Ecology of an elusive endemic shrub, Pittosporum obcordatum Raoul

Abstract

The ecology of Pittosporum obcordatum Raoul (heart-leaved kohuhu), an endemic shrub or small tree, was investigated to explain its sporadic distribution. The species is characteristically found on lowland (<500 m a.s.l.) river flats where local climates have frequent summer drought and winter frost, and soils are waterlogged in winter. Population structures reveal no recent regeneration at some sites while at others there is recruitment in the smaller height classes. This pattern reflects mainly the frequency and intensity of browsing by domestic stock. The primary reason for the species' uncommonness appears to be strict habitat specificity combined with habitat destruction and fragmentation. Factors potentially contributing to its vulnerability include slow relative growth rate, restricted seed dispersal, unbalanced population sex ratios, and inability of seedlings and small juveniles to survive heavy browsing.

Keywords:

• Pittosporaceae
• heart-leaved kohuhu
• Pittosporum obcordatum
• threatened species
• distribution
• population structure
• reproductive biology
• phenology
• conservation