COMPARATIVE SEEDLING GROWTH OF 5 ENDEMIC NEW-ZEALAND PODOCARP SPECIESUNDER DIFFERENT LIGHT REGIMES

The comparative growth of seedlings of Dacrycarpus dacrydioides, Podoc arpus total-a:. Dacrydium cupressinum, Prumnopitys ferruginea, and P. taxifolia was investigated at different light levels. Five light regim es were achieved using shade cloth for glasshouse seedlings (2-25% of full sunlight) and under different canopy vegetation types (5-30% of f ull sunlight) in dense lowland podocarp forest at Whirinaki Forest San ctuary, Central North Island, New Zealand. Height growth, stem diamete r growth, and dry weight increase were measured for a 15 month period over two spring seasons in both glasshouse and forest environments. Th e five podocarp species show significant differences in height growth, stem diameter growth, and dry weight increase under the different lig ht regimes of both glasshouse and forest environments. Seasonal height growth rates were examined in the forest, and species exhibited diffe rent responses to the climatic parameters of rainfall, humidity, tempe rature, and solar radiation. Comparative growth rates are used to infe r regeneration strategies of the five podocarp species, particularly i n response to elevated light levels. Totara and kahikatea are consider ed to be light demanding and have the ability to respond to increased light levels. Both rimu and matai do not appear to have the ability to respond to elevated light levels and it may be more appropriate to co nsider these two species as consistently slow growers. Mire is often c onsidered the most shade tolerant of the five podocarp species and in the present study it exhibited an increased growth response to elevate d light levels, especially in the forest.