fauna conservation.  Nearly all sites that support Eucalyptus aggregata show signs of heavy disturbance with non-native species, some of them aggressive weeds, making up the bulk of the understory vegetation.  The species has been classified as endangered in Victoria and has also been listed under the Flora and Fauna Guarantee Act (FFG).

The evidence presented in the above paragraph seems more than enough for the conservation classifications that have been applied to Black Gum provided that two things are true.  First, that it is the same species as the much more widespread population in NSW, and second, that it is indeed native to Victoria.

Eucalyptus aggregata is moderately widespread, although seldom abundant, in NSW in a broad east-west band from Orange to the ACT.  It is listed as Vulnerable in that state as most stands are in places that are heavily grazed and contain few individual trees.  The population in Victoria is 500 km away from the nearest NSW record and this in itself is often reason to question whether they might represent another species.  This is quite a commonplace event in botanical identification, for example, Boronia citriodora is an aromatic shrub which is widespread in Tasmania but in 1973 was discovered in a single location about 5 km east of Licola, in Victoria's high country - about 500 km from the nearest Tasmania populations.  Subsequent close comparison of specimens collected from the Licola area with those from Tasmania determined that it was a new species unique to Victoria - now called Boronia citrata.

Victorian botanist, Dianne Simmons (Deakin University), making a similar comparison of Eucalyptus aggregata specimens from Woodend with those from NSW, found no significant differences between plants from the two states.  This is unusual as plant populations which have been geographically and reproductively isolated for a long time usually show distinct differences.  Nevertheless there seems to be little doubt that the Eucalyptus aggregata in Woodend is the same species as that in NSW.  But is it native to the Woodend area?

Woodend, like Orange, in NSW was established during the gold rush years of the 1850s and therefore has a long history of European settlement and was an important service centre for the Bendigo and Castlemaine goldfields.  It had a large number of inns and other accommodation centres and was heavily used by travellers and temporary residents, including those involved in botanical exploration.  It is perhaps a little surprising then, that Eucalyptus aggregata, which was first described from Orange in 1900, from a specimen collected 14 years earlier, was not discovered in Woodend until 1964.  This would be understandable if the species was very similar to other local trees or that is was very rare and restricted to a few locations, but neither of these are true.  Eucalyptus aggregata is quite distinct from the other local tree species, all of which are represented by specimens from the late 1800s or early 1900s.   And while it is comparatively rare the known locations are all around the township, not just one or two sites, and there are 10,000 or so existing trees in an area where much of the native woodland has been removed.  An added complication is that there are no populations in recognisably native vegetation, they are all in disturbed sites and all within a few km of the town centre; that is, there is no clear evidence that the tree is part of a native vegetation community.  The only record away from Woodend is from the township of Daylesford and both the identity and location of this record is, according to the DELWP Action Statement, now in doubt.

It is quite possible that plants from the NSW goldfields were transported to those in Victoria, either deliberately or accidentally, during the gold rush years or later on.  These plants may have taken some time to establish in any numbers and this may account for both the late discovery of the species and its high similarity to those from NSW.

If this interpretation is correct - although the current determination by DELWP and the Melbourne Herbarium is that it isn't - then it has a number of precedents.  For example, Eucalyptus macarthurii, a widespread but uncommon tree of the Sydney region (classified as Vulnerable in NSW), has been recorded several times around the township of Emerald east of Melbourne.  When it was first discovered, however, a taxonomist described it as a new species for Victoria because it appeared to be behaving as a native.  It was only a year or so later that it was determined to be the same as E. macarthurii from NSW which had become established in the local vegetation from earlier and undated plantings.

The above argument is probably irrelevant in the specific case of Eucalyptus aggregata as it has already been accepted by the relevant authorities as native to Victoria and threatened.  Nevertheless, the basic premise that small, isolated populations of plant species may not always be as they seem, is one that needs to be kept in mind when assigning a conservation status.