Studies on the vegetation of Mount Colenso New Zealand 1. The forest continuum.
Plotless methods were used to sample four forest stands situated at different altitudes on Mount Colenso, Ruahine mountain range, North Island, New Zealand. The altitudinal distributions of the main woody species are described graphically. All species have overlapping altitudinal ranges, so that no clear altitudinal 'belts' can be distinguished. The forest composition is regarded as a continuum showing gradual variation from diverse mixed (podocarp-beach) forest on the terraces of the Kawhatau river (c. 2000 ft. above sea level), through red beach (Nothofagus fusca) dominated forest at intermediate altitudes, to Libocedrus / Dacrydium forest at the upper limits of tree growth (c. 4000 ft. a.s.l.). The splitting of this continuum into forest types defined by canopy dominants is briefly discussed. Tree seedling populations show a decrease in specific diversity, though not in total numbers, with increasing altitude. A significant decline in soil pH with altitude is demonstrated. Surface soils with a pH greater than 5.5 are rare above c. 3500 ft. a.s.l. but frequent at lower altitudes.