New Zealand’s formerly extensive lowland native forests have been comprehensively cleared or modified, and large areas of secondary-growth vegetation have subsequently established. These areas are comprised of native, exotic, and mixed tree and shrub species assemblages. The mature-phase canopy and emergent tree species representative of pre-human New Zealand forests are often rare or locally extinct in these forests, indicating negative ramifications for long-term biodiversity conservation and ecosystem service provision, especially such as carbon sequestration.
The Hutt catchment has an area of 245 square miles, most of which is hilly and mountainous country above 1,000 ft. The average rainfall in the lower part of the valley (south of Te Marua) and on the Eastern and Western Hutt hills is 50-60 in.; eslewhere it is 80-100 in. or more, probably exceeding 150 in. at 4,000 ft. Originally more than 95% of the catchment was in forest. Today, approximately 42% (103 sq. miles) still carries primary forest, although nearly all of it is to a greater or less extent modified.