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Effects of forest loss are evident in NZ streams, with key species absent

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“Dramatic” biological shifts are taking place in our freshwater ecosystems as a result of deforestation around New Zealand, and several key forest species are now rare or absent in affected areas.

University of Otago zoology researchers have studied more than 100 freshwater environmental DNA (eDNA) samples from across Otago and Southland, to compare the biodiversity between forested and deforested streams.

eDNA measures all the tiny traces of genetic material left behind as living things pass through water or soil.

By focusing on about 100 species of ecologically important freshwater insects, such as mayflies and stoneflies, lead author Prof Jon Waters and fellow researchers found a distinct insect group linked to forest loss.

He was surprised by how substantially and predictably the forested and deforested eDNA samples differed.

“We could easily tell whether a stream was forested or deforested, just from looking at the insect eDNA data.

The Lyvia River in the Dingwall Mountains, which flows into Doubtful Sound at Deep Cove. Photo / Stephen Jaquiery
The Lyvia River in the Dingwall Mountains, which flows into Doubtful Sound at Deep Cove. Photo / Stephen Jaquiery

“Deforestation clearly has had major impacts on the diversity of species present in our rivers, and also on ecosystem function, with several key forest species now being rare or absent in deforested regions.”

He said the study was important because freshwater quality and biodiversity were significant environmental issues, both here and overseas.

“New Zealand was fully forested before humans arrived just a few centuries ago.

“With only a quarter of the original cover left, the associated environmental impacts have been severe, and degradation of our waterways has been widespread.

“One major concern relates to the loss of wetland vegetation cover and its potential effects on freshwater ecosystem health.”

As efforts turn to mitigating these impacts and restore freshwater ecosystems, Prof Waters believed eDNA represented a key tool for efficiently and rapidly monitoring ecosystem-wide health, and for testing the success of restoration efforts.

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