Comparative seedling growth of five endemic New Zealand podocarp species under different light regimes

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Abstract
The comparative growth of seedlings of Dacrycarpus dacrydioides, Podocarpus totara, Dacrydium cupressinum, Prumnopitys ferruginea, and P. taxifolia was investigated at different light levels. Five light regimes were achieved using shade cloth for glasshouse seedlings (2–25% of full sunlight) and under different canopy vegetation types (5–30% of full sunlight) in dense lowland podocarp forest at Whirinaki Forest Sanctuary, Central North Island, New Zealand. Height growth, stem diameter growth, and dry weight increase were measured for a 15 month period over two spring seasons in both glasshouse and forest environments. The five podocarp species show significant differences in height growth, stem diameter growth, and dry weight increase under the different light regimes of both glasshouse and forest environments. Seasonal height growth rates were examined in the forest, and species exhibited different responses to the climatic parameters of rainfall, humidity, temperature, and solar radiation. Comparative growth rates are used to infer regeneration strategies of the five podocarp species, particularly in response to elevated light levels. Totara and kahikatea are considered 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 consider these two species as consistently slow growers. Miro is often considered the most shade tolerant of the five podocarp species and in the present study it exhibited an increased growth response to elevated light levels, especially in the forest.