Judith Wright's poem "Bora Ring" is all about the loss of the Aboriginal culture in Australia, and the lines in question sadly note that only the trees are left to mimic the Aboriginal dances now. Let's look at the poem in more detail to help you understand.

In the first stanza, the speaker laments that the song and dance are gone, and their secrets have passed with them. The tribes' stories are faded and lost. Then in the second stanza, the sadness is increased by the barrenness of the landscape. Now not only the songs and dances have gone, but the people, too. Only the grass and the trees stand. The grass marks the dance area. The apple gum trees (a kind of eucalyptus) seem to be performing a corroboree (an Aboriginal ceremony). But the trees can only mimic the dance and the ceremony through their swaying and the murmuring of their leaves. It may sound something like a chant, but it is not. The chant is now broken.

In the third stanza, the speaker refers directly to the lost people. The hunters are gone now. The nomads have stopped traveling. The person riding by, the speaker concludes in the fourth stanza, is struck by the emptiness and senses a hidden curse.