Expert explains value of trees

Remnants of kanuka and kowhai as well as willow stands growing alongside the Wairau River are ecologically valuable, TrustPower expert witness Ruth Bartlett told the Environment Court in Blenheim yesterday.

Dr Bartlett said the vegetation was valuable because it protected riverbanks from erosion, added to the natural character of the river margin, provided continuous wildlife habitat and added to the biodiversity of river flats dominated by exotic plant species.

Most willow and native forest stands along the river were not wetlands, said Dr Bartlett. She did not think these ecosystems were likely to be affected by a reduced flow in the river resulting from TrustPower's hydro-electric scheme and associated draw-down of groundwater levels.

This was because most of the plants found normally grew in well-drained soils and were highly drought tolerant. The willows that dominated were deep-rooting so would seek out water while the ferns and other shallow-rooted small plants had adapted to grow in places where their root zone dried out under natural conditions.

The willow stands were dominated by exotic vine and shrub species, said Dr Bartlett. While providing habitat to a limited number of native and exotic bird species including quail, they were not of botanical value.

Dr Bartlett said that the best stands of native vegetation on the northbank of the river along small tributaries of the Wairau and spring-fed creeks, should be retained. While unlikely to be threatened by predicted lowering of the groundwater, she recommended that a sample area should be monitored until it was clear there were no adverse changes that could be attributed to the scheme.

Wetlands, riparian native forest and scrub on especially the south bank should also be monitored, she said.

- The Marlborough Express

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