A round up of Walker Swamp’s Eucalypt diversity with expert Dean Nicolle

In early December, a band of twenty botanical enthusiasts spent a great morning with Eucalyptus expert Dean Nicolle exploring the diversity of Eucalyptus species found across NGT’s Walker Swamp Restoration Reserve. Dean is an authority on the Eucalyptus species of Australia and has written a number of books on the topic. You can find out more about Dean and purchase his excellent books on his website.

Dean took a couple of days to explore the site, identifying all the species, and he found some pretty interesting things that he shared with us on the day. So here’s a rundown of all the species we now know to occur across the Reserve:

Eucalyptus cygnetensis subsp. viminalis (Rough-barked Manna Gum)

Rough-barked Manna Gum is relatively common across the sandy lunettes that separate the wetland basins on the property, which would have been part of the once widespread Sand Forest ecological community. Sand Forest is also the dominant vegetation type found in the bush block that we added to the property in 2023. Rough-barked Manna Gum is the most common overstorey species in the Sand Forest remnants found on the property. Sand Forest itself,  as a vegetation community, is fairly rare across the Grampians area.  It’s an important community for us to understand the structure of because most of the revegetation required at Walker Swamp will be Sand Forest.

The interesting thing about the manna gums across the property is the sheer diversity of different bark types, leaf sizes and tree forms that are present. They are surely one of the most morphologically diverse species of eucalypts. At Walker Swamp we see quite smooth-barked forms with white or orange bark to very shaggy forms with deeply fissured bark and a variety in between. Dean thinks that age, and possibly environmental conditions, are responsible for the physical diversity.

Manna Gum, we have noticed, doesn’t seem to recruit very readily across the property but there are some younger plants scattered about.

Eucalyptus camaldulensis (River Red Gum)

No surprises here, we know that the Reserve supports a large number of River Red Gums, including over 100 large old individuals across the heavier soils of the flats that surround the numerous wetlands of the Reserve. We monitor the health of these trees each summer, and you can read more about what we have learnt from six years of monitoring here.

We see good recruitment of Red Gums across the Reserve, particularly after a very wet year, as the seeds germinate in response to a good long soak. So, there is a good diversity of different age classes throughout the property.

Eucalyptus melliodora (Yellow Box)

Yellow Box at Walker Swamp occurs on the edge of the Sand Forest block in small numbers. There are scattered records of Yellow Box throughout the Grampians, so this isn’t entirely unexpected. Yellow Box-dominated woodlands were heavily cleared across Victoria as it grows on soils that are heavier and were preferentially cleared for agriculture. Because of this historic clearing, much of the remaining Yellow-box woodlands occur as a subdominant species on the fringes of other remnants, as it does here. At Walker Swamp they are slender, tall upright trees of various ages with characteristic ‘box’ bark.

Eucalyptus ovata (Swamp Gum)

We discovered that we have a nice patch of Swamp Gum which occur in a narrow band on the eastern side of the main Walker Swamp wetland. Interestingly, we found one very old individual with what appears to be two very large trunks growing from one lignotuber. Given the size of the two trunks and the gap between them,  the tree must be very old. Having lignotubers (or mallee roots) is how many Eucalypt species survive fire, because they can be destroyed above ground, but resprout from the lignotuber. Dean says that when we see multiple stems the same age growing close together like this, it’s because the lignotuber has resprouted in multiple places, which makes it likely that the rootstock has been there for a very long time! Unfortunately, it’s impossible to accurately age a tree based on the trunk size, or the lignotuber size, so we are unlikely to ever know how old it is but it is certainly many decades old.

As you can see, this tree (or trees) certainly looks like it would have some tales to tell. The little Swamp Gum population at the site appears to be quite healthy with lots of different age classes,  including some seedlings.  We speculated that possibly the Swamp Gums are prevalent in this little patch because it’s an area along the lake edge where freshwater springs discharge,  meaning it’s probably a little bit wetter and therefore a bit better suited to Swamp Gums rather than Red Gums.

Eucalyptus sabulosa (Scentbark)

We were wondering if this species was a possibility at the site,   as it occurs in small numbers in the Grampians,  so we were excited when Dean identified one lone specimen of the species growing amongst planted trees in an old tree line.  The tree is definitely not planted,  and must have been there when they planted out the tree line.  It’s both a tall and large specimen,  and Dean says it’s certainly the biggest one he’s ever seen.  As you can see, it looks very similar to the older, shaggier Rough-barked Manna Gums on the property.

Other Eucalypts that have been planted at the site

There is a planted treeline that runs along the eastern side of Walker Swamp, which is a pretty old Landcare style planting with lots of mature plants, including local species and a mixture of species that don’t occur naturally at the site, such as Eucalyptus leucoxylon var. megalocarpa (SA Blue Gum), Eucalyptus viminalis subsp. viminalis (Smooth-barked Manna Gum) and a Yate species from Western Australia. And of course, despite our best efforts to remove them, there is still an occasional coppicing Tasmanian Blue Gum to be found on the southern part of the property.

And… one mystery species to keep an eye on

In amongst the remnants of the blue gum plantation on the south side of the property, Dean discovered a small patch of Eucalyptus kitsoniana (Bog Gum), which is intriguing because, while it occurs in the region, it is usually found along the coast.  However, there are some old records of it from the western side of the Grampians,  so there is a remote possibility it’s a natural population. Eucalyptus kitsoniana was pretty commonly planted as a garden and revegetation species in the past so the most likely scenario is that it was planted, or it’s spread from a planted population. But you never know, so in the meantime, we will leave it to its own devices. Eucalyptus kitsonia has very distinctive, large juvenile leaves.

Not content with just what was found on the site, Dean also brought along a range of specimens from around the Grampians district, so in total, we got up close and personal with 18 different species, highlighting the wonderful floristic diversity of overstorey species found within the Grampians and surrounds.

Much more than just a great day out, Dean’s insights into the species at the site, the growing conditions they favour and the best ways to propagate and manage them is invaluable as we start to think about large-scale revegetation of the cleared parts of the property.

Thanks to everyone who came along, there was a great deal of in-depth discussion about plant biology, genetics, seed collection and propagation and the various unique characteristics and adaptations of our Eucalyptus species.

The Expanding Walker Swamp project is being delivered by

with the generous support of
the Glenelg Hopkins CMA,
the Hamilton Field Naturalists Club, and
the Victorian Government through the Nature Fund Program