Beech and Conifer Community Interactions in Moawhango Ecological Region, North Island, New Zealand

Relict forests within tussock grassland and abundant subsoil charcoal indicate that prior to Polynesian conflagrations, conifer forests dominated by kaikawaka covered the upper montane plateaux in Moawhango Ecological Region. Much forest remains in peripheral districts where the plateaux border the encircling Kaimanawa, Kaweka and Ruahine greywacke uplands; in these districts, beech forest of the ranges extends on to plateaux surfaces as a narrow, variable-width strip intermixed with conifer forest. Factors considered in an investigation of the dynamics of the boundary zone between beech and conifer forest include the distribution pattern of beech outlier stands within conifer forest, stand structure, tree architecture and age hierarchies at the boundary, spreading rates of beech, seedling microsite requirements and radial increment growth rates. The study shows a centripetal spread of beech from the ranges at the expense of the conifer community. Range expansion occurs by both the slow marginal spread of beech trees and the establishment of outlier stands of beech within the conifer community. Spreading rates are comparable to those deduced from South Island forests. The chief limitation to beech spreading is lack of opportunities for seedling establishment beneath the dense, lower canopy of small trees and shrubs of the conifer community. Population growth of beech in the late Holocene, which is evident in the palynological records from the adjacent Ruahine Range, has probably been regulated by slope and how closely regional environments approximate the optimum conditions for beech.