How to harvest trees sustainably

Published 24 April 2019

Sustainable forestry works — at least for sub-tropical forest streams and the small creatures that live in them.

That was the conclusion of a five-member research team that examined the effects of selective tree harvesting on the waterways of sub-tropical forests in northern NSW.

“By using best management practice to selectively harvest trees, we can maintain the ecological integrity of forest streams,” said one of the researchers, ecologist Dr Rob Rolls, a Research Fellow with the University of New England’s Aquatic Ecology and Restoration Research Centre (AERRC).

“The ecological benefits of selective tree harvesting have long been demonstrated in temperate forests, and our study extended those findings to the sub-tropical forests of northern NSW.”

Forestry Corporation of NSW was a funding and research partner in the project and the research reinforced the effectiveness of the organisation’s sustainable harvesting practices.

Forestry and forest products contribute $2.4 billion annually to the NSW economy, but historically there have been ecological costs associated with some outdated forestry industry practices.

Where intensive tree harvesting is done without using measures to protect streams, substantial impacts occur in vulnerable aquatic ecosystems. Increased runoff of water and inputs of sediment, and an influx of organic matter (such as plant litter and branches) from felled trees are frequently reported impacts of unprotected timber harvesting.

Harvesting Best Management Practices (BMPs) have been adopted globally to minimise these effects. BMPs include constructing bridges and causeways to reduce traffic in sensitive areas, putting seasonal restrictions on harvesting and wet weather restrictions on high-disturbance activities like log felling, and leaving riparian buffer zones. Yet the effects of harvesting BMPs on aquatic ecosystems have until now been much less well understood compared to those of intensive harvesting.

Combined with selective tree harvesting, Dr Rolls said, BMPs yielded good results for the northern NSW streams.

Data from three streams in logged catchments were assessed by the study team, and compared with streams in adjacent catchments that were not harvested.

In two of the three catchments where selective harvesting was undertaken using BMPs to protect environmental features, there were brief increases in stream flow, and sediment increased in one stream, but the effects only lasted up to one year from harvesting.

Selective harvesting had no effects on the types and amount of plant litter, or on the abundance or diversity of aquatic invertebrates, compared to streams in unlogged catchments.

“We now have robust evidence robust that best management practices for selective harvesting are effective for preserving stream ecosystem health draining harvested forests,” Dr Rolls said.

“We have to be careful about drawing the same conclusions for other climates and forest types, but our study is a clear guide for stream-friendly harvesting in Australia’s valuable sub-tropical forests.”

The study team included another UNE ecologist, Dr Andrew Boulton; Dr Kate Smolders and Professor Fran Sheldon of Griffith University; and Dr Ashley Webb of NSW Primary Industries.

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