Population Studies of Isolated Nothofagus fusca Stands in the Lower Otira Valley, South Island, New Zealand

Population size and structure of 52 isolated Nothofagus fusca stands were investigated in the lower Otira Valley, 3-6 km from a major population centre in the upper Taramakau catchment. The approximate age of N. fusca pioneer trees, estimated from partial increment cores and calculations based on diameter growth rates, indicated that nearly all isolated stands originated after 1600 AD, predominantly during the periods 1600-1760 AD and 1865-1910 AD. Age and location of pioneer trees from the latter time span suggest that their establishment was a result of human disturbance associated with European settlement of the region. Most of the sites occupied by the older N. fusca outliers are prone to intermittent natural disturbance, creating temporary gaps in the generally forested habitat. Reduced competition from both other tree species and ground cover in these habitats may have allowed establishment of N. fusca pioneer trees, but subsequent recruitment was limited except in floodplain stands. The comparatively abrupt regional geographical limit of N. fusca is discussed in relation to the local rainfall regime.