Chinese celtis, Celtis sinensis

Chinese celtis is a priority invasive plant in the Sunshine Coast Region. In the new Biosecurity Plan 2024, it is listed as an “asset protection” species: These species occur across the whole of the Sunshine Coast. They cause some impacts where they occur. These species should be managed when they threaten or impact high-value assets. This may include important environmental, agriculture, or community areas. Under the Biosecurity Act 2014 it is classified as a a category 3 restricted invasive plant. It must not be given away, sold, or released into the environment. Further information on it can be found here: Celtis sinensis.

Information and identification

This tree originates from Asia and is now naturalised throughout south-eastern Queensland. It can grow into a quite large tree, and tends to occur mainly along riverbanks and gullies. It produces masses of fruit, which are dispersed by birds and flying foxes. The literature says it is deciduous, but I haven’t seen it without leaves here!

Identification:

Tree 10-30m tall with smooth greyish bark.
The leaves are glossy on top, paler underneath, with very distinct veins and arranged alternately on the stems. The leaf margins are bluntly toothed.
Younger stems have a somewhat zig-zagged appearance and are green or pale brown in colour. These stems have a relatively rough surface texture, and are sparsely covered in small whitish spots (i.e. lenticels).
The flowers are inconspicuous and short-lived.
The fruit are initially yellowish, turning orange then red then brown over time.
Large trees tend to blend into the mix of rainforest species that we have along our creeks and gullies. I only find them easy to distinguish if there are some leaves closer to ground level: they are very distinctive, as are smaller plants where the leaves are easily seen.
When there is a flush of new growth these trees sometimes stand out, as the new growth is a paler green than the old growth.

Impacts

Environmental

Invasive in riparian areas – it can form dense infestations, preventing regeneration of native species. It can also suck up large amounts of water and has the potential to degrade habitat for native animals.

Distribution at Crystal Waters

Pretty widespead! Particularly along the Mary River, Scrub Creek and Kilcoy Creek. It also occurs in most of the wetter areas of forest on the property.

Control methods and efforts

There hasn’t been any concerted effort to control this species here, although I think most of us who work on weeds try to remove them whenever we find them.

Small seedlings and saplings are relatively easy to pull out if the ground conditions are good. Slightly larger ones can be removed with a tree popper or cut-and-dabbed with glyphosate. It’s not worth just cutting them off, as they will resprout and can sucker as well, making a bigger problem.

Trees may be best controlled by ring-barking. I’m copying in Evan Millwood’s description of how to do this here:

1.Begin the ringbark in the dead of Winter. This reduces epicormic growth (shoots) below the wound (doesn’t eliminate) and reduces bridging (repair) of wound. The ones I’ve done in growing seasons increase the maintenance work significantly (don’t do it!). Plan your ringbarking around the seasons.
2.Use a hammer-like tool or axe poll (back of axe – not sharp edge). The reason for using a blunt tool is that you don’t want to overcut into ‘xylem’ of tree, you want to remove ‘phloem’ only (transport bundles) – https://mammothmemory.net/images/user/base/uncategorised/1.24.4%20Xylem%20and%20phloem%20cross%20section%202.jpg – this may sound confusing but you are removing bark only, nothing else, which will remove the phloem. Phloem mostly takes carbohydrates from leaves to roots, xylem sends nutrients from roots to leaves. Removing phloem exhausts roots as they receive no energy while the tree keeps growing, it basically grows itself to death. Take a 10-15cm ring of bark away, this helps reduce bridging of wound by new phloem/callousing. Try and do the ring on a single stemmed tree and high enough you can access the under wound section easily enough and visually see it for maintenance purposes. You can technically ringbark anywhere on tree as long as it’s below all the leaves, working at approx 900-1400mm is better for the back.
3.Maintenance of ringbarked area. Remove any shoots below the wound on a schedule, usually Spring to mid-Spring and Summer but some species throw shoots regularly. Remove any missed phloem that attempts to regrow or bridge the wound. This part is critical, any shoots below wound will feed tree through photosynthesis as will bridging callous. Do not ringbark something and then not maintain it as you only really get one chance to do it properly. Maintenance can be a fingernail, a hand, a knife, secateurs, a shoe, anything to remove the shoots below the wound, not above. A light hammering, even with a stick, will remove any new phloem if apparent.
4.Continue maintenance until tree death. If you didn’t cut into xylem when doing the initial work, physiologically, the tree will have to exhaust itself in most cases. If you did cut too far, the top will die and the tree will continue shooting for years from stump or roots, like the cut Tipuanas about the place. Check the tissue for life above and below the wound with a scratch. Theoretically, complete death under the wound is what you are after, some trees can grow from simple cuttings in contact with ground (Umbrella or Coral Trees will remain alive above wound for a while, manage this when the tree falls and hits the ground).

Evan notes that he has had good success with this method on Celtis (his photos below). I treated a couple of trees in the gully below Lots 61-62 at the beginning of winter last year, and have been back a couple of times to remove sprouts and regrowth of bark across the cuts, but I’m still waiting for them to die!