AGE STRUCTURE AND DYNAMICS OF A PODOCARP BROADLEAF FOREST IN TONGARIRO-NATIONAL-PARK, NEW-ZEALAND

1. Regeneration patterns of three emergent conifers (Dacrydium cupressinum, Prumnopitys ferruginea and P. taxifolia) and three broadleaved canopy species (Elaeocarpus dentatus, Nestegis cunninghamii and Weinmannia racemosa) were inferred from population age structures and spatial patterns in podocarp-broadleaf forest in Tongariro National Park, North Island, New Zealand, Age data were obtained from three clear-felled plots. 2. All three podocarp species had highly discontinuous age-distributions, with different age ranges reflecting differing light requirements and longevities of the three species. Dating of scars and releases on stem cross-sections suggested that the main podocarp age classes established during a period of progressive overstorey mortality rather than as a result of a single massive exogenous disturbance. 3. Elaeocarpus dentatus regenerates mainly by rapid growth in small canopy gaps. Both Nestegis cunninghamii and Weinmannia racemosa had all-aged populations. Nestegis cunninghamii appears to regenerate continuously beneath the canopy. Regeneration mechanisms of Weinmannia racemosa were unclear, but seedlings of this species depend mainly on elevated surfaces, and vegetative reproduction also occurs. 4. Continuous occupancy of the study area by high-density podocarp stands of restricted age-range is likely. Wind disturbances and cohort senescence are envisaged as dominant factors in the dynamics of these podocarp stands. A variable cycle is postulated which involves episodic widespread overstorey mortality effected mainly by wind disturbances. This mortality may be progressive or catastrophic - both these circumstances apparently producing podocarp regeneration.