Australasian Science: Australia's authority on science since 1938

To Thin or Not to Thin

By Chris Jones

Stands of dense woody regrowth are increasing in extent across Australia and around the world. The effect of dense stands and thinning on tree growth is well understood but the impacts on the understorey are not.

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Dense woody regrowth commonly pops up on cleared land where there has been some change in land use, usually a reduction in grazing pressure. In some places, this regrowth is considered a bad outcome.

In parts of Europe, for example, the grasslands that may have been grazed for centuries are considered valuable for biodiversity in their own right. In Australia, on the other hand, woody regrowth is often considered a good outcome for biodiversity as it represents a transition back to the pre-cleared vegetation state.

However, it is common for these regrowth stands to be much denser than undisturbed forest. They are often structurally simplistic with a high density of similar-sized stems. These stems grow more slowly than in natural systems due to competition for resources, and this competition also suppresses the understorey vegetation.

In Victoria there is an increasing call for management of dense eucalypt stands on both private and public land. The most commonly cited management option is thinning – cutting down a proportion of stems and applying herbicide to prevent regrowth. The theory is that the release from competition should make the remaining stems grow faster, larger and broader, as well allowing the recovery of understorey vegetation.

Self-thinning does occur in these systems and, given enough time, dense stands are generally...

The full text of this article can be purchased from Informit.