The spatial distribution of indigenous forest and its composition in the Wellington region, New Zealand, from ETM+ satellite imagery John R. Dymond * , James D. Shepherd Landcare Research, Private Bag 11052, Palmerston North, New Zealand Received 8 June 2003; received in revised form 12 November 2003; accepted 14 November 2003 Abstract In order to improve biodiversity management in the Wellington region of New Zealand, it is necessary to make an inventory of the indigenous forest—where is it, and what type is it? The single greatest impediment to making a spatially (i.e., 1:50,000 scale) and thematically detailed inventory from satellite imagery has been the topography of the three mountainous ranges in the Wellington region. The effective irradiance of incoming light varies with slope orientation, as does the proportion of light that is reflected towards the satellite (the bidirectional reflectance). In this paper, we show how satellite imagery may be processed to standardised spectral reflectance, which is a property of the vegetation alone, independent of sun position, slope, and view direction. Because of this, the use of automatic methods to map vegetation and provide spatially and thematically detailed maps is greatly simplified. Using this method, we produce a land-cover map of the Wellington region, with eight classes, to a classification accuracy of approximately 95%. We also show how the proportions of conifer, broad- leaved, and beech trees may be determined for indigenous forest to provide a framework for forest-type inventory. D 2004 Elsevier Inc. All rights reserved. Keywords: Indigenous forest; Topographic correction; Bidirectional reflectance; Forest inventory; Standardised reflectance; Biodiversity 1. Introduction The Wellington region, in the lower part of the North Island (Fig. 1), New Zealand, has 23% of its 813,000 ha covered in indigenous forest. In pre-Maori times, nearly all the Wellington region was covered by indigenous forest, but after the arrival of Maori (ca. 1000 A.D.), a significant proportion was burned for shifting agriculture, and after the arrival of Europeans (ca. 1840 A.D.) an even larger propor- tion was burned and cleared for pastoral agriculture. Most of the indigenous forest is now confined to the protected mountainous areas of the Tararua, Rimutaka, and Aorangi forest parks. There are also many small remnants of indig- enous forest spread throughout the rest of the region, and there are large blocks of shrubland reverting to indigenous forest on the east coast. In response to the Convention on Biological Diversity, land managers in New Zealand are increasingly concerned with identifying and protecting in- digenous habitats for biodiversity. An important part of a regional approach to biodiversity management is an inven- tory of the indigenous forest. We need to know where it is and what type it is. The climate of the Wellington region is mild and wet: annual rainfall varies between 800 mm in the eastern Wairarapa and 7000 mm at the tops of the Tararua range (ca. 1500 m), and mean monthly temperatures at Wellington city range between 8 jC in July and 16 jC in January. The forests of the region are dominated by various mixtures of species from three groups: conifers, all from the Podocar- paceae family (Table 1); broad-leaved evergreen species from a wide range of families (Table 2 lists the more common broad-leaved species); and four species of Notho- fagus, or southern beech (Table 3). Forests dominated by broad-leaved trees with scattered emergent conifers (conifer/ broadleaf forest) occur on most lowland sites, although conifers have been selectively removed by logging over sometimes large areas to leave forests now dominated by broad-leaved species. Conifer/broadleaf forest is usually luxuriant with small trees, shrubs, and ferns forming under- storeys, and mosses, lichens, lianes, and epiphytes are plentiful. There is a general shift to dominance by Notho- fagus (beech forest) at higher elevations, or on sites with dry climates or infertile soils. Beech forest tends to be domi- 0034-4257/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.rse.2003.11.013 * Corresponding author. Tel.: +64-6-356-7154; fax: +64-6-355-9230. E-mail address: dymondj@landcare.cri.nz (J.R. Dymond). www.elsevier.com/locate/rse Remote Sensing of Environment 90 (2004) 116 – 125