Conservation of forest remnants and other natural features on Bell Hill Farm Settlement, North Westland, New Zealand

Abstract

Two hundred and four forest remnants, several peat swamps and two induced pakihis on the Bell Hill Farm Settlement in North Westland have been surveyed and classified according to their nature conservation value. The study is part of an endeavour to incorporate nature conservation requirements into the farm development programme of the Department of Lands and Survey.

The land and biological resources of the Farm Settlement are described. Terraces and rolling hill country are the predominant landforms, underlain respectively by fluvioglacial outwash gravels and morainic till deposited by late Otiran glacial advances. There are small areas of alluvial terrace and of hill country underlain by late Tertiary sandstones and siltstones. The soils are gleyed and podzolised to various extents, reflecting the interaction over postglacial time of the parent materials, the predominant mor-forming podocarp-hardwood forest vegetation, local topography, and the humid climate.

Before European settlement dense rimu-dominant forest predominated on the glacial terraces. Matai and kahikatea were dominant on the alluvial terraces, and mixed podocarp-hardwood forests covered the hill country. North Westland beech forests extended as far south as the Arnold River, and there were many beech outliers on the Farm Settlement. Most of the forests were destroyed or modified over a century of ' European settlement by timber milling and agricultural settlement. Twenty-one vegetation associations are identified in the remaining forest remnants separated on the basis of landform, canopy species composition, and extent of human modification.

The formerly diverse avifauna in the district was reduced from 34 to 22 species during the settlement process. Bird species richness in individual remnants is now restricted, and is found to be directly related to area.

A scientific rationale for nature conservation is presented. Strategies of nature conservation are derived from consideration of its objectives and from empirical studies in island biogeography and population genetics. Scientific criteria for the selection and design of nature reserves include representativeness, naturalness, area, ecological diversity, rarity, ecological gradients, spatial distribution of and corridors between reserves, and buffer zones. Systems of nature conservation value assessment are described.

The richness and uniqueness of the New Zealand biota is outlined, and the high natural values of the former North Westland landscape are established. During the European period in North Westland there has been major modification of the natural landscape, particularly reduction of the lowland forests of the river valleys, hill country and coastal margins. The adequacy for nature conservation of the present system of ecological and scenic reserves in North Westland is assessed and is found to be wanting.

Forest associations in remnants on the Bell Hill Farm Settlement are shown to be poorly represented in existing regional reserves. A method of assessing the nature conservation value of the forest remnants is developed. Remnants are scored on four ecological criteria to produce an index and relative numerical assessment of their conservation value. The criteria selected are: regional community representativeness and relationship to beech-podocarp boundary; area; degree of modification; and number of forest bird species.

The key factor in successfully integrating nature conservation with farm development on Bell Hill and other farm development blocks is identified as the management plan. General recommendations to minimise the impacts of farm development operations on forest remnants and other natural features are formulated. Reservation, retention as Crown land, and conservation covenants are identified as options for status and management of natural features after settlement.

Specific recommendations are made for the protection on the Bell Hill Farm Settlement of 59 forest remnants, two peat swamps of palynological significance, and an induced pakihi. Priorities are assigned to each recommendation. The recommendations include the establishment of two scenic reserves and the transfer of five remnants to existing adjacent reserves. An inventory summarising salient features of each remnant is appended.