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A new method of biodiversity assessment is developed to characterise the biodiversity values of roads across New Zealand. The methodology blends rigorous probability sampling and PNAP sampling methodology with environmental domains analyses to characterise the biodiversity attributes of highways. It demonstrates the usefulness of this methodology in allowing regional reporting and integrating biodiversity conservation with road management by applying it to a particular road segment, State Highway 3 from Hamilton to New Plymouth.

The data gathered is also used to develop an overall biodiversity enhancement and restoration plan for the studied segment of road. The biodiversity attributes of the road reserve differed markedly between the environmental sectors, and showed a strong effect from the surrounding land cover. Results indicate that the road reserve is both a biodiversity asset and a liability.

The road reserve is an asset, in that it provides public lands for conservation that are highly visible to the public, often in habitats that are under-represented in the reserve network, and can provide links between existing reserves. The road reserve may be a liability in that it has reduced biodiversity value in the surrounding forests and can act as corridors for the spread of weeds into agricultural areas or indigenous forests.

Effective integration of biodiversity conservation and road management can increase these assets and reduce these liabilities. This can be achieved by changing policy at all levels (Transfund NZ, Transit NZ, other roading authorities), by increasing awareness of the biodiversity value of road reserves, and by providing specific guidelines for the management and protection of roadside biodiversity.

Keywords: biodiversity, conservation, road reserve, probability sampling, PNAP, surveys, State Highway 3, geographic information systems, environmental domains, land cover, road management